Investigation of the influence of the draw ratio on the enzyme catalysed degradation of poly(ethylene terephthalate) fibres using nanoscale surface thermal analysis

Enzyme catalysed hydrolysis provides an environmentally friendly route for controlled degradation of poly (ethylene terephthalate) fibres. In this work, the hydrolysis of PET fibres with different degrees of orientation by a cutinase from Humicola insolens (HiC) was investigated using the advanced nanoscale surface sensitive thermal analysis (nanoTA) with the aim, to better understand the mechanism of the enzyme catalysed degradation. The hydrolysis was found to occur preferentially at the outer fibre layer, leading to a release of monomer and ablation of the fibre surface. As polymer amorphous regions are more susceptible to enzymatic hydrolysis and since initially hydrolysis is limited to the outer fibre layer, the change in crystallinity occurs mainly in the fibre surface region and does not contribute to the overall crystallinity of the fibre. A higher degree of fibre orientation by drawing reduces the attack of the enzyme and preserves the high order and strength of the fibres during the hydrolysis. The results provide further basis for the optimisation of enzyme catalysed surface hydrolysis and polymer degradation processes of PET fibres.