Kannika Sahakaro

Silica-reinforced natural rubber (NR) tire tread compounds with epoxidized natural rubber (ENR) as a compatibilizer are investigated. The ENRs consisting of 10, 38 and 51 mole% epoxide are used in a range of 2.5–15.0 parts per hundred parts of rubber (phr). The addition of ENRs, especially ENR-38 and ENR-51, decreases the Mooney viscosity, Payne effect, flocculation rate constant and filler networking factor, which implies an improvement of silica dispersion in the compounds. Chemically bound rubber contents and interaction parameters of the compounds also increase with higher epoxide-contents of the ENRs, indicating more interactions and/or reaction between the epoxide-groups of the ENR and silanol groups on the silica surface. Tensile strength of the vulcanizates is improved with increasing mole% epoxide, and the optimum value is observed at 7.5 phr of ENR-51. The overall results show that silica-reinforced NR can be substantially improved by adding ENR as a compatibilizer, when compared to a compound without ENR, but somewhat less than with using a silane coupling agent.

After cellulose, lignin is the most commonly used natural polymer in green biomaterials. Pulp and paper mills and emerging cellulosic biorefineries are the main sources of technical lignin. However, only 2–5% of lignin has been converted into biomaterials. Making lignin-based polymer biocomposites to replace petroleum-based composites has piqued the interest of many researchers worldwide due to the positive environmental impact of traditional composites over time. In composite development, lignin is being used as a filler in commercial polymers to improve biodegradability and possibly lower production costs. As a natural polymer, lignin may have different properties depending on the isolation method and source, affecting polymer-based composites. The application has been affected by the characteristics of lignin and the uniform distribution of lignin in polymers. The review’s goal was to provide an overview of technical lignin extraction, properties, and its potential appropriate utilization. It was also planned to revisit the lignin-based composites’ preparation procedure as well as their composite characteristics. Solvent casting and extrusion methods are used to fabricate lignin from polymeric matrices such as polypropylene, epoxy, polyvinyl alcohol, polylactic acid, starch, wood fiber, natural rubber, and chitosan. Packaging, biomedical materials, automotive, advanced biocomposites, flame retardant, and other applications for lignin-based composites has existed. As a result, the technology is still being refined to increase the performance of lignin-based biocomposites in several applications. This review could assist explain lignin’s position as a composite additive, which could lead to more efficient processing and application strategies.

Abstract Composites of natural rubber (NR) and short pineapple leaf fiber (PALF) were prepared on a laboratory two‐roll mill. The influences of untreated fiber content and orientation on the processing and mechanical properties of the composites were investigated. The dependence of extent of orientation on fiber concentration was also established. Sodium hydroxide (NaOH) solutions (1, 3, 5, and 7% w/v) and benzoyl peroxide (BPO) (1, 3, and 5 wt % of fiber) were used to treat the surfaces of PALFs. FTIR and scanning electron microscope (SEM) observations were made of the treatments in terms of chemical composition and surface structure. The tensile strength and elongation at break of the composites were later studied. The fiber–matrix adhesion was also investigated using SEM technique. It was found that all surface modifications enhanced adhesion and tensile properties. The treatments with 5% NaOH and 1% BPO provided the best improvement of composite strength (28 and 57% respectively) when compared with that of untreated fiber. The PALF‐NR composites also exhibited better resistance to aging than its gum vulcanizate, especially when combined with the treated fibers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1974–1984, 2006

Abstract The dump temperature and mixing interval between rubber, silica, and silane coupling agent for silica-filled natural rubber (NR) tire tread compounds using bis-triethoxysilylpropyl tetrasulfide (TESPT) as silane were optimized. The dump temperature turns out to be the key parameter governing the properties of the silica-filled NR compounds. The increase in viscosity of the compounds by changing the dump temperature from 100 to 150 °C indicates that inevitably some cross-linking of NR occurs by sulfur contained in TESPT, simultaneous with the silanization reaction between silica and silane. However, the viscosity decreases again when dump temperatures above 150 °C are applied, indicating a dominant occurrence of degradation of the NR molecules. The results are in good agreement with bound rubber contents. The overall properties indicate that a dump temperature in the range of 135–150 °C and a silica–silane–rubber mixing interval of 10 min are the most appropriate mixing conditions for silica-filled NR compounds with TESPT as coupling agent.

Silane coupling agents containing different specific functionalities are studied to gain understanding of their roles in silica‐filled natural rubber (NR) compounds. Five different silane coupling agents, that is bis ‐(triethoxysilylpropyl) tetrasulfide (TESPT), bis ‐(triethoxysilylpropyl) disulfide (TESPD), octyltriethoxysilane, vinyltrimethoxysilane, and bis ‐(trimethyl‐silylmethyl) tetrasulfide (TMSMT), are comparatively investigated, by taking the most commonly used TESPT as a reference. The results reveal that alkoxy‐based silanes can effectively reduce the filler–filler interaction and lower compound viscosity owing to the effect of silane‐to‐silica hydrophobation which contributes to better compatibility between silica and NR. The alkoxy‐silanes with a sulfur moiety, that is TESPT and TESPD, show more pronounced improvement in overall properties as a result of filler–rubber interactions. The use of TMSMT which has no alkoxy groups but contains only a sulfur moiety elucidates that there are three reaction mechanisms involved in systems with sulfur‐alkoxy‐based silane. These are as follows: (1) the silane‐to‐silica or silanization/hydrophobation reaction; (2) the silane‐to‐rubber or coupling reaction; and (3) rubber–rubber crosslinking originating from active sulfur released by the polysulfide‐based silane TESPT. These simultaneous reactions are temperature dependent, and show an optimum level at a dump temperature of approximately 140–150°C, as depicted by filler–filler and filler–rubber interactions, as well as mechanical properties of such compounds. POLYM. ENG. SCI., 55:836–842, 2015. © 2014 Society of Plastics Engineers

The partial replacement of silica by high specific surface area and high structure Carbon Black (CB) N134 as secondary filler, keeping the same total filler content at 55 phr, shows a clear synergistic effect on overall performance. At low content of CB, i.e. in the range of 0–36 wt% of CB relative to total filler amount, the Payne effect and tan delta at both 0 °C and 60 °C change marginally, but thereafter gradually increase. Cure times are shortened in the presence of CB, facilitating an increase of productivity. Bound rubber content and mechanical properties show an optimum at 18 wt% of CB relative to total filler amount or at a ratio of silica/CB 45/10 phr. With regard to tire performance as indicated by the laboratory test results, the abrasion resistance, wet grip and ice traction can therefore be enhanced while maintaining the tire rolling resistance at the optimum level for this silica/CB ratio.

Lignin has a potential reinforcing filler and alternative to carbon black in rubber industry. This is due to cheaper materials, abundant with yearly renewable source, low weight, high biological efficiency and wide ecological adaptability. Utilization of bio-filler in rubber industry has increased more attention among the researchers due to increasing environmental concerns and toxicological effect of carbon black towards health and environment. This article is intended to summarize the current efforts in development of green and sustainable of rubber product. Instead of focused to silica and alternative rubber matrix like guayule and Russian dandelion, lignin also has potential as reinforcing filler and lead to development of competitive green rubber composites. Lignin has several special properties such as good mechanical, physico-chemical, biodegradability, antioxidant and excellent thermal stability. However, incorporation of lignin in rubber matrix is not a straightforward and needs to overcome with certain suitable solution because of the polarity of lignin molecules which contribute to strong self-interactions. Consequently, chemical modification of lignin is often used to improve the dispersion of lignin in elastomers, or compatibilizer is added to enhance interfacial of adhesion between lignin and rubber matrix. This review attempts to compile relevant knowledge about the performance of lignin-filled rubber composite from different approach such as mixing method, surface modification, hybrid filler etc. This study is expected to gain significance interest of researcher globally on the subject of lignin-based rubber composites and the advancement of development in green rubber product.

Modern fuel-saving tire treads are commonly reinforced by silica due to the fact that this leads to lower rolling resistance and higher wet grip compared to carbon black-filled alternatives. The introduction of secondary fillers into the silica-reinforced tread compounds, often named hybrid fillers, may have the potential to improve tire performance further. In the present work, two secondary fillers organoclay nanofiller and N134 carbon black were added to silica-based natural rubber compounds at a proportion of silica/secondary filler of 45/10 phr. The compounds were prepared with variable mixing temperatures based on the mixing procedure commonly in use for silica-filled NR systems. The results of Mooney viscosity, Payne effect, cure behavior, and mechanical properties imply that the silica hydrophobation and coupling reaction of the silane coupling agent with silica and elastomer are significantly influenced by organoclay due to an effect of its modifier: an organic ammonium derivative. This has an effect on scorch safety and cure rate. The compounds where carbon black was added as a secondary filler do not show this behavior. They give inferior filler dispersion compared to the pure silica-filled compound, attributed to an inappropriate high mixing temperature and the high specific surface area of the carbon black used. The dynamic properties indicate that there is a potential to improve wet traction and rolling resistance of a tire tread when using organoclay as secondary filler, while the combination of carbon black in silica-filled NR does not change these properties.

Influences of various types and concentrations of peroxides on the properties of thermoplastic vulcanizates based on natural rubber/polypropylene (PP) blends were investigated. The objective was to find a proper balance between the influences of degree of crosslinking of the rubber and degradation of the PP phase on the rheological, mechanical, and morphological properties. The typical crosslinking temperature and crosslink efficiency and also relative amounts of decomposition products of each peroxide play an important role in the properties of the TPVs. In this work, the TPVs prepared with DCP or DTBPIB give a superior overall balance of properties relative to the TPVs crosslinked with DTBPH or DTBPHY.

Reactive double bonds of natural rubber (NR) enable several possibilities for chemical modification. This present study prepared novel modified NRs with both grafted poly(methyl methacrylate (PMMA) and epoxide groups on the molecules. NR was firstly grafted with PMMA using a NR/MMA ratio of 90/10 by weight, and cumene hydroperoxide/tetraethylene pentamine (CHP/TEPA) as a redox initiator. The grafted NR latex was subsequently modified by an in situ epoxidation reaction using performic acid and finally neutralized using an aqueous solution of ammonium hydroxide. The presence of grafted PMMA and epoxide groups on the modified rubbers was examined by Fourier-transform infrared (FT-IR) and proton nuclear magnetic resonance (1H NMR) spectroscopy. The thermal properties were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The epoxidized NR-g-PMMA showed higher glass transition temperatures (Tg) when compared to NR-g-PMMA and virgin NR, and the Tg was shifted toward higher temperature with increasing epoxide contents. The thermal stability, wettability by water and diethylene glycol, rubber plasticity and oil resistance of the modified NRs increased after the introduction of PMMA grafted onto the NR chains, and were further enhanced by the presence of epoxide groups in the structures. The material consisting of 6 mol% of grafted PMMA and 30 mol% of epoxide groups showed superior thermal stability, wettability and swelling resistance compared to the modified rubber having only epoxide groups at the same level.

Diphenyl guanidine (DPG) is an essential ingredient in silica-reinforced rubber compounds for low rolling resistance tires, as it not only acts as a secondary accelerator, but also as a catalyst for the silanization reaction.However, because of concern over the toxicity of DPG that liberates aniline during high-temperature processing, safe alternatives are required.The present work studies several amines as potential alternatives for DPG.Different amines (i.e., hexylamine, decylamine, octadecylamine, cyclohexylamine, dicyclohexylamine, and quinuclidine) are investigated in a model system, as well as in a practical rubber compound by taking the ones with DPG and without amine as references.The kinetics of the silanization reaction of the silica/silane mixtures are evaluated using model compounds.The mixtures with amines show up to 3.7 times higher rate constants of the primary silanization reaction compared to the compound without amine.Linear aliphatic amines promote the rate constant of the primary silanization reaction to a greater extent compared to amines with a cyclic structure.The amines with short-alkyl chains that provide better accessibility towards the silica surface, enhance the primary silanization reaction more than the ones with long-alkyl chains.The different amines have no significant influence on the rate constant of the secondary silanization reaction.The amine types that give a higher primary silanization reaction rate constant show a lower flocculation rate in the practical compounds.For the systems with a bit lower primary silanization reaction rate, but higher extent of shielding or physical adsorption that still promotes higher interfacial compatibility between the elastomer and the filler surface, the rubber compounds show a lower Payne effect which would indicate lower filler-filler interaction.However, the flocculation rate constant remained high.

Kraft lignin was modified by using hydroxymethylation to enhance the compatibility between rubber based on a blend of natural rubber/polybutadiene rubber (NR/BR) and lignin. To confirm this modification, the resultant hydroxymethylated kraft lignin (HMKL) was characterized using Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy. It was then incorporated into rubber composites and compared with unmodified rubber. All rubber composites were investigated in terms of rheology, mechanical properties, aging, thermal properties, and morphology. The results show that the HMKL influenced the mechanical properties (tensile properties, hardness, and compression set) of NR/BR composites compared to unmodified lignin. Further evidence also revealed better dispersion and good interaction between the HMKL and the rubber matrix. Based on its performance in NR/BR composites, hydroxymethylated lignin can be used as a filler in the rubber industry.

The optimal mixing conditions for silica-filled NR compounds dictate the need to proceed at a high temperature, i.e., 150 °C, to achieve a sufficient degree of silanization. On the other hand, natural rubber is prone to degradation due to mechanical shear and thermal effects during mixing, particularly at long exposure times. The present work investigates NR rubber degradation during mixing in relation to prolonged silanization times. The Mooney viscosity and stress relaxation rates, bound rubber content, storage modulus (G'), and delta δ were investigated to indicate the changes in the elastic/viscous responses of NR molecules related to rubber degradation, molecular chain modifications, and premature crosslinking/interaction. In Gum NR (unfilled), an increase in the viscous response with increasing mixing times indicates a major chain scission that causes a decreased molecular weight and risen chain mobility. For silica-filled NR, an initial decrease in the Mooney viscosity with increasing silanization time is attributed to the chain scission first, but thereafter the effect of the degradation is counterbalanced by a sufficient silanization/coupling reaction which leads to leveling off of the viscous response. Finally, the higher viscous response due to degradation leads to the deterioration of the mechanical properties and rolling resistance performance of tire treads made from such silica-filled NR, particularly when the silanization time exceeds 495 s.

This study reports the effect of two different types of compatibilizer, namely epoxidized natural rubber with 50 mol% of epoxide group (ENR-50) and liquid butadiene rubber (LBR-352) for carbon black/lignin-filled natural rubber/polybutadiene rubber (NR/BR) composites in the range of 5–15 parts per hundred rubber (phr). The presence of ENR at concentrations up to 10 phr in carbon black/lignin-filled NR/BR composites reduced cure and scorch time by 33.7% and 21.1% respectively, compared to composites without ENR. This contributed to a better dispersion of the filler and an increase of the 300% modulus by 28.1%. Scanning electron microscopy results (SEM) showed better interaction between carbon black/lignin-filled NR/BR with ENR. Meanwhile, the composites with LBR showed the lowest filler-filler interaction, indicated by a decrease in storage modulus with an increase in strain in the filled compound i.e., Payne effect. Moreover, the utilization of LBR was increased by 168.8% compared to 18.3% with the addition of ENR. It can be concluded that the presence of ENR can enhance the mechanical, flexibility and dynamical properties, while the use of LBR can improve the process-ability and flexibility of rubber composites.

Abstract Graft copolymers of maleic anhydride and natural rubber or so‐called maleated natural rubbers (MNRs) were prepared in a molten state with varying maleic anhydride contents from 4 to 10 phr. In this work, the filler–filler and filler–rubber interactions of the MNR and precipitated silica were investigated. The MNR compounds containing 40 phr of silica both with and without 9 wt % of silane coupling agent were prepared. By increasing the maleic anhydride contents, the Mooney viscosity and cure times were increased, but the torque differences and cure rate indices were decreased. Bound rubber was increased with increasing maleic anhydride content, indicating an increase of filler–rubber interaction. In case of the compounds without silane, the MNR with 6 phr of maleic anhydride showed the lowest filler–filler interaction as indicated by a decrease of storage modulus upon an increase of strain in the filled compound i.e., Payne effect. This MNR compound also yielded the optimum mechanical properties. It has been demonstrated that a use of MNR with appropriate maleic anhydride content can reduce filler–filler interaction dramatically and hence improve a silica dispersion, as confirmed by SEM micrographs, resulting in an enhancement of the mechanical and dynamical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

ABSTRACT The rubber formulation plays a significant role in the properties of NR compounds filled with silica. In this work, the influences of various silicas, silane coupling agents, and diphenylguanidine (DPG) on the properties of compounds and vulcanizates—that is, cure characteristics, Mooney viscosity, flocculation kinetics, bound rubber content, Payne effect, tan δ at 60°C, tensile properties, and tear properties—are investigated. The results demonstrate that compound viscosity and curing behavior, as well as vulcanizate properties of the silica-filled NR, are much improved by incorporating silane coupling agents. Bis-triethoxysilylpropyltetrasulfide clearly gives better overall properties than the disulfide-based silane bis-triethoxysilylpropyldisulfide, except for scorch safety. DPG acts as a synergist to sulfenamide primary accelerators, as well as activator for the silanization reaction. Highly dispersible (HD) silicas can significantly enhance the degree of dispersion and so lead to higher filler–rubber interaction. As a consequence, the HD silicas provide better dynamic and mechanical properties for filled NR vulcanizates compared with conventional counterparts. The optimal quantities of both silane coupling agent and DPG required in the formulation are correlated to the cetyl trimethylammonium bromide specific surface area of the silicas. Furthermore, the results reveal that the silica structure as characterized by the dibutylphthalate adsorption also strongly influences the reinforcing efficiency.

Abstract Due to the toxicity of aromatic oils derived from polycyclic aromatic hydrocarbons (PAHs), safe process oils are required for a replacement in rubber compounds. The properties of tire tread compounds filled with high abrasion furnace black (HAF) when epoxidized palm oil (EPO) and epoxidized soybean oil (ESBO) are used as the processing oils, in comparison with the use of conventional distillate aromatic extract (DAE) were investigated. The oil characteristics were analyzed by spectroscopic techniques (FTIR and NMR), differential scanning calorimetry and elemental analysis. Influence of the oils on the properties of natural rubber (NR), NR/styrene butadiene rubber (SBR) blend, and SBR compounds was investigated. All compounds with the EPO and DAE oils have similar cure characteristics (i.e., scorch and cure times, torque differences) and processing properties (i.e., minimum torques and Mooney viscosities). However, the use of ESBO oil clearly retards the curing reaction, resulting in lower extent of crosslinking, and thus inferior vulcanizate properties. The mechanical properties, e.g., hardness, modulus, tensile strength, elongation at break, tear, and abrasion resistance, of the compounds utilizing the EPO and DAE oils are comparable and superior to those of the ESBO added compound. In addition, the use of EPO results in similar dynamic mechanical properties of rubber vulcanizates when compared with conventional DAE. The results indicate that EPO is a potential candidate for the placement of DAE oil in rubber compounds.

ABSTRACT Polar functionality attached onto natural rubber has a significant impact on the reinforcing efficiency of silica. Parallel studies involving various levels of epoxidation on natural rubber (ENR) in the absence of bis-(triethoxysilylpropyl) tetrasulfide (TESPT) coupling agent, as well as a combination of ENRs with different loadings of TESPT, provide a better understanding of the various factors that influence the properties of silica-filled ENR compounds. Based on the overall properties, the best possible combination to optimize processability, to reduce filler–filler interaction, and improve vulcanization rate as well as vulcanizate properties, is to use ENR with an epoxide content in the range of 20–30 mol%, together with a small portion of TESPT, that is, 2–4 wt% relative to the silica content. This leads to a reduction of approximately 60–80% of TESPT when compared with the conventional NR compounds, where the optimal loading of TESPT was 9.0 wt% relative to the silica content.

The performance of rubber composite relies on the compatibility between rubber and filler. This is specifically of concern when preparing composites with very different polarities of the rubber matrix and the filler. However, a suitable compatibilizer can mediate the interactions. In this study, composites of natural rubber (NR) with halloysite nanotubes (HNT) were prepared with maleated natural rubber (MNR) and modified palm stearin (MPS) as dual compatibilizers. The MPS dose ranged within 0.5-1.5 phr, while the MNR dose was fixed at 10 phr in all formulations. It was found that the mixed MNR/MPS significantly enhanced modulus, tensile strength, and tear strength of the composites. The improvements were mainly due to improved rubber-HNT interactions arising from hydrogen bonds formed in the presence of these two compatibilizers. This was clearly verified by observing the Payne effect. Apart from that, the MPS also acted as a plasticizer to provide improved dispersion of HNT. It was clearly demonstrated that MNR and MPS as dual compatibilizers improved rubber-HNT interactions and reduced filler-filler interactions, which then improved tensile and tear strengths, as well as dynamical properties. Therefore, the mix of MNR and MPS had a great potential to compatibilize non-polar rubber with HNT filler.

A proper balance between degree crosslinking of ENR and degradation of PP-phase, and the tendency of peroxide to form smelly by-products, in particular acetophenone are investigated on a 60/40 ENR/PP TPV. Four types of peroxides were used at two mixing temperatures: 160 and 180 oC. The maximum and final mixing torques are clearly related to the intrinsic decomposition temperature of the particular peroxide used, where DCP and DTBPIB turn out to be effective at 160 °C, whereas the other two type of peroxides require a higher temperature of 180 °C. The best mechanical properties are obtained at lower mixing temperature with DCP and DTBPIB, presumably due to less degradation of the PP and ENR. Unfortunately, these two types of peroxides form more smelly by-products and blooming than those of the DTBPHY and DTBPH. Dependent on the requirements of the pertinent application, a balanced selection needs to be made between the various factors involved to obtain an optimal product performance of these ENR/PP TPVs.

ABSTRACT In an attempt to reduce the high volatile organic compound (ethanol) emissions from silica-reinforced NR compounds, this work aimed to, at least partially, replace the use of large quantities of silane coupling agent bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT). The use of 7.5 phr of epoxidized natural rubber (ENR-51) as compatibilizer between NR and silica enhances the properties, which can be further improved by half or even lower amounts than required with TESPT alone. The properties obtained with TESPT are nearly matched, except for steric limitations imposed upon the ENR molecules to cap the silanol groups on the silica surface to the same extent as TESPT can do. Furthermore, TESPT donates reactive elemental sulfur to the compound during vulcanization, which needs to be compensated for in use with ENR.

The oil extended natural rubber (OENR) and HDPE blends with different rubber–plastic components (i.e., OENR/HDPE=0/100, 20/80, 30/70, 40/60, 50/50, 60/40, 70/30, 80/20 and 100/0) were prepared by a melt mixing process at 160 °C. Effect of blend compatibilizer (i.e., phenolic modified polyethylene, PhHRJ-PE) and proportions of OENR/HDPE in the blend on rheological, tensile, morphological and hardness properties were investigated. It was found that the blend with compatibilizer exhibited higher flow and viscosity curves as well as mechanical properties in terms of 100% modulus, tensile strength and elongation at break. SEM micrographs and rheological properties indicated that the blends of OENR/HDPE are two-phase systems (i.e., separation of rubber and plastic phases). The component with the lower proportion was found to be a dispersed phase in the major continuous matrix phase. Co-continuous phase morphology was also observed in the blend with the blend ratios of OENR/HDPE=50/50 and 60/40, where the materials behave as thermoplastic elastomers. The predictions using various models found that the phase inversion composition was in agreement with the experimental results. It was also found that the tensile strength, elongation at break, tension set and hardness properties were strongly dependent on the blend proportions.

Abstract Thermoplastic vulcanizates (TPVs) from natural rubber (NR) and polypropylene (PP) were studied, prepared by dynamic vulcanization during melt mixing, using various peroxides to crosslink the rubber phase. The objective was to find a proper balance between degree of crosslinking of the rubber and degradation of the PP‐phase, and the tendency of the peroxide to form smelly by‐products, in particular acetophenone. Four types of peroxides were investigated: 2,5‐dimethyl‐2,5‐di( tert ‐butyl‐peroxy) hexyne‐3 (DTBPHY), 2,5‐dimethyl‐2,5‐di( tert ‐butyl‐peroxy) hexane (DTBPH), di( tert ‐butylperoxyisopropyl) benzene (DTBPIB), and dicumyl peroxide (DCP), at two mixing temperatures: 160 and 180°C for a 60/40 NR/PP TPV. The maximum and final mixing torques are clearly related to the intrinsic decomposition temperature of the particular peroxide used, where DCP and DTBPIB turn out to be effective at 160°C, whereas the other two require a higher temperature of 180°C. The best mechanical properties, tensile strength, elongation at break and compression set are obtained at lower mixing temperature with DCP and DTBPIB, presumably due to less degradation of the NR and PP. Unfortunately, these two peroxides form more smelly by‐products than DTBPHY and DTBPH. Dependent on the requirements of the pertinent application, a balanced selection needs to be made between the various factors involved to obtain an optimal product performance of these NR/PP TPVs. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Abstract Thermal and mechanical degradation of natural rubber (NR) mixed with N ‐(1,3‐dimethylbutyl)‐ N ′‐phenyl‐ p ‐phenylenediamine (6PPD), polymerized 1,2‐dihydro‐2,2,4‐trimethyl‐quinoline (TMQ), and 50/50 weight basis mixture under high temperature and shearing conditions were investigated using a moving die processability test and FTIR spectroscopy. Relationship between dynamic properties in terms of tan δ value and chemical changes of NR molecules during degradation were correlated. The results indicated that the NR mixed with antioxidants caused decreased level of chain scission and oxidative degradation. The 6PPD provided better protection of NR against degradation at elevated temperature than TMQ. Furthermore, it was found that a prolonged mixing time caused more pronounced oxidative degradation on NR molecules than increased mixing temperature. The antioxidative capability of those antioxidants on NR was ordered based on their effectiveness as follows: 6PPD > 6PPD mixed with TMQ > TMQ. It was also found that the moving die processability test and FTIR spectroscopy are efficient routes to estimate the oxidative degradation of NR molecules. Therefore, the techniques could be applied to assess or compare antioxidative capability of various types and amounts of antioxidants used in the rubber formulation within a reasonable testing time. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Nanofillers are important to the success of rubber reinforcement. They have tremendously increased the specific surface area when compared to the conventional fillers. Some of them do have an outstanding strength and high aspect ratio. However, the strength of the filler material is not the dominant factor governing the properties of the nanocomposites since the reinforcement efficiency is influenced by several concomitant factors. Up to now, several reinforcement mechanisms have been studied and discussed, and yet there is no finite conclusion on the best model that describes the rubber reinforcement mechanisms. The response behavior of the rubber nanocomposites under mechanical load has contributions from various components such as from the matrix, filler, and interfaces. The reinforcement mechanisms which have been discussed involved various aspects, such as, the filler–filler and the filler–rubber interactions, the filler network at low strain and/or over the percolation threshold, the dispersion degree, the efficiency of stress transfer between the interface, the physical entanglement and the volume of polymer chains constrained in the proximity of the filler surface, and the occurrence of the glassy layer around the nanoparticles.

Natural Rubber (NR) grafted with 3-octanoylthio-1-propyltriethoxysilane (NXT) was prepared by melt mixing using 1,1′-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane as initiator at 140 °C with NXT contents of 10 and 20 parts per hundred rubber [phr] and initiator 0.1 phr.The silane grafted on NR molecules was confirmed by Fourier transform infrared (FTIR), proton nuclear magnetic resonance ( 1 H-NMR) and scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM-EDX).Based on 1 H-NMR, the use of 10 and 20 phr (parts per hundred resin) of silane resulted in grafted NXT onto NR of 0.66 and 1.32 mol%, respectively, or a grafting efficiency of approx.38%.The use of NXT-grafted NR as compatibilizer in silica-filled NR compounds, to give a total amount of NXT in both grafted and non-grafted forms in the range of 0.8-6.1 wt% relative to the silica, decreases the Mooney viscosity and Payne effect of the compounds, improves filler-rubber interaction, and significantly increases the tensile properties of the silica-filled NR-compounds compared to the non-compatibilized one.At the same silane-content, the use of silane-grafted NR gives slightly better properties than the straight use of the same silane.With sulfur compensation, the use of NXT-grafted-NR with about 6 wt% NXT relative to the silica gives technical properties that reach the levels obtained for straight use of bis-(3-triethoxysilyl-propyl)tetrasulfide (TESPT) at 8.6 wt% relative to the silica.

Abstract Graft copolymers of NR and PMMA (i.e., NR‐ g ‐PMMA) were prepared with the bipolar redox initiation system, using various percentages of molar ratios of NR/MMA at 95/5, 90/10, 80/20, 70/30, and 60/40. It was found that the Mooney viscosity, shear stress, and shear viscosity of the NR‐ g ‐PMMA increased with an increase in the molar ratio of MMA used in the graft copolymerization. This may be attributed to an increasing trend of the chemical interaction between polar functional groups within the grafted PMMA molecules. Furthermore, a decreasing trend of storage moduli was observed with increasing molar ratios of MMA. The glass transition temperature was obtained from the tan δ curves. We found a slightly increasing trend of the T g 's with an increase in molar ratios of MMA used in the grafting reaction. The NR‐ g ‐PMMA was later compounded using TBBS as an accelerator. With an increase in molar ratios of MMA in the grafting reaction, we observed an increasing trend of minimum torque, maximum torque, cure time, and scorch time, but quite similar levels of torque difference and crosslink density. Furthermore, the tensile strength of the NR‐ g ‐PMMA gum vulcanizate increased with an increase in molar ratios of MMA, whereas the elongation at break decreased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1600–1614, 2006

Abstract Graft copolymers of natural rubber and poly (methyl methacrylate) (NR‐ g ‐PMMA) were prepared in a laboratory scale, and then extended to a pilot scale production. Reaction conditions were first assessed based on a preparation in the laboratory scale with a reactor capacity of 1.5 l. An optimum grafting efficiency was obtained when cumene hydroperoxide/tetraethylenepentamine (CHP/TEPA) redox initiator was used at the reaction temperature and time of 50°C and 3 h, respectively. MMA monomer was used without purification in the polymerization process comparing with the purified one by means of extraction. It was found that only a slight decrease of grafting efficiency was observed when the nonpurified monomer was used in the reaction. The nonpurified monomer was therefore used to prepare the NR‐ g ‐PMMA in a pilot scale production with a reactor capacity of 260 L. Various weight ratios of NR/MMA at 50/50, 60/40, 70/30, and 85/15 were studied. The resulting graft copolymers were characterized by FTIR and 1 H‐NMR techniques. It was found that increasing concentration of MMA caused an increase of free PMMA (i.e., homopolymer) but a decrease of free NR (i.e., ungrafted NR) and grafting efficiency. Quantity of grafted PMMA on the NR backbone was estimated using the integrated peak areas of 1 H‐NMR spectra and quantitative analysis by extraction method. The results were found to be in good agreement. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Abstract A simple blend (i.e., blend without curative) of 60/40 rubber/nylon‐12 with three different types of natural rubber (i.e., air‐dried sheet natural rubber (ADS) and epoxidized natural rubbers (ENR) with 25 and 50 mol% epoxide) was prepared by the melt‐mixing process. Influence of different types of rubbers and the level of epoxide groups in ENR molecules on the properties of the blends were investigated. It was found that all the blends exhibited a co‐continuous phase morphology. Furthermore, the ENR/nylon‐12 blends exhibited superior mechanical properties, stress relaxation behavior, thermal and rheological properties, and a finer grain morphology than that of the ADS/nylon‐12 blend. This may be attributed to the higher interfacial adhesion between the ENR and nylon‐12 phases via a chemical interaction of epoxide groups in ENR molecules and polar functional groups in the nylon‐12 molecules. Temperature scanning stress relaxation (TSSR) measurement was also performed. Improvement in stress relaxation and thermal resistance of the blends with ENR was observed. Moreover, the higher temperature coefficient and lower glass transition temperature ( T g ) of the nylon‐12 phase in the ENR‐50/nylon‐12 blends were found. © 2011 Wiley Periodicals, Inc. Adv Polym Techn 32: 118–129, 2012; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.20243

ABSTRACT This work investigates the effect of epoxidized low molecular weight natural rubber (ELMWNR) in silica- and carbon black-filled natural rubber (NR) compounds on processing and mechanical and dynamic mechanical properties. The ELMWNRs with different mol% epoxide content were prepared from depolymerization of epoxidized NR using periodic acid in latex state to have a molecular weight in a range of 50 000–60 000 g/mol. Their chemical structures and actual mol% of epoxide were analyzed by 1H NMR. The ELMWNRs were added to the filled NR compounds as compatibilizers at varying loadings from 0 to 15 phr. The addition of ELMWNR decreases compound viscosity and the Payne effect, that is, filler–filler interaction, of the silica-filled compound. In the silica–silane compound and the compound with 28 mol% epoxide (ELMWNR-28), the compound viscosities are comparable. The optimal mechanical properties of silica-filled vulcanizates are obtained at the ELMWNR-28 loading of 10 phr. In contrast, the addition of ELMWNR to a carbon black-filled compound shows only a plasticizing effect. The incorporation of ELMWNR into NR compounds introduces a second glass transition temperature and affects their dynamic mechanical properties. Higher epoxide contents lead to higher loss tangent values of the rubber vulcanizates in the range of the normal service temperature of a tire.

ABSTRACT Diphenyl guanidine (DPG) is the most commonly used secondary accelerator in silica-reinforced rubber compounds because of its additional positive effect on the silanization reaction and deactivation of free silanol groups that are left over after the silanization. However, because of health and safety concerns about the use of DPG, which decomposes to give highly toxic aniline during high processing temperature, safe alternatives are required. This work investigates the effect of various types of aliphatic amines having alkyl or cyclic structures and similar pKa (i.e., hexylamine [HEX], decylamine [DEC], octadecylamine [OCT], cyclohexylamine [CYC], dicyclohexylamine [DIC], and quinuclidine [QUI]) on the properties of silica-reinforced natural rubber (NR) compounds by taking the ones with DPG and without amine as references. When compared with the compound without amine, the use of all amine types reduces filler–filler interaction (i.e., the Payne effect) and enhances filler–rubber interaction, as indicated by bound rubber content and decreased heat capacity increment. The amines with alkyl chains can reduce the Payne effect and enhance cure rate to a greater extent compared with the amines with cyclic rings as a result of better accessibility toward the silica surface and a shielding effect because of less steric hindrance. The longer carbon tails on linear aliphatic amines ranging from HEX, DEC, to OCT lead to a lower Payne effect, lower heat capacity increment, higher bound rubber content, and higher modulus as well as tensile strength. Overall, the use of OCT provides silica-reinforced NR compounds with properties closest to the reference one with DPG and can act as a potential alternative for DPG.

ABSTRACT The feasibility of the use of epoxidized palm oil (EPO) and amine-modified epoxidized palm oil (mEPO) as process oils in silica-reinforced natural rubber compounds is studied. The chemical structures of EPO and mEPO are characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy (1H-NMR). Amine modification for 3 and 5 h leads to mEPOs with 0.03 and 0.04 mmol of amine in 1 g of oil, referred to as 0.03 mEPO and 0.04 mEPO, respectively. The properties of rubber compounds containing modified palm oils are investigated by taking those with TDAE oil and those without oil as references. The use of process oils clearly enhances the processibility (i.e., lower mixing torque and complex viscosity) and mechanical and dynamic mechanical properties of the rubber compounds as compared with compounds without oil. The rubber compounds with EPO and 0.03 mEPO show a lower Payne effect (i.e., less filler–filler interaction) than the rubber compound with TDAE because of the shielding effect of the oils on the silica surface. The use of mEPO boosts the vulcanization reaction, resulting in much better cure torque difference, which indicates a higher crosslink density due to the amino groups present in mEPO as compared with TDAE. Therefore, rubber compounds with mEPOs have better mechanical properties (i.e., reinforcement index, tensile strength, and elongation at break) and better elastic response under dynamic deformation, as indicated by a lower loss tangent at 60 °C as compared with the mix with TDAE.

Lignin from kenaf (Hibiscus cannabinus) core was investigated as an alternative filler for rubber. Three types of extraction methods were used to isolate lignin from kenaf, namely kraft, soda and organosolv process. The particle size, surface area, functionalities changes, molecular weight and thermal properties of the lignin were characterized. The results showed that Kraft lignin (KL) has the smallest particle size (40.41 μm) compared to soda lignin (SL) (63.85 μm) and organosolv lignin (OL) (66.85 μm). This is in good agreement with the BET surface area of 9.52 m2/g, 1.25 m2/g and 2.40 m2/g respectively. However, the smaller surface area of SL compared to OL is due to the smaller pore size and pore volume of SL. KL also showed high hydroxyl content with corresponding high thermal stability as confirmed by NMR and TGA. The thermal stability of the lignin correlates well with the molecular weight (MW). From the overall characteristics, it can be concluded that KL, SL and OL can be used as an alternative filler in rubber compounds to substitute common fillers like silica and carbon.

Abstract Dynamically cured 60/40 NR/HDPE blends with various amounts of phenolic curative were prepared in an internal mixer at 160°C. A simple blend (i.e., the blend without curative) was also prepared using the same materials and blend proportion for comparison purposes. Mechanical, dynamic, and morphological properties; swelling resistance and crosslink density of the blends were investigated. It was found that the thermoplastic vulcanizates (TPVs) gave superior mechanical and dynamic properties than the simple blend. Furthermore, the mechanical properties in terms of elongation at break, modulus and tensile strength and elastic response in dynamic test in terms of storage modulus increased with increased loading amount of the curative. The complex viscosity also increased but the tan δ and tension set decreased with increased loading level of the curative. The crosslink density of the TPVs was estimated based on the elastic shear modulus. It was found that the crosslink density of the blends increased with increased loading levels of the curative while the degree of swelling decreased. This correlated well with the trend of mechanical and dynamic properties. SEM micrographs were used to confirm the level of mechanical and dynamic properties. It was found that the simple blend at a given blend ratio exhibited co‐continuous phase morphology. However, the TPVs showed micron scale of vulcanized rubber domains dispersed in a continuous HDPE matrix. The size of vulcanized rubber domains decreased with increasing amounts of the curative. This led to greater interfacial adhesion between the phase and hence superior mechanical and dynamic properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Epoxidized low molecular weight natural rubber (ELMWNR) with 28 mol% epoxide groups and weight average molecular weight of 49,000 g mol −1 was prepared by oxidative degradation of epoxidized natural rubber (NR) using periodic acid in the latex state. ELMWNR-28 was used at 10 parts per hundred parts of rubber (phr) loading in combination with bis-(triethoxysilylpropyl) tetrasulfide (TESPT) as the silane coupling agent in the range of 0–4.5 phr in silica-reinforced NR compounds. The use of TESPT in combination with ELMWNR-28 gives lower mixing torques and compound viscosities compared with the use of TESPT alone and the system without any compatibilizer. The bound rubber content, modulus, and tensile strength of the compounds with only TESPT strongly depend on the TESPT loading. The use of ELMWNR-28 as a compatibilizer clearly improves such properties compared with the non-compatibilized systems. By adding TESPT into the compound with ELMWNR-28, the properties further improve with increasing TESPT loading. The combined effect of ELMWNR-28 at 10 phr with a small amount of TESPT at 1.5 phr results in compounds with superior processability (i.e. low Mooney viscosity and Payne effect), and only slightly lower modulus and reinforcement index (M300/M100) compared with the use of the optimum content of TESPT. This compatibilizer/TESPT combination has the environmental benefits that the ELMWNR is a naturally based product, and that the reduced amount of TESPT silane coupling agent emits a greatly reduced amount of ethanol during processing.

Modern high-performance tire treads are presently commonly reinforced with silica as rubber fillers because they raise key tire performance criteria such as lower rolling resistance and higher wet grip compared to carbon black-filled rubber. The present work aims at a synergistic effect of silica with different additional fillers in order to shift tire performance with respect to wet grip and rolling resistance for safety and fuel savings, respectively towards a better abrasion resistance, all characterized by the dynamic mechanical properties of the vulcanized compounds. The use of small amounts of secondary fillers or hybrid fillers in silica-reinforced tire tread compounds has the potential to improve tire performance further. In the present work, two secondary fillers: organoclay nanofiller and N134 carbon black were added to silica-based natural rubber compounds at a proportion of silica/secondary filler of 45/10 phr. The compounds were prepared with variable mixing temperatures based on the procedure commonly used for silica-filled NR systems. The results of Mooney viscosity, Payne effect, cure behavior and mechanical properties imply that the silica hydrophobation and coupling reaction of the silane coupling agent between the silica and elastomer are significantly enhanced by organoclay due to an effect of its modifier: an organic ammonium derivative. This modifier has an effect on scorch safety and cure rate. The compounds where carbon black was added as a secondary filler do not show this improvement. They give inferior filler dispersion compared to the pure silica-filled compound, attributed to an inappropriate high mixing temperature and the large specific surface area of the carbon black used. The dynamic mechanical properties indicate that organoclay as a secondary filler has the potential to improve the wet traction and rolling resistance of a tire tread, while the use of carbon black in silica-filled NR does not change these properties.

Abstract Graft copolymer of natural rubber and poly(methyl methacrylate) (NR‐g‐PMMA) was prepared using semi‐batch emulsion polymerization technique via bipolar redox initiation system. It was found that the grafted PMMA increased with the increase of methyl methacrylate (MMA) concentration used in the graft copolymerization. The NR‐g‐PMMA was later used to prepare thermoplastic vulcanizates (TPVs) by blending with PMMA through dynamic vulcanization technique. Conventional vulcanization (CV) and efficient sulphur vulcanization (EV) systems were studied. It was found that the CV system provided polymer melt with lower shear stress and viscosity at a given shear rate. This causes ease of processability of the TPVs via extrusion and injection molding processes. Furthermore, the TPVs with the CV system showed higher ultimate tensile strength and elongation. The results correspond to the morphological properties of the TPVs. That is, finer dispersion of the small vulcanized rubber particles were observed in the PMMA matrix. Various blend ratios of the NR‐g‐PMMA/PMMA blends using various types of NR‐g‐PMMA (i.e. prepared using various percentage molar ratios of NR and MMA) were later studied via dynamic vulcanization by a conventional sulphur vulcanization system. It was found that increasing the level of PMMA caused increasing trend of the tensile strength and hardness properties but decreasing level of elongation properties. Increasing level of the grafted PMMA in NR molecules showed the same trend of mechanical properties as in the case of increasing concentration of PMMA used as a blend component. From morphological studies, two phase morphologies were observed with a continuous PMMA phase and dispersed elastomeric phase. It was also found that more finely dispersed elastomeric phase was obtained with increasing the grafted PMMA in the NR molecules. Copyright © 2005 John Wiley & Sons, Ltd.

In this study, maleic anhydride (MA) grafted natural rubber (NR), known as maleated natural rubber (MNR), was melt-prepared with the MA content varied within 1–8 phr. MNR was used as the main matrix, with Halloysite Nanotubes (HNT) as a filler, in order to obtain composites with improved performance. The compounds were investigated for their filler–filler interactions by considering their Payne effect. On increasing the MA content, scorch and cure times increased along with maximum torque and torque difference. The MNR with 4 phr of MA exhibited the least filler–filler interactions, as indicated by the retention of the storage modulus after applying a large strain to the filled compound. This MNR compound also provided the highest tensile strength among the cases tested. It is interesting to highlight that MNR, with an appropriate MA content, reduces filler–filler interactions, and, thereby, enhances the HNT filler dispersion, as verified by SEM images, leading to improved mechanical and dynamical properties.

Abstract The NR/BR blend compound formulations for tire sidewall applications contain a set of stabilizers added to prevent degradation mainly due to oxygen, ozone, and heat. 6PPD is the most effective and widely used antiozonant in tire compounds, but is a highly staining material causing a surface discoloration of the tire sidewall. Incorporation of 30 phr EPDM into blends of NR/BR improves the ozone resistance to the required level, without the need of 6PPD. The first two parts of this series have described a reactive processing technique applied to enhance the covulcanization and blend homogeneity, together with their characterization. In the present article, the properties of the NR/BR/EPDM blends prepared by both reactive and straight mixing are tested in comparison with those of equivalent conventional NR/BR compounds. The reactive NR/BR/EPDM blend vulcanizates show excellent tensile strength, elongation at break, tear strength, fatigue‐to‐failure, and ozone resistance in both static and dynamic conditions. The properties are equivalent or even superior to those of the conventional NR/BR tire sidewall compounds. The simple straight mixed NR/BR/EPDM blend vulcanizates distinctively possess inferior mechanical properties compared to those of the reactive mix. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2555–2563, 2007

Abstract EPDM incorporated into blends of natural rubber/butadiene rubber (NR/BR) improves ozone resistance. In this work, the inferior mechanical properties of NR/BR/EPDM blends generally obtained by conventional straight mixing are overcome by utilizing a reactive processing technique. The entire amount of curatives, based on a commonly employed accelerator N ‐cyclohexyl‐2‐benzothiazole sulfenamide (CBS) and sulfur, is first added into the EPDM phase. After a thermal pretreatment step tuned to the scorch time of the EPDM phase, the modified EPDM is mixed with premasticated NR/BR. The reactive blend vulcanizates show a significant improvement in tensile properties: tensile strength and elongation at break, as compared to those prepared by straight mixing, in both gum and carbon black‐filled blends. The increase of tensile properties in gum and filled reactive blend vulcanizates does suggest that the reactive processing technique leads to more homogeneous blends due to, either a better crosslink distribution, or more homogeneous filler distribution, or both. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:2538–2546, 2007

The dispersion stability of silica aggregates in the rubber matrix is one of the concerns for silica-filled compounds. Silica aggregates tend to flocculate due to their poor compatibility with the rubbers and consequent strong tendency for self-association. The flocculation process can occur during compound storage as well as at the onset of vulcanization. This present work studies the kinetics of the flocculation process in silica-reinforced natural rubber (NR) compounds by following the changes of the storage modulus during thermal annealing under conditions applied for vulcanization. The results demonstrate that silica flocculation can be effectively suppressed by increasing compound dump temperature and amount of silane, as these result in a better degree of dispersion, higher degrees of hydrophobation, and filler–rubber interaction. The compounds containing highly dispersible silicas exhibit greater filler–rubber interaction, but their flocculation processes develop faster when compared to the compounds filled with conventional silicas. Epoxidation of NR clearly influences the filler–rubber interaction but shows no clear evidence of a change of flocculation rate.

ABSTRACT Octadecylamine (OCT) as an alternative for diphenyl guanidine (DPG) in silica-reinforced NR tire compounds with bis-(triethoxysilyl-propyl)tetrasulfide (TESPT) as silane coupling agent was investigated with focus on the improvement of compatibility between the silica surface and rubber molecules, by taking the amine-free rubber compound as a reference. The quantity of OCT and DPG was varied in a range of 2.4–9.5 mmol per 100 parts of rubber by weight (i.e., 0.5–2.5 phr). Bound rubber contents, changes in heat capacity (ΔCp), and immobilized polymer layer (χim) data prove an enhanced interfacial compatibility as the amines are absorbed on the polar silica surface and catalyze the silanization reaction. Comparing the two different amine types, the rubber compounds with OCT show higher interfacial compatibility than the ones with DPG, because of an additional shielding effect promoted by the long alkyl chain that leads to more hydrophobicity. Thus, the rubber compounds with OCT show higher physically bound rubber contents and consequently higher total bound rubber, a higher immobilized polymer layer, as well as a lower Payne effect. However, the compounds with OCT show a higher flocculation rate constant because the physical interactions between amine and silanol groups decrease under thermal treatment. The compounds with OCT show a lower cure torque difference that indicates a lower crosslink density, but because of the good interfacial interaction combining both chemical and physical interactions, the vulcanized rubber with OCT at optimum loading shows better mechanical properties and tan δ at 60 °C when compared with the DPG counterpart. At high (excessive) loading of amines, the compounds with DPG clearly have higher crosslink density and thus higher modulus as well as tensile strength compared with the use of OCT.

ABSTRACT A bio-based process oil for rubber compounds is one of the compounding ingredients to be used toward an eco-friendly and more sustainable rubber technology. This work investigates epoxidized palm oil (EPO) as an alternative for petroleum-based process oil in silica-reinforced natural rubber (NR) tire tread compounds. The effect of different incorporating steps of EPO on the properties of the rubber compounds is first studied, taking into account that the polar functional groups in the oil molecules may interact with the silanol groups on the silica surface. The properties of silica-reinforced NR compounds with EPO oil are compared with that of reference mixes with treated distillate aromatic extract (TDAE) and without oil. The compounds with EPO show a lower viscosity, filler–filler interaction, and flocculation rate constant but higher cure reaction rate constants compared with the compound with TDAE. The results indicate that the epoxide groups in EPO interact with the silanol groups on the silica surface, promoting a greater shielding effect on the polar surface and thus better silica dispersion and less interference with the vulcanization reaction. The different incorporating steps of EPO show no significant effect on the viscosity, filler–filler interaction, or flocculation rate constant but clearly affect the extent of crosslinking, as indicated by the cure torque difference. The presence of EPO in an early stage of the mixing together with the first half addition of silica and silane results in the lowest cure torque difference, modulus, and tensile strength (i.e., the highest tan δ at 60 °C), which indicates a possible obstruction for the interaction between the silanol groups and silane coupling agent by the EPO molecules. Comparing EPO with different epoxide contents in the range of 1–3 mol%, the increase in epoxide content gives similar Payne effects but enhances the cure reaction, resulting in improved tensile properties and tan δ at 60 °C. The results clearly prove that EPO can be used as a TDAE alternative.

ABSTRACT Reinforcement of silica in tire tread compounds is known to reduce hysteresis or energy loss, which leads to a production of energy-saving tires. Even though silica–silane technology has been well established, further development to enhance its performance is still needed. One of the approaches is to use hybrid or dual filler. The use of silica-organomodified montmorillonite (MMT) dual filler in the reinforcement of natural rubber (NR) truck tire tread compounds is investigated. The NR-MMT master batches were prepared by using the in situ organomodified and latex compounding method. Because the surface-modifying agent or surfactant is a key factor in determining the level of MMT dispersion in the rubber matrix, the effect of quaternary amine salt (Q) contents on mechanical and dynamic properties of NR tread compounds reinforced by silica-MMT was studied. The results revealed that MMT and Q can effectively reduce the filler–filler interaction and complex viscosity owing to a good dispersion of MMT and silica in the NR matrix and Q, which acts as a dispersing agent in addition to the silane coupling agent used in the compound, leading to improvement in tensile, abrasion resistance, and dynamic mechanical properties with an increasing amount of Q. Furthermore, at the optimum content of the surfactant used (36 wt%), the silica-MMT–reinforced NR exhibited improved tensile strength (+4%), wet grip, and rolling resistance, respectively, as indicated by loss tangent at 0 °C (+6%) and 60 °C (−15%), while maintaining a modulus at 300% strain and abrasion resistance as compared with the silica-NR reference compound. Such a dual-filler system demonstrates its potential use for tire treads with better performance.

Natural rubber (NR) is known as hydrophobic material and is incompatible with hydrophilic filler such as halloysite nanotubes (HNTs). To overcome this obstacle, the compatibilizer is a material of choice to incorporate in such compound. In this study, bio-based compatibilizer was used which was prepared by modification of palm stearin. The presence of special functionalities of modified palm stearin (MPS) was confirmed by Fourier transform infrared (FTIR) analysis. It was then varied from 0.5 phr to 2 phr to the NR matrix. Here, the properties were evaluated through the mechanical properties with special attention to the relationship between their reinforcement and crystallization behavior after stretching. It was found that the addition of MPS significantly enhanced the modulus, tensile strength, and tear strength of the composites. This clearly corresponded to interaction between NR and HNT promoted by MPS. The FTIR spectrum, X-ray diffraction patterns, and scanning electron microscopy images were also utilized to verify the behavior of MPS in the NR/HNT composites. As for the crystallization of the composites, the results obtained from stress–strain curves are in very good agreement to the outputs observed by the synchrotron wide-angle X-ray scattering. This corresponding interaction of MPS has greatly influenced on assisting the strain-induced crystallization of composites.

Abstract Simple blending of natural rubber/ethylene–propylene–diene rubber (NR/EPDM) generally results in inferior mechanical properties because of curative migration and their differences for filler affinity. In this work, the 70/30 and 50/50 NR/EPDM blends prepared by reactive processing techniques were investigated and compared with the simple, nonreactive blends. The reactive blend compounds were prepared by preheating EPDM, containing all curatives to a predetermined time related to their scorch time prior to blending with NR. For the 70/30 gum blends, four types of accelerators were studied: 2,2‐mercaptobenzothiazole (MBT), 2,2‐dithiobis‐ (benzothiazole) (MBTS), N ‐cyclohexyl‐2‐benzothiazolesulfenamide (CBS), and N ‐ tert ‐butyl‐2‐benzothiazolesulfenamide (TBBS). When compared with the simple blends, the reactive blends cured with CBS and MBTS showed a clearly improved tensile strength whereas the increase of tensile strength in the blends cured with TBBS and MBT was marginal. However, a dramatic improvement of ultimate tensile properties in the reactive 50/50 NR/EPDM blends cured with TBBS was observed when compared with the simple blend. For the N ‐550‐filled blends at the blend ratios of 70/30 and 50/50, the reactive‐filled blends prepared under the optimized preheating times demonstrated superior tensile strength and elongation at break over the simple blends. The improved crosslink and/or filler distribution between the two rubber phases in the reactive blends accounts for such improvement in their mechanical properties. This is shown in the scanning electron micrographs of the tensile fractured surfaces of the reactive blends, which indicate a more homogeneous blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Abstract Commonly used dicumyl peroxide (DCP) in combination with coagent, triallyl cyanurate (TAC), as a crosslinking agent is well acceptable for dynamically vulcanized rubber phase of thermoplastic vulcanizates (TPVs). However, it generally produces volatile decomposition products, which cause a typical unpleasant smell and a blooming phenomenon. In this work, influence of two types of multifunctional peroxides: 2,4‐diallyloxy‐6‐ tert ‐butylperoxy‐1,3,5‐triazine (DTBT) and 1‐(2‐ tert ‐butylperoxyisopropyl)‐3‐isopropenyl benzene (TBIB), on properties of TPVs based on epoxidized natural rubber (ENR)/polypropylene (PP) blends were investigated. The conventional peroxide/coagent combinations, i.e., DCP/TAC and tert ‐butyl cumyl peroxide (TBCP)/α‐methyl styrene (α‐MeS) were also used to prepare the TPVs for a comparison purpose. The TPVs with multifunctional peroxide, DTBT, provided good mechanical properties and phase morphology of small dispersed vulcanized rubber domains in the PP matrix which were comparable with the DCP/TAC cured TPVs. However, the TPVs with TBIB/α‐MeS and TBCP/α‐MeS showed comparatively low values of the tensile properties as well as rather large phase morphology. The results were interpreted by three main factors: the kinetic aspects of the various peroxides, solubility parameters of respective peroxide/coagent combinations in the ENR and PP phases, and the tendency to form unpleasantly smelling byproducts. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Abstract Cure incompatibility in NR/BR/EPDM blends is a crucial problem, affecting blend properties. In a previous study, it was demonstrated that the mechanical properties of such blends can be significantly improved by utilizing a reactive processing technique, in which a pretreated EPDM is first prepared by incorporating all compounding ingredients in the EPDM and subsequent preheating, prior to crossblending with premasticated NR/BR. In the present article, the pretreated EPDM‐moieties are prepared using two different accelerators, N ‐cyclohexyl‐2‐benzothiazole sulfenamide (CBS) and 6‐nitro MBTS. The latter was synthesized and applied for the purpose of IR characterization. The infrared (IR) spectra of the pretreated, extracted EPDM demonstrate absorption peaks associated with the IR absorption of the functional groups in the accelerator fragments, attached to the EPDM. NR/BR/EPDM (35/35/30) ternary blends are prepared by reactive mixing of the pretreated EPDM with CBS fragments attached with premasticated NR/BR on a two‐roll mill. Their blend morphological features are studied using the atomic force microscopy (AFM) and transmission electron microscopy (TEM) microscopic techniques, in comparison with those of blends prepared by a conventional straight mixing method. Both the tapping mode AFM phase images and TEM micrographs clearly show that reactive mixing leads to more homogeneous blends. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103:2547–2554, 2007

Graft copolymer of natural rubber and poly(methyl methacrylate) was prepared using CHP/TEPA redox initiators at 50°C and a reaction time of 3 h. Various reaction volumes (i.e., 0.5, 100, and 200 L) were used to prepare the graft copolymer which was then characterized by Fourier transform infrared spectrophotometer and proton nuclear magnetic resonance spectrophotometer ( 1 H-NMR) techniques. It was found that conversion of monomer to polymer and grafting efficiency slightly decreased with increasing reaction volumes. Quantity of grafted poly(methyl methacrylate) was calculated based on the integrated peak areas of the 1 H-NMR spectra and quantitative analysis by extraction method. It was found that both techniques gave similar level of the grafted poly(methyl methacrylate) onto the natural rubber backbone. Furthermore, Mooney viscosities, glass transition temperature (T g ) and degradation temperature (T d ) of the natural rubber and poly(methyl methacrylate) were slightly decreased with increasing the reaction volumes.

Titanium dioxide (TiO 2 ) possesses excellent photocatalytic activity and provides UV protection for polymeric materials. The nanosized TiO 2 particles with larger surface area to volume ratio and an increased surface reactivity shall impart better photocatalysis and UV protection efficiency to the rubber compounds, compared to the use of conventional micron-sized particles. Direct incorporation of TiO 2 nanoparticles (n-TiO 2 ) into non-polar rubbers faces incompatibility problem between the two phases. One of the solutions to overcome this problem is to treat the nanoparticle surface by using silane coupling agent such as bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT). This work prepared n-TiO 2 from commercial micron sized-TiO 2 by ultrasonication technique. Particle size of TiO 2 was measured by laser light scattering particle size analyzer. The morphology of TiO 2 nanoparticles was characterized by field emission scanning electron microscope (FESEM). The grafting reaction of silane on TiO 2 nanoparticles surface was studied at varying reaction temperatures and times. The purified grafted materials were characterized by energy dispersive X-ray analysis (EDX), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The characterization data confirm a presence of grafted silane on the TiO 2 nanoparticles surface. The result shows that ultrasonication technique can effectively decrease particle size and the grafting reaction of silane coupling agent onto TiO 2 nanoparticles can be successfully carried out at 140°C for 8 h.

Organoclay (OC) is one of the potential secondary fillers to be applied in silica-reinforced rubber compounds for tire applications.Commercial OC contains a large proportion of surface modifier, i.e., dimethyl dihydrogenated tallow ammonium chloride (2HT) type, that has an influence on the compound properties.To elucidate the effect of 2HT on the properties of silica-Natural Rubber (NR) compounds, a silica-only system, silica/OC, and silica/montmorillonite (MMT)/2HT added in situ during mixing, were comparatively studied.Irrespective in which form 2HT is added, it has potential to further enhance the performance of silica-NR compounds.Incorporation of 2HT suppresses filler flocculation and improves processability.Overall, the silica-only filled compound shows better mechanical properties than the silica/clay dual filler systems.The use of a small amount (2.4-4.7 phr) of 2HT improves 300% modulus, tear strength and abrasion resistance.The silica/OC gives better mechanical properties than the silica/MMT/2HT.With the optimum content of 2HT, a higher tan δ at -20 °C and lower tan δ at 60 °C can be achieved, all showing the beneficial potential of utilization of the modifying agent to improve wet traction and rolling resistance of silica-based tire tread compounds.

Eight statistical copolymers were prepared by anionic copolymerisation of ethylene oxide and 1,2-butylene oxide initiated by diethylene glycol. The difference in reactivity ratios of the two monomers ensured that the composition of the copolymers tapered from high E content (E denotes an oxyethylene unit) at the centre of a chain to high B content (B denotes an oxybutylene unit) at the chain ends, giving the copolymers the character of a triblock copolymer, type BEB. For comparison two true triblock (type BEB) copolymers were prepared by sequential anionic copolymerisation. Cloud point curves of aqueous solutions of the soluble copolymers were determined. These showed interesting features attributable to association, in particular sharp transitions at the points (concentration and temperature) at which the solutions attained their critical condition for micellisation. This explanation was verified by examining solutions below the cloud point by dynamic light scattering and noting the presence of micelles in appropriate cases. The range of copolymers available allowed the effects of overall composition and chain length to be explored, as well as the difference in behaviours resulting from the tapered-statistical and block copolymer architectures.

Abstract Tire sidewall compounds are generally formulated using NR and BR to achieve the required dynamical properties. The most widely used antiozonant, N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD), is a staining, toxic and environmentally unfriendly substance. Incorporation of EPDM into NR/BR blends improves ozone resistance, but leads to poor properties because of differences in filler affinity and cure incompatibility of the rubber components. In this work, the cure incompatibility is overcome by utilizing a reactive processing technique, making use of the most commonly used accelerator CBS and sulfur. The entire amount of curatives is first added into the EPDM. After a thermal pretreatment step related to the scorch time of the EPDM, the modified EPDM is mixed with pre-blended NR/BR. The reactive blends show significant improvements of physical properties in comparison with those of conventional straight mixes, due to improvement of the crosslink and carbon black distributions, confirmed by AFM and TEM images. The physical properties of the reactive mixed NR/BR/EPDM blends are equivalent or even superior to regular filled NR/BR blends for tire sidewall applications. The blend with 30 phr of EPDM has excellent ozone resistance while 6PPD can be totally omitted from the formulation.

This study investigated the effect of hybrid carbon black/lignin on the rheological, mechanical and thermal stability of NR/BR composites. Three types of lignin, namely, Kraft lignin (KL), organosolv lignin (OL) and soda lignin (SL) were incorporated into rubber matrix at the filler loadings of 5–20 phr, where the total filler content was fixed at 50 phr. Based on the performance of the three types of lignin, the KL and OL-filled NR/BR composites showed better properties compared to SL-filled NR/BR composite. However, the inclusion of KL up to a loading of 10 phr in the rubber matrix showed comparable results with those of the NR/BR/CB50 (without lignin). It was observed that the minimum and maximum torque (ML and MH, respectively) of the composite with KL were improved. Furthermore, the incorporation of lignin in the NR/BR matrix reduced the Payne effect and enhanced their processability, thermal stability and aging resistance.

Natural rubber (NR)‐montmorillonite (MMT) nanocomposites were prepared by a novel in situ organomodified and latex compounding method, followed by melt compounding technique. Effects of cationic surfactant on MMT dispersion, curing characteristic, mechanical, and dynamical properties were investigated. The number of layers in the layered MMT stack was determined by Small‐Angle X‐Ray Scattering (SAXS). The dispersion of MMT tends to form high ordered structure in NR‐MMT masterbatch when cationic surfactant of more than 4 phr was used. The morphology of Na‐MMT shows partly intercalated and exfoliated structure in the matrix after mixing and hot pressing process with reduced number of layers compared to the pristine MMT. The use of cationic surfactant over 4 phr introduces a plasticizing effect resulting in the reduction of crosslink density, hardness and modulus, but increase in tensile strength due to higher interfacial adhesion between NR and MMT as determined by Maeir‐Goritz model and Field Emission Scanning Electron Microscopy (FESEM). The optimum cationic surfactant loading is observed at 4 phr with the highest stable bonds, which result in the highest crosslink density, tear strength and storage modulus while the lowest Payne effect and tan delta at 60°C. POLYM. ENG. SCI., 59:1830–1839, 2019. © 2019 Society of Plastics Engineers

Parallel studies on the influence of epoxide contents in epoxidized natural rubbers (ENRs) in the absence of bis-(triethoxysilylpropyl) tetrasulfide (TESPT) coupling agent, as well as a combination of ENRs with different loadings of TESPT on the properties of ENR compounds, are carried out in this work. The results suggests that the best possible combination to optimize processibility and to improve reinforcement efficiency is to utilize ENR with an epoxide content in the range of 20 30 mol%, together with 2 4 wt% relative to the silica content of TESPT. This leads to a reduction of TESPT when compared to the conventional natural rubber compounds.

Abstract Deproteinized natural rubber (DPNR) latex, prepared by digesting the protein within low‐ammonia preserved concentrated (NR‐LA) latex with alcalase enzyme at 40°C for 24 h, has the nitrogen content of 0.039 wt %. Poly(methyl methacrylate) (PMMA) and graft copolymers (DPNR‐ g ‐PMMA) latices were synthesized by emulsion polymerization technique for blending or coating on DPNR or NR‐LA. Their general properties of natural and synthesized latices including compounded latex were verified. The friction coefficient of a homogenous film obtained from PMMA blended DPNR or NR‐LA latex and a DPNR‐ g ‐PMMA coated DPNR and NR‐LA film was found to be lower than those of films prepared by using DPNR or NR‐LA latex. Furthermore, the DPNR‐ g ‐PMMA coated films had lower friction coefficient than those of PMMA blended films. The physical properties in terms of 300% modulus, tensile strength, and elongation at break of those rubbers were tested and confined to the ASTM 3377‐78a and ASTM 3378‐99 standards for dipping products of surgical gloves and examination gloves, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 833–844, 2004

ABSTRACT Silica-reinforced natural rubber (NR) tire tread compounds are investigated using organoclay (OC) as secondary filler. By varying mixer temperature settings at a silica/OC ratio of 45/10 phr, dump temperatures are reached of approximately 120, 140, 150, and 160 °C. The increased dump temperature leads to a better silanization reaction resulting in lower mixing torque, Mooney viscosity, and Payne effect. The optimum mixing dump temperature was found to be around 150 °C. By varying the loadings of OC in the silica-filled NR compounds from 0 to 36 wt% relative to total filler amount, the increased OC loadings decreased the Payne effect and compound viscosities, significantly shortened scorch and cure times, and raised the tan delta at −20 and 0 °C as indications for ice traction and wet skid resistance of tire treads made therefrom. The optimum loading of OC of 9 wt% relative to total filler content shows better Payne effect, cure rate index, tan delta at −20 and 60 °C indicative for rolling resistance, and DIN (German Institute of Standardization) abrasion resistance index. The results indicate that the use of this hybrid filler may provide tires with better wet traction and lower rolling resistance and wear resistance compared with the pure silica-filled system.

Introducing silica into tire tread rubber compounds offers at least two advantages: a reduction in heat build-up as well as an improvement in mechanical properties, in particular tear strength, cut, chip, and chunking resistance, when compared with the use of carbon black. Silica itself gives a lower degree of reinforcement when compared to carbon black of the same primary particle size due to the different nature of the surface chemistry of the fillers. In general, silica can reinforce better in more polar rubbers when compared to nonpolar rubbers due to stronger silica-to-rubber interactions. The insufficient reinforcement efficiency of silica-filled nonpolar rubbers—general purpose rubbers, for example, natural rubber (NR)—can be improved by using silane coupling agents. The quality of silica-filled rubber compounds significantly depends upon mixing conditions and key ingredients in the compounds. These parameters are crucial and need to be optimized to obtain desirable hydrophobation and micro-dispersion of silica as well as appropriate filler–rubber and rubber–rubber networks in the compounds, leading to the optimum properties of the final vulcanizates. Epoxidized NR (ENR) is often quoted to be suitable for easy-dispersion precipitated silica-reinforced passenger car tire treads compounds, without the need to use a silane coupling agent. The epoxy-moieties on the ENR backbone enable a chemical reaction with the silanol groups on the silica, thereby creating a solid chemical bond between rubber and silica, similar to what the silane coupling agent can achieve. There are several approaches to this technology, each with their own merits and potential success: (1) The full use of ENR instead of NR, whereby the degree of epoxidation of the ENR plays an important dual role: first, there should be a high enough degree of epoxidation to guarantee sufficient reactivity toward the silica; on the opposite side the epoxidation raises the glass transition temperature of the NR, which tends to become too high for tire applications; (2) The use of ENR in small quantities as compatibilizer and/or reactive species between the silica and otherwise pristine NR as the main component. This enables to use ENR with higher epoxide contents without major adverse effects on the glass transition temperature; (3) Epoxidized low molecular weight NR has a potential to improve both processing and vulcanizate properties, due to its plasticizing effect and epoxide–silica interactions; and (4) In all three cases the use of small amounts of silane coupling agents relative to the quantities used for pure NR–silica compounds helps to overcome eventual shortcomings. The present chapter provides a review of the developments over time, the advantages and disadvantages of the various approaches, highlighted on the basis of laboratory-scale compounding and characterizations, like Mooney viscosities, Payne effects, dynamic mechanical analyses, and vulcanized tensile mechanical properties.

In principle, it is possible to exercise control over the molecular weight distribution (MWD) of the polymers produced from living polymerisation processes in flow reactors through the control of reactant feeds in a predetermined fashion. Some of the factors that influence the extent to which control can be achieved with feed perturbations to a single stage continuous flow stirred tank (CSTR) reactor have been reported previously. Here, attention is given to the problem of establishing inverse process models as a first step towards a fully automatic control strategy for the synthesis of polymers with pre-ordained MWD in a real process. Particular attention is given to the development of a neural network model for predicting the instantaneous reactor feed conditions for a specified product MWD and characterising the MWD for the purpose of dimension reduction using principal component analysis. Data collected from a simulated ideal reactor process are used in the study. The way in which this approach will underpin a real laboratory-scale polymerisation system is briefly outlined.

Epoxidized natural rubber (ENR) and bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT) were used to improve the properties of silica-filled NR. The use of ENR containing 51 mol% epoxide groups (ENR-51) as a compatibilizer without TESPT was optimized at 7.5 phr, based on the results of Payne effect and tensile strength. By using 7.5 phr of ENR-51 with varying amounts of TESPT in a range of 2 to 5 wt% relative to the silica, the properties of compounds were compared to those of the ones with optimum TESPT content (i.e. 8.6 wt% relative to the silica) and without. The addition of TESPT to the ENR-51 compatibilized silica-filled NR compound had no effect on Mooney viscosity but lowered the Payne effect to the same level as that of the silica/TESPT compound, and significantly decreased both scorch and optimum cure times. The silica-filled NR with ENR and the small amount of TESPT combination showed a further increase in tensile strength to match that of the optimized silica/TESPT system, while maintained the elongation at break. This work demonstrates that the use of ENR as compatibilizer clearly enhances the properties of silica-filled NR compounds, and that such properties can be further improved by adding TESPT at a half or less amount of TESPT normally needed for silica-filled compounds.

ABSTRACT To improve the properties of silica-reinforced truck tire tread compounds, especially abrasion resistance, the effect of vinyl contents in butadiene rubber (BR) or solution styrene–butadiene rubber (SSBR) as secondary polymers in silica-filled natural rubber (NR) compounds at a ratio of 80/20 phr is investigated in the first part of this study. By increasing the levels of vinyl contents in BR in combination with NR, a better Payne effect, 300% modulus, reinforcement index, and tan delta at −20 and 0 ° C are obtained, whereas the tensile strength, elongation at break, and DIN abrasion resistance index decrease with increasing vinyl contents. Higher vinyl contents in SSBR result in improvements in Payne effect, 300% modulus, tan delta at −20 and 0 °C but only a small improvement in DIN abrasion resistance index. Combinations of secondary fillers and polymers in silica-filled NR are covered in the second part of present study. Silica/carbon black–filled NR/BR and NR/SSBR, respectively, and silica/organoclay–filled NR/BR and NR/SSBR show positive effects on scorch time and optimum cure time, with only slight changes in Payne effect, tensile properties, tan delta at −20 and 0 ° C and DIN abrasion resistance as compared with compounds with carbon black N134. The use of organoclay results in an enhanced Payne effect and tan delta at 60 °C, indicative of reduced filler–filler networking and consequently a lower rolling resistance of tire tread compounds as compared with the compound without organoclay. The specific combination of a small amount of organoclay replacing the same amount of silica, together with some of the NR replaced by high-vinyl BR, promises a substantial overall boost in wet and ice traction, abrasion, and wear resistance as compared with straight NR/silica tire treads. This new observation helps to overcome one of the main shortcomings of NR/silica compounds: their generally low wear resistance.

This work investigates the effect of epoxidized low molecular weight natural rubber (ELMWNR) in silica-filled NR compounds on processing, mechanical and dynamic mechanical properties. The ELMWNRs with mol% epoxide groups varying from 0-50 and molecular weight in a range of 50,000-60,000 g/mol were prepared from depolymerization of epoxidized natural rubber using periodic acid in latex state. They were then added in the silica-filled NR compounds as a compatibilizer at varying loading from 0-15 phr. The addition of ELMWNR decreases compound viscosity and Payne effect, i.e. filler-filler interaction. The optimal mechanical properties of silica-filled vulcanizates are observed at the ELMWNR-28 (28 mol% epoxide) loading of 10 phr. The incorporation of ELMWNR with 28 and 51 mol% epoxide groups into NR compounds introduces a second glass transition temperature and affects on their dynamic mechanical properties. Higher epoxide content leads to higher Tan δ of the rubber vulcanizates in the range of normal service temperature.

AJC-

Abstract Natural rubber (NR)‐montmorillonite (MMT) nanocomposites with different organomodified MMT contents prepared by in situ organomodified and latex compounding method, followed by melt compounding technique are reported in this work. The morphology as well as the static and dynamic mechanical properties of the nanocomposites, are investigated. By means of SAXS and FESEM analysis, MMT is found to have partly intercalated and exfoliated structure in NR matrix. The modulus, tensile strength, and storage modulus at low strain of NR‐MMT are enhanced compared to unfilled NR but hysteresis loss tended to increase with raising organomodified MMT content. The overall results showed that the presence of 5 phr of organomodified MMT filled NR gave the best balance between mechanical and dynamical properties.

Abstract Epoxidized natural rubber with 30 mol.% of epoxide (ENR-30) was blended with medium nitrile rubber (NBR) at the blend weight ratios of 30/70 and 70/30. Blend compounds were prepared via simple mixing and masterbatch techniques using TBBS as an accelerator. The masterbatches of ENR-30 initially consisted of higher accelerator concentrations compared with those of NBR, in order to compensate an effect of accelerator partition towards NBR phase. The initial accelerator concentration ratios in ENR-30 and NBR masterbatches before blending were at 50/50, 60/40, 70/30 and 80/20, respectively. The blend vulcanizates prepared by masterbatch mixing showed a significant improvement in tensile properties in comparison with those prepared by simple blend, and the initial accelerator concentration ratio in ENR-30/NBR masterbatches at 70/30 gave the highest ultimate tensile properties. The improvement in tensile properties was clearly observed for all the blends vulcanized with conventional, semi-EV and EV sulfur-vulcanization systems. The increase of tensile properties does suggest a better curative distribution, and hence a better crosslink distribution.

Abstract Silica-silane technology for low rolling resistance tire compounds requires efficient bridging between the silica surface and rubber molecules through silanization and coupling reactions. The presence of diphenylguanidine (DPG) as secondary vulcanization accelerator is also needed to catalyze the silanization reaction between the alkoxy groups of silane coupling agents and the silanol groups on the silica surface. However, DPG can liberate toxic aniline under high mixing temperatures and therefore safer alternatives are required. This study investigates the influence of amines with different structures, i.e. hexylamine (HEX), octadecylamine (OCT), cyclohexylamine (CYC) and dicyclohexylamine (DIC) on the primary silanization reaction rate constant in a model system, and on interfacial compatibility of practical silica-reinforced NR compounds. Compared to the system without, the amines clearly increase the reaction rate constant for which linear aliphatic amines work better than cyclic ones. This is due to better accessibility of the amines towards the silica surface, in agreement with the values of Payne effect as observed in the rubber compounds, except for the OCT case. The lowest Payne effect of the OCT-containing rubber compound is attributed to the additional shielding effect obtained from the long alkyl-chain that leads to more hydrophobicity, resulting in good physical interaction between silica and rubber. The presence of all amines improves the cure properties in which the linear aliphatic amines give shorter cure times than the cyclic aliphatic ones. As a result of good interfacial compatibility, the OCT-containing compound which shows lowest filler-filler interaction gives good mechanical properties that are closest to the reference compound with DPG.

The dump temperature and mixing interval between rubber, silica, and silane coupling agent for silica-filled natural rubber (NR) tire tread compounds using bis-triethoxysilylpropyl tetrasulfide (TESPT) as silane were optimized. The dump temperature turns out to be the key parameter governing the properties of the silica-filled NR compounds. The increase in viscosity of the compounds by changing the dump temperature from 100 to 150 °C indicates that inevitably some cross-linking of NR occurs by sulfur contained in TESPT, simultaneous with the silanization reaction between silica and silane. However, the viscosity decreases again when dump temperatures above 150 °C are applied, indicating a dominant occurrence of degradation of the NR molecules. The results are in good agreement with bound rubber contents. The overall properties indicate that a dump temperature in the range of 135–150 °C and a silica–silane–rubber mixing interval of 10 min are the most appropriate mixing conditions for silica-filled NR compounds with TESPT as coupling agent.

Mixing silica-reinforced rubber for tire tread compounds involves high shear forces and temperatures to obtain a sufficient degree of silanization. Natural Rubber (NR) is sensitive to mastication and chemical reactions, and thus, silica-NR mixing encounters both mechanical and thermal degradation. The present work investigates the degradation phenomena during the mixing of silica-reinforced NR compounds in-depth. The Mooney stress relaxation rates, the dynamic properties with frequency sweep, a novel characterization of branch formation on NR using Δδ values acc. Booij and van Gurp-Palmen plots, together, indicate two major competitive reactions taking place: chain scission or degradation and preliminary cross-linking or branch formation. For masticated pure NR and gum compounds, the viscous responses increase, and the changes in all parameters indicate the dominance of chain scission with increasing dump temperature. It causes molecular weight decrease, broader molecular weight distribution, and branched structures. Different behavior is observed for silica-filled NR compounds in which both physical and chemical cross-links are promoted by silanization and coupling reactions. At high dump temperatures above 150 °C, the results indicate a significant increase in branching due to preliminary cross-linking. These molecular chain modifications that cause network heterogeneity deteriorate the mechanical properties of resulting vulcanizates.

Safe rubber process oils containing low Polycyclic Aromatic Hydrocarbons (PAHs) are in need for replacement of toxic distillate aromatic extract (DAE). Potential and commercially available petroleum-based safe process oils are: Treated Distillate Aromatic Extract (TDAE), Mildly Extracted Solvate (MES) and Naphthenics (NAP). This work investigates the petroleum-based TDAE and MES safe process oils for replacement of DAE. The characteristics of DAE-, TDAE- and MES oils, and solubility in unfilled NR, SBR and 50/50 NR/SBR blends are analyzed. The solubility parameters (δ) are calculated based on the group contribution method, and the difference of δ values between oils and rubbers are correlated with the mass swelling of lightly crosslinked NR and SBR at different temperatures. At high temperature in the range of mixing temperature, MES oil shows less compatibility compared to TDAE and DAE, respectively. The replacement of DAE with TDAE and MES oils in unfilled NR, SBR and 50/50 NR/SBR had only minor effects on Mooney viscosity and mechanical properties of all the compound types. When considering the overall changes in properties, NR is most sensitive to a change of oil types. For carbon black filled NR and NR/SBR blend compounds, typically applied in tires, the properties are strongly affected by oil contents, but less by the oil types. The compounds with DAE oil have a lower Mooney viscosity but higher complex viscosity as well as higher Payne effect when compared to the mixes with TDAE- and MES-oils. The replacement of DAE- with TDAE- and MES-oils in NR compounds has only small effects on the vulcanization characteristics and mechanical properties, but clearly influences the properties which are related to changes of the glass transition temperature (Tg) and viscoelastic behavior. The lowest Tg of MES leads to the best elastic response in the NR vulcanizates, but TDAE gives the best overall elastic response for the NR/SBR blend vulcanizates.

The rubber formulation plays a significant role in the properties of NR compounds filled with silica. In this work, the influences of various silicas, silane coupling agents and diphenylguanidine (DPG) on the properties of compounds and vulcanizates, i. e. cure characteristics, Mooney viscosity, flocculation kinetics, bound rubber content, Payne effect, tan δ at 60 °C, tensile and tear properties are investigated. The results demonstrate that compound viscosity and curing behavior, as well as vulcanizate properties of the silica-filled NR are much improved by incorporating silane coupling agents. Bis-triethoxysilylpropyltetrasulfide (TESPT) clearly gives better overall properties than the disulfide-based silane (TESPD), except for scorch safety. DPG acts as a synergist to sulfenamide primary accelerators, as well as activator for the silanization reaction. Highly dispersible (HD) silicas can significantly enhance the degree of dispersion, and so lead to higher filler-rubber interaction. As a consequence, the HD silicas provide better dynamic and mechanical properties for filled NR vulcanizates compared to conventional (CV) counterparts. The optimal quantities of both, silane coupling agent and DPG, required in the formulation are correlated to the cetyl trimethylammonium bromide (CTAB) specific surface area of the silicas. Furthermore, the results reveal that the silica structure as characterized by the dibutylphthalate (DBP) adsorption also strongly influences the reinforcing efficiency

Titanium dioxide (TiO 2 ) is normally added into the rubber compounds as a white pigment and inorganic filler for an improvement of thermal property. TiO 2 is also known to have an outstanding photocatalytic activity. This work investigates the properties of natural rubber (NR) compounds filled with 5 phr of nanoTiO 2 (n-TiO 2 ). Since the direct incorporation of n-TiO 2 into NR encounters incompatibility problem, therefore two types of coupling agent (i.e. bis-(3-triethoxysilylpropyl) tetrasulfide (TESPT) and isopropyl trioleyl titanate (ITT)) are used. The coupling agent loading is varied in a range of 0-20 wt% relative to the n-TiO 2 . Mooney viscosities and minimum cure torque (M L ) of the compounds increase with increasing coupling agent content and the ones with ITT show higher viscosity than the mixes with TESPT. The use of TESPT leads to shorter optimum cure time and higher torque difference compared to the use of ITT. The addition of n-TiO 2 results in the improved modulus, reinforcing index and tensile strength compared to the unfilled vulcanizate. The presence of both TESPT and ITT significantly reduces a photodegradation efficiency. The difference in the properties and photocatalytic activity of n-TiO 2 filled NR having TESPT and ITT as coupling agent indicates their possible different level of dispersion and interactions at the interphases.

Rubber processing oil based on modified epoxidized vegetable oils (m-EVO) was prepared by a reaction of epoxidized palm oil EPO) or epoxidized soybean oil (ESBO) with N-Phenyl- ρ -phenylenediamine (PPD) at a mole ratio of 1:0.5. The comparison of m-EVO with aromatic oil (Treated distillate aromatic extract, TDAE) on extrusion process behaviors (output rate, extrusion rate, screw efficiency, heat generation, die swell, extrudate appearance) of carbon black (N330) filled natural rubber (NR) compound was made. It was found that the mooney viscosity of m-EVO based natural rubber compounds are slightly higher than that of the TDAE based natural rubber compound (ML(1+4)100°C: m-ESBO 65.5±0.7; m-EPO 59.7±0.2; TDAE 56.5±1.0), which probably due to the poorer filler dispersion in the compounds. The extrusion process behaviors for output rate (g/min: m-ESBO 191.0±0.6; m-EPO 191.2±0.4; TDAE 195.5±0.6), extrusion rate (cm 3 /min: m-ESBO 179.6±0.6; m-EPO 183.2±0.4; TDAE 186.4±0.6) and screw efficiency (%: m-ESBO 30.8±0.6; m-EPO 31.4±0.4; TDAE 32.0±0.6). All the three compounds show similar extrusion process behaviors in which the TDAE based compounds shows a marginal higher values than the m-EVO as its lower mooney viscosity lead to a better flow. The m-EPO and m-ESBO based natural rubber compounds show very similar extrusion process behaviors. The heat generation (°C: m-ESBO 61.0±0.8; m-EPO 62.1±0.4; TDAE 63.1±1.0) and die swell (%: m-ESBO 11.0±0.7; m-EPO 11.0±0.5; TDAE 12.7±0.3) of the m-EVO based natural rubber compounds are slightly lower than those of the TDAE based natural rubber compound. As there are no significant differences in the extrusion process behaviors, with respect to extrusion process, m-EVO can be used to replace TDAE oil.

Silica-reinforced natural rubber (NR) tire tread compounds with epoxidized natural rubber (ENR) as a compatibilizer are investigated. ENR contents of 2.5-15.0 phr, with epoxide levels of 10, 38 and 51 mol%, are used. The addition of ENRs, especially ENR-38 and ENR-51, as compatibilizers decreases the Mooney viscosity and Payne effect (i.e. filler-filler interaction), which implies an improvement of silica dispersion in the compounds. Chemically bound rubber contents of the compounds, indicative for interaction/reaction between the epoxidegroups of the ENR and silanol-groups on the silica surfaces, also increase with higher epoxide-contents of the ENR. Raising the ENR contents and mole% of epoxide prolongs cure and scorch times of the silica-filled compounds, when compared with a silica-filled NRcompound without ENR. Tensile strength of vulcanizates is improved with increasing mole% of epoxide, and an optimum value is observed when 7.5 phr of ENR-51 was used. The results show overall, that the properties of silica-reinforced NR can be substantially improved by adding ENR as a compatibilizer, when compared with a compound without.

The properties of both compounds and vulcanizates of silica-filled natural rubber (NR) compatibilized with epoxidized low molecular weight natural rubbers (ELMWNRs) consisting of 12 and 28 mol% epoxide are investigated. The ELMWNRs with a molecular weight range of 50,000 to 60,000 g/mol are produced by depolymerization of epoxidized natural rubber (ENR) latex using periodic acid, and then used as compatibilizer in a range of 0 to 15 phr in virgin NR. The compounds with LMWNR without epoxide groups, and with bis-(triethoxysilylpropyl) tetrasulfide (TESPT) coupling agent are also prepared for comparison purpose. Incorporation of ELMWNRs lowers Mooney viscosity and Payne effect to the level closed to that of silica/TESPT compound, and clearly enhances the modulus and tensile strength of vulcanizates compared to the compounds with no compatibilizer and LMWNR. The higher epoxide groups content results in the better tensile properties but somewhat less than the compound with TESPT. Addition of extra sulfur into the compounds with LMWNR and ELMWNRs to compensate for the sulfur released from silane molecule in the silica/TESPT system shows small influence on Mooney viscosity, but remarkably enhances 300% modulus, tensile strength and loss tangent at 60°C as a result of the better network formation.

Dithiophosphate (DTP) displays a good efficiency towards improved overall properties of silica-reinforced natural rubber compounds, when it is used as secondary accelerator in a sulfenamide primary accelerated sulfur vulcanization system. Comparing DTP with diphenylguanidine (DPG), DTP is more reactive and gives lower reversion leading to a lower amount required for vulcanization and better aging properties. An increase of chemically bound rubber content accompanied with a lowered Payne effect is obtained when secondary accelerator is used. A potential coupling ability of DTP can be postulated. The optimal amounts of DTP and DPG are approximately 0.8 and 1.1 phr, i.e. 1.4 and 2.0 wt% relative to silica content, respectively.

Silica-filled natural rubber (NR) tire tread compounds with epoxidized natural rubber (ENR) as a compatibilizer were investigated. The ENRs were prepared by an in-situ performic epoxidation reaction and characterized by proton nuclear magnetic resonance spectroscopy. The epoxide levels of 10, 38 and 51 mole% with ENR contents of 2.5-15.0 phr were used as compatibilizers in the silica-filled NR compounds. Cure characteristics, flocculation rate constant, bound rubber contents, and mechanical properties of the silica-filled NR were studied. Increasing the mole% of epoxide and ENR contents increased cure and scorch times of the silica-filled compounds, while silica flocculation decreased, when compared with a silica-filled compound without ENR. Total bound rubber and chemically bound rubber contents of the compounds which indicate interaction/reaction between the epoxide groups of ENR and silanol groups on the silica surface also increased with increasing epoxide levels. The addition of ENR as a compatibilizer decreased the Mooney viscosity of the compounds, which can be related to an improvement of silica dispersion in the compounds. Tensile strength and reinforcing index of the vulcanizates increased with increasing mole% of epoxide and ENR contents up to 7.5-10.0 phr.