热经时处理对聚甲醛结晶行为的影响

INFLUENCE OF HEAT TREATMENT ON CRYSTALLIZATION BEHAVIOR OF POM

考察了热经时处理对聚甲醛(POM)结晶行为的影响。结果表明,纯POM结晶是一个成核控制的过程,随着热处理温度的提高或热处理时间的延长,POM的晶核数目明显减少,球晶尺寸和半结晶时间t1/2显著增大,且与片晶相关的球晶显微结构上的有序性也将发生不可逆转的下降;而热稳定剂对POM的结晶产生抑制作用,并通过阻止和延缓POM的热分解对POM结晶速率变慢起到稳定的作用,但这两种作用在某种程度上是相互制约的,随着热处理时间的延长,两种作用将达到平衡;POM的分子量越小,半结晶时间t1/2增加的速度越大,但无论POM分子量大或小,其热处理条件下的结晶行为如晶核数目、球晶尺寸、半结晶时间t1/2等变化规律都反映出与纯POM相同的倾向。

The influence of heat treatment on the crystallization behavior of polyoxymethylene （POM） was investigated. The results showed that the crystallization of pure POM was found to be a process dominated by nucleation. The quantity of crystal nucleus clearly lessened, whereas the spherulite dimension and half crystallization time t1/2 markedly increased, and the ordered state of the spherulite microstructure corresponding to the lamellar crystal irreversibly decreased, with the increase of temperature or time during the heat treatment. Besides, the addition of thermal stabilizer restrained the crystallization of POM, together with leveling off the decreasing tendency of crystallization rate by preventing and retarding the thermal decomposition of POM ; these two functions restricted each other to certain extent and achieved equilibrium as the heat treatment time increased. POM with lower molecular weight manifested more rapidly increasing of half crystallization time t1/2 during the heat treatment process. However, the crystallization behavior （ e. g. crystal nucleus quantity, spherulite dimension, t1/2, etc. ） all reflected the same changing tendency as those of pure POM under the condition of heat treatment whether POM had high or low molecular weight.