The Study On PP/PET Blend And Its Composite Fiber

Polypropylene (PP) fiber is one of the most widely used synthetic fibers. PP fibre has wide applications in many fields with its excellent properties. The output of PP fiber in the world had doubled in the years from 1993 to 2003, but paced up and down in recent years. It is also difficult to step forward for many domestic companies of PP fiber. One of the reasons for that is the rising price of international crude oil. Another important factor is the deficiency in development of new products and support of high and new technologies.Polypropylene is a kind of plastic with excellent comprehensive properties. However, its low Young's modulus limits its further applications to meet the requirement such as for shape-keeping of garments, carpets and technical fiber applications. In this paper, the method of blending and direct spinning was initially employed to produce the composite fibers in which the dispersed phase PET was formed into micro-fibers in the course of hot stretching. The PET micro-fibers served as the framework of PP and so enhanced the strength and modulus of PP fiber. Two patents concern with the issue have been applied (Application number: 200610029033.4/ 200620043679.3).Since PP/PET blend was thermodynamically immiscible, thedispersed phase in the simple blending was big and inhomogeneousand the compatibility between PP and PET was quite bad, whichwould cause the mechanical properties descending. The compatilizerof PP-g-AA was employed to improve the interracial tensionbetween PP and PET in this paper. The effects of compatilizercontent, different components, mixing time, temperature, shear rateand blending machines on blend morphology such as size and sizedistribution of island component were investigated. The resultsshowed that the best content of compatilizer was 50% of PET weight,and the best blending time, temperature, shear rate was 15min, 285℃and 150rpm, respectively. The rheological behavior of PP/PETblends was also investigated. It was found that the apparent viscosityof blends decreased with the increase of shear rate, temperature orthe content of PET and the compatilizer. PET and the compatilizerserved as the plasticizing agent in the blends.The fiber surface saturated in alkali solution, the fractured and riven surface of composite fibers were observed by SEM. The results showed that the component PET was indeed formed into micro-fibers. The mechanical properties, such as tensile strength, Young's modulus and elongation at break were tested in this paper. The results showed that the composite fibers had much better properties than pure PP fiber. The fiber with the component of 90/10/5 (PP/PET/PP-g-AA) had the best mechanical properties and its tensile strength increased by 20%, the modulus by 38.5% and the elongation at break decreased by 21% respectively comparing with pure PP fiber.The crystallization characteristic was investigated in this paper. It was found that PET micro-fibers served as a heterogeneous nucleation agent. The study of non-isothermal crystallization kinetics showed there were two stages in the PP crystallization process. During the early stage, PP molecules crystallized on the surface of PET micro-fibers and formed transcrystalline. PP spherulite was formed in the place far from PET micro-fibers during the later stage.