Defeng Wu

Poly(epsilon-caprolactone)/polylactide blend (PCL/PLA) is an interesting biomaterial because PCL and PLA present good complementarity in their physical properties and biodegradability. However, the thermodynamic incompatibility between two component polymers restricts further applications of their blend. In this work, we used functionalized multiwalled carbon nanotube (MWCNT) to control the morphology of immiscible PCL/PLA blend. The ternary PCL/PLA/MWCNTs composites were hence prepared by melt mixing for the morphology and the properties investigation. It is interesting to find that the functionalized MWCNTs are selectively dispersed in the matrix PCL phase and on the interface between two polymer phases, leading to simultaneous occurrence of thermodynamically and kinetically driven compatibility. Those interface-localized MWCNTs prevent coalescence of the discrete domains and enhance the phase interfacial adhesion as well. As a result, the phase morphology of the ternary composites is improved remarkably in contrast to that of the blank PCL/PLA blend. Owing to that unique selective interface-localization and improved phase morphology, the ternary composites present far lower rheological and conductive percolation thresholds than those of the binary composites, and also present extraordinary mechanical properties even at very low loading levels of the MWCNTs. Therefore, the amphiphilic MWCNTs are believed to act as the reinforcements as well as the compatibilizer in the immiscible PCL/PLA blend.

Abstract Adding nanofillers to PLA/PCL blends to change their surface and interface properties can improve their phase morphology. Here the selective localization of CNTs and organoclays as the third component in the blend is studied. It is found that clay is selectively localized in the PLA phase and at the phase interface whereas CNTs are mainly found in the PCL phase and at the phase interface. With a reduced viscosity ratio of the blend matrices, the CNTs change their preferred localization from PCL to PLA. The effects of the different selective localization of clay and CNTs on the morphologies are studied. In addition, the crystallization behavior of ternary systems also shows a strong dependence on the selective localization of nanofillers. magnified image

Three types of nanocelluloses, including bacterial cellulose (BC), cellulose nanofiber (CNF) and cellulose nanocrystal (CNC), were used to prepare oil-in-water Pickering emulsions with the objective to disclose the effect of fiber flexibility on emulsification. In aqueous suspensions, the shortest CNC is rigid, while the longest BC fully flexible, which result in large difference in their dilute-to-semi-dilute concentrations, and in the rheological percolations. Thus, these cellulosic nanofibers play different roles during emulsification. Flexible BC nearly has no emulsifying capacity, whereas semi-flexible CNF and rigid CNC can be well used to stabilize emulsions. For the CNF-stabilized system, depletion effect is dominant, leading to the formation of droplet clusters easily, while for the CNC-stabilized one, repulsive effect plays more important role. Visible evidence regarding relaxation of long-term structure of droplets is further disclosed by dynamic rheology. This work proposes interesting views around tailoring morphology and viscoelasticity of Pickering emulsions by regulating fiber flexibility.

Bilayer hydrogel-based actuators have attracted much interest because inhomogeneous structures are easily constructed in hydrogels. We used three kinds of polysaccharides, including anionic carboxymethyl cellulose (CMC), cationic chitosan (CS), and amphoteric carboxymethyl chitosan (CMCS), as both structure-constructing units and actuation-controlling units in this work to fabricate physically crosslinked poly(vinyl alcohol) bilayer hydrogels. The spatial heterogeneity was tuned by changing the types and concentrations of polysaccharides in different layers, to regulate pH- and humidity-driven actions of bilayer hydrogels. Based on the distortion of the ionic channel during the humidity-motivated deformation of bilayer hydrogels, a two-in-one flexible device integrating a humidity-driven actuator and humidity-responsive sensor was then developed, which could detect the alterations of environmental humidity in real time. Moreover, good tensile toughness and interfacial bonding as well as the strain-resistance effect endowed the bilayer hydrogels with the capability of identifying human motion as a strain sensor, unlocking more application scenarios. This work provides an overall insight into the heterogeneity regulation of bilayer hydrogels using polysaccharides as stimulus-responsive units and also proposes an interesting strategy of manufacturing hydrogel-based flexible devices with both actuating and sensing capabilities.

Polylactide (PLA) nanocomposites containing various functionalized multi-walled carbon nanotubes (MWCNTs) were prepared directly by melt compounding. The linear rheology and thermal stability of the PLA nanocomposites were, respectively, investigated by the parallel plate rheometer and TGA, aiming at examining the effect of surface functionalization on the dispersion of MWCNTs by using viscoelastic and thermal properties. Among three MWCNTs used in this work, the carboxylic MWCNTs present better dispersion in PLA matrix than the hydroxy and purified MWCNTs because the corresponding composite shows the lowest rheological percolation threshold, which is further confirmed by the TEM and solution experiments. The presence of all these three MWCNTs, however, nearly cannot improve the thermal stability effectively at the initial stage of degradation and the temperature corresponding to a weight loss of 5 wt% (T5 wt%) only shows slight increase in contrast to that of the neat PLA while with increase of decomposition level, the presence of carboxylic and purified MWCNTs retards the depolymerization of PLA evidently, showing remarkable increase in the temperature corresponding to maximum rate of decomposition (Tmax). Both the dispersion state and the surface functionalization of MWCNTs are very important to the thermal stability of PLA matrix.

Polylactide (PLA)/polycaprolactone (PCL) blends with various blend ratios were prepared via melt mixing. The morphology, linear and non-linear viscoelastic properties of the blend were studied using scanning electron microscope (SEM) and cone-plate rheometer. Three typical immiscible morphologies, i.e., spherical droplet, fibrous and co-continuous structure can be observed at various compositions. The elasticity ratio was proposed to play an important role together with the viscosity on the phase inversion because PLA/PCL blend presents a high viscosity ratio between two components. Two emulsion models were used to predict the linear viscoelastic properties of the blend with various morphologies. The Palierne model gives better fit compared with the G–M model, but both fail to predict the viscoelastic properties of the co-continuous blend. The viscoelastic behavior of those blends shows different temperature dependence due to their different morphologies. The principle of time–temperature superposition (TTS) is only valid for the co-continuous blend while fails with the rheological data of those blends with discrete spherical and fibrous domain structure. Moreover, although the discrete phase is difficult to be broken up due to the high viscosity ratio of the systems, the change of viscoelastic responses of those blends before and after preshear shows large difference, indicating that different morphologies have different sensitivity to the steady shear flow.

Abstract The nonisothermal cold crystallization behavior of intercalated polylactide (PLA)/clay nanocomposites (PLACNs) was studied using differential scanning calorimetry, polarized optical microscope, X‐ray diffractometer, dynamic mechanical thermal analysis, and Fourier transform infrared spectrometer. The results show that both the cold crystallization temperature ( T cc ) and melting point ( T m ) of PLA matrix decreases monotonously with increasing of clay loadings, accompanied by the decreasing degree of crystallinity ( X c %) at the low heating rates (≤5 °C/min). However, the X c % of PLACNs presents a remarkable increase at the high heating rate of 10 °C/min in contrast to that of neat PLA. The crystallization kinetics was then analyzed by the Avrami, Jezioney, Ozawa, Mo, Kissinger and Lauritzen–Hoffman kinetic models. It can be concluded that at the low heating rate, the cold crystallization of both the neat PLA and nanocomposites proceeds by regime III kinetics. The nucleation effect of clay promote the crystallization to some extent, while the impeding effect of clay results in the decrease of crystallization rate with increasing of clay loadings. At the high heating rate of 10 °C/min, crystallization proceeds mainly by regime II kinetics. Thus, the formation of much more incomplete crystals in the PLACNs with high clay loadings due to the dominant multiple nucleations mechanism in regime II, may have primary contribution to the lower crystallization kinetics, also as a result to the higher degree of crystallinity and lower melting point in contrast to that of neat PLA. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1100–1113, 2007

Abstract Multi‐walled carbon nanotube/poly(ε‐caprolactone) composites (PCLCNs) were prepared by melt compounding. The rheology, nonisothermal crystallization behavior, and thermal stability of PCLCNs were, respectively, investigated by the parallel‐plate rheometer, differential scanning calorimeter, and TGA. Cole–Cole plots were employed successfully to detect the rheological percolation of PCLCNs under small amplitude oscillatory shear. PCLCNs present a low percolation threshold of about 2–3 wt % in contrast to that of clay‐based nanocomposites. The percolated nanotube network is very sensitive to the steady shear deformation, and is also to the temperature, which makes the principle of time‐temperature superposition be invalid on those percolated PCLCNs. Small addition of nanotube cannot improve the thermal stability of PCL but can increase crystallization temperature remarkably due to the nucleating effect. As the nanotube is much enough to be percolated, however, the impeding effect becomes the dominant role on the crystallization, and the thermal stability increases to some extent. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3137–3147, 2007

Abstract The biodegradable polylactide composites containing carbon nanotubes (CNTs) with high aspect ratio (HAR) and low aspect ratio (LAR) were prepared by melt mixing. The physical properties of those two systems were characterized in terms of rheology, conductivity, and mechanical properties for establishing preliminary structure–property relations. Several viscoelastic models were then used to further describe the relations between aspect ratio and percolation network of CNTs. The results show that these two CNTs present different structural characteristics in the polylactide (PLA) matrix during melt mixing: the LAR CNTs are far stiffer than the HAR CNTs. At low loading levels, the former is dispersed as bent fibers or their small bundles, whereas the latter is dispersed as self‐entangled flocs, presenting far larger hydrodynamic radius than the former. At high loading levels, both are dispersed as flocs due to strong tube–tube interactions. However, the two CNTs show approximate average floc size and mesh size because they present same rigid length and effective aspect ratio. At identical loadings, therefore, the HAR CNTs have more total number of flocs than that of the LAR CNTs, forming network with more compact structure and imparting higher contributions to properties of the composites as a result. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 479–489, 2010

Polylactide (PLA) composites containing graphene nanosheets were prepared by the approach of solution mixing for a crystallization study. The results revealed that the graphene nanosheets are well distributed in the PLA matrix, leading to an evident viscosity increase despite their dispersion as multilayered structures in stack form. Both the cold and melt crystallization behaviors of PLA were found to depend strongly on the presence of the graphene nanosheets. During cold crystallization, the graphene nanosheets merely act as an inert filler, and the increased viscosity results in a decrease of the overall crystallization rate of the composite relative to neat PLA. However, the graphene nanosheets can act as a heterogeneous nucleating agent, which is their dominant role during melt crystallization. As a result, the composite shows a higher crystallization rate than neat PLA under these conditions.

Biodegradable poly(butylene succinate)/polylactide (PBS/PLA) blends with various blending ratios were prepared by melt mixing for morphological and rheological studies. Dynamic rheological measurements were performed on the blend systems and the viscoelastic responses were analyzed with several emulsion models. The results show that the PBS/PLA is an immiscible blend system with very narrow cocontinuous region and high percolation threshold. The phase inversion point could be precisely predicted by the small-amplitude oscillatory shear (SAOS) response. The Palierne model gave a better description of the viscoelastic response of PBS/PLA blends than that of the Gramespacher and Meissner (G-M) model. In addition, the interfacial tension between the two polymers was measured by several techniques, such as surface property characterizations, deformed drop retraction, and rheological approaches. The differences observed by these various methodologies were then further explored. Moreover, the melting and crystallization behaviors of the blends were also studied in order to reach a deeper insight into the relations between the phase behavior and the macroscopic thermal properties of the PBS/PLA blends.

DC and AC electrical conductivity of bionanocomposites based on the immiscible polymer blend poly(epsilon-caprolactone)/polylactide (PCL/PLA, w/w 70/30), loaded with multiwall carbon nanotubes (CNT), were studied in a wide frequency range, 10(-3) < or = f < or = 10(7) Hz from 143 to 313 K. The nanofiller concentration ranged from 0 to 4 wt % and it was shown to be selectively located in the PCL phase. The PCL crystallinity degree was not affected by the presence of CNT. The variation of the DC conductivity allowed the determination of the percolation threshold, p(c) = 0.98 wt %, and the critical exponent t = 2.2 of the scaling law. The linear dependence of log (sigma(DC)) versus p(-1/3) showed the existence of tunneling conduction among CNT not yet in physical contact. The temperature independent results indicated a conventional tunnel effect. The AC conductivity of the nanocomposites followed the predictions of the universal dynamic response and the s exponents were determined at low concentrations. Master curves are presented showing the length and temperature-time superpositions.

Two kinds of carbonaceous particles, carbon black (CB) and carbon nanotubes (CNTs) were used as the filler to prepare biodegradable polylactide (PLA) composites for the study of synergistic effect of fillers on the electrical conductivity. The results reveal that the CB particles and CNTs are loosely entangled with each other in PLA matrix, instead of forming two independent phases. Therefore, there is no synergistic effect of these two fillers, and the ternary composites containing both the CB and CNTs present electrical conductivity ranged between those of the CB-based and CNT-based single-filler samples. However, after foaming with supercritical carbon dioxide, the ternary composite system reveals evident synergistic effect of fillers because the symbiotic structure between CB and CNTs favors the formation of the PLA cells with unbroken wall structure, which is propitious to the formation of the conductive filler networks with less defective structure in PLA bulk. As a result, the ternary composite foam shows better electrical conductivity than both the CB-based and CNT-based single-filler foams.

The polyurethane (PU) nanocomposites containing carbon nanotubes (CNTs) were prepared through in situ polymerization for the creep study. The results show that the presence of CNTs leads to a significant improvement of creep resistance of PU. However, this creep resistance does not increase monotonously with increase of CNT contents because it is highly dependent on the dispersion of CNTs. Several theoretical models were then used to establish the relations between CNT dispersion and final creep and creep–recovery behaviors of nanocomposites. The as-obtained viscoelastic and viscoplastic parameters of PU matrix and structural parameters of CNTs further confirmed the retardation effect by CNTs during creep of the nanocomposite systems. Besides, the time–temperature superposition (TTS) principle was also employed in this work to make a further evaluation on the creep of PU/CNT nanocomposites with long-term time scale.

The sesame oil-in-water Pickering emulsions using cellulose nanofibers (CNF) as the emulsifier were prepared for the rheological study, aiming at establishing relationship between emulsion viscoelasticity and morphology. A droplet cluster structure forms in those systems due to multicomponent properties of sesame oil and fibrillar structure of CNF. Its deformation and relaxations result in weak strain overshoot behavior in large amplitude oscillatory shear (LAOS) flow, but not affect the scaling behavior of small amplitude oscillatory shear (SAOS) responses. The relaxation time scales can be evaluated by creep of emulsions. This structure can evolve during ramp shear flow, rearranged and oriented at the higher flow rates, which has evident influence on the thixotropic behavior of emulsions. The mechanisms of evolution and relaxations of droplet cluster structure are traced through rheo-optical way. This work presents some interesting results and paves a possible way to control morphology and viscoelasticity of edible Pickering emulsions.

A 'continuous route' was developed in this work for the preparation of nanocrystalline cellulose (NCC) filled polylactide (PLA) composites. It combines several separated steps, including extraction of NCC, surface acetylation of NCC, and final composite preparation, into a continuous process, without traditional freeze drying. The obtained PLA composites were then studied in terms of phase interface structure, rheological and mechanical properties. The results reveal that surface acetylation of NCC can improve its affinity to PLA evidently. The thickened interfacial layer makes the system filled with modified NCC show lower percolation threshold than the one filled with pristine NCC; and the former presents a typical strain-scaling stress overshoot behavior in the start-up shear flow because the network structure of modified NCC presents stronger characteristics of self-similarity. The phase interface adhesion also plays an important role in the mechanical behavior of PLA/NCC composites, which is further revealed by the nanomechanical analysis using atom force microscopy.

Construction of hierarchical networks of anisotropic hydrogels has attracted much attention recently. We developed a simple strategy to fabricate anisotropic hydrogels with rich structural hierarchy and tunable mechanical properties by using the minor polymer as the performance and network regulators in this work. Poly(vinyl alcohol) (PVA)/poly(vinylpyrrolidone) (PVP) solution was used as precursor to build networks across multiple length scales via the directional freezing/salting-out treatments. The presence of PVP, as minor component, promoted the formation of the bridging fibers across the oriented channel-like pores. Thus, as-prepared two-component anisotropic hydrogels revealed superior mechanical strengths as compared to the two-component isotropic hydrogels or the single-component anisotropic ones. On the other hand, the formation of this dendritic structure improved the strength perpendicular to aligned direction, and therefore, the PVA/PVP anisotropic hydrogels possessed more balanced mechanical performance. In brief, PVP acted as the roles of network and performance regulators in this kind of anisotropic hydrogels. This work provides an interesting way to regulate morphology and overall properties of the PVA based anisotropic hydrogels.

Cellulose nanofibers are one of the most frequently used fillers for reinforcing hydrogels. The reinforcement, however, is commonly accompanied by the decrease of deformability. Inspired by the armor structured with overall flexible but locally rigid characteristics, we proposed a strategy of constructing chemical networks of bacterial cellulose (BC) in this work to improve the overall mechanical performance of hydrogels. The PAM hydrogels with borax-crosslinked BC nanofibers were prepared. The BC networks are multiscaled, and different levels of structures play different roles. As the flexible networks, the crosslinked BC endows the hydrogels with superior stretchability (7710%) and improves anticutting property as well as crack growth resistance. The crosslinks composed of boronic ester bonds act as “sacrificial bonds”, improving the fatigue resistance to the cyclic tensile with large strain (500%). The mechanical strength of the hydrogels is also significantly enhanced due to the reinforcement role of BC nanofibers. Moreover, the remained sodium ions and borate ions give the hydrogels good conductivity and decreased freezing point. Accordingly, the as-prepared flexible sensor has superior sensitivity (Gauge factor 10.1 for stretching) with satisfactory environmental adaptability. This work proposes an effective strategy of structural regulation for the cellulosic particle-containing hydrogel to improve the overall performance.

Acetylated chitin nanocrystals (ChNCs) were used as stabilizer in this work to prepare sunflower seed oil-in-water emulsions for the morphological and rheological studies. The results revealed that the acetylation with moderate degree of substitution (0.38) reduced hydrophilicity and increased surface charge level of rod-like ChNCs, and as a result, significantly improved the emulsifying ability of ChNCs. At the same oil/water ratio and particle loading, the emulsions stabilized with the acetylated ChNCs had far smaller droplet size (~3 μm) as compared to the emulsions stabilized with the pristine ChNCs (5–7 μm). The increased droplets numbers and improved surface coating level resulted in the enhanced viscous resistance and yield stress level, which improved the physical stability of the acetylated ChNC-stabilized emulsions as a result. In addition, the droplet clusters easily formed in this system, contributing to weak strain overshoot and decreased large-deformation sensitivity during dynamic shear flow. Therefore, the acetylated ChNC-stabilized system showed enhanced transient stress overshoot during startup flow and weakened thixotropy during cyclic ramp shear flow as compared to the pristine ChNC-stabilized system. The relationships between surface acetylation of ChNCs and flow behavior of emulsions were then established, which provide valuable information on the modulation of the ChNC-stabilized Pickering emulsions.

Polylactide/clay nanocomposites (PLACNs) were prepared by melt intercalation. The intercalated structure of PLACNs was investigated using XRD and TEM. Both the linear and nonlinear rheological properties of PLACNs were measured by parallel plate rheometer. The results reveal that percolation threshold of the PLACNs is about 4 wt%, and the network structure is very sensitive to both the quiescent and the large amplitude oscillatory shear (LAOS) deformation. The stress overshoots in the reverse flow experiments were strongly dependent on the rest time and shear rate but shows a strain-scaling response to the startup of steady shear flow, indicating that the formation of the long-range structure in PLACNs may be the major driving force for the reorganization of the clay network. The thermal behavior of PLACNs was also characterized. However, the results show that with the addition of clay, the thermal stability of PLACNs decreases in contrast to that of pure PLA.

Abstract Multi‐walled carbon nanotube/Poly(butylene terephthalate) nanocomposites (PCTs) were prepared by melt compounding. The microstructure of PCTs was investigated using transmission electron micrographs and Fourier transform infra‐red spectrometer. The linear and nonlinear as well as transient rheological properties of PCTs were characterized by the parallel plate rheometer. The results reveal that the surface modification can improve the dispersion state of nanotube in matrix. PCTs present a low percolation threshold of about 1–2 wt % in contrast to that of Poly‐(butylene terephthalate)/clay nanocomposites. The network structure is very sensitive to both the quiescent and large amplitude oscillatory shear deformation, and is also to the temperature, which makes the principle of time‐temperature superposition (TTS) be valid on PCTs only in a very restricted temperature range. The stress overshoots to the reverse flow are strongly dependent on both the rest time and shear rate but show a strain‐scaling response to the startup of steady shear, indicating that the broken network can reorganize even under quiescent condition. The nanotube may experience the long‐range, more or less order during annealing process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2239–2251, 2007

Abstract The crystallization behavior of polylactide/carbon nanotube composites was studied using differential scanning calorimeter and polarized optical microscope. The nucleation mechanisms and the crystallization kinetics were explored. The results show that the presence of nanotubes has nucleating effect on both the melt crystallization and the cold crystallization of PLA. However, the nanotubes also play the role of physical barrier, impeding the crystal growth dynamically. In the experimental range of temperatures, the presence of nanotubes accelerates the melt crystallization, while retards the overall kinetics of the cold crystallization. The biodegradability of the samples with various crystallization histories was then further examined. The results show that the presence of nanotubes reduces the biodegradation rate of PLA, and the amorphous sample shows the highest degradation levels. Moreover, a lower degradation level is observed both on the surface and inside the sample with melt crystallization history in contrast to the one with cold crystallization history. POLYM. ENG. SCI., 50:1721–1733, 2010. © 2010 Society of Plastics Engineers

Abstract Poly(ε‐caprolactone)/polylactide blend (PCL/PLA) is an interesting biomaterial because the two component polymers show good complementarity in their physical properties. However, PCL and PLA are incompatible thermodynamically and hence the interfacial properties act as the important roles controlling the final properties of their blends. Thus, in this work, the PCL/PLA blends were prepared by melt mixing using the block copolymers as compatibilizer for the studies of interfacial properties. Several rheological methods and viscoelastic models were used to establish the relations between improved phase morphologies and interfacial properties. The results show that the interfacial behaviors of the PCL/PLA blends highly depend on the interface‐located copolymers. The presence of copolymers reduces the interfacial tension and emulsified the phase interface, leading to stabilization of the interface and retarding both the shape relaxation and the elastic interface relaxation. As a result, besides the relaxation of matrices (τ m ) and the shape relaxation of the dispersed PLA phase (τ F ), a new relaxation behavior (τ β ), which is attribute to the relaxation of Marangoni stresses tangential to the interface between dispersed PLA phase and matrix PCL, is observed on the compatibilized blends. In contrast to that of the diblock copolymers, the triblock copolymers show higher emulsifying level. However, both can improve the overall interfacial properties and enhance the mechanical strength of the PCL/PLA blends as a result. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 756–765, 2010

Ring-opening polymerization of l-lactide from cellulose nanocrystal (CNC) surface yielded polylactide-grafted CNC (CNC-g-PLA). The structure and chemical composition of the CNC-g-PLA were characterized by FT-IR, 1H NMR, XPS and XRD. The crystallization behavior and lamellar structure of poly(β-hydroxybutyrate) (PHB) in the presence of pristine CNC and CNC-g-PLA were elucidated via DSC and SAXS, and Babinet's reciprocity theory was applied. Crystallization kinetics were further analyzed using Ozawa, Mo and Kissinger models. In the presence of pristine CNC, nucleation of PHB crystals led to an increase in the crystallization temperature (Tc) of PHB; while CNC-g-PLA acted as antinucleation agent, resulting in a remarkable reduction in Tc of PHB. Accordingly, the composite with pristine CNC possessed a higher crystallization rate than neat PHB, while CNC-g-PLA displayed the lowest crystallization rate. However, the lamellar structure of PHB was not affected by the presence of pristine and modified CNCs, and almost identical crystallization activation energies as the neat PHB were observed, indicating that nucleation is dominant during PHB crystallization, instead of crystal growth. This study offers a promising approach of using pristine and modified CNCs to control the crystallization of biodegradable aliphatic polyesters.

Basalt fiber (BF) was used to reinforce polylactide (PLA) to obtain new composites with potential structural or engineering applications. The composites with pristine BFs present evidently increased strength and modulus relative to neat PLA. After surface treatment, BF shows more evident reinforcing effect because the interfacial energy between BF and PLA decreases sharply from 27.40 to 8.58 mJ m−2. The physical network structure of BFs is also improved after their surface treatment, and as a result, the composites with treated BF have more tensile cycles and higher elongation levels than the one with pristine BF. After solid annealing, the mechanical strengths of systems were further improved because of cold crystallization of PLA. But composites show higher improvement level relative to neat PLA because the nucleation effect of BF enhances fiber-matrix interfacial adhesion. This work provides useful information on the preparation of BF filled PLA composites with tailorable structure and properties.

Rheological behavior, including linear and nonlinear, as well as transient rheology of nanocrystalline cellulose (NCC) suspensions was studied in this work. Two kinds of polymer solutions, aqueous poly(vinyl alcohol) (PVA) with flexible chain structure and aqueous carboxymethyl cellulose (CMC) with semi-rigid chain structure, were used as the suspension media to further explore the role that the interactions among NCC and polymers played during shear flow. The results reveal that NCC has lower values of percolation threshold in the PVA solution than in the CMC one during small amplitude oscillatory shear (SAOS) flow because the flexible PVA chain has higher adsorbed level onto NCC particles than the negatively charged semi-rigid CMC chain, which is further confirmed by the Fourier transformed infrared (FT-IR) spectroscopy tests. As a result, the NCC suspension shows a weak strain overshoot in PVA solution during large amplitude oscillatory shear (LAOS) flow, which cannot be seen on the one in CMC solution. During startup shear flow, both of these two suspensions show evident stress overshoot behavior with the strain-scaling characteristics, indicating the formation of ordered long-term structure of rod-like NCC particles with self-similarity during flow. However, NCC suspension have far stronger stress overshoot response in CMC solution relative to the one in PVA solution. A possible synergy mechanism between NCC and CMC chain is hence proposed.

Cellulose crystals, including microcrystalline cellulose (MCC) and nanocrystalline cellulose (NCC), were used as the fillers to prepare green composites with poly(β-hydroxybutyrate) (PHB) by melt mixing for crystallization study. The results reveal that the spherulite morphology of PHB and its composites depends highly on the crystallization temperature, evolving from bundle shaped to ring-banded and finally to irregular or zigzag textures with increase of temperature. However, the ring-banded structure is strongly affected by the presence of cellulose crystals, and the average band space decreases evidently with the addition of MCC or NCC. Compared with PHB/MCC composite, PHB/NCC composite shows degraded spherulite structure with smaller band space and higher flocculation level of peak-to-valley height because of stronger unbalanced stresses in this system. Besides, cellulose crystals can act as good heterogeneous nucleating agent to accelerate the crystallization of PHB, which is further confirmed by the polarized optical microscopy observations and the kinetic analyses.

Poly(ε-caprolactone) (PCL) composites with pristine nanocrystalline cellulose (NCC) and acetylated nanocrystalline cellulose (aNCC) (with 1.85 ± 0.15 degree of substitution) were prepared. Different roles of NCC and aNCC to the crystallization of PCL were explored. NCC acts as the nucleation agent, promoting the formation of thickened PCL lamellae. Thus, PCL-NCC sample shows higher melting point (Tm) and degree of crystallinity (Xc) than neat PCL. However, aNCC plays the role of antinucleation agent, decreasing Xc and crystallization temperature (Tc) of PCL. This is because the relaxation of PCL chain segments is restrained by the presence of aNCC through hydrogen bonding between two phases. As a result, the looser fold surfaces of lamellae form in PCL-aNCC sample, with decreased lamellar thickness. The ring-banded morphology is therefore observed on this sample because of good compatibility between aNCC and PCL and higher level of surface stress of PCL lamellae, which is not observed on PCL-NCC one.

The olive oil-in-water Pickering emulsions stabilized with starch nanocrystal (SNC) were prepared for the morphological and rheological studies. Different kinds of shear flows were applied and the viscoelastic responses of emulsions were detected in terms of SNC concentrations (0.2-2.0 wt%) and surface acetylation levels (0.11-0.41° of substitution). The results show that the emulsifying capacity of SNC is improved evidently after surface acetylation due to decreased surface hydrophilicity of SNC and to enhanced electrostatic repulsive effect during emulsification, which is evidenced by the gelation behavior in small amplitude oscillatory shear (SAOS) flow. The modulus and viscosity of the emulsion with acetylated SNC increase by about two orders of magnitude as compared to those of the emulsion with pristine one. The former even shows weak overshoot behavior during large amplitude oscillatory shear (LAOS) flow. This work provides valuable information on motivating development of the Pickering emulsions using SNC as particle emulsifier.

Using the platelet-like starch nanocrystals (SNCs) to stabilize emulsions is attractive because as-prepared emulsions have promising applications in cosmetics and food fields. Limited studies mainly focus on the oil-in-water system, and another important system, the water-in-water emulsions stabilized by SNCs, has not yet been unveiled.Two surface modification strategies, crosslinking and acetylation, were applied to tune surface property and aggregation of SNCs, and a common all-aqueous system (dextran/poly(ethylene glycol)) was used here as template. The viscoelasticity and morphology of emulsions were studied in terms of the SNC loadings and polymer ratios.Crosslinking results in aggregation of SNCs, and the particle size increases (from 110 nm to 370 nm) with increased levels of substitution. This favors improving emulsifying ability of particles. Acetylation decreases the particle size (∼90 nm) and weakens the affinity of SNCs to the two aqueous phases, improving the emulsifying efficiency of SNCs. More intriguingly, the two emulsion systems show different phase inversion behaviors. The depletion-stabilization mechanism for the cross-linked SNCs and the diffusion-controlled mechanism for the acetylated SNCs are proposed using the emulsion viscoelasticity as probe. This study makes a comprehensive insight into the regulation of water-in-water emulsion morphology and types with the platelet-like SNCs.

For the rational use of agricultural wastes, bagasse, orange peel and wheat bran were used to fabricate bio-based polymer materials. Cellulose was extracted from the three different agricultural wastes, and poly(ε-caprolactone) (PCL) was used as the matrix material. PCL was mixed with nanocrystalline cellulose (CNC), extracted bagasse cellulose (GC), orange peel cellulose (JC) and wheat bran cellulose (MC) by solution casting. Morphology and structure of the extracted cellulose were studied by Scanning Electron Microscope, Fourier Infrared spectrometer, thermogravimetry and X-ray diffractometer. The influence of GC, JC, MC on the crystallization process and mechanical properties of PCL was investigated by DSC and tensile test. Experimental results show that the addition of CNC, GC, JC, MC increases the crystallization temperature of PCL, accelerates the crystallization process of PCL, and improves the tensile property of PCL.

Poly(butylene terephthalate)/montmorillonite composites (PBT/MMT) were prepared by melt intercalation and then investigated using X-ray diffractometer (XRD) and transmission electron microscope (TEM) as well as parallel plate rheometer. It was found that the composites had various phase morphologies with nanoscales and distinct behaviours of a percolation network structure under certain conditions. The linear viscoelastic region of the composites is much narrower than that for PBT matrix, the percolation threshold of the composites is near 3 wt.%, and the percolation network structure is not stable under a shear as well as in a quiescent annealing process. Moreover, PBT/MMT presents the nature of temperature independence of G′ versus G″ whether the internal percolated tactoids network formed or not. The magnitudes of the stress overshoots observed in the reverse flow experiments were strongly dependent on the rest time, which could be inferred that the ruptured network is reorganized under the quiescent annealing process. Furthermore, PBT/MMT shows a strain-scaling stress response to the startup of steady shear, indicating that the formation of the liquid crystalline-like phase structure in the nanocomposites may be the major drive force for the reorganization of the internal network.

Randomly oriented fiber mats and well-aligned fiber bundles of the biodegradable polylactide (PLA)/poly(ε-caprolactone) (PCL) blends were successfully produced by electrospinning in the present study. For the reticulate fibers, the effects of the blending ratio of two polymers and compositions of mixed solvents on fiber morphology were investigated. The results reveal that the fibers with lower PCL mass fraction show better morphology with larger average fiber diameter than those of the fibers with higher PCL mass fraction. Besides, a small addition of dimethylformamide (DMF) as the assistant solvent favors further improvement of fiber morphology because of the synergistic effects by improved conductivity and altered viscosity of the electrospun solutions. Although the as-obtained blend fibers show smooth surface structure, the phase separation between PCL and PLA occurs inside the fibers because the two components are thermodynamically immiscible, and the discrete phase shows an elongated morphology along with the fiber axis, instead of the droplet structure. For the aligned fiber bundles collected on a rotating disk, the degree of order increases with increase of the tangential velocity, accompanied by reduced average fiber diameter. Hierarchical orientations including the macroscopic fiber alignment, the elongation of discrete PCL phase, and the molecular orientation of both the PLA and PCL can be observed within the aligned blend fibers.

Poly(trimethylene terephthalate) (PTT) nanocomposites containing carbon nanotubes (CNTs) with different surface structure and aspect ratio were prepared by melt compounding for electrospinning. The dispersion state of the CNTs in the composites was then examined utilizing rheology tools. The results show that carboxylic surface functionalized CNTs present better dispersion in the matrix than hydroxy surface functionalized CNTs because the former has stronger affinity to the PTT. Besides surface functionalization, the aspect ratio of CNTs is also vital to their final dispersion. The CNTs with lower aspect ratio are dispersed as individuals or small bundles while those with higher aspect ratio are dispersed mainly as flocs with large hydrodynamic radius, showing higher effective volume fraction. The presence of CNTs has a large influence on the morphologies of electrospun fiber and on the appearances of CNTs in the fibers. In the presence of CNTs with lower aspect ratio, continuous composite fibers are obtained. But the structure of those continuous fibers highly depends on the surface group of CNTs. Carboxylic surface functionalized CNTs are well embedded by the PTT and oriented along the fiber axis during electrospinning, leading to bead-free and uniform fiber morphology; while hydroxy surface functionalized CNTs show tortuous conformations with less orientation in the fibers, and as a result, the obtained fibers show beaded and misshaped morphologies. In the case of higher aspect ratio, however, the CNTs prefer to exist as entanglements or knots in the streamlines, and thereby only beaded or even uncontinuous fibers are obtained. Therefore, the formation and fiber morphology of PTT/CNT composite fibers obtained by electrospinning strongly depend on the surface functional groups of the CNTs, as well as on the CNT structure.

The polylactide (PLA) composites with various layered graphite particles were prepared by the approach of solution mixing for the viscoelasticity study. Four kinds of particles with various layered structures, including natural graphite flakes, and graphite nanosheets with the thickness of ∼25 nm and ∼5 nm, as well as graphene were used as the filler, aiming at establishing the relationship between viscoelasticity of composites and filler structure and networks. The results reveal that transient rheological response of PLA composites shows evident sheet thickness dependence, and the stress overshoot behavior is closely related to the percolation network density during startup and reverse flow. But the strain-scaling characteristic of overshoots is independent of thickness of nanosheets and their networks. The linear dynamic rheology (molten state) and creep measurements (solid state) as well as thermal analyses were then performed to further explore the difference in dispersion and distribution among those layered graphite fillers.

Graphene nanosheets (GNS) with and without surface functionalization were used as the reinforcements to prepared the composites with thermoplastic polyester elastomer (TPEE) by melting mixing. The results show that the presence of GNS improves modulus, yield and tensile strengths of TPEE, and the surface functionalization of GNS further improves its reinforcing effect because of enhanced interfacial interactions. However, the elongation levels also increase in the presence of GNS, which indicates the increased elastoplasticity and viscoplasticity of system. This is because the discrete hard poly(butylene terephthalate) domains of TPEE are enriched on the surface of GNS and form 'ball bearing' structure in composites, leading to increased deformation ability of soft continuous poly(tetramethylene glycol) of TPEE during large-scale deformation. Thus, the composites show more amounts of tensile cycles with shorter true strain plateau associated with onset of chain disentangling during cyclic tensile tests. This 'bearing ball' effect, however, is not evident in small-scale viscoelastic deformation because the presence of GNS restrains creep of TPEE. In this case, the impeding effect of GNS on the deformation of TPEE chain coils is the dominant role. This work provides useful information on structure design and control of the GNS filled thermoplastic elastomer composites.

As two typical aliphatic polyesters, biodegradable poly(ε-caprolactone) (PCL) and polylactide (PLA) show quite different mechanical properties. Compounding them together is therefore an interesting topic on the fabrication of biomaterials with tailorable properties. The composite technology was used in this work to prepare a new PCL/PLA system, the green PCL composites reinforced with the electrospun PLA fibers. The minor PCL was then introduced into the PLA fibers to improve the reinforcing effect further. The results reveal that PLA can act as good reinforcement to PCL in the way of continuous fibers because the PCL composites reinforced with the PLA fiber mats show far higher strength and modulus than those of neat PCL and the PCL/PLA blend samples prepared by melt mixing. In comparison with the neat PLA fibers, the PLA/PCL blend fibers have a better reinforcing effect to PCL. The presence of a minor PCL component in the electrospun blend fibers improves the affinity between the fibers and PCL matrix by reducing fiber–matrix interfacial tension and enhances interfacial adhesion via mutual fusion between the fiber surface PCL phase and matrix PCL during hot compression. Both the mechanical properties and the viscoelastic responses of the composites are highly dependent on the fiber contents and PLA/PCL ratios of the blend fibers. The presence of superfluous fiber-contained PCL has no more contribution to affinity improvement and could even decrease the reinforcing effect because of degraded fiber strength. Thus, the PLA/PCL weight ratio of the blend fibers is vital to the final properties of the fiber-reinforced PCL green composites.

Cold crystallization of PLA can improve its affinity to PCL in their blends, and crystallized PLA domains have better nucleation effect to PCL crystallization relative to amorphous PLA ones.

The pristine and acetylated cellulose nanocrystal (CNC) particles were incorporated with poly(ε-caprolactone) to prepare two kinds of green nanocomposite systems: the former is incompatible, while the latter compatible thermodynamically. A rheological study was then performed systematically with various flow fields, including linear and nonlinear dynamic shear flow, creep and start-up flow. Some interesting results were shown then. The pristine CNC filled system shows far lower percolation threshold than the acetylated CNC filled one because the improved phase affinity yields diluent effect. The formation and rebuild-up of percolated network is driven by the Brownian motion of particles, which are nearly independent of altered phase affinity. However, the improved phase affinity makes the system more sensitive to the strain-responded deformation, leading to the reinforced Maxwell spring unit during creep and to a weak strain overshoot during dynamic flow. The structural evolution and relaxations of two systems were further evaluated from different perspectives.

Two kinds of anisotropic cellulosic nanoparticles, cellulose nanocrystal (CNC) and nanofiber (CNF), were used as additives for the aqueous carbonyl iron particles (CIPs) based magnetorheological (MR) fluids, aiming at disclosing effect of nanocelluloses on the magneto-responsive behavior and stability of MR fluids. Both CNC and CNF can stabilize MR fluids, and improve their sensitivity to alterations of magnetic field strengths. Relative to electrostatic repulsion, physical hindrance is more important to the stability improvement. Thus, CNF is the better option because it has higher aspect ratio and surface charge. Moreover, the presence of cellulosic nanoparticles hinders coalescence of CIP chains to stronger columns, and hence the nanoparticles stabilized MR fluids show thixotropy evidently. At the comparative concentration (0.3 wt%), the presence of CNF even enhances the magneto-responsive levels because the percolated CNF network acts as stress amplifier. This work opens up a new door for applications of nanocelluloses in MR fluids.

Using polysaccharide nanocrystals such as chitin nanocrystals (ChNCs) or cellulose nanocrystals (CNCs) as fillers of biodegradable aliphatic polyesters is an attractive approach of fabricating completely biodegradable nanocomposites. Most aliphatic polyesters are semi-crystalline and hence to reveal the effect of nanocrystals on their crystallization behaviors is key to regulate final properties of the nanocomposites. In this work, poly(ε-caprolactone) (PCL) nanocomposites filled with ChNCs and CNCs were prepared as templates for the study. It is intriguing that these two nanocrystals play completely different roles towards crystallization of PCL. CNCs are nucleating agent, promoting nucleation of PCL and accelerating subsequent crystal growth; while ChNCs are anti-nucleation agent, retarding nucleation of PCL and depressing whole process of PCL crystallization. This difference arises from different particle-polymer affinities in the nanocomposites, which is confirmed by the thermodynamic and rheological tests. This work provides valuable information around tuning the thermal properties of polysaccharide nanocrystals filled polymeric nanocomposites.

Rod-like polysaccharide particles such as chitin nanocrystals (ChNCs) and cellulose nanocrystals (CNCs) have been widely used for the preparation of Pickering emulsion. Both are believed playing good role of particle emulsifiers. However, these two kinds of nanocrystals have completely different surface properties: electronegative CNC is more hydrophilic and has higher surface charge level as compared to electropositive ChNC. To reveal their difference as emulsifiers in Pickering emulsions is therefore of interest. In this work, ChNCs and CNCs with the same structural parameters (aspect ratio = 28) were used to prepare olive oil-in-water emulsions for a comparative study. The two kinds of nanocrystals show the same mechanical state in emulsions, behaving like rigid rods, instead flexible fibers because they have 104 level of effective stiffness. Therefore, their roles of emulsifying oil/water system are dominated by their surface properties: ChNCs reveal higher emulsifying capacity relative to CNCs due to better ChNC-oil affinity, and can even emulsify the oil/water (7/3 w/w) system with high oil fractions. However, ChNC-stabilized emulsions are not that stable to centrifugation as compared to CNC-stabilized emulsions at low oil fractions due to the formation of the cluster structure resulted from less coating of droplets. Thus, the former reveals higher strain sensitivity and stronger thixotropy than the latter in shear flow. The correlation between viscoelasticity and morphology/phase behavior of the two kinds of Pickering systems was assessed, then. This work provides valuable information on formulating preparation of Pickering emulsions by using different types of rod-like polysaccharide nanocrystals.

Building multiple cross-links or networks is a favorable way of diversifying applications of the hydrogels, which is also available for the organohydrogels prepared via the solvent replacement way. However, the situations become more complicated for organohydrogels due to the presence of replaced solvents. Therefore, the correlations between the multiple cross-links and final performance need to be better understood for the organohydrogels, which is vital for tailoring their inherent properties to expand final application scenarios. Polyacrylamide (PAM)/poly(vinyl alcohol) (PVA)/MXene composite organohydrogels with dual cross-links, namely, the covalently cross-linked PAM chains as the primary network and the physically cross-linked PVA/PAM chains with MXene particles as the secondary cross-links, were developed here for the study. The occurrence of the secondary cross-links plays multiple roles as sacrificial units endowing the system with ultrastretchability with an excellent strain-resistance effect and as temperature-sensitive units endowing the system with thermosensation ability with an outstanding temperature coefficient of resistance. Thus, the optimized sample can be used as a strain sensor with excellent environmental tolerance for detecting human motion as a pressure sensor to probe compression with weak deformation and as a thermal sensor to capture environmental temperature changes. This work provides valuable information on developing organohydrogels with superior performance for multimodal sensors.

Sufficient water supply and evaporation interfaces are vital for hydrogels as solar evaporators, which require ingenious structural design, from the networks and porous structure inside the bulk to the surface morphology outside the hydrogel.

Network optimization is vital for the polysaccharide based hydrogels with multiple crosslinks. In this study, we developed a 'two-step' strategy to activate synergistic effect of chemical and physical crosslinks using a poly (vinyl alcohol) (PVA)/bacterial cellulose (BC) hydrogel as a template. The BC nanofibers, on the one hand, acted as nucleating agents, participating in the crystallization of PVA, and on the other hand, were also involved in the formation of boronic ester bond, anchored with the PVA chains via chemical bonding. Therefore, the existence of BC nanofibers, as 'bridge', linked the crystalline regions and amorphous parts of PVA together, associating the two characteristic crosslinks, which was conducive to load transfer. The mechanical properties of resultant hydrogels, including the tensile elongation and strength, as well as fracture toughness, were significantly improved. Moreover, the dually cross-linked hydrogels possessed ionic conductivity, which was sensitive to the tensile deformation and environmental temperature. This study clarifies a unique role of BC nanofibers in hydrogels, and proposes an effective approach to construct multiple networks in the nanocellulose reinforced PVA hydrogels.

Abstract Polymer blend nanocomposites containing poly(butylene terephthalate) (PBT), polyethylene (PE), and organoclay were prepared by direct melt compounding. Their immiscible morphologies weree investigated using electronmicroscopy, X‐ray diffraction, and parallel plate rheometry. The PE domain sizes were reduced when the polar PBT phase was continuous (PBT/PE = 60/40) because the clay tactoids effectively prevented the coalescence of the dispersed PE domains. However, when the PBT component presented domains dispersed in the rich PE matrix (PBT/PE = 40/60), the addition of clay (&gt;2 wt %) changed the phase morphology into a novel cocontinuous one, which was further confirmed by rheological measurements. The existence of clay tactoids led to a sharp enhancement in the viscosity of the PBT phase, changing the viscosity ratio between the PBT and PE phases remarkably, which may have promoted the phase inversion. As a result, clay had significant effects on the morphology of the polymer blend. © 2006 Wiley Periodicals Inc. J Appl Polym Sci 102: 3628–3633, 2006

Abstract The multiwalled carbon nanotubes/polypropylene nanocomposites (PP/CNTs) were prepared by melt mixing using maleic anhydride grafted polypropylene ( m PP) as the compatibilizer. The effect of m PP on dispersion of CNTs was then studied using the tool of rheology, aiming at relating the viscoelastic behaviors to the mesoscopic structure of CNTs. To further explore the kinetics of hybrid formation, a multilayered sample with alternatively superposed neat m PP and binary PP/CNTs microcomposites (without addition of m PP) sheets was prepared and experienced dynamic annealing in the small amplitude oscillatory shear flow. The results show that melt blending CNTs with PP can only yield the composites with microscale dispersion of CNTs, while adding m PP promotes nanoscale dispersion of CNTs as smaller bundles or even as individual nanotubes, reducing percolation threshold as a result. However, the values of apparent diffusivities of the composites are in same order with that of self‐diffusion coefficients of the neat PP, indicating that the presence of detached CNTs nearly does not inhibit PP chain motion. Hence, the activation energy of hybrid formation is close to the self‐diffusion of PP. This also indicates that although addition of m PP can improve the compatibility between CNTs and PP thermodynamically, those dynamic factors, such as shear flow, however, may be the dominant role on hybrid formation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 608–618, 2009

Abstract Multiwalled carbon nanotube/poly(butylene terephthalate) composites (PCTs) were prepared by melt mixing. The nonisothermal crystallization and thermal behavior of PCTs were respectively investigated by X‐ray diffractometer, polarized optical microscope, differential scanning calorimeter, dynamic mechanical thermal analyzer, and thermogravimetric analyzer. The presence of nanotubes has two disparate effects on the crystallization of PBT: the nucleation effect promotes kinetics, while the impeding effect reduces the chain mobility and retards crystallization. The kinetics was then analyzed using Ozawa, Mo, Kissinger, Lauritzen‐Hoffman, and Ziabicki model, and the results reveal that the nucleation effect is always the dominant role on the crystallization of PBT matrix. Thus the crystallizability increases with increase of nanotube loadings. In addition, the presence of nanotubes nearly has no remarkable contribution to thermal stability because nanotubes also play two disparate roles on the degradation of PBT matrix: the Lewis acid sites to facilitate decomposition and the physical hindrance to retard decomposition. Hence the nanotubes act merely as inert‐like filler to thermal stability. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers

Abstract The multiwalled carbon nanotubes were directly compounded with poly(phenylene sulfide) (PPS) via melt mixing. The morphology and physical properties, including viscoelasticity, electrical conductivity, and thermal and mechanical properties, of the obtained composites were investigated. The results show that the purified nanotubes can be fully dispersed in the PPS matrix especially at low loading levels because of their good affinity. The composites hence present relative low rheological and electrical percolation thresholds. The presence of nanotubes, on the one hand, shows good reinforcement effect because of the strong interfacial interactions with the PPS matrix, which is confirmed by the strain overshoot flow behavior, and, on the other hand, acts as a nucleation agent, promoting crystallization of the PPS matrix. Both contribute to evident improvement of tensile strength and dynamic mechanical properties of the composites. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

Abstract Electrospinning of the biodegradable polylactide (PLA) and its composites containing carbon nanotubes (CNTs) was studied in terms of solution concentrations and solvents effects as well as CNT loadings. The results reveal that the PLA fibers obtained from the solutions using the mixed solvents of chloroform/assistant solvent (v/v 3/1) show better morphologies than those from the solutions using chloroform as the single solvent. This is due to the synergistic effect by the improved conductivity and altered viscosity with addition of assistant solvent. Moreover, the surface structure of fibers depends on the volatility of assistant solvents strongly. Using volatile acrylonitrile or acetone as the assistant solvents, the columned fibers with porous surface structure are obtained; while the flat fibers with fluted surface are formed using nonvolatile dimethyl sulfoxide as the assistant solvents. As for electrospinning of the PLA/CNT composites, the morphology of obtained fibers is closely related to the dispersion of CNTs in the fibers. At low loading levels, the CNTs can be well embedded in the PLA matrix and oriented along the fiber axis, forming nanowire structure. At high loading levels, the CNTs are mainly dispersed as entangled bundles along the fiber axis, and as a result, the obtained fibers show tortuous or misshaped morphologies. Compared with that of the neat PLA fibers, the overall morphologies of the composite fibers are more or less degraded because the presence of some small CNT aggregates in the solutions easily leads to the formation of beaded fiber structure during electrospinning. The conductivity of the obtained composite fiber mats was further studied in terms of CNT loadings. POLYM. COMPOS., © 2011 Society of Plastics Engineers.

Abstract The selective localization of carbon nanotubes (CNTs) in an immiscible polymer blend has attracted much attention. If the two component polymers could react with each other, do selectively located CNTs affect those reactions? Here, an immiscible polyester blend based on polycarbonate/poly(trimethylene terephthalate) (PC/PTT) is studied. CNTs introduced during melt mixing are selectively located in the PTT phase and on the phase interface during the middle stage of melt mixing. The interface‐located CNTs can act as additional substrate to catalyze or even participate in the transesterification themselves, homogenizing the phase morphology of the matrix blend. The degree of randomness of the composite systems is increased, accompanied by a reduced number‐average length of the copolymer sequences. magnified image

The carbon nanotubes (CNTs)–filled poly(vinylidene fluoride) (PVDF) composites (PCTs) were prepared by melt compounding for rheological study. The steady and oscillatory flow behaviors were then explored. The results show that the presence of CNTs enhances the pseudoplastic flow accompanied by the increased flow activation energy. However, the linear flow region is not sensitive to the temperature whether driven by shear rate or by strain. During oscillatory shear flow, the solid-like response is attributed to the percolation of CNTs, but the formation of a percolated CNT network is temperature-dependent, and the percolation threshold values reduce with an increase of temperature. The two-phase viscoelastic model was then used to further describe the linear responses of composites, aiming at relating hierarchical structures of the CNTs to flow behaviors of the composites.

The platelet-like starch nanocrystal (SNC) particles were used to prepare composite membrane with biodegradable poly(ε-caprolactone) (PCL) for the potential packaging membrane application. The presence of SNC particles improves gas barrier properties, tearing strength, as well as the creep resistance of the PCL membrane evidently at the lower loading levels. This improvement effect can be further enhanced by the surface acetylation of SNC. The presence of acetylated SNC particles (1wt%) can reduce the oxygen transmission rate by about 70% and increase the tearing strength by about 68%, which is due to the improved phase adhesion. The strain failure stage of the membrane is also highly delayed in the presence of acetylated SNC, from hour-time scale to day-time one. Therefore, the biodegradable SNC is a promising candidate to be used as the filler to improve the key properties of biodegradable PCL membrane, but the chemically modified SNC is the better option.

Poly(ϵ-caprolactone) (PCL) composites containing graphite with various layered platelet structures were prepared by solution mixing for crystallization study. The results reveal that the crystallization of PCL is highly dependent on the graphite structure. All three kinds of graphite particles, including graphene nanosheets, graphite nanoplatelets and natural graphite flakes, show evident nucleating effect on the PCL crystallization. But their nucleation activity reduces with increased platelet thickness. However, the presence of graphite particles, especially graphite nanoplatelets and graphene nanosheets, also impedes the movements of PCL chain and increases the system viscosity, resulting in an evident increase of crystallization activation energy. But the nucleating effect is dominant role in the current system because all composites show higher crystallization rates than the neat PCL. The obtained results of this work can provide additional way to design or to control crystallization of PCL composites.

Poly(ε-caprolactone) composites containing the acetylated cellulose nanocrystal (aCNC) with various degrees of substitution (DS) were prepared for the phase compatibility study. An interesting phenomenon around the alteration of crystallization temperature (Tc) was reported here. Tc of PCL increases evidently in the presence of pristine CNC (DS = 0) due to its nucleation effect. However, for the composites with aCNCs, Tc decreases monotonously with increasing DSs of aCNCs and is even lower than that of the neat PCL at higher DSs. This is attributed to the improved compatibility between the matrix and particles, which is further evaluated by the Flory–Huggins parameters. Therefore, the alteration of Tc can be used as the probe to detect the compatibility between two phases in aliphatic polyester composites with chemically modified CNCs. From another perspective, crystallization of aliphatic polyesters can be controlled using aCNCs with different DSs.

Ethyl cellulose (EC) was blended with poly(β-hydroxybutyrate) (PHB), aiming at controlling crystallization and mechanical properties of PHB. The obtained PHB/EC blend is an immiscible system, and the discrete EC phase behaves dual characteristics in the PHB matrix, as the viscoelastic droplets during processing, and as the rigid filler particles during shear flow. This is confirmed by the rheological tests. The presence of EC domains acts as the tackifier, sharply increasing system viscosity from 1000 Pa s to 5000 Pa s, and as a result, has large influence on the spherulite morphology of PHB and its crystallization kinetics. The PHB spherulite growth rate reduces in the presence of inert EC, accompanied by decreased degree of crystallinity and reduced lamella defects. These affect the mechanical properties of PHB strongly, together with reinforcing effect of EC itself. At the lower content level, EC can act as both reinforcement and toughener. The presence of 1 wt% EC enhances the tensile strength of PHB by about 22%, from 27.5 MPa to 33.3 MPa, accompanied by 15% increase of impact strength. This work provide an easy way to control the structure and properties of PHB using EC.

Thermoplastic polyester elastomer (TPEE) blends with poly(butylene terephthalate) (PBT) were prepared by melt compounding for the phase morphology and mechanical property studies. Although PBT is immiscible with the continuous soft poly(tetramethylene glycol) (PTMEG) phase of TPEE, it is miscible with the discrete hard PBT one of TPEE. Therefore, PBT and TPEE are compatible and their blends reveal very low level of interfacial tension and very small size of discrete domains, as well as good interfacial adhesion between two phases, which provide high possibility to prepare TPEE alloys with controllable properties. Mechanical test results reveal that both the modulus and yield and tensile strengths increase with increasing weight ratios of PBT. The increased system rigidity and decreased system plasticity are further confirmed by the cyclic tensile tests. The main objective of this work is to provide useful information on the structure and property control of TPEE by simple mixing with aromatic polyesters.

The rigid microcrystalline cellulose (MCC) particles and semi-rigid ethyl cellulose (EC) were used to control phase morphology and mechanical properties of immiscible poly(β-hydroxybutyrate) (PHB)/poly(ε-caprolactone) (PCL) blends. The interfacial properties were evaluated by the fiber retraction and contact angle methods MCC is incompatible with PHB and PCL, and dispersed independently in the two polymer phases in their blends. However, EC is more compatible with the two polymers, with a higher affinity for PCL. And EC prefers locating in PCL domains and at the phase interface. Selective localization of MCC and EC affects the mechanical properties and phase structure of PHB/PCL blends strongly. For the co-continuous samples, the presence of MCC and EC improves both the tensile and impact strengths. For the ‘sea-island’ ones, however, the changes of strengths depends strongly on the phase adhesion. This work will help focus efforts on moderating structure and properties of immiscible polymer blends using cellulose particles.

Blending two biodegradable aliphatic polyesters with complementary bulk properties is an easy way of tuning their final properties. In this work, the ductile poly(butylene succinate) was mixed with polylactide, and as expectable, the blends show improved toughness with sharply reduced strengths. The pristine cellulose nanofibers were then used as the reinforcement for the blends. It is found that most nanofibers are dispersed in the polylactide phase because polylactide has better affinity to nanofibers, and the lower viscosity level of polylactide also favors driving nanofibers into the continuous polylactide phase during melting mixing. In this case, the strength and rigidity losses resulted from the presence of soft poly(butylene succinate) phase are compensated to some extent. To further improve mechanical properties, a two-step approach (reactive processing of blends, followed by the incorporation with nanofibers) was developed. This work provides an interesting way of fabricating fully biodegradable composites with well-balanced mechanical performance.

Discriminating the roles of different networks in the multiply cross-linked hydrogels is vital to optimize their overall performance. Poly(vinyl alcohol)/cellulose nanofiber composite hydrogels were used as template for the study. Three types of characteristic networks, including chemical network cross-linked with boronic ester bonds, physical network cross-linked with microcrystallites, and coexistence of these two networks, were constructed in the system, and the viscoelastic responses were used to detect the characteristic relaxation behavior of those networks. The physical network is more sensitive to stress-induced deformation, whereas the chemical network more sensitive to strain-induced one. The former has lower level of viscous dissipation and higher level of elastic storage as compared to the latter, and dominates linear viscoelasticity of hydrogels as the two networks coexist. Their synergistic effect can be well defined by the scaling behavior of hysteretic work. This work proposes an interesting method of probing networks in the multiply cross-linked hydrogels.

Abstract The melt intercalation method was employed to prepare poly(butylene terephthalate) (PBT)/montmorillonite (MMT) nanocomposites, and the microstructures were characterized with X‐ray diffraction and transmission electron microscopy. Then, the nonisothermal crystallization behavior of the nanocomposites was studied with differential scanning calorimetry (DSC). The DSC results showed that the exothermic peaks for the nanocomposites distinctly shifted to lower temperatures at various cooling rates in comparison with that for pure PBT, and with increasing MMT content, the peak crystallization temperature of the PBT/MMT hybrids declined gradually. The nonisothermal crystallization kinetics were analyzed by the Avrami, Jeziorny, Ozawa, and Mo methods on the basis of the DSC data. The results revealed that very small amounts of clay (1 wt %) could accelerate the crystallization process, whereas higher clay loadings reduced the rate of crystallization. In addition, the activation energy for the transport of the macromolecular segments to the growing surface was determined by the Kissinger method. The results clearly indicated that the hybrids with small amounts of clay presented lower activation energy than PBT, whereas those with higher clay loadings showed higher activation energy. The MMT content and the crystallization conditions as well as the nature of the matrix itself affected the crystallization behavior of the hybrids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3257–3265, 2006

Abstract Poly(ethylene terephthalate)/expanded graphite conductive composites were prepared by the melt‐blending method. The relationships between the preparation methods, microstructures, and conductivity properties of the composites were studied with scanning electron microscopy and conductivity measurements. The results showed that the composites presented a low percolation threshold and strong anisotropic conductivity. The epoxy resin had a strong intercalation effect on the expanded graphite that led to the easy formation of the conductive network. With classical statistical percolation theory, the conductivity behaviors of the composites were investigated. The results indicated that the nonuniversal critical exponent should be attributed to the anisotropy of conductivity, the tunneling conduction, and the particular structure. In addition, preliminary studies on the crystallization and dynamic mechanical behavior of the composites were performed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Abstract Multi‐walled carbon nanotube/polypropylene composites (PPCNs) were prepared by melt compounding. The linear viscoelastic properties, nonisothermal crystallization behavior, and kinetics of PPCNs were, respectively, investigated by the parallel plate rheometer, differential scanning calorimeter (DSC), X‐ray diffractometer (XRD), and polarized optical microscope (POM). PPCNs show the typical nonterminal viscoelastic response because of the percolation of nanotubes. The rheological percolation threshold of about 2 wt % is determined using Cole‐Cole method. Small addition of nanotube can highly promote crystallization of PP matrix because of the heterogeneous nucleating effect. With increasing nanotube loadings, however, the crystallization rate decreases gradually because the mobility of PP chain is restrained by the presence of nanotube, especially at high loading levels. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Abstract Poly(phenylene sulfide) (PPS)/poly(butylene terephthalate) (PBT) (60/40 w/w) blend nanocomposites (PPS/PBTs) were prepared by direct melt compounding of PPS, PBT, and organoclay. The morphology and rheology of PPS/PBTs were investigated using scanning electron microscope and transmission electron microscope as well as parallel plate rheometer. The intercalated clay tactoids are selectively located in the continuous PBT phase due to their nice affinity. A novel morphology evolution of the immiscible blend matrices is observed with increase of clay loadings. Small addition of clay increases the discrete PPS spherulite domain size. With increasing loading levels, the PPS phase transform to the fibrous structure and finally, to the partial laminar structure at the high loading levels, in which shows a characteristic of large‐scaled phase separation. The presence of clay, however, does not impede the coalescence of the PPS phase because the phase size increases with increasing clay loadings. The elasticity and blend ratio of two matrices are proposed as the important roles on the morphological evolution. Moreover, the laminar structure of PPS phase is very sensitive to the steady shear flow and is easy to be broken down to spherulite droplet at the low shear rate. However, high shear level is likely to facilitate the coalescence of those PPS phase and finally to phase inversion, both contributing to increases of the dynamic modulus after steady shear flow. In conclusion, the morphology of the immiscible polymer blend nanocomposites depends strongly on both the clay loadings and shear history. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1265–1279, 2008

Biodegradable poly(butylene adipate-co-terephthalate) (PBAT) composites containing graphite nanosheets were prepared by melt compounding. The results reveal that the nanosheets have full distribution throughout the PBAT matrix, although they are still dispersed as the multilayered stack. Those well distributed graphite nanosheets act as the heterogeneous nucleating agent to facilitate formation of crystal nucleus and also as the physical hindrance to retard crystal growth. But the nucleation dominates overall crystallization kinetics at experimental graphite loading levels because the composites show higher crystallization rates and lower activation energies than those of the neat PBAT. The results from creep study further confirm the role of physical hindrance played by graphite nanosheets because the creep strain of system is highly restrained by the presence of nanosheets. However, this inhibiting effect is attributed to suppressed relaxation of chain coins, rather than confinement to chain segments.

Pristine cellulose nanocrystal (CNC) and acetylated one (aCNC) were used as the modifier to change the surface properties of poly(trimethylene terephthalate) (PTT) fibers for the transcrystallization study of polypropylene (PP). The results reveal that all three kinds of fibers, including the neat PTT, PTT/CNC and PTT/aCNC ones can induce PP transcrystallization. But the PTT/aCNC fiber-filled PP system shows the most remarkable transcrystallization behavior because of the highest nucleation density of PTT/aCNC fiber. The long period and lamellar thickness of two composite fiber-filled PP systems increase as compared with the neat PTT fiber-filled one, which is caused by the reduced system undercooling and higher surface energy level of composite fibers. Accordingly, the former two systems show the lower transcrystal growth rates than the latter, which is further analyzed by the secondary nucleation theory. This work can provide useful information on the control of PP transcrystallization using the CNC-filled polyester composite fibers.

Cellulose nanocrystal (CNC) particles were used as the solid emulsifier to stabilize poly(ε-caprolactone) (PCL) solution-in-poly(vinyl alcohol) (PVA) solution emulsions (oil-in-water), with the objective to prepare ternary nanocomposites using as-obtained Pickering emulsions as the templates. The morphology of emulsions and mechanical properties of nanocomposites were studied, aiming at establishing a convenient route to regulate selective localization of CNCs and multiphase structures. The results show that emulsion stability depend strongly on CNC loadings and PVA concentrations in continuous phase. The evolution of multiphase morphology of emulsions from locally coalesced droplet structure to interfacial saturation one, and finally to droplet-particle interfacial flocculation, shows scaling characteristics with increasing CNC loadings, and can be detected through rheological way. The interfacial localization makes CNCs show excellent reinforcement to ternary nanocomposites because of their two-phase bridging effect. This work provides an interesting strategy of fabrication of the CNC reinforced polymer blend composites with controllable multiphase structures.

Starch nanocrystal (SNC), was used as the third component to prepare nanocomposites with biodegradable poly(β-hydroxybutyrate)/poly(butylene succinate) (PHB/PBS) blend. The results reveal that SNC shows strong nucleation to the two matrix polymers. However, the crystallization temperature of PHB is highly dependent on the SNC loadings, whereas that of PBS not. This is because SNCs have preferential localization in the immiscible matrix polymers: mainly dispersed in the continuous PHB phase and on PHB/PBS phase interfaces. Therefore, alteration trend of crystallization temperatures can be used as good probe to evaluate selective localization of SNCs in the immiscible blends containing two semicrystalline polymers. The nucleation activities of SNCs, and their interaction energy densities in the two polyesters, as well as the tensile behaviors of ternary nanocomposites, were then detected, aiming at establishing a simple route to prepare green nanocomposites with tailorable multi-phase morphology and balanced mechanical properties using starch and biodegradable aliphatic polyester blends.

For shape-memory polymers (SMPs), introducing material heterogeneity is vital to tailor shape-shifting pathways. However, it is hard to reprogram the heterogeneity for both covalent networks and dynamic covalent networks after these networks are encoded. Here, photoactive coumarin derivative end-capped dangling chains were used to participate in building photoreversible polycaprolactone/poly(malic acid) networks, endowing the networks with reprogrammable heterogeneity and a capability of room-temperature storage of entropic energy. The alternations of network topology with 365/254 nm UV irradiation and strain-induced crystallization behavior of as-prepared bio-based elastomers were studied, aiming at quantitatively guiding the spatiotemporal release of entropic energy to regulate asynchronous deformations. This work provides applicable methods for simplifying shaping manipulation or for diversifying shape-shifting pathways of SMPs.

Dispersion states are vital for fibrous nanocelluloses to be used as reinforcements for polymers, which is highly dependent on geometry of nanocelluloses. Three types of nanocelluloses with various fiber aspect ratios were used to prepare target composite samples with poly(β-hydroxybutyrate) in this work. Viscoelasticity/elastoplasticity were used as probes to detect the flexibility-morphology relations of nanocelluloses in polymer. Cellulose nanocrystals (aspect ratio = 8) were rigid in polymer, retaining their rod-like shape, whereas bacterial celluloses (aspect ratio = 600) fully flexible, forming closely networked structure, and cellulose nanofibers (aspect ratio = 70) semi-flexible, dispersing as loosely flocculated clusters. Owing to these differences, the viscoelastic flow and elastoplastic deformation of three kinds of composites differed from one another. The strain-scaling and hysteresis work-scaling behaviors were then used to establish relaxation scale-structure correlations of target samples. This work provides interesting information around regulating the dispersion of nanocelluloses in polymer composites by tailoring aspect ratios of nanocelluloses.

Abstract The microstructure and rheological property of poly(butylene terephthalate) (PBT)/epoxy/montmorillonite nanocomposites (PCNs) were investigated. For the study, PCNs were prepared by melt intercalation in clay content of 4 wt % and, epoxy loadings were varied from 2 to 4 wt %. The intercalated PCNs are characterized by different techniques such as transmission electron microscopy, Fourier transform infrared and rheology. It is interesting that the percolated tactoids network in the ternary hybrids becomes insensitive to the shear deformation with the addition of epoxy in contrast to that in the sample without epoxy, which can be attributed to the formation of a flocculated structure of clay tactoids because of the chain‐extension reactions between PBT matrix and epoxy and possible hydrogen bonding. The flocculated structure has influence on the rheological behavior of the hybrids remarkably, strengthening the percolated strong‐associated‐tactoids network and reducing the percolation threshold, while not changing the strain‐scaling. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2807–2818, 2005

Epoxy resin was used as a compatibiliser to prepare poly(butylene terephthalate)/clay nanocomposites (PCN) via melt intercalation. The morphology of PCN hybrids was investigated using XRD and TEM. The results reveal that with the addition of epoxy, the silicates are easily intercalated and present a nice dispersion in the matrix. The linear viscoelastic behaviour of the nanocomposites was measured by the parallel plate rheometer. The ternary hybrids show a stronger solid-like response at terminal zone than that of the sample without epoxy. However, with the epoxy loading up to 6 wt% and above, the loss modulus and high-frequency storage modulus for ternary hybrids decline. Thermogravimetric analysis shows that only the hybrids with lower epoxy loading (2–4 wt%) show a higher thermal stability than that of the sample without epoxy, while with increase in epoxy content, the thermal stability of the ternary nanocomposites declines somewhat. The compatibiliser loadings do have an influence on the performance of nanocomposites and, the best compatibiliser dosage, 4 wt%, is decided by a new ‘crossover point’ rheological method.

Polycarbonate/clay nanocomposites (PCNs) were prepared by melt intercalation using epoxy resin as a compatibilizer. The intercalated structure of PCNs was investigated using XRD and TEM. The linear and nonlinear dynamic rheological properties of PCNs were measured by the use of a parallel plate rheometer. The results reveal that the presence of epoxy influences rheological behavior of PCNs significantly. Addition of epoxy can improve dispersion of clay, enhancing the low-frequency viscoelastic responses; while high loadings of epoxy lead to a severe degradation of PC matrix, decreasing the high-frequency responses together with the plasticizing effect of excessive epoxy. Both of these two effects result in invalidity of time–temperature superposition. Moreover, all samples show high sensitivity to both the quiescent and large amplitude oscillatory shear (LAOS) deformation, despite enhanced percolation of tactoids due to the compatibilization of epoxy.

Carbon nanotube (CNT) filled poly(butylene succinate) composites (PBSCNs) were prepared by melt compounding. The oscillatory rheological properties and crystallization behavior and kinetics were then investigated. The results show that the percolation network of CNTs in the small amplitude oscillatory shear flow is temperature dependent and the values of percolation thresholds reduce gradually with an increase of temperature. Therefore, the principle of time–temperature superposition is invalid on the dynamic rheological responses of those percolated PBSCNs. Besides, the presence of CNTs highly promotes the crystallization of PBS, increasing the overall crystallization rate. But the nucleation mechanism of PBS is not altered with addition of CNTs because the PBS itself is nucleated heterogeneously.

Crystallization control of the hard polyester segments is an important way to design the final properties of a thermoplastic polyester elastomer (TPEE). In this work, the crystallization behavior of TPEE with nanosilica as the nucleating agent was studied. Three kinds of nanosilica with various sizes and surface treatments were chosen for nucleation design. The results reveal that all types of nanosilicas have evident nucleating effects, leading to a remarkable increase of the crystallization temperature of TPEE even by about 30 °C. However, the overall crystallization process is highly dependent on the particle size and surface treatment of silica because it is closely related to the nucleation ability of the particles and alteration of the system viscosities. The crystallization temperature of TPEE is more sensitive to the surface treatment of silica, while its crystallization rate shows a higher dependence on the particle size of silica. This work provides a facile way to well tailor crystallization of TPEE.

The recycling of spodumene slag is studied in this work, with the objective of exploring the possibility of using spodumene slag as a common polymer filler.

Starch nanocrystal (SNC) particles were used as the filler to prepare green composites with biodegradable poly(β-hydroxybutyrate) (PHB). An interesting way to tune the nucleation and banded morphology of composites by the surface acetylation of SNC was proposed. Pristine SNC acts as the nucleating agent, while acetylated SNC as the antinucleation one to PHB. This role switching is due to improved polymer-particle compatibility after surface acetylation of SNC particles. The banded structure of PHB spherulites degrades evidently in the presence of two kinds of SNC particles, showing decreased ring-band space, with deteriorated periodicity and increased flocculation of peak-to-valley height. But the two kinds of composites have different mechanisms on the degradation of their ring-bands because the two kinds of SNC particles, pristine SNC and acetylated one, have different influences on the PHB spherulite growth rates and system undercooling. This work also opens a new window for the applications of SNC particles.

Chitin nanocrystal (ChNC) is good nucleation agent for aliphatic polyesters because of its high-energy surface. To moderate its nucleation activity, silane coupling agents with different chain lengths or functional groups were used to modify ChNCs in this work, and biodegradable poly(β-hydroxybutyrate) (PHB) was used as target polymer for crystallization study. Surface coupling of ChNCs improves their phase adhesion to PHB chain and weakens their nucleation activities. The alterations strongly depend on the surface chain structure of ChNCs: sulfhydryl silane-coupled ChNC shows lowered nucleation activity, whereas amino silane-coupled ChNCs even become antinucleation agents. The interfacial compatibility is vital to altered role of ChNCs and to following changes in spherulite growth and ring-banded morphology, which is further disclosed using Flory-Huggins interaction parameters and rheological responses as probes. This work provides useful information on tailoring the functions of ChNCs as nanoadditive for biodegradable aliphatic polyesters by the way of surface chain engineering.

Abstract The biodegradable polymer blend containing 70/30 weight ratio of poly(ε‐caprolactone) (PCL) and polylactide (PLA) was prepared by means of melt mixing. The evolution of the “sea‐island” phase structure in the steady shear flow was studied using scanning electron microscope (SEM) and parallel‐plate rheometer. The results show that the morphological evolution induced by steady shear follows different mechanisms at various flow rates. The lower shear rates (Newtonian flow) promote coalescence of the discrete PLA droplets, whereas higher shear rates (non‐Newtonian flow) promote break‐up of the droplets. The dynamic rheological responses of PCL/PLA blend before and after steady preshear were then analyzed using emulsion model and Taylor equation. The results show that the evolution approaches of the morphology highly depend on changed level of the critical effective interfacial tension in the steady shear flow, which are further confirmed by the transient rheological measurements. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

In this work, thermal behaviors and viscoelasticity of the PPS/epoxy resin mixtures prepared by melt mixing were studied, and the rheology was used as a tool to further explore the relation between chain structures and properties of the mixtures. The results show that the epoxy resin can promotes degradation and branching of the PPS during melt mixing due to its poor thermal stability. The formation of long chain branched and partly crosslinked structures in the mixtures together with the residual decomposed components hence result in broadening of molecular weight distribution in comparison with those of the neat PPS. As a consequence, the mixtures show the viscoelastic behaviors far different from the neat PPS: the presence of crosslinked structure leads to the strong solid-like responses in the small amplitude oscillatory shear (SAOS) flow, and the presence of long chain branched structure to the weak strain overshoots in the large amplitude oscillatory shear (LAOS) flow. Moreover, after quiescent annealing, a strain-scaling transient stress behavior is observed in the mixtures in the reverse flow.

Poly(ε-caprolactone) (PCL) was filled with a very small amount of starch nanocrystals (SNC), with the objective being to control its crystallization. Three kinds of SNC particles, including a pristine one and ones acetylated with low- and middle-level substitutions, were used. Their roles during PCL crystallization were studied. The results reveal that pristine SNC acts as the nucleating agent, evidently increasing crystallization temperature and spherulite growth rate. However, nucleation activity of SNC particles reduces with their increasing level of surface acetylation. The middle-level-acetylated SNC particles even act as the antinucleation agent, impeding nucleation and subsequent spherulite growth of PCL. The phase affinity in those systems was then evaluated by the interaction energy parameter, aiming at a better understanding of the mechanism of role alterations of SNC particles. This work provides an interesting way to control PCL crystallization and opens a new door to extend applications of SNC particles.

An interesting biomass-derived shape memory polymer (SMP) based on cross-linked poly(l-malic acid) (PMA), with reconfigurable permanent shape and tunable shape memory transition temperature (Ttrans), was developed in this work. The amorphous cross-linked network was constructed in PMA using eco-friendly 1,8-octanediol as the cross-linker through a catalyst-free two-step way. The relations between crosslinking density (d) and glass transition temperature (Tg), as well as the mechanical strengths of as-obtained cross-linked PMA (CPMA) were then evaluated. Both the strengths and the Ttrans are easily tunable by controlling curing times. Moreover, the permanent shape of CPMA is reconfigurable due to additional crosslinking in the heat treatment process. It also shows good diversity of processing approaches. This work is the first report to achieve good strengths on the biodegradable PMA and to activate its shape memory effect, opening up a window of application of PMA as the smart material or even as the common plastics.

To investigate the relationship between functional groups on cellulose nanocrystals (CNC) and the performance of poly(β-hydroxybutyrate-co-valerate) (PHBV), the surface of CNC was modified by surface graft modification and PHBV/CNC biocomposites were prepared by melt blending. To demonstrate the interfacial adhesion difference between hydrophobic PHBV and hydrophilic CNC, palmitoyl chloride and ε-caprolactone had been used to tailor the oleophilic property of CNC. Results showed that CNC had heterogeneous nucleation effect on the crystallization process of PHBV, while the entanglement of molecular chains weakened the promoting functions of CNC-g-C16 (CNC grafted with palmitoyl chloride) and CNC-g-CL (CNC grafted with ε-caprolactone). Furthermore, CNC-g-CL exhibited better interfacial adhesion with PHBV when compared with CNC-g-C16. And 1 wt% CNC-g-CL improved the tensile strength of PHBV biocomposite to 38.09 MPa, which is 26.25% higher than PHBV.

Starch nanocrystals (SNCs) grafted with octenyl succinic anhydride (OSA) were used to stabilize caprylic/capric triglycerides (GTCC)-in-water emulsions. The morphology and viscoelasticity of emulsions were studied in terms of particle loadings and degrees of substitution (DSs). It is found that the emulsifying capacities of SNCs increase with increased DSs. Both the pristine SNC and modified ones can be well used to stabilize emulsions, whereas the emulsification follows different mechanisms. The platelet-like structure of SNCs, together with its improved amphiphilicity after surface treatments, are important to the formation and evolution of droplet clusters. The deformation and relaxation of those clusters result in weak flow overshoots and strong thixotropy in different shear flow fields, which favor storage and applications of GTCC-in-water emulsions as hydrocolloids. The mechanisms were then discussed in terms of rigidity of SNC and relaxations of clusters. This work proposes a promising application of SNC in food and cosmetic industries.

Chitin nanocrystal (ChNC) was used to prepare fully biodegradable nanocomposites with polylactide (PLA). The nucleation and melting behavior of nanocomposites were studied with the objective to correlate PLA-ChNC affinity to PLA crystallization. The results disclose that the PLA nanocomposites with pristine ChNCs and the ones with acetylated ChNCs show completely different nucleation and melting behavior because the role of ChNCs is altered after acetylation. Pristine ChNC acts as inert filler, with weak nucleating activity, while acetylated ChNCs as anti-nucleation agent, restraining crystallization of PLA. Accordingly, the nanocomposites with acetylated ChNCs show melting point depression, with reduced nucleation capability. The recrystallization and self-nucleation, as well as the double-melting behaviors were then studied in terms of acetylation levels of ChNCs and annealing temperatures, in order to better understand the relations between two-phase affinity and PLA chain dynamics. This work provides interesting information around designing thermal properties of the ChNC-filled PLA nanocomposites.

The isothermal cold and melt crystallization behavior of intercalated polylactide (PLA)/clay nanocomposites (PLACNs) were studied using differential scanning calorimetry (DSC), polarized optical microscope (POM), X-ray diffractometer (XRD) and Fourier Transform Infra-Red Spectrometer (FT-IR). The results show that the degree of crystallinity of PLA matrix decreases monotonously with increasing clay loadings for both the cold and melt crystallization. The cold crystallized sample shows a double melting behavior and lower melting temperature compared to that of melt-crystallized sample, especially in the presence of clay. The crystallization kinetics was then analyzed by the Avrami and Lauritzen-Hoffman methods for further comparison between these two crystallization behaviors. The results reveal that PLA and its nanocomposites present higher activation energy in melt crystallization than that in cold crystallization due to the reptation of entire polymer chains. The addition of clay facilitates the overall kinetics of melt crystallization, which is attributed to both the nucleation effect of clay and enhanced diffusion of PLA chains. However, for cold crystallization, only very small amounts of clay can slightly increase the kinetics, while larger amounts impede the process. The presence of clay leads to a diffusion-controlled growth of nucleation of PLA matrix in the cold crystallization process and, the hindrance effect of clay hence becomes the dominant factor gradually with increasing clay loadings in the case of high-rate nucleation.

The early stages of the cold crystallization process and the formation of a rigid amorphous phase as seen by the dielectric response of polylactide, PLA, and composites polylactide/carbon nanotubes, PLA/CNT, are studied here by broadband dielectric spectroscopy for CNT concentrations below percolation. The presence of precursors during the nucleation and crystallization process is demonstrated by the existence of a time shift between the decline in the number of mobile segments and the growth of a 3D ordered phase as seen by variable temperature wide angle X-ray scattering measurements. Also, the loss of the mobile amorphous phase is not justified by the slow lamellar growth in identical conditions. The variation of the molecular dynamics, either for short range reorientations or cooperative motions, is followed in both amorphous and semicrystalline states. The changes observed in the composites PLA/CNT show a moderate heterogeneous nucleating effect of the nanofiller and a sensitivity of the three subglass transitions to the chain ordering. The relaxation parameters of the segmental relaxation are not very sensitive to the presence either of lamellae or of the nanofiller.

Abstract The crystallization of poly(trimethylene terephthalate) (PTT) composites containing carbon nanotubes (CNTs) were studied in this work. The electrospinning technology was employed successfully to fabricate thin film samples with well‐embedded CNTs for spherulite observations using atom force microscopy. The results show that the composites present a higher overall crystallization rate than that of the neat PTT due to the nucleation effect of the CNTs. Banded spherulites can be observed on both the neat PTT and the composites. The presence of CNTs does not change the twisting mode of PTT crystal, but reduces band spacing and twist period. This is attributed to the enhanced fold staggering level of lamellae caused by the narrowed lamellae size and accelerated spherulite growth, which is further confirmed by analysis through secondary nucleation theory. Copyright © 2011 Society of Chemical Industry

A biomass-derived and biocompatible poly(l-malic acid) (PMA) based material with shape memory effect (SME) was developed in this work. 1,8-Octanediol was used as the cross-linker to construct cross-linking networks with hydrophilic backbone chain of PMA, tuning the density of networks and their swelling capacities by controlling −COOH/–OH ratios. The solvent-induced SME of as-obtained cross-linked PMAs was activated under mild conditions in this way. Using the shape recovery levels of U-shaped samples as the probes, the mixed methanol/ethanol/water systems with various ratios could be easily discriminated because the cross-linked PMAs show different sensing capacities to different components. The mechanisms were then studied in terms of the solvent molecule–polymer interactions. This work provides an interesting approach of visible discrimination of the solvents with similar structures, or their mixtures with various ratios, and also opens applications of biocompatible shape memory polymers in biomedical and chemical industries.

Extensive use of chemical fertilizers in agriculture can induce high concentration of ammonium nitrogen (NH4+-N) in soil. Desorption and leaching of NH4+-N has led to pollution of natural waters. The adsorption of NH4+-N in soil plays an important role in the fate of the NH4+-N. Understanding the adsorption characteristics of NH4+-N is necessary to ascertain and predict its fate in the soil-water environment, and pedotransfer functions (PTFs) could be a convenient method for quantification of the adsorption parameters. Ammonium nitrogen adsorption capacity, isotherms, and their influencing factors were investigated for various soils in an irrigation district of the North China Plain. Fourteen agricultural soils with three types of texture (silt, silty loam, and sandy loam) were collected from topsoil to perform batch experiments. Silt and silty loam soils had higher NH4+-N adsorption capacity than sandy loam soils. Clay and silt contents significantly affected the adsorption capacity of NH4+-N in the different soils. The adsorption isotherms of NH4+-N in the 14 soils fit well using the Freundlich, Langmuir, and Temkin models. The models’ adsorption parameters were significantly related to soil properties including clay, silt, and organic carbon contents and Fe2+ and Fe3+ ion concentrations in the groundwater. The PTFs that relate soil and groundwater properties to soil NH4+-N adsorption isotherms were derived using multiple regressions where the coefficients were predicted using the Bayesian method. The PTFs of the three adsorption isotherm models were successfully verified and could be useful tools to help predict NH4+-N adsorption at a regional scale in irrigation districts.

Soil contamination by heavy metals due to metal smelting activities poses a serious threat to the ecological environment and to human health, as it is considered to be one of the most significant sources of soil pollution. The objective of this study was to analyze the pollution status and human health risks of heavy metals emitted from metal smelting activities of a Pb-Zn smelter. The results of mean values of Zn, Pb, Cd, Cr, Cu and Mn should be incorporated and mention the status in respect to background value. Contamination levels of heavy metals were evaluated using the potential ecological risk index (RI). Possible human health risks were assessed using the health risk assessment model developed by the US EPA. The results showed that the soils are seriously polluted, and migrated down the soil vertical profile. The index of RI indicated a very high potential ecological risk overall in the entire study area, especially for Cd. The health risk analysis showed that adults and children are exposed to significant non-carcinogenic health risks, and there are higher non-carcinogenic health risks for children than for adults. Additionally, the carcinogenic risks of Cr were higher than those of Cd for the two population groups, and children were more susceptible than adults. These results are useful for management, prevention, control and remediation of heavy-metal contamination. Meanwhile, this research provides methods, experiences, and reference to other study of similar heavy-metal soil pollution. Bangladesh J. Bot. 51(4): 995-1015, 2022 (December) Special

Using polysaccharide nanocrystals such as chitin nanocrystals (ChNCs) as nanofiller for biodegradable aliphatic polymers is an attractive way of developing all-degradable nanocomposites. Crystallization study is vital for well regulating final performance of these type polymeric nanocomposites. In this work, ChNCs were incorporated with the poly(l-lactide)/poly(d-lactide) blends and as-obtained nanocomposites were used as target samples for the study. The results showed that ChNCs acted as nucleating agent, promoting the formation of stereocomplex (SC) crystallites and accelerating overall crystallization kinetics as a result. Therefore, the nanocomposites possessed higher SC crystallization temperatures and lower apparent activation energy as compared to the blend. However, the formation of homocrystallites (HC) was dominated by nucleation effect of SC crystallites and accordingly, the fraction of SC crystallites reduced more or less in the presence of ChNCs, despite the nanocomposites possessed higher rate of HC crystallization. This study also provided valuable information on accessing more applications of ChNCs to be used as SC nucleator for polylactide.

One of the promising applications of rod-like chitin nanocrystals (ChNCs) is the use as particle emulsifier to develop Pickering emulsions. We reported a ChNC-stabilized oil-in-water emulsion system, and developed a Pickering emulsion-templated method to prepare polylactide (PLA) hollow microspheres here. The results showed that both non-modified ChNCs and acetylated ChNCs could well emulsify the dichloromethane (DCM) solution of PLA-in-aqueous mannitol solution systems, forming very stable emulsions. At the same oil-to-water ratios and ChNC loadings, the emulsion stability was improved with increasing acetylation levels of ChNCs, accompanied by reduced size of droplets. Through the solvent evaporation, the PLA hollow microspheres were templated successfully, and the surface structure was also strongly dependent on the acetylation level of ChNCs. At a low level of acetylation, the single-hole or multi-hole surface structure formed, which was attributed to the out-diffusion of DCM caused by the solvent extraction and evaporation. These surface defects decreased with increased acetylation levels of ChNCs. Moreover, the aqueous suspension with as-obtained PLA microspheres revealed shear-thinning property and good biocompatibility, thereby had promising application as injectable fillers. This work can provide useful information around tuning surface structures of the Pickering emulsion-templated polymer hollow microspheres by regulating acetylation level of ChNCs.

Biodegradable polymer blends filled with rod-like polysaccharide nanocrystals have attracted much attention because each component in this type of ternary composites is biodegradable, and the final properties are more easily tailored comparing to those of binary composites. In this work, chitin nanocrystals (ChNCs) were used as nanofiller for the biodegradable poly(ε-caprolactone) (PCL)/polylactide (PLA) immiscible blend to prepare ternary composites for a crystallization study. The results revealed that the crystallization behavior of PCL/PLA blend matrices strongly depended on the surface properties of ChNCs. Non-modified ChNCs and modified ChNCs played completely different roles during crystallization of the ternary systems: the former was inert filler, while the latter acted as anti-nucleator to the PCL phase. This alteration was resulted from the improved ChNC-PCL affinity after modification of ChNCs, which was due to the 'interfacial dilution effect' and the preferential dispersion of ChNCs. This work presents a unique perspective on the nucleation role of ChNCs in the crystallization of immiscible PCL/PLA blends, and opens up a new application scenario for ChNCs as anti-nucleator.

Abstract The morphology and nonisothermal crystallization behavior of blends made of poly(phenylene sulfide) (PPS), with a amorphous polycarbonate (PC) were studied. The blend is found to be partially miscible by the dynamic mechanical thermal analysis (DMTA) and melt rheological measurements. The nonisothermal crystallization behavior of blend was studied by differential scanning calorimetry (DSC). The results show clearly that the crystallization temperatures of PPS component in the blend decrease with increasing of PC contents. The crystallization kinetics was then analyzed by Avrami, Jeziorny, and Ozawa methods. It can be concluded that the addition of PC decreases the PPS overall crystallization rate because of the higher viscosity of PC and/or partial miscibility of blend, despite of small heterogeneous nucleation effect by the PC phase and/or phase interface. The results of the activation energy obtained by Kissinger method further confirm that the amorphous PC in the partial miscible PPS/PC blend may act as a crystallization inhibitor of PPS. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007