~2.,-~...'~'J~/ ELSEVIER PolvmerDegradationand Stability 45 (1994) 187-196 © 1994Elsevier ScienceLimited Printed in Northern Ireland. All rights reserved 0141-3910/94/$(17.IX) Chemical, enzymatic and microbial degradation of bacterial and synthetic poly- -hydroxyalkanoates R. H. Marchessault,* C. J. Monasterios, J. J. Jesudason Department of Chemistry, McGill University, Pulp and Paper Center, 3420 University Street, Montreal, Quebec, Canada, H3A 2A7 B. Ramsay, I. Saracovan, J. Ramsay D~partement de G~nie chimique, Universit~ de Montreal, l~cole Polytechnique, CP 6079, Succursale 'Centreville', Montreal, Quebec, Canada, H3C 3A7 & T. Saito Department of Biological Sciences, Kanagawa University, 2946 Tsuchiya Hiratsuka-City, Kanagawa Prefecture, Japan 259-12 The chemical, enzymatic and microbial degradation of bacterial and synthetic poly-/3-hydroxybutyrate (PHB) and its copolymers with /3-hydroxyvalerate (PHB/HV) were evaluated. Alkaline hydrolysis (7.4 and 10pH units) was carried out at 70°C. Samples were treated with purified extracellular PHB depolymerase from Alcaligenes faecalis T1. Microbial degradation was studied using a chemostat with an inoculum of activated sludge under carbon limited conditions. Samples studied were synthetic PHB, bacterial PHB and PHB/HV. Samples were in the form of dry powders, a 'never dried' aqueous dispersion (latex) of native granules or films made from these materials. The microbial degradation of PHB/HV latex coated paper samples was also studied. Bacterial PHA samples degraded completely after 12 h exposure to PHB depolymerase. Degradation in a microbial environment was within a matter of days. Conversely, synthetic PHB samples which degraded more readily than bacterial PHB by alkaline hydrolysis did not degrade as readily upon exposure to a microbial environment. The extent of degradation was determined quantitatively by weight loss and was followed qualitatively by scanning electron microscopy. The degradation rate depended on sample crystallinity, tacticity, morphology and composition. In general PHB]HV films and coated paper made with the 'never dried' latex degraded more quickly than solvent cast films. Synthetic PHB of intermediate tacticity exposed to depolymerase enzyme biodegraded more extensively than highly isotactic synthetic PHB. INTRODUCTION Polymer degradation phenomena can be clas- sified into four distinct groups depending on the mechanism: chemical degradation, biodegrada- tion, environmental degradation and photodeg- * To whom correspondence should be addressed. 187 radation. The first is by purely chemical reaction such as hydrolysis or pyrolysis. The second process occurs in animal bodies with prosthetic devices and is usually attributed to enzyme action although simple chemical hydrolysis may also be operative. The third is a combination of processes (chemical, microbial and physical)