Biodegradability of polyurethanes and morphology formation during coagulation process

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. Hydrolytic and enzymatic degradation decreased with the increase of the diol carbon chains in polyol, and increased by substituting aromatic diisocyanate with aliphatic diisocyanate. 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 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 indicates that presence and content of hard segment in polyurethane affect 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 or 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. Immersion precipitation method is a general technique in preparation of polyurethane membrane and coated fabric. A thin film of a homogeneous polymer solution is contacted with a nonsolvent. Exchange of solvent and nonsolvent across the interface introduces phase separation of polymer film into polymer-rich phase and polymer-lean phase. The former results in a rigid, structural for...