Surface modification of poly-(ethylene terephthalate) by lipolytic enzymes.

Poly-(ethylene terephthalate) (PET) is the most important polymer used for the production of synthetic textile fibres. Polyester shows various disadvantages in processability mostly due to high hydrophobicity. In particular, the surface is not easily wettable thus impeding the application of dye compounds or functionalisation. High temperature alkali treatment with sodium hydroxide is the conventional way of rendering PET fibres hydrophilic. Although hydrophilicity is achieved, the favourable bulk properties of fibres, particularly mechanical strength, are affected. Recent studies have demonstrated that lipolytic enzymes, such as lipases, esterases and cutinases are able to hydrolyze superficial ester bonds of aliphatic and aromatic polyesters, among which PET granules, films and fibres. In the present work the effect of a commercial cutinase on PET fibres and films, with different crystallinity and molecular orientation was investigated. Experimental parameters were varied, such as enzyme/substrate ratio and reaction time. Cutinase, a small member of the  hydrolase fold family, was found to successfully modify PET. The wettability of the samples, measured by the water contact angle, improved. In particular, FTIR measurements confirmed that cutinase displays significant hydrolytic activity towards amorphous PET. We found that as the crystallinity of the material increases the efficiency of enzyme decreases. Futhermore, FTIR analyses on PET films, before and after cutinase treatment, point out some spectral alterations, due to enzymatic chemical modification. In particular, this aspect is remarkable on amorphous films. Since, hydrolysis reaction of ester bonds releases hydroxyl and carboxyl groups on the surface, the formation of reactive groups opens the possibility to taking a new approach to PET finishing and functionalisation.