An investigation on the effects of heat-setting process on the properties of polypropylene bulked continuous filament yarns

摘要

Heat-set bulked continuous filament (BCF) polypropylene yarns constitute one of the most important pile yarns used in the production of machine-woven carpets. As carpets made from non-heat-set BCF polypropylene yarns lack resiliency and loss of appearance, heat setting of BCF yarns has proved to be very useful in overcoming these deficiencies. This work aimed to investigate the effects of dry steam heat setting on the structure, properties and structural-property relationship of industrially produced heat-set BCF polypropylene yarns. It was ascertained that while tenacity, initial modulus, bending rigidity, crimp contraction and shrinkage decrease as a result of heat setting process, there is an increase in the yarn linear density. Because of these mechanical changes, the resiliency of BCF polypropylene yarns is positively affected by heat-setting process, and as a result, a better wear and look for the carpet pile yarns. Changes in mechanical properties result from microstructural changes, namely, recrystallization induced by heat-setting process. Recrystallization leads to a higher overall crystallinity, with a higher number of smaller crystallites giving improved orientation. Lower initial modulus leads to a lower flexural rigidity or stiffness, thus giving rise to a better resiliency of heat-set BCF polypropylene yarns. This is related to the formation of smaller size crystallites in spite of the higher degree of crystallinity.