Silica-Reinforced Deproteinized Natural Rubber

Reinforcement effect of silica-silane system in deproteinized natural rubber (DPNR) is reported. The influence of mixing temperature and sulfur ranks in silane bis-triethoxysilylpropyl-polysulfide is compared between silica-DPNR and silica-natural rubber (NR). Dispersion morphology of silica and rubber-to-filler interaction in DPNR is visualized by atomic force microscopy and TEM network visualization, respectively. DPNR compound shows smaller influence of dump temperature and more constant mechanical properties as compared to NR compound. Establishment of the silica-silane-rubber coupling in DPNR tread compound results in an improvement in dynamic properties especially the lower tan δ at 60°C which indicates the lower rolling resistance of tire. DPNR shows better mechanical and dynamic properties as compared to NR

Effect of a Silane Coupling Agent on the Morphology of Silica Reinforced Natural Rubber

Filler-to-rubber interaction is a key parameter in reinforcement of rubber. This paper presents an investigation into the morphology of silica-reinforced Natural Rubber (NR) in presence and absence of a silane coupling agent, bis(triethoxysilylpropyl) tetrasulfide (TESPT). Improvement of the microdispersion of silica in NR with the use of TESPT is observed by Atomic Force Microscopy (AFM) imaging. Using a special network visualization technique based on Transmission Electron Microscopy (TEM), insight into the silica-torubber interaction in NR is gained. The presence of TESPT leads to strong-rubber bonding, which prevents formation of vacuoles

Alleviating molecular-scale damages in silica-reinforced natural rubber compounds by a self-healing modifier

The property retentions of silica-reinforced natural rubber vulcanizates with various contents of a self-healing modifier called EMZ, which is based on epoxidized natural rubber (ENR) modified with hydrolyzed maleic anhydride (HMA) as an ester crosslinking agent plus zinc acetate dihydrate (ZAD) as a transesterification catalyst, were investigated. To validate its self-healing efficiency, the molecular-scale damages were introduced to vulcanizates using a tensile stress–strain cyclic test following the Mullins effect concept. The processing characteristics, reinforcing indicators, and physicomechanical and viscoelastic properties of the compounds were evaluated to identify the influences of plausible interactions in the system. Overall results demonstrate that the property re-tentions are significantly enhanced with increasing EMZ content at elevated treatment temperatures, because the EMZ modifier potentially contributes to reversible linkages leading to the intermolecular reparation of rubber network. Furthermore, a thermally annealing treatment of the damaged vul-canizates at a high temperature, e.g., 120◦ C, substantially enhances the property recovery degree, most likely due to an impact of the transesterification reaction of the ester crosslinks adjacent to the molecular damages. This reaction can enable bond interchanges of the ester crosslinks, resulting in the feasibly exchanged positions of the ester crosslinks between the broken rubber molecules and, thus, achievable self-reparation of the damages

Significant factors affecting the thermo-chemical de-vulcanization efficiency of tire rubber

In this study, the influence of the molecular structure of the rubber, the carbon black loading and de-vulcanization time and temperature on the thermo-chemical de-vulcanization efficiency of whole tire rubber was investigated by correlating sol fraction and crosslink density (Horikx-Verbruggen method). Differences in molecular structure influence the de-vulcanization mechanisms of rubbers as well as the efficiency. Increasing carbon black loadings result in higher crosslink densities due to a deactivation of the de-vulcanization aid. Variation of de-vulcanization temperature and time results in different degrees of heat accumulation in the rubber during de-vulcanization and thus leads to different de-vulcanization efficiencies

A self-healing system based on ester crosslinks for carbon black-filled rubber compounds

Carbon black-reinforced rubber compounds based on the blends of natural rubber (NR) and butadiene rubber (BR) for tire sidewall applications were formulated to investigate the self-healing efficacy of a modifier called EMZ. This modifier is based on epoxidized natural rubber (ENR) modified with hydrolyzed maleic anhydride (HMA) as the ester crosslinking agent plus zinc acetate dihydrate (ZAD) as the transesterification catalyst. The influence of EMZ modifier content in sidewall compounds on processing characteristics, reinforcement, mechanical and fatigue properties, as well as property retentions, was investigated. Increasing the content of EMZ, the dump temperatures and Mooney viscosities of the compounds slightly increase, attributed to the presence of extra polymer networks and filler–rubber interactions. The bound rubber content and Payne effect show a good correction that essentially supports that the EMZ modifier gives enhanced filler–rubber interaction and reduced filler–filler interaction, reflecting the improved homogeneity of the composites. This is the key contribution to a better flex cracking resistance and a high fatigue-to-failure resistance when utilizing the EMZ modifier. To validate the property retentions, molecular damages were introduced to vulcanizates using a tensile stress–strain cyclic test following the Mullins effect concept. The property retentions are significantly enhanced with increasing EMZ content because the EMZ self-healing modifier provides reversible or dynamic ester linkages that potentially enable a bond-interchange mechanism of the crosslinks, leading to the intermolecular reparation of the rubber network

Influence of filler network on thermo-chemical de-vulcanization efficiency of carbon black filled natural rubber

Carbon black is often used as the reinforcing filler in tires since it plays an important role in improvement of tires mechanical properties such as abrasion, stiffness, modulus and fatigue life. In this study, natural rubber (NR) filled with various loadings of carbon black was prepared. Then, the NR vulcanizates were de-vulcanized via thermo-chemical method using diphenyl disulfide as de-vulcanization aid. The de-vulcanization efficiency was analyzed by relationship between sol fraction and crosslink density of the de-vulcanizates. It is found that the de-vulcanization efficiency is influenced by filler loading. This is attributed to the degree of filler network formation in a rubber matrix which is depended on the filler loadings. In the unfilled de-vulcanizates the results showed that almost 100% of sol fraction and the crosslink density reduced to almost zero are observed. Adding carbon black results in a decrease of sol fraction and increase of crosslink densities. This is due to during de-vulcanization some occurred reactive radicals reacted with active site of carbon black surfaces in filler network to form gels of complex compound. Hence, the de-vulcanization efficiency is lower with increasing carbon black loadings

Synergistic Effect of Partial Replacement of Carbon Black by Palm Kernel Shell Biochar in Carboxylated Nitrile Butadiene Rubber Composites

With the rapid development of the palm oil-related industry, this has resulted in the high production of palm oil waste. The increasing amount of palm oil waste has become an alarming issue in which researchers have carried out studies that this palm oil waste has the potential to be used as a biomass source. Carbon black (CB) is the most preferred reinforcing filler in the rubber industry but it has a disadvantage where CB is carcinogenic and a petroleum-based product. Hence CB is less sustainable. Palm kernel shell (PKS) derived from palm oil waste can be turned into palm kernel shell biochar (PKSBc) which can potentially be a value-added, sustainable biofiller as reinforcement in rubber composites. In this study, PKSBc is hybridized with CB (N660) at different loading ratios to be filled in carboxylated nitrile butadiene rubber (XNBR). This study aims to elucidate the effect of the varying ratios of hybrid CB/PKSBc on the rheological properties, abrasion resistance, and hardness of XNBR composites. In this study, both CB and PKSBc are incorporated into XNBR and were then cured with sulphur. The composites were prepared by using a two-roll mill. Different compositions of hybrid CB/PKSBc were incorporated. The rheological properties and physicomechanical properties, such as abrasion resistance and hardness of the vulcanizates, were investigated. Based on the results, as the loading ratio of PKSBc in hybrid CB/PKSBc increases, the cure time decreases, and the cure rate index increases. The abrasion resistance and hardness values of vulcanizates were maintained by the high loading of PKSBc which was due to the porous structure of PKSBc as shown in the morphological analysis of PKSBc. The pores of PKSBc provided mechanical interlocking to reduce volume loss and maintain the hardness of vulcanizates when subjected to force. With this, PKSBc is proven to be a semi-reinforcing filler that could not only act as a co-filler to existing commercialized CB, but PKSBc could also fully substitute CB as reinforcement in rubber, specifically XNBR as it is able to provide high abrasion resistance and hardness to the rubber composites. This would mean the performance of PKSBc is comparable with CB (N660) when it comes to maintaining the physicomechanical properties of XNBR composites in terms of abrasion resistance and hardness. Therefore, this approach of using eco-friendly filler derived from palm oil agricultural waste (PKSBc) can reduce the abundance of palm oil waste, be a sustainable alternative to act as a co-filler in hybrid CB/PKSBc to decrease the usage of CB, and helps to enhance the quality of existing rubber-based products