聚碳硅烷纤维的热交联研究

STUDY ON THERMAL-CURING OF POLYCARBOSILANE FIBERS

在无氧的情况下对PCS纤维进行热交联时 ,发现在热交联前纤维必须有一个最低的预氧化程度 ,然后通过PCS纤维自身热交联实现预氧化 ,这样可降低纤维 1 3的氧含量 ,制备性能优良的SiC纤维 .研究了低预氧化PCS纤维热交联反应的机理 ,并对引入氧在热交联中所起的作用进行了分析 .研究结果表明 ,PCS纤维能够进行热交联处理所需的最低预氧化程度为纤维氧增重 9% ;热交联的过程主要是消耗了PCS中的SiH键 ,生成SiCH2 Si键 ,形成分子间交联 ;引入的少量氧预氧化时生成SiOH键 ,热交联中发生脱水反应生成SiOSi键 ,在纤维表层形成保护层 。

Polycarbosilane (PCS) is the precursor of SiC ceramic fibers, and oxidation-curing process of PCS fibers is an essential step of making Nicalon style SiC fibers.The oxygen introduced into PCS fibers seriously affects the mechanical properties of SiC fibers at high temperature.In this paper,the probability whether PCS fibers can be thermal-cured without oxygen was investigated.It was found that a minimal degree of oxidation-curing of PCS fibers was necessary for their further thermal curing.Under these conditions the oxygen content of fibers decreases, and their properties can be improved.The mechanism of thermal-curing of low degree oxidation-curing PCS fibers and the function of oxygen were investigated.Results showed that the minimal degree of oxidation-curing was corresponding to a 9% weight gain of PCS fibers. During the thermal-curing process,the SiH of bonds PCS were mostly consumed and Si CH 2 Si structure was formed; Si OH was formed when a little oxygen was introduced into PCS fibers in the oxidation-curing process and may form SiO Si structure during further thermal-curing,making a protective layer on the surface of PCS fibers.