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ABSTRACT:The structures of polypropylene fibers, spun according to a factorial experimental design, have been studied with the aid of wide angle X-ray diffraction and birefringence measurements. From statistical analysis of the results, the fibers have been characterized in terms of their crystallographic order and the overall orientation of their constituent polymer chains. These properties have been quantitatively assessed as responses to seven specially selected process control parameters in the extrusion equipment used to process the fibers. For both crystallographic order and overall orientation, the metering pump speed (MPS) at which the fibers are extruded and the speed (WS) at which the extruded fibers are wound exert significant effects. Moreover, the interaction, WS ϫ MPS, between these two control parameters also significantly influences orientation. For crystallographic order, two further significant parameters are the melt flow index (MFI) of the grade of polypropylene used and the temperature (ST) at which the polymer melt passes through the spinneret. The roles of these two factors in the development of crystallites within the fibers are discussed. No interaction effects, however, appear to be significant for crystallographic order. Models that specify the direction of change of the significant parameters for increasing or reducing both responses are given.

The structure and quality characteristics of gimp fancy yarns were studied using an experimental design of seven factors with eight experimental runs. Non-gimp projections were considered to be structural defects; thus, they were counted and their numbers, average areas, and average circularity ratios were measured to account for those defects. Assigning the effects to factors and interactions was completed by taking into account gimp yarn structure and its manufacturing process. It was found that using two threads for the core component of gimp yarn, rather than only one thread, was an advantage because two threads improved the structure and appearance of the fancy yarn. Moreover, suitable stiffness for the effect component may yield the best results. The overfeed ratio must be as small as possible to make yarn with corrugations. It was possible to improve the manufacturing process, to study properties of gimp fancy yarns, to build statistical models to quantify each of the defect features and to minimize variability and resources. Such improvements play a major role in improving the quality of fancy fabrics and clothes made from these fancy yarns.

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