Plasma and electron-beam processes as pretreatments for enzymatic processes

Plasma generated by non-polymerizing gases (oxygen, air and nitrogen) and electron-beam irradiation under different atmospheres were studied as possible pretreatments to an enzymatic process with transglutaminase (TGase). The aim was to improve the accessibility of target groups of TGase present in wool fabrics to the enzyme, thanks to chemical etching or the removal of the epicuticle layer by physical etching, thus leading to increased formation of cross-links or incorporation of primary amine compounds. For the plasma treatment, we found that oxygen promotes the cleavage of disulphide bonds by oxidation of sulphur species: a reduction of oxygen content in the gas plasma induced a reduction in oxidation yield, as shown by FTIR measurements. Conversely, nitrogen promoted a chemical etching reaction. The most significant effects were observed at high treatment power (400 W), where both cleavage of polymer chains and removal of the epicuticle layer were promoted. Air plasma at high power was the most promising pretreatment to the enzymatic process. The modifications induced a good penetration of the enzyme into the fibre core and no significant changes in enzyme activity were observed in contact with the plasma-treated fabrics. In contrast, by increasing the energy of the electrons in E-beam treatments no significant superficial modifications were observed. In fact, they promoted the cleavage of high-energy bond, such as S–S linkage, by enhancing depolymerization reaction.