STUDY ON THE FORMATION OF BETA-CRYSTALLINE FROM ISOTACTIC POLYPROPYLENE FIBER

In this paper the conditions for the manufacture of high content beta-form crystal isotactic polypropylene fiber in the presence of beta nucleation and the beta to alpha form transition during processing were studied. The results showed that the melt temperature had little effect on the relative content of beta-form (K value) presented in as-spun fibers within a certain temperature range (210 to 230-degrees-C) while the cooling rate and cooling medium had a significant effect on it. In the case of a constant pump deliver (Q), the K value in the as-spun fiber decreased from 0.95 to 0 as the spinning speed increased from 3.25 m/min to 70 m/min. The smaller the thermal conductivity of cooling medium, the greater was the K value. After stretching the beta-form PP fiber, there were many crevices at the fiber surface. It was confirmed by the mercury porosimetry that the drawn fiber possessed microvoid structure. The size and quantity of microvoids were closely related to the K value, stretching temperature and stretching ratio. Compared with PP fiber without nucleating agent, the drawn fiber had a lower apparent density and its moisture absorption was improved.