PAN纤维的结构对纤维强度的影响

分别采用纤维强伸度仪、乌氏粘度计、X射线衍射仪等测定了4种不同PAN纤维的抗拉强度、分子量、结晶度以及沸水收缩率.结果表明,拉伸速率对4种纤维的强度测试方法的准确性都有影响.在低速拉伸时,由于拉伸速率的增加使分子链段的松弛时间缩短,测试强度随拉伸速率的增加而升高;而在高速拉伸情况下,缺陷成为导致纤维断裂的主要因素,测试强度又随拉伸速率的增加而逐渐降低.在一定范围内,分子量越大、结晶度越高,PAN纤维的强度就越高;作为表征纤维中非晶含量的一项指标,沸水收缩率越大,说明非晶区的比例越大.因此应控制PAN纤维的分子量,提高纤维结晶度,降低纤维的沸水收缩率,从而为制备高性能的碳纤维提供优质原丝.

Effect of structure on tensile strength of PAN fiber

Studies have been carried out on the tensile strength, molecular weight, crystallinity and the shrinkage rate in boiling water of four different PAN fibers by strength and elongation instrument, viscometer, X-ray diffractometer, and so on. The results indicate that stretching rate has great influence on the testing value of tensile strength. When being stretched at low rate, the testing value increases with the increasing of stretching rate due to the reduction of relaxation time in chain segments. However, it decreases when being stretched at high rate, mainly because defects become the main factor that leads to the fracture of fibers. To some extent, the higher the molecular weight and crystallinity is, the higher the tensile strength of PAN fibers is. The shrinkage rate in boiling water can be used as an index that characterizes the amount of amorphous phase. High shrinkage rate in boiling water suggests large amount of amorphous regions of fibers. Therefore suitable molecular weight, high crystallinity and low shrinkage rate in boiling water should be controlled in the production of PAN fibers in order to fabricate high quality carbon fibers.