Thermosetting Polymers: A Review on Primary, Secondary, Tertiary and Quaternary Recycling

Abstract

Polymers have emerged as an indispensable part of human life due to demand of low cost, low density and esthetic products with shorter life cycle as compared to conventional materials. Rapid increase in population in last fifty years has significantly increased the demand of polymers which possess grave threat to the environment as most of the synthetic polymers are non-biodegradable. Thus, recycling is only dynamic and obvious alternative to conserve environment and reduce cost of waste disposal. Recycling of thermosets is difficult as compared to thermoplastics as former cannot be remolded and remelted into another shape due to inherent molecular structure. The recycling methods are broadly divided into four types i.e., primary, secondary, tertiary and quaternary. The article focus on review current scenario and future challenges of four recycling methods for thermosets. Primary recycling aims to reuse product in original state while mechanical processing is required in secondary recycling. In tertiary, both mechanical and chemical processes are used to reduce the polymer waste into smaller units to be used for further applications. Tertiary recycling involves breaking down the longer chains using chemical processes to extract energy and fuel form polymers. The methodology, applications area, advantages and challenges of each recycling methods are discussed in detail in light of extensive literature survey. A case study has been presented to investigate the thermal properties of thermosetting polymers during primary, secondary, tertiary and quaternary recycling.