不同初始结构间规聚丙烯纤维熔融过程中的结晶转变行为

通过熔融纺丝及随后的热处理制备了具有不同初始结构的间规聚丙烯纤维(sPP).采用差示扫描量热仪(DSC)和变温广角X-射线衍射仪详细研究了sPP纤维在升温过程中的结构转变和熔融行为.结果表明,不同初始结构sPP纤维的晶型不同,卷绕纤维和退火处理纤维以Ⅰ型和Ⅱ型晶型为主,牵伸纤维介晶相占优;升高温度导致Ⅰ型和Ⅱ型两种晶型直接熔融,没有出现Ⅱ型向Ⅰ型的晶型转变;初始结构为介晶相的纤维在升温过程中部分介晶相直接转变为Ⅱ型晶型,还有一部分介晶相直接熔融,并在随后的升温过程中,形成Ⅰ型晶型.sPP纤维的多重熔融行为与其初始结构和纤维制备条件密切相关.

MELTING BEHAVIOR OF SYNDIOTACTIC POLYPROPYLENE FIBERS WITH DIFFERENT INITIAL STRUCTURES

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.