Silica-filled Natural Rubber Compounds Research Articles

The Effects of a “Palm Oil” Faiiy Acid Additive and a Silane Coupling Agent on the Curing Characteristics and Vulcanizate Properties of Silica-Filled Natural Rubber Compounds

Comparison study on effects of a “palm oil” fatty acid additive (POFA) and a silane coupling agent on the curing characteristics and vulcan-izates properties of silica-filled natural rubber were studied. Compared to the control compound, the incorporation of both ingredients enhances the cure rate and cure state of the rubber compounds. Both ingredients were found to be effective in reducing the viscosity of the rubber compounds. Swelling measurement and scanning electron microscopy studies indicate that both ingredients increase the cross-link density, improve filler dispersion, and, consequently, enhance the vulcanizate properties.

Effect of silane coupling agents on the mooney scorch time of silica-filled natural rubber compound

Mooney scorch time and cure index of silica-filled natural rubber ( Hevea Brasiliensis type) compound with and without the presence of silane coupling agents were studied in the temperature range 110–160°C using a Mooney Shearing Disk Viscometer. Two types of silane coupling agents, viz γ-mercaptopropyltrimethoxysilane (A-189) and bis(triethoxysilylpropyl)tetrasulphide (Si-69) of various loadings were used to study the effect of silane coupling agents on the scorch property of natural rubber. Results indicate that the Mooney scorch time and cure index decreases with increasing A-189, but increases with increasing Si-69. This observation is attributed to the catalytic effect of the thiol group in A-189 which enhances the rate of vulcanization, whereas in the case of Si-69, cure retardation is associated with the steric hindrance effect of its bulky end groups. The apparent activation energy for various loadings of silane coupling agents was determined and discussed.

Effect of Multifunctional Additive on Filler Dispersion in Carbon-Black- and Silica-Filled Natural Rubber Compounds

The effect of multifunctional additive (MFA) on filler dispersion in carbon-black- (CB) and silica-filled natural rubber (NR) compounds has been studied. Silica dispersion, measured by computer-aided image analysis and scanning electron microscopy (SEM), showed a substantial improvement when MFA concentration is increased from 1 to 3 phr. After this level, there is a further but small improvement. However, for CB-filled NR compounds, CB dispersion showed a substantial improvement when the MFA used between 0 and 1 phr. As in silica-Filled NR compounds, there is only a small improvement in dispersion after 1 phr.

Determination of the modes of action of a cationic surfactant for property development in silica-filled natural rubber compounds

Work has been carried out to separate the contributions of a diamine salt of fatty acid [termed a multifunctional additive (MFA)] of a silica-filled natural rubber (NR) compound to property development by (1) improved filler dispersion from elastomer-filler interface, (2) mastication of the NR, (3) modification of the NR-silica interface, and [4] cross-link density effect. Results have shown that there is a substantial increase in mechanical properties at equivalent filler dispersion level due to the effect of MFA on cross-link density. Between 0 and 0.3 phr of MFA, the enhancement of the mechanical properties is due to improvement in silica dispersion. The addition of MFA accelerates filler disagglomeration and results in reduction of the effective volume fraction of filler, as agglomerate breakdown releases immobilized rubber. When the level of MFA is more than 0.3 phr, the cross-link density becomes the dominant factor for mechanical property enhancement. However, after the optimum amount of MFA is exceeded, the properties start to deteriorate owing to weak interfacial interaction between adjacent layers of MFA molecules.

Mixing and Extrusion of High Silica and all Silica-natural Rubber Compounds

Abstract This work is an investigation on causes of extrusion problem of a high silica- and all silica-filled natural rubber compounds containing a coupling agent. The 67% silica and 33% carbon black, N110 compound (Compound 3) gave a wavy surface of extrudate from a profile die. The 100% silica-filled compound (Compound 4) was too stiff to be extruded. Reference compounds, 100% carbon black (Compound 1) and 33% silica with 67% carbon black (Compound 2), gave smooth extrudates. The amplitude dependence of storage modulus measurements indicated Compound 4 had a poorer dispersion of the filler. Scanning electron microscopy also showed a poorer dispersion for this compound. However, Compound 3 could not be distinguished from Compounds 1 and 2 in the above investigation. Transient shear measurements at very low deformation rate indicated a reaction between natural rubber and the coupling agent, resulting in gel and long-branch formation. Differential scanning calorimetry indicated the coupling reaction was completed at 140°C within the mixing time. By holding the maximum temperature of mixing as low as possible, the extrudate of Compound 3 became smooth, but Compound 4 still did not perform well. Improvement of dispersion is necessary to make Compound 4 extrudable.