自由基引发活性聚碳硅烷交联及其在制备SiC纤维中的应用

在基于先驱体聚碳硅烷转化制备SiC陶瓷纤维过程中, 交联过程是保持纤维形貌和提高陶瓷产率的必要条件。本研究以含丙烯酸酯基的聚碳硅烷(A-PCS)为原料, 通过引入自由基热引发剂在热解升温过程中实现原料的交联成型。采用红外光谱仪(FT-IR)和差示扫描量热仪(DSC)研究了引发剂含量对A-PCS交联程度、交联速率以及热降解速率的影响规律; 采用热失重(TG)、元素分析仪和X射线衍射仪(XRD)分析了陶瓷产率、陶瓷产物组成以及无定形态随温度的变化。研究结果表明: 加入自由基热引发剂可提高A-PCS中的丙烯酸酯基的交联速率, 减少交联阶段的热失重; 将质量百分比为1%自由基热引发剂的A-PCS以5 ℃/min升至250 ℃时, 丙烯酸酯基反应完全, 1500 ℃的陶瓷产率为69.5%; 通过静电纺丝加工工艺可获得直径介于2~5 μm的A-PCS原丝, 并通过后续升温热解转化为SiC纤维; 所得SiC纤维形貌规整、无熔并现象, 且随着热解温度的升高从无定形态向结晶形态转变。

Crosslinking of Active Polycarbosilane Initiated by Free Radical and Its Application in the Preparation of SiC Fibers

In the preparation of SiC ceramic fibers based on precursor polycarbosilane, the crosslinking treatment is a neccessary process to maintain the fiber morphology and improve the ceramic yield. In this study, polycarbosilane containing acrylate group (A-PCS) was used as raw material, and the thermal free radical initiator was introduced to realize the crosslinking formation during the pyrolysis process. FT-IR and DSC were used to analyze the influence of initiator content on crosslinking degree, crosslinking rate and thermal degradation rate of A-PCS; TG, elemental analysis and XRD were used to analyze the evolution of ceramic yield, composition and amorphous change with temperature. The introduction of free radical thermal initiator can improve the crosslinking rate of acrylate group in A-PCS and reduce the thermal weight loss at the crosslinking stage. When free radical thermal initiator (weight percent 1%) was added, the acrylate group was consumed completely after heating to 250 ℃ at 5 ℃/min and the ceramic yield at 1500 ℃ was 69.5%. A-PCS fibers with diameter of 2-5 μm were obtained by electrospinning process, and then transformed into SiC fibers by subsequent pyrolysis. The morphology of the SiC fibers was regular with no fusion phenomenon. In addition, with the increase of pyrolysis temperature, the amorphous SiC fiber can be transformed into crystalline structure.