Influence of n-ZnO Morphology on Sulfur Crosslinking and Properties of Styrene-Butadiene Rubber Vulcanizates

Degradation by Electron Beam Irradiation of Some Elastomeric Composites Sulphur Vulcanized

Composites based on natural rubber and plasticized starch obtained by the conventional method of sulfur cross-linking using four types of vulcanization accelerators (Diphenyl guanidine, 2-Mercaptobenzothiazole, N-Cyclohexyl-2-benzothiazole sulfenamide, and Tetramethylthiuram disulfide) were irradiated with an electron beam in the dose range of 150 and 450 kGy for the purpose of degradation. The vulcanization accelerators were used in different percentages and combinations, resulting in four mixtures with different potential during the cross-linking process (synergistic, activator, or additive). The resulting composites were investigated before and after irradiation in order to establish a connection between the type of accelerator mixture, irradiation dose, and composite properties (gel fraction, cross-linking degree, water absorption, mass loss in water and toluene, mechanical properties, and structural and morphological properties). The results showed that the mixtures became sensitive at the irradiation dose of 300 kGy and at the irradiation dose of 450 kGy, and the consequences of the degradation processes were discussed.

Effects of the surface chemical groups of cellulose nanocrystals on the vulcanization and mechanical properties of natural rubber/cellulose nanocrystals nanocomposites

Cellulose nanocrystals (CNCs), as the promising reinforcing fillers in the rubber industry, their surface chemical groups have vital effects on the vulcanization kinetics, cross-linking densities, and mechanical properties of rubber composites. Herein, CNCs with acidic carboxyl (CCA) and alkaline amino groups (CCP) were produced by modifying the sulfonic CNCs (CCS) in environment-friendly ways. Studies found the CCS and CCA with acid groups have obvious inhibiting effects on the vulcanization of natural rubber (NR), while CCP with alkaline amino groups accelerates the vulcanization of NR. Differential scanning calorimeter, Fourier transform infrared spectroscopy, and Electron paramagnetic resonance, etc. were performed to clarify the effecting mechanisms of CNCs surface groups on NR vulcanization. It was found that NR/CCS and NR/CCA nanocomposites vulcanize through radical reactions, and the surface acidic groups of CCS and CCA, i.e., hydroxyl, sulfonate, and carboxyl groups inactivate the sulfur radicals generated during vulcanization and depress the vulcanization activity. The amino groups of the polyethyleneimine of CCP promote the ring opening of sulfur (S₈) or the breaking of polysulfide bonds connected to NR molecular chains to form sulfur anion with a strong nucleophilic ability, which leads to the cross-linking of NR/CCP reacts via ionic reaction mainly. The vulcanization rate and cross-linking density of NR/CCP are improved by the ionic reaction. And benefiting from the higher cross-linking density and the reinforcement of CCP, NR/CCP had the best physical and mechanical properties. Our work elucidates the mechanism of the surface chemical groups of CNCs affecting NR vulcanization and may provide ideas for the preparation of high-performance rubber composites reinforced by CNCs.

A Multifaceted Approach for Cryogenic Waste Tire Recycling

One of the important aspects for degradation of the life quality is the ever increasing volume and range of industrial wastes. Polymer wastes, such as automotive tire rubber, are a source of long-term environmental pollution. This paper presents an approach to simplifying the rubber waste recycling process using cryogenic temperatures. The temperature of cryogenic treatment is ranged from 77 K to 280 K. Liquid nitrogen was used as a cryoagent for laboratory tests. Experimental and numerical studies have been carried out to determine the optimal conditions for the recycling process. Numerical studies were performed using the COMSOL Multiphysics cross-platform software. The optimal force of mechanical shock for the destruction of a tire which turned into a glassy state after cryoexposure was determined experimentally. The chemical and physical properties of the final product (crumb rubber) have been studied by scanning electron microscopy and energy dispersive X-ray spectroscopy. The analysis shows that the morphology and elemental composition of the samples remain practically unchanged, demonstrating environmental friendliness of the proposed process.