Abstract:

Objective Polypropylene (PP) fibers are characterized by their low density (0.91 g/cm³) and superior thermal insulation properties, with a thermal insulation efficiency of up to 36.49%. Polybutylene terephthalate(PBT) fibers exhibit excellent elasticity, bending recovery, and a higher elastic recovery rate compared to polyester fibers. Moreover, PBT fibers possess a soft, fluffy texture and demonstrate good moisture absorption capabilities. To investigate the morphological structure of PP/PBT blend fibers produced via melt spinning using polypropylene and polybutylene terephthalate blend chips with varying blending ratios, the mass fractions of PBT added were set at 5%, 10%, 15%, 20%, 25%, and 30%, respectively.

Method After uniformly mixing the PP and PBT slices, a twin-screw extruder is utilized for blending and granulation. Subsequently, a capillary rheometer is employed to prepare the blended fibers with varying component ratios. The fibers are then subjected to ultrasonic vibration and drying using an ultrasonic instrument, resulting in fibrillated blended fibers. By exploiting the incompatibility and viscosity differences between the two components, the dispersed phase forms a network of microfibers within the continuous phase.

Results In this study, a rotational rheometer is employed to investigate the steady-state rheological properties of polymer melts under varying temperature conditions. Both materials exhibit typical shear-thinning characteristics, with the shear viscosity of the melt decreasing as temperature increases. Fitting analysis based on the Carreau model is conducted to determine the zero shear viscosity values of these two raw materials. The zero shear viscosity ratios of PP and PBT melts at different temperatures are presented. The n values for the PP melt are all less than 1, indicating significant non-Newtonian characteristics. Under varying shear rates, the apparent viscosity of the PP melt undergoes considerable changes. However, the n value does not vary significantly with temperature, suggesting that temperature has a relatively minor effect on the apparent viscosity of PP. It can be concluded that the viscosity of PBT is lower than that of PP under the same testing conditions, with all zero shear viscosity ratios for the system being less than 1. PP displays a distinct endothermic peak at 156 ℃, corresponding to its melting temperature, while the endothermic peak of PBT occurs at 220 ℃, indicating its melting temperature. Additionally, it is found that the blend system is incompatible. The initial decomposition temperature of PP is 350 ℃, reaching the decomposition endpoint at 420 ℃, whereas PBT has an initial decomposition temperature of 390 ℃ and a termination decomposition temperature of 430 ℃. As the proportion of system components increases, the groove structure on the fiber surface becomes increasingly pronounced. When the PBT mass fraction reaches 30%, microfiber delamination occurs on the fiber surface, forming a unique structure resembling goose down. Through ultrasonic vibration treatment of fibers, it is observed that the surface of blended fibers with a PBT mass fraction below 30% did not undergo significant changes. However, a substantial number of microfibers adhered to the surface of PP/PBT fibers with a 30% PBT content, resulting in a fiber morphology resembling that of goose down.

Conclusion In this research, the PP/PBT blend fibers were prepared using the melt spinning method. The preparation process parameters for the PP/PBT blend fibers were optimized by varying the component ratio, leading to a fiber surface characterized by a groove-like and microfiber structure. The PP/PBT blend fibers spun at a temperature of 250 ℃ demonstrated the best performance. As the dispersed phase component ratio increased, the groove-like structure became more pronounced. The most distinct groove-like structure and a considerable quantity of microfibers were observed with a PBT content of 30%. Following further processing of the PP/PBT blend fibers with ultrasound, a significant amount of PBT microfibers emerged, resulting in a goose-down-like fiber morphology.

Key words: polypropylene, polybutylene terephthalate, blend fiber, component ratio, microfiber structure, melt spinning, rheological hehavior