A strategy for environmentally-friendly removal of impurities from cotton based on biocatalytic reaction in supercritical carbon dioxide

A novel and environmentally-friendly strategy for integrated bio-treatment (namely the biodesizing and bioscouring) of grey cotton in one-step to degrade and/or remove impurities was constructed on the basis of catalytic reactions from mixed enzymes, by employing reverse microemulsion in supercritical carbon dioxide fluid (SCF-CO₂) media as an alternative to heavily polluting wet-chemical processes. Moreover, a subsequent supercritical washing procedure was also involved. Then the proposed strategy was further explored and characterized by the observation of the formation of reverse microemulsion, impurity removal efficiency and wickability of the treated substrate, the results of static water contact angle measurements, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The results demonstrate that an efficient degradation and/or removal of various impurities could be achieved by the proposed strategy from grey cotton with enhanced properties. A successful formation of microemulsion for transfer of enzymes into supercritical carbon dioxide was observed with the presence of an emulsifying agent of sodium bis (2-ethylhexyl) sulfosuccinate (AOT) and the auxiliary of ethanol. The efficiency of impurity removal could also be improved at an appropriate system temperature and composite enzyme dosage, as well as by a subsequent washing in SCF-CO₂ media. Furthermore, the results of the static water contact angle measurement, XPS spectra and SEM analysis further confirmed the feasibility, validation and reliability of the constructed strategy. Additionally, an integrated removal mechanism was also proposed for impurity degradation and/or removal from grey cotton, with mixed enzymes transferred by reverse microemulsion in supercritical carbon dioxide media.