Journal of Elastomers & Plastics

Ground rubber tire (GRT) is devulcanized using a coaxial ultrasonic devulcanization reactor at different ultrasonic amplitudes. The devulcanized samples are revulcanized isothermally using a sulfur-based recipe at various temperatures utilizing an advanced polymer analyzer (APA 2000). The curves obtained showed a reversion in the cure that is more pronounced at higher temperatures. A simple vulcanization model is used to fit these cure curves and the corresponding kinetic model parameters are determined. Devulcanized samples are cured nonisothermally in the APA at various constant heating rates and multiple heating steps to verify the ability of this model to predict nonisothermal curing behavior, including reversion. In addition, the cross-link density and gel fraction of the samples cured in the APA are measured and correlated to the state of cure at different times during the curing reaction. Using this information along with the cure kinetics the cross-link density distribution of compression-molded disks are predicted and compared to experimental data.

This article describes the graft copolymerization of methyl methacrylate (MMA) on to natural rubber (NR) by emulsion polymerization using cumene hydroperoxide and tetraethylene pentamine as redox initiators in NR latex. The effect of surfactants, cross-link density of NR, NR/MMA ratio, and mode of addition of monomer on particle morphology is investigated by a transmission electron microscope (TEM). The percent grafting increases with the increasing MMA content while the grafting efficiency decreases. Secondary nucleation of poly(methyl methacrylate) (PMMA) is observed when oleic acid is used as a surfactant, while sodium dioctyl sulphosuccinate (SDSS) and nonionic nonyl phenol poly(ethylene oxide), give core-shell morphology. In all the samples, the smaller rubber particles are heavily coated with PMMA while the larger particles are coated only at higher MMA content. At a given feed rate of the monomer, higher cross-link density of NR results in a more uniform shell. Ultramicrotomed sections of the latex particles show an interpenetrating network-like structure.

Recently, it has been reported that prevulcanization of natural rubber (NR) latex does not hinder the formation of conjugated sequences, which is a precondition for developing intrinsic electrical conductivity in polymers. In this article, the authors report for the first time that incorporation of a steric stabilizer such as starch enhances the solution doping of the prevulcanized NR latex resulting in flexible semiconducting thin films with an optimum enhancement in the electrical conductivity behavior and a decrease in optical band gap. However, the characteristic color changes and the insulator-conductor transitions are gradual, indicating a lower doping rate and hence a longer doping period for the system. Moreover, the complexation of the doped iodine (I₂) atom with the starch molecule prevents the out-diffusion of I₂, and hence imparts stability in the electrical conductivity. The mechanical studies reveal desirable strength for the doped films. The formation of conjugated sequences of double bonds in the poly isoprene (PI) backbone is examined using a UV/VIS and an FTIR-ATR spectroscopy. The swelling studies indicate a reinforcement effect in starch containing composite films at low proportions. The scanning electron micrographs (SEM) of the fabricated films show a compatible phase for the composite and hence a better perfection of the surface.

Maleated ethylene-propylene diene monomer rubber (MAH-g-EPDM) was prepared on a two-roll mill and tested as a compatibilizer for EPDM/NBR (butadiene-acrylonitrile rubber) blend. Intrinsic viscosity measurements and scanning electron microscopy revealed that MAH-g-EPDM improved the compatibility and morphology of EPDM/NBR blend. The uncompatibilized blend showed a negative deviation in the mechanical properties after aging, from the straight line of the additive rule. However, the compatibilized blend showed a positive deviation. Also, MAH-g-EPDM improved the co-curing of EPDM and NBR rubbers. The effect of blend ratio on the heat resistance and upon the stability against UV of the elastomer blend is discussed in terms of the mechanical properties.