Comparative study of plasma-induced and wet-chemical cleaning of synthetic fibers

To obtain strongly adherent coatings on polymeric fibers, like metallizations, it is important that the fiber surfaces must be clean. Therefore, five different cleaning methods were compared in order to remove manufacturing residuals (sizes) on PET multifilament fibers, namely chemical cleaning by Soxhlet extraction and in a home-built cleaning bath, as well as etching in atmospheric and low pressure microwave and RF plasmas. Different criteria, such as efficiency, flexibility, ecology and industrial applicability are considered. In terms of these criteria, the RF plasma process performs the best. The continuous fiber treatment in a low pressure He/O2 discharge enables the complete removal of 4.4 wt.% size at a velocity of 10 m/min and a power of 50 W. Although atmospheric and low pressure MW plasmas show higher efficiencies (etching rates), their application is limited due to high heat loads yielding degradation of the PET fibers before cleaning is completed. On the contrary, both chemical methods evaluated are producing large volumes of waste and a nanolayer of size remains on the fiber surfaces.