Depolymerization, alternative recycling

Depolymerization of polymers to monomers conversion of polymers to the corresponding monomers can provide an alternative to recycling of the polymer, reduce landfill burden, and provide a new source of monomer with lower consumption of new raw materials ... 

Chemical depolymerization of polyamides is mainly carried out by hydrolysis. Acid hydrolysis of nylon-6 allows the starting monomer, e-caprolactam, to be recovered. Likewise, basic hydrolysis of nylon-6,6 leads to hexamethylene diamine and adipic acid. Degradation of polyamides by ammonolysis has also been reported as an interesting alternative for the chemical recycling of nylon-6 and nylon-6,6 mixtures. 

Most polymers such as PE, PP, PS, HOPE and PET (for non-food applications) are recycled after purification while others such as PET (for food applications) are first depolymerized, then purified and repolymerized. Other polymers such as ABS and PVC are rarely recycled. Currently, most recycled polymers end up as the same polymer, but because the recycled polymer is often less pure, there can be issues with degradation of physical properties and with meeting regulatory requirements for food packaging. Therefore, there is potential for finding alternative, higher value uses for these waste materials. 

Waste materials such as municipal solid waste, scrap tires, and waste plastics have traditionally been placed in sanitary landfills. However, with landfill space rapidly decreasing in the United States and worldwide, an alternative disposal method for these waste materials becomes imperative. The recycling of solid wastes is a challenging problem, with both economic and environmental constraints. Recently, two broad approaches have been attempted to reclaim solid wastes. The first approach relies on thermal or catalytic conversion of waste materials into fuel and valuable chemical feedstocks. Examples of this approach include gasification, pyrolysis, depolymerization, and liquefaction. The second approach relies on the physical recovery of valuable ingredients in the waste materials. 

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