Recycling degradable polyesters

Hie ester linkage of aliphatic and aliphatic-aromatic copolyesters can easily be cleaved by hydrolysis under alkaline, acid, or enzymatic catalysis. This feature makes polyesters very attractive for two related, but quite different, applications (i) bioresorbable, bioabsorbable, or bioerodible polymers and (ii) environmentally degradable and recyclable polymers. 

For recycling uses, degradable polyesters are desirable for relatively small mass applications, such as glues, thin coatings or labels, in order to facilitate the rapid cleaning of the primary structure for recycling. These applications may be rigid structures such as plastic containers or modifiers for paper products. 

Mueller RJ (2006) Biological degradation of synthetic polyesters - enzymes as potential catalysts for polyester recycling. Process Biochem 41 2124-2128... 

Research by Matsumura et al (19) describes a different concept whereby lipase-catalysis is used to first degrade polyesters into cylic oligomers. Subsequently, cyclic oligomers formed are then polymerized using the same enzyme-catalyst to prepare high molecular weight polyesters. If such a process could be efficient performed with commercial polyesters, it could function as a method to recycle existing materials into new polyesters. 

Unsaturated polyesters (UPs) crosslinked with styrene are often used as a matrix of fiber reinforced plastics. Several reports treated the degradation of the crosslinked UPs with high temperature treatment in water (1,2), acetic acid (5), alcohols including glycols (4,5), and amines (6), often in the presence of catalysts. In these literatures, recovery of polymeric materials from the crosslinked UPs was not a main objective. However, in case we can hydrolyze polyester chains selectively, linear polystyrene derivatives can be obtained as recycled materials. 

As it is both inexpensive and easy to handle, steam is a potential candidate carrier gas for waste plastic recycling in chemical plants. Furthermore, as mentioned in Section 2.1, the degradation temperatures for polyester resins are remarkably shifted to low-temperature regions, and the amount of carbonaceous residue produced in the degradation process is reduced in a steam atmosphere, as compared with that in a nitrogen atmosphere. Accordingly, the preparation of a catalyst that could demonstrate both stable activity for the catalytic cracking of PE-derived heavy oil, but that would also remain stable in a steam atmosphere, was examined [16],... 

Thermoset plastics have also been pyrolysed with a view to obtain chemicals for recycling into the petrochemical industry. Pyrolysis of a polyester/styrene copolymer resin composite produced a wax which consisted of 96 wt% of phthalic anhydride and an oil composed of 26 wt% styrene. The phthalic anhydride is used as a modifying agent in polyester resin manufacture and can also be used as a cross-linking agent for epoxy resins. Phthalic anhydride is a characteristic early degradation product of unsaturated thermoset polyesters derived from orf/io-phthalic acid [56, 57]. Kaminsky et al. [9] investigated the pyrolysis of polyester at 768°C in a fiuidized-bed reactor and reported 18.1 wt% conversion to benzene. 

A. M. CunUffe and P. T. Williams, Characterisation of products from the recycling of glass fibre reinforced polyester waste by pyrolysis. Fuel, 82, 2223-2230, (2003). J. H. Harker and J. R. Backhurst, Fuel and Energy, Academic Press London, 1981. A. C. Albertson and S. Karlsson, Polyethylene degradation products, In Agricultural and Synthetic Polymers, ACS Symposium Series 433, J. E. Glass and G. Swift (eds), American Chemical Society, Washington DC, 60-64, 1990. 

Recycling is one choice for reducing the polymer waste. But, recycling is only effective when waste materials are easily collectable and can be recycled to useful materials without significant deterioration of properties. Recycling also includes the chemical degradation of plastics to monomeric materials which are renewable to give polymeric materials. At present, only a few kinds of plastics, such as polystyrene, polyolefins and polyesters, are recycled on a trial scale. 

Enzymatic Degradation of Diol-Diacid Type Polyesters into Cyclic Oligomers and Its Application for the Selective Chemical Recycling of PLLA-Based... 

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