Novel Sustainable chemical recycling of green polymers using environmentally benign catalytic process

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In this study, sustainable chemical recycling of biodegradable poly(lactic acid) and bio-based polymers, which were produced from renewable resources, were developed using environmentally benign catalysts, such as enzymes and solid acids. Also, enzyme-catalyzed synthesis and chemical recycling of biopolythioesters were also studied. Summaries of the results are as follows.(1)Transformation of bio-based polymers into repolymerizable cyclic oligomersEnzyme-catalyzed cyclic oligomerization of poly(butylene adipate) was studied with respect to the basic reaction parameters. It was found that in certain organic solvents cyclic oligomerization was quickly occurred by lipase. The affinities toward lipase as well as the molecular weight of the repolymerization products were significantly influenced by the cyclic oligomer size.(2)Developing of novel chemical recycling of poly(L-lactic acid) using solid acidIt was found that poly(L-lactic acid) was efficiently degraded into oligomers by montmorillonite. The obtained lactic acid oligomer was readily repolymerized by solid state polymerization to regenerate the polylactic acid with a molecular weight of greater than 100,000. Based on these results, sustainable chemical recycling of bio-based polymers was proposed.(3)Novel enzymatic synthesis and properties of polythioestersIt was first found that mercaptocarboxylic acid was readily polymerized by enzyme to produce polythioester with a molecular weight of several ten thousands. Thus produced polythioester showed a higher melting temperature and resistance against organic solvents comparing to those of the corresponding polyoxyesters. Also, a series of polythioesters were produced by the polycondensation of alkanedithiol with alkanedicarobxylic acid, and their chemical recycling was established using an enzyme.