Effect of chemical structure on the biodegradation of polyurethanes under composting conditions

Abstract

Polyester-polyurethanes having different chemical structure were synthesized and their biodegradabilities were investigated. Average molecular weight of the synthesized polyurethanes ranged from 79 106 to 161 715 (M(w)) by gel permeation chromatography. Degradation experiments were conducted by: hydrolytic degradation in NaOH solution; enzymatic degradation by lipase; and composting. Hydrolytic and enzymatic degradation decreased with the increase of the diol carbon chains in polyol, and increased by substituting aromatic diisocyanate with aliphatic diisocyante. It is considered that hydrophobicity and hard segment formation seem to resist the hydrolytic and enzymatic degradation of polyurethanes. Synthesized polyurethanes were biodegradable under composting condition to a certain extent depending on their chemical structures. As the hard segment content was increased, biodegradation rate decreased. Biodegradation rate of polyurethanes increased with the following order of diisocyanate used: MDI<H(12)MDI<HDI. Polyurethane composed of aliphatic diisocyanate showed higher biodegradation rate than polyurethane composed of aromatic diisocyanate. These facts indicate that the presence and content of hard segment in polyurethane effect the biodegradability under composting condition. As the diol carbon chains of polyol increased, biodegradation rate under composting condition increased. When the polyol used is poly(hexamethylene adipate)diol of poly(caprolactone)diol, polyurethane showed maximum biodegradation rate under composting condition. Surface hydrophobicity, which is related to good adhesion of bacteria on the polymer surface, is considered to be a factor on biodegradation rate under composting condition. (C) 1998 Elsevier Science Limited. All rights reserved.