Enzymatic Degradation of Polymers

The ASTM definition, updated in 1994 (ASTM Standard D-5488-84d), has led to the establishment of labeling terminology for packaging materials wherein biodegradable is defined as 

The versatiUty of carbon-earbon bonds and carbon to non-carbon bonds and other substituent groups with several configurations, orientation and stereo- 

Enzymes are essentially biological catalysts, which enhance the reaction rates by redueing the activation energies of the reaction. The vast majority of enzymes are proteins with a complex three-dimensional strueture and their activity is closely related to conformational stmcture. The three-dimensional structure of enzymes with folds and pockets creates certain regions on the surface with eharaeteristic primary structures that constitutes an aetive site, wherein interaetion between the enzyme and substrate oeeurs leading to a chemical 

Among the various biological, chemical and physical phenomena involved in the microbial degradation of polymers the biocatalytic reaction at the solid surface of the usually hydrophobic material is assumed to play an important role in the overall process. Factors such as the chemical environment of the cleaved bonds, rigidity of the polymer chain, the molar mass of the polymer, adsorption and surface activation of the enzyme, removal and dissolution of scission products from the surface are often used to control the degradation process (Chandra and Rustgi, 1998 Huang et al, 1994). 

The purpose of this chapter is to summarize the research findings on the degradation of various polymers and contribute to a better understanding of the biodegradation mechanism of polymers that may possibly lead to novel engineered polymers with tailor-made properties and biodegradation 

High molecular weight poly(trimethylene carbonate) PTMC (Mn 300 k g/mol, Mw/Mn 1.46), synthesized, purified, and characterized as described in reference [72] is dissolved in chloroform (3 mg/mL). Thin films are prepared by spin-coating these solutions on cleaned Si wafers at 3,000 rpm (film thickness obtained 25 50 nm). Film thicknesses can be determined by AFM imaging using the scratch method described in Chap. 2 (see also above, hands-on example 47). The enzymatic reaction takes place in situ in the liquid cells filled with lipase solutions (lipase from Thermomyces lanuginosus (EC3.1.1.3, minimum 50,000 units/g purchased from Sigma, U.S.A.) at 37°C for 30 s, 1 min, and 2 min, respectively. 

4 Polymer Surface and Interface Properties and (Dynamic) Processes 

Howald L, Liithi R, Meyer E, Giithner P Giintherodt HJ Z Phys B (1994) 93 267 

Ulman A (1991) An introduction to ultrathin organic films from Langmuir-Blodgett to self-assembly. Academic, New York 

Schonherr H, Feng CL, Tomczak N, Vancso GJ (2005) Macromol Symp 230 149-157 

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Chemical properties with an important role for the enzymatic degradation of polymers are ... 

The type of reaction which is probably of most importance in the enzymatic degradation of polymers is the bimolecular reaction illustrated above, in which the enzyme catalyzes the interaction of the polymer and a low molecular reagent (such as water in a hydrolysis reaction). These reactions can occur by either a single displacement or a double displacement mechanism. In the former, both substrates, A and B below, are bound to the enzyme by consecutive, reversible reactions, after which the final complex, EAB, dissociates into the products, C and D, and the free enzyme, as follows ... 

Williams, D.F., Smith, R. and Oliver, C. (1987) The enzymatic degradation of polymers in vitro. Journal of Biomedical Materials Research, 21, 991-1003. Williams, D.F. and Zhong, S.P. (1991) Are free radicals involved in the biodegradation of implanted polymers Advanced Materials, 3, 623-626. Williams, D.F., Black, J. and Doherty, P.J. (1992), in Doherty, P.J., Williams, R.L., Williams, D.F. et al (eds.) Biomaterial-Tissue Interfaces, Advances in Biomaterials, Volume 10. Elsevier, Amsterdam, pp. 525-533. 

Williams, D.F., Smith, R. and Oliver, C. (1987) The enzymatic degradation of polymers in vitro. Journal of Biomedical Materials Research, 21, 991-1003. 

D Goldberg, JF Rocky, RF Eaton, BS Samuels, KL La Cavao INDA-TEC, Int. Nonwoven Fabrics Conf., Book of Papers, (1990) 55-66 ABIPST, 62 13412, 1992 Y Tokiawa, A Iwamoto, MK Yama. Enzymatic degradation of polymer blends. Proc 3rd Int Scientific Workshop on Biodegradable Plastics and Polymers, Osaka, Japan, 1993 p 36. 

In vitro chemical and enzymatic degradations of polymers, especially polyesters, were analyzed with respect to chemical compositions and physical properties. It was found quite often that the composition of a copolymer giving the lowest melting point is most susceptible to degradation. The lowest packing order, as expected, corresponds with fastest degradation rate. 

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