Comparative properties of silica- and carbon black-reinforced natural rubber in the presence of epoxidized low molecular weight polymer

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 tir

Compatibilization of Silica-filled Natural Rubber Compounds by Combined Effects of Functionalized Low Molecular Weight Rubber and Silane

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 processin

Property enhancement of silica-filled natural rubber compatibilized with epoxidized low molecular weight rubber by extra sulfur

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

Compatibilisation of Silica-filled Natural Rubber Compounds by Functionalized Low Molecular Weight Polymer

In silica-filled natural rubber, it is essential to use coupling agents or compatibilisers to enhance filler-rubber interactions, reduce silica network formation and hence to obtain good reinforcement. This work investigates the effect of epoxidised low molecular weight natural rubber (ELMWNR) in silica-filled NR compounds on processing, mechanical, dynamic-mechanical and morphological properties. ELMWNRs with 12 and 28 mol% epoxide groups having a molecular weight in the range of 50,000-60,000 g/mol were added into the compounds as compatibilisers at varying loadings from 0-15 phr. The reference compound containing bis-(triethoxysilylpropyl) tetrasulfide (TESPT) as coupling agent was also prepared for comparison. The addition of 10 phr ELMWNR-28 in the silica-filled NR compounds not only decreases mixing torque, compound viscosity and Payne effect to the levels close to those of the compound with TESPT, but also increases bound rubber content and filler dispersion resulting in improvement of mechanical properties. However, the TESPT-silica system still provides better mechanical and dynamic mechanical properties compared to the alternative ELMWNR-silica systems. Overall, ELMWNR can be an alternative as natural-based compatibiliser with no ethanol emission like in the case with TESPT

Silica-reinforced natural rubber with epoxidized low molecular weight rubber as a compatibilizer

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

Natural rubber and epoxidized natural rubber in combination with silica fillers for low rolling resistance tires

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