MELTING BEHAVIOR OF SYNDIOTACTIC POLYPROPYLENE FIBERS WITH DIFFERENT INITIAL STRUCTURES

Abstract

Syndiotactic polypropylene(sPP)fibers with different initial structures were prepared by melt-spinning and subsequent heat treatment.Structure transition and melting behavior during the heating process were systematically investigated by a combination of differential scanning calorimetry(DSC)and temperature variable wide angle X-ray diffraction(WAXD).The results indicate that the melting peak at temperatures lower than 100℃ is attributed to the melting or transition of mesophase.With increasing temperature,the crystals form I and form Ⅱ in as-spun and annealed fibers melt directly,indicating that no occurrence of the transition from form Ⅱ to form I.For sPP fibers with mesophase,partial mesophase can transform directly to form Ⅱ,and some mesophase melts and forms crystal form I in the following heating process.For annealed sPP fibers with crystals form I and Ⅱ(sPP-300-1.5-80),the highest-temperature melting peak(T_ m,3)is mainly attributed to the melting of crystal form Ⅰ produced during the course of melt recrystallization at T_ m,2.Structure transition and multiple melting peaks of the sPP fibers during heating process are determined by the initial structure and the preparation conditions of the fibers.