Rubber Recycling

Abstract For both environmental and economic reasons, there is a continuing broad based interest in recycling of scrap rubber and development of recycling technologies. The use of post- industrial scrap is established as a systematic business. However, the disposal and reuse of scrap tires remains a serious environmental concern and a business opportunity. The method for reclaiming rubber utilizing aqueous alkaline solutions has been abandoned in North America because of environmental pollution hazards. The focus of more recent research is to apply processes that do not generate disposal hazards and that might be carried out directly in the product manufacturer's factory. The major process at the present time is to utilize the scrap rubber as a very finely ground crumb. Crumb is produced either by ambient temperature mechanical grinding or by cryogenic shattering. In general, the crumb rubber is combined with virgin elastomer compounds to reduce cost. However, there is some loss in physical properties and performance. This factor has motivated the search for cost effective in-situ regeneration or devulcanization of the scrap rubber to provide superior properties. Some progress has been achieved utilizing mechanical shear, heat and other energy input, and a combination of chemicals such as oils, accelerators, amines, etc. to reduce the concentration of sulfur crosslinks in the vulcanized rubber. The major application of scrap rubber, particularly as crumb, is outside the conventional rubber industry. More than half of the scrap is burned for its fuel value for generation of electricity and as a component in cement production. The utilization in extension of asphalt in road construction is now recognized to provide superior road performance and reduced cost. The simple use of crumb rubber as a component in artificial turf is developing into a significant industry. Rubber crumb is now widely utilized in rubber products such as mats, floor tiles, carpet undercushion, etc., where the crumb is rebonded using polyurethane or latex adhesives. Other applications, such as in landfill, concrete, thermoplastic blends, pyrolysis to generate carbon black and chemicals, are discussed. The tire industry does utilize a significant proportion of fine crumb rubber in tire compounds. This is likely to not increase much due to the concern about tire performance and safety. However, there is a serious interest by tire manufacturers to increase the use of scrap tire rubber, if the recycled rubber could be regenerated to improve compatibility and performance in tire compounds.