Johan-Fredrik Selin

Hydrolytic degradation of peroxide modified poly(L-lactide)

Abstract Poly(L-lactide) (PLLA) was prepared by a tin(II)-octanoate initiated ring-opening polymerization in the melt and separately melt modified with tert -butylperoxy benzoate (0.1, 0.25 and 0.5 wt%) in order to deactivate the residual tin compounds and reduce melt degradation. Injection molded specimens of unmodified and peroxide-modified PLLA were prepared for a hydrolytic degradation study, where the changes in the weight, mechanical strength, molar mass and morphology were studied during the immersion in buffer solutions (pH 7.4) at 37 °C. The hydrolytic degradation of both the unmodified and the peroxide-modified PLLA was rapid. This was found to depend on the residual dilactide content, which in all samples was above 11% before the immersion. The peroxide modified samples underwent a more rapid hydrolytic degradation than the unmodified ones, which can be related to the morphological changes caused by the peroxide modification.

Microbial degradation of poly-(L-lactic acid) oligomers

Biotic and abiotic degradation of poly-(l-lactic acid) (PLLA) oligomers of molecular weight (MW) 260–2880 g mol−1 has been studied in an aquatic aerobic headspace biodegradation test for six months. Water soluble/dispersable PLLA oligomers (MW 260–550 g mol−1) biodegraded at 25 °C and at 58 °C. Larger, crystalline and hydrophobic oligomers (MW 550–2880 g mol−1) biodegraded only at 58 °C. Weight-average molecular weights of PLLA-oligomers decreased both during biotic and abiotic degradation, although slightly more during biotic degradation. The surface and inner structures of biotically incubated PLLA oligomers were more porous than those of abiotically degraded oligomers. Thus abiotic hydrolysis of PLLA-structure to lactic acid appears to be an essential, but not the only explanation for its degradation. PLLA polymer chain seems to be cleaved also enzymatically to lactic acid.

Environmental degradation of peroxide modified poly(L-lactide)

Poly(L-lactide) (PLLA), prepared by a tin(II)-octoate initiated ring-opening melt-polymerization was separately modified with tert-butylperoxy benzoate (0.1, 0.25 and 0.5 wt%) in an extruder. The peroxide modification retarded the melt degradation and caused changes in the morphology of the polymer. Injection molded specimens of unmodified and peroxide modified PLLA were prepared. Changes in weight, mechanical strength, molar mass and in the morphology were studied during degradation in soil. The peroxide modified samples underwent a more rapid degradation than the unmodified ones, which can be related to the morphological changes caused by the peroxide modification. The degradation behavior could mainly be related to accessibility to water.