Effects of spin finish on fiber surface hardness: An investigation with atomic force microscopy and frictional measurements

Abstract

ABSTRACT:Spin finishes are applied to melt-spun fibers to protect them from abrasion during processing. The principal component of the fiber finish is a lubricant, which generally is a random or block copolymer of ethylene oxide/propylene oxide. Although these polymers do not penetrate the fiber because of their high molecular weight, depending on the nature of the fiber polymer, they interact to cause changes in the hardness of the fiber surface. This happens to be the case with acidic polymer fibers such as nylon-6 and polyester [poly(ethylene terephthalate], both of which are softened by the ethylene oxide/propylene oxide lubricant. We used atomic force microscopy with nanoindentation capability to study the effect of lubricants on the microhardness of nylon-6 and poly(ethylene terephthalate) fiber surfaces. Softening of the fiber surface by plasticization generally results in an increase in fiber friction because of shear deformation at the interface. We made an effort to determine the friction of fibers against a hard stainless steel surface after coating them with the finish lubricant for different lengths of time. The relevance of these results to fiber processing is discussed.