BIODEGRADABILITY OF NOVEL COPOLYESTERS OF POLY(BUTYLENE SUCCINATE) CONTAINING SULPHUR ATOMS

In recent years, biodegradable polymers have gained much attention as green materials and biomaterials. Aliphatic polyesters, due to their favorable features of biodegradability and biocompatibility, are one of the most important classes of synthetic biodegradable polymers. Among all, PBS is used in a wide range of applications, such as packaging film, bags, flushable hygienic products and garden mulch, but shows a quire slow rate of degradation. As is well known enzymatic biodegradation of a polymer is controlled by several factors: the most important one is the nature of the polymer itself, i.e. its chemical structure; hydrophilicity and consequently water uptake increases degradation rate; moreover, the degree of crystallinity is a crucial factor, since enzymes preferably attack the amorphous domains of a polymer. Conditions like temperature, pH and concentration of enzyme also play a important role. In our study, the effect of chemical modification as well as of molecular architecture on PBS biodegradation rate has been investigated. Copolymers of PBS containing thiodiethylene succinate sequences with different molecular architecture have been prepared in our laboratories via reactive blending in the presence of Ti-based catalyst (PBSPTDGS). In particular, a block copolymer with long sequences and the random one have been considered. For comparison the parent homopolymer PBS has been also synthesized by the usual two-stage melt polycondensation. To evaluate the biodegradability of the polymers under investigation, two kind of tests were carried out: i) turbidimetric film assay, which has high sensitivity to very small extents of degradation and ii) weight loss measurements. ATRIR analysis and DSC measurements have been performed to correlate degradation rate with crystallinity degree. Lastly, NMR analysis was performed to follow changes in composition of the copolymers under investigation. Copolymers degrade to a much higher extent than PBS. Moreover, random copolymer degrades faster than the block one, probably due to its lower degree of crystallinity. ATRIR and DSC analyses confirm that the amorphous phase is the region attacked first by enzyme. Lastly, in the case of PBSPTDGSblock an evident decrease of TDGS content is observed by means of NMR analysis with the proceeding of degradation, indicating that enzyme hydrolysis involves preferentially ester groups of TDGS sequences, probably because of their higher hydrophilicity. The results obtained from the present research can be summarized as follow: 1. Copolymerization is an efficacious way to increase PBS biodegradability. 2. Biodegradation rate can be modulated changing the molecular architecture, which affects the crystallinity degree.