Rice husk ash (RHA) obtained from agricultural waste, by using rice husk as a power source, is mainly composed of silica and carbon black. A two-stage conventional mixing procedure was used to incorporate rice husk ash into natural rubber. For comparison purposes, two commercial reinforcing fillers, silica and carbon black, were also used. The effect of these fillers on cure characteristics and mechanical properties of natural rubber materials at various loadings, ranging from 0 to 40 phr, was investigated. The results indicated that RHA filler resulted in lower Mooney viscosity and shorter cure time of the natural rubber materials. The incorporation of RHA into natural rubber improved hardness but decreased tensile strength and tear strength. Other properties, such as Young's modulus and abrasion loss, show no significant change. However, RHA is characterized by a better resilience property than that of silica and carbon black. Scanning electron micrographs revealed that the dispersion of RHA filler in the rubber matrix is discontinuous, which in turn generates a weak structure compared with that of carbon black and silica. Overall results indicate that RHA can be used as a cheaper filler for natural rubber materials where improved mechanical properties are not critical.

ABSTRACT:The graft copolymerization of 50/50 (w/w) styrene/methyl methacrylate mixtures onto natural rubber seed latex were carried out by using cumene hydroperoxide/sodium formaldehyde sulfoxylate dihydrate/EDTA-chelated Fe 2ϩ as a redox initiator. The effects of the process factors such as the amount of initiator, emulsifier, and chain-transfer agent; monomer-to-rubber ratio; and temperature on the grafting efficiency (GE) and grafting level (GL) are reported. The mechanism of graft copolymerization was investigated. The synthesized graft copolymers were purified and then characterized by proton nuclear magnetic resonance ( 1 H-NMR) analysis. Transmission electron microscopy (TEM) was used to study the morphology of the graft copolymers. It appears that the formation of graft copolymers occurs on the surface of the latex particles through a chain-transfer process.

The performance of rice husk ash (RHA), obtained by burning rice husks, as a filler for natural rubber (NR)/ethylene-propylene-diene monomer (EPDM) blends was investigated. For comparison purposes, two commercial reinforcing fillers, silica and carbon black were also used. A fixed 75 : 25 blend ratio (wt %) of NR and EPDM was prepared using a two-stage conventional mixing procedure. Filler loading was varied from 0 to 60 parts per hundred of resin (phr) at 15 phr intervals. The results indicated that RHA offers processing advantages over silica and carbon black. The use of RHA as an additional filler provided almost no improvement in the tensile strength and abrasion resistance of the 75 : 25 NR/EPDM blends. The ozone resistance of the blends was inferior to those obtained from the addition of RHA. However, RHA was better in resilience property than that of silica and carbon black. Scanning electron micrographs revealed that the dispersion of RHA filler in the rubber matrix is discontinuous, which in turn generates weak structure when compared with carbon black and silica. According to these observations, RHA could be used as a diluent filler for the 75 : 25 NR/EPDM blend, while silica and carbon black can be used as a reinforcing filler.

The redox initiator, cumene hydroperoxide/ tetraethylenepentamine (CHPO/TEPA), was used to initiate the emulsion polymerizations of styrene and methyl methacrylate (MMA). The hydrophobic CHPO acting as oxidizer would interact with the hydrophilic TEPA employed as the reducer at the particle-water interface where the vinyl monomer is present. The kinetics of the styrene and MMA polymerizations were studied under a temperature range of 30-70°C. The polymerization rate, the concentration of monomer in the particles, the average number of latex particles and the number of radicals per particle were investigated to evaluate the propagation rate constant during interval II of the polymerization. With increasing temperature, the number of latex particles increases while the monomer concentration in the particles slightly decreases. The observed number of radicals per particle, calculated from the number average volume of the particles and the relation between the entry rate coefficients of free radicals into the particles and the exit rate coefficients of free radicals from the particle, was found to be approximately 0.47 and 0.5 in case of styrene and MMA polymerization, respectively. The calculation shows that the propagation rate constant, k p = 6.84 × 10 7 e −37.65/RT and k p =3.4×10 7 e −31.05/RT L/mol s for styrene and MMA polymerizations over the temperature range studied, respectively.

ABSTRACT:The graft copolymerization of styrene and methyl methacrylate onto natural rubber latex was studied under various reaction conditions using a cumene hydroperoxide redox initiator. The monomer conversion, graft copolymer compositions, and grafting efficiency were determined. The synthesized graft copolymers were purified and then characterized by proton nuclear magnetic resonance ( 1 H-NMR) analysis and differential scanning calorimetry (DSC). A 2 IV 6-2 fractional factorial experimental design was applied to study the main effects on the grafting. The variables investigated in this work were the amount of the initiator and emulsifier, the presence or absence of a chaintransfer agent, the styrene-to-methyl methacrylate ratio, the monomer-to-rubber ratio, and the reaction temperature. The measured response for the experimental design was the grafting efficiency. The analysis of the results from the design showed the sequence of the main effects on the observed response of the grafting of styrene and methyl methacrylate onto natural rubber, in ascending order. The amount of the chain-transfer agent and the reaction temperature in the range of the test had significant effects and one marginally significant effect was the monomer-to-rubber ratio.