Synthesis of Biodegradable Polyurethane Foams from Condensed Tannin and Bark of Acacia mearnsii

Utilization of wattle tannin (WT) and Acacia meamsii bark (BK) was studied as a partial replacement for synthetic polyols in formulation of polyurethane (PU) preparation. Based on the urethane formation from (+ )-catechin, it is suggested that polyhydric condensed tannin can be utilized as a polyol and constitutes hard segments in a PU polymer molecule. Rigid PU foams were prepared from WT and BK and their biodegradability was investigated. Various types of PU foams can be obtained by selecting the appropriate diisocyanates. Hydroxyl groups in B-ring of WT react with isocyanate, and hence WT and BK act as cross-linking agents as well as hard segments in PU foams so as to produce rigid foams at high levels of WT or BK contents. The PU foams derived from WT and BK obviously were degraded by some wood-rotting fungi. The BK moiety was degraded preferentially by fungi and soil microorganisms. The urethanes derived from catechin and WT were relatively stable under hydrolytic and aminolytic conditions at room temperature. The rates of decompo­ sition of urethanes derived from catechin and WT in both hydrolysis and aminolysis conditions at high temperatures were much faster than those of urethanes derived from phenethyl alcohol and trirnethylolpropane.