Global production and consumption of poly­(ethylene terephthalate) (PET) products has increased dramatically over the past few decades. World consumption of PET has exceeded 13 million tonnes, of which about 1.5 million tonnes is exclusively consumed by the packaging sector itself. However, this tremendous increase in PET consumption has resulted in the accumulation of an enormous quantity of waste, the disposal of which is complex day by day. Among different PET recycling methods, chemical recycling (chemolysis) is the most successful method to convert PET into its monomers/oligomers. This review presents in detail recent developments in the chemical recycling (glycolysis and aminolysis) of PET. The wide spectrum of depolymerizing agents used, the reaction conditions, catalysts, products of depolymerization, and their potential applications are described.

Hydrated silicas impart better physical properties to polar rubbers, compared to those of hydrocarbon rubbers. However, to achieve optimum properties silane coupling agents are crucial in such formulations. Epoxidized natural rubber (ENR) in small proportions is used as a reinforcement modifier for silica-filled nitrile rubber (NBR). Two systems of cure were used: N-cyclohexyl-2-benzthiazyl sulfenamide (CBS) alone and in combination with diphenyl guanidine (DPG). In the CBS accelerated system, incorporation of an optimum concentration of about 15% of ENR on total rubber was found to improve technological properties. Addition of a secondary accelerator further improves these properties. Comparable results are obtained with those containing coupling agent and NBR-ISAF. High bound rubber and volume fraction values indicate a high polymer-filler interaction and gel content resulting from the NBR-ENR interaction. Results of this study reveal that ENR could be used as a reinforcement modifier for the NBR-silica system.

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Skim natural rubber latex is a protein-rich byproduct obtained during the centrifugal concentration of natural rubber latex. Skim latex has a very low dry rubber content (4-8%), and the rubber particles are smaller in size. It has a higher proportion of nonrubber solids, which are mostly proteinaceous in nature. It is difficult to coagulate, and it takes more processing time. The proteins in skim latex can be decomposed by proteolytic enzymes. This article discusses the use of stabilized liquid papain from the papaya plant (Carica papaya) for deproteinization followed by creaming for quick and easy coagulation of skim latex. The technological properties and aging characteristics of the deproteinized skim rubber are compared with those of conventionally prepared skim rubber and block rubber. The deproteinized skim rubber showed enhanced quality parameters. Particle size analysis revealed that deproteinization and creaming of the skim latex did not markedly change the particle size. Gel permeation chromatography showed a reduction in the quantity of fatty acids after deproteinization and creaming, which was reflected in the improvement of the aging characteristics in comparison with the control sample. Vulcanizates prepared with the deproteinized skim rubber had higher resilience, lower heat buildup, lower compression set, and good tensile strength and elongation at break in comparison with conventionally prepared skim rubber, and the properties were almost comparable to those of block rubber. The improvement in the mechanical properties and aging characteristics could be attributed to the reduction of the protein content, the partial removal of unsaturated fatty acids, and the removal of metal ions that were pro-oxidants during the deproteinization and creaming process.

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Nitrosamines (NA) reported to be found in rubber products vulcanized using conventional accelerators such as tetramethylthiuramdisulphide (TMTD) are carcinogenic. Tetra benzyl thiuramdisulphide (TBzTD) has been used in an efficient vulcanisation (EV) system to prepare rubber vulcanisates having properties comparable to the vulcanisate prepared using TMTD. TBzTD is reported to be non regulated and safe. The compound containing TBzTD shows better scorch safety. The novel safe vulcanisate shows comparable mechanical properties, crosslink density and improved aging resistance.

High styrene rubber ionomers were prepared by sulfonating styrene-butadiene rubber of high styrene content (high styrene rubber) in 1,2-dichloroethane using acetyl sulfate reagent, followed by neutralization of the precursor acids using methanolic zinc acetate. The ionomers were characterized using X-ray fluorescence spectroscopy, Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), dynamic mechanical analysis (DMA), and also by the evaluation of mechanical properties. The FTIR studies of the ionomer reveal that the sulfonate groups are attached to the benzene ring. The NMR spectra give credence to this observation. Results of DMA show an ionic transition (T i ) in addition to glass-rubber transition (T g ). Incorporation of ionic groups results in improved mechanical properties as well as retention of properties after three cycles of processing.

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