Corona discharge treatment is frequently used to enhance the adhesion between laminations, coatings, and inks to polymeric films and metal foils. This investigation concerns the application of corona discharge treatment to the enhancement of the interfacial adhesion in viscose / nylon-66 and viscose rayon / polyester (PET) sheath-core type composite fibers.
Nylon-66 and polyester (PET) core fibers were pretreated in dry air and dry nitrogen coronas prior to coating (in-line) with a viscose rayon solution (sodium cellulose xanthate) and regeneration of the (cellulosic) viscose rayon. Corona power levels of 100, 250, and 400 watts were used in conjunction with line speeds of 0.43, 0.54, and 0.66 meters per second. The path length through the corona was 25.4 centimeters.
Uncoated, corona-treated samples were analyzed to determine the effects of the corona discharge on the morphology, wettability, surface radical density, linear density, and tensile properties of the core fibers. Morphological studies were conducted using scanning electron microscopy. Wettability was measured by means of a modified Washburn technique, and reported in terms of the cosine of the (liquid-solid) contact angle. Surface radical density was measured indirectly by measuring the depletion of a free radical scavenger from a solution through which the fibers were passed. Linear density and tensile properties were measured in accordance with American Society for Testing and Materials (ASTM) standards. Significance of the effects of corona power and line speed on core fiber properties was determined by analysis of variance (ANOVA) using SAS version 5.08.
Coated samples were analyzed to determine the effects of corona discharge treatment on the interfacial adhesion between the core fibers and rayon coating and on the cohesive integrity of the coating. Interfacial adhesion was measured by means of a single fiber pullout test, and reported as an adhesion number which was defined as the average interfacial shear strength between the rayon coating and a corona pretreated core fiber relative to that of an un (corona) treated core fiber coated at the same line speed. The cohesive integrity of the coating was measured following American Association of Textile Chemists and Colorists (AATCC) guidelines for the abrasion resistance of fabrics, and was reported in terms of per cent weight loss of the rayon coating from a given sample. Linear density and tensile properties of the coated fibers were measured in accordance with ASTM standards. Significance of the effects of corona power and line speed on interfacial adhesion and coated fiber properties was also determined by ANOVA using SAS version 5.08.
Results indicate that corona discharge can be used to enhance the adhesion between a viscose rayon coating and nylon-66 or polyester (PET) core fibers without detracting from the mechanical properties of the core fibers. Single fiber pullout tests indicate that the adhesion between the rayon coating and nylon-66 core fiber can be doubled in magnitude, and the adhesion between the rayon coating and polyester (PET) core fiber can be increased as much as sixfold.
It is apparent from the results that the enhancement in adhesion is related to an increase in surface radical density on the core fibers, rather than to changes in morphology or wettability. It is also apparent that although adhesion is enhanced as a result of the corona discharge treatment, the effects are limited to the interface, and no enhancement in the cohesive integrity of the coating occurs.