Development of Biodegradable Plastics from Cellulose Acetate

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Cellulose diacetate (CDA) was recently proved to be a biodegradable polymer. CDA is, however, suffered from an insufficiency of thermoplasticity when compared with wide-use plastics. This study has been carried out to develop novel methods plasticizing effectively the CDA.For this purpose, grafting methods for the internal-plasticization of CDA, which has not been studied sufficiently, have been tried to develop. In the methods, the biodegradability of CDA should be maintained or developed, and the grafting efficiency and the reaction rate should be enhanced. Concretely, the grafting of cyclic esters and/or hydroxy acids have been studied. In the former case, the ring-opening graft copolymerization of ε -caprolactone (CLN) into CDA was conducted to satisfy the above requirements by using Tin( II )2-ethylhexanoate (SnEht2) as the catalyst. This grafting was found to be effectively achievable by reactive-processing using twin-screw extruder, which enables reactions with a low liquid-ratio (esterifying agent / CDA weight ratio) as low as 0.4. As the result, products with the wide range of molar substitutions (MS) were obtained, and their thermal and mechanical properties were systematically studied. In the ranges with MS less than 1 and/or up to 8. the grafted CDAs (g-CDA) don't have well-defined crystallized structures, but in the ranges with the higher MS more than 8, the grafted branch chains of polycaprolactone condense each other to cause their crystallization. The tensile properties of the sheets prepared by hot-press molding of the g-CDA, as well as the appearances of non-transparencies and/or turbidities of the sheets can support these phenomena. Non occurrence of this grafted branch chain crystallization was found when CLN was graft co-polymerized with other cyclic esters including lactide. The plasticization of CDA was also systematically conducted by graft co-polymerization of CLN and lactic acid.