Chemical Engineering Science 58 (2003) 2911–2919 www.elsevier.com/locate/ces Enzymatic degradation of poly (-caprolactone), poly (vinyl acetate) and their blends by lipases G. Sivalingam, S. Chattopadhyay, G. Madras * Department of Chemical Engineering, Indian Institute of Science, Bangalore-560012, India Received 22 August 2002; received in revised form 3 March 2003; accepted 13 March 2003 Abstract Poly (-caprolactone) (PCL) and poly (vinyl acetate) (PVAc) and their blends were degraded in toluene by two lipases (Novozym 435 and Candida Rugosa) at 60 ◦ C. The degradation of PCL and side-chain hydrolysis of PVAc yielded specic products of molecular weight ∼500 and ∼700, respectively. FTIR analysis of the polymer before and after enzyme treatment and the specic products show that there is large reduction of ester linkages and generation of –OH, –COO (-) , –COOH groups in the broken chains. The optimal temperature for the side-chain hydrolysis of PVAc was 60 and 65 ◦ C and the optimal temperature for the biodegradation of PCL was 55 and 60 ◦ C for Candida Rugosa and Novozym 435, respectively. Continuous distribution kinetics was proposed for determining the rate coecients of the polymers and deactivation of the enzyme. Enzymatic degradation studies of PCL–PVAc blends showed that there is a drastic reduction in the degradation of PCL in the blends. This was modeled by the interaction between polymers. ? 2003 Elsevier Science Ltd. All rights reserved. Keywords: Polymers; Kinetics; Enzyme; Population balances; Continuous distribution kinetics; Polymer blends 1. Introduction The use of biodegradable polymers has been widely accepted in biomedical applications. Due to the environ- mental issues with the commercial plastics, biodegradable polymers have attracted much attention recently (Gan, Yu, Zhong, Liang, & Jing, 1999). Most of the degradable poly- mers are ester bonded and have dierent properties such as mechanical strength, biodegradation rate, morphology, etc. Poly (-caprolactone) (PCL) is a well-known biodegrad- able polyester used in biomedical applications (Woodward, Brewer, Moatamed, Schindler, & Pitt, 1985), especially in controlled drug delivery. Good mechanical strength and biodegradability are expected of biodegradable polymers for practical applications. Random and block co-polymerization have been proposed to increase the mechanical and physi- cal properties of the biodegradable polymers (Pitt, Gratzl, Kimmet, Surles, & Schindler, 1981). Physical blends of aliphatic polyesters with these polymers were also shown to change the morphologies and physical characteristics of biodegradable polyesters (Tsuji & Ikada, 1992, 1996). ∗ Corresponding author. Tel.: +91-080-309-2321; fax: +91-080-360-0683. E-mail address: giridhar@chemeng.iisc.ernet.in (G. Madras). Most of the biodegradable polymers have hydrolysable and/or oxidizable linkages along the main chain (Guillet, 1984). Polymers like poly (vinyl acetate) (PVAc) is known to undergo hydrolysis by side-chain breakage due to their hydrolysable groups in the side chain (Chattopadhyay & Madras, 2003). One of the most widely used techniques to modify the properties of the polymers is to blend them (Gajria, Dave, Gross, & McCarthy, 1996). Blending of PVAc and PCL may yield better properties, like higher mechanical strength. This study investigates the biodegrad- ability of this blend. Studies of the pyrolytic degradation of polymer mixtures have generated varied results. Some investigators have observed, during degradation, signicant interaction between polymers, while others observed no interaction (Karmore & Madras, 2001). The degradation of homopolymers has been extensively studied. The degrada- tion in solution of a mixture of poly(-methylstyrene) and polystyrene has been studied (Madras & McCoy, 1999). In this system, the former polymer degrades by chain end scission while the latter degrades by random chain scission. The degradation of a mixture of polystyrene and PVAc, in which both the polymers degrade by random chain scission, has also been investigated (Karmore & Madras, 2001). In the current investigation, the degradation of PCL and hydrolysis of PVAc and their blends have been 0009-2509/03/$ - see front matter ? 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0009-2509(03)00155-6