Dynamics of Lipase Catalyzed Enzymatic Degradation of Poly(bisphenol-A carbonate) G. Sivalingam, Giridhar Madras Department of Chemical Engineering, Indian Institute of Science, Bangalore-12, India Received 19 February 2003; accepted 21 May 2003 ABSTRACT: Poly(bisphenol-A carbonate) (PC) was de- graded in solution at various temperatures (26 –70°C) by different lipases, Candida Rugosa (CR), Hog Pancreas (HP), Lipolase (LL), and Novozyme (NV), in various solvents. The degradation of PC was monitored using gel permeation chromatography (GPC). The molecular weights of oligomers obtained were around 1,400 irrespective of the lipases used. Continuous distribution kinetics was proposed to de- termine the rate coefficients of the polymers and deactiva- tion of the enzyme. The FTIR analysis of the polymer before and after degradation showed that there is large reduction of carbonate linkages and generation of hydroxyl and acidic groups in the broken chains. The optimal temperatures for HP and other lipases were 50 and 60°C, respectively. HP showed higher degradation activity at lower temperatures and the overall degradability of the lipases was in the order of LL  CR  NV  HP. The effect of viscosity and polarity of the solvents on the degradation of the polycarbonate was also investigated. While the degradation rate decreased with viscosity, it increased with polarity for the solvents. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2391–2396, 2004 Key words: enzymes; degradation; polycarbonate; continu- ous distribution kinetics; lipases; solvent effect INTRODUCTION Biodegradable polymers provide an attractive alterna- tive to conventional nonbiodegradable polymers, both from environmental and biomedical applications. En- zymes are effective in a wide variety of commercial reactions, such as hydrolysis, transesterification, and acylation. 1 Some enzymes, such as lipases, are stable and active in nearly water-immiscible organic sol- vents. 2,3 It is speculated that a thin layer of water remains tightly bound to the enzyme. This water acts as a protective sheath along the enzyme’s hydrophilic surfaces and allows retention of its native confirma- tion and hence activity, even in abiotic solvents. 4 These desirable properties of lipases make them ver- satile in biodegradation of polymers in organic sol- vents. Poly(bisphenol-A carbonate) is currently of great commercial importance as high-performance plastic, such as bulletproof and eye glasses, sheathings, and computer disks. It is of interest to examine the biode- gradability of such polymers from their end applica- tion and ecological viewpoints. There are reports on the biodegradation of aliphatic polyesters by lipases 5,6 and by microorganisms in soil. 7 Polycarbonates with aliphatic components are also degradable by microor- ganisms. 8,9 It has also been reported that the polycar- bonates with side chains connected by a polycarbon- ate are degraded by lipases and the hydrolysis of the main chain has remained questionable. 4 Recently Sivalingam et al. 10 showed that the en- zyme activity on biodegradation of polymers is mainly dependent on the solvent properties and showed that the enzyme activity increases with polar- ity and decreases with viscosity of the solvent. The organic species such as nucleophiles are reported to alter the substrate specificity and improve the stability of the enzymes. 11 The products obtained by biodegra- dation of aliphatic polycarbonate are CO 2 and acids. 9 For degradation of polymers in solution, the solubility of polymer in organic solvent is crucial. In the present study, the biodegradation kinetics of poly(bisphenol-A carbonate), optimal temperatures, and the influence of solvent with different lipases were investigated. Continuous distribution kinetics models were developed taking the enzyme deactiva- tion into account and the rate coefficients and enzyme deactivation coefficients were determined. Experimental section Materials Poly(bisphenol-A carbonate) [average molecular weight 64,000 and polydispersity 1.23] was obtained from Sigma Aldrich. Two commercial immobilized lipases, viz Lipolase and Novozyme, were obtained from Novo Nordisk (Denmark) as a gift. Candida Rugosa (activity of 724 units/mg) and hog pancreas Correspondence to: G. Madras (giridhar@chemeng.iisc. ernet.in). Journal of Applied Polymer Science, Vol. 91, 2391–2396 (2004) © 2003 Wiley Periodicals, Inc.