Fabrication of Continuous Fiber-reinforced Thermoplastic Composites from Sheath-core Type Bicomponent Fibers

采用高速熔融纺丝工艺制备了以聚丙烯(PP)或聚对苯二甲酸乙二酯(PP)为鞘组分，以热塑性液晶聚合物(TLCP)为芯组分的皮芯型双组分纤维。以热塑性弹性体(TLCP)为增强纤维，PP或PET为基体聚合物，通过模压成型制备了连续纤维增强热塑性复合材料。在熔融纺丝过程中，PP或PET共混可提高TLCP的最高卷取速度，PP/TLCP和PET/TLCP双组分纤维中TLCP组分的伸长率和强度均随卷取速度的提高而提高。对制备的双组分纤维和复合材料的广角X射线衍射图的对比表明，TLCP在压缩成型过程中没有发生明显的取向松弛。因此，PP/TLCP和PET/TLCP复合材料的拉伸模量和强度与各自的双组分纤维相似。通过在纺丝过程中逐渐改变皮芯组成制备了双组分纤维，制备了具有不同结构梯度的连续纤维增强热塑性复合材料。在厚度方向具有非对称结构梯度的复合材料的三点弯曲试验中，屈服行为和最大弯曲载荷随载荷方向的变化而变化，但初始弯曲弹性系数不随载荷方向变化。制备的复合材料具有对称的结构，但具有两种不同的结构梯度，一种是TLCP含量近表面较高，核心较低，另一种是TLCP含量较低，中心较高。在TLCP含量相近的情况下，这些复合材料表现出不同的初始弹性模量和屈服行为。

Sheath-core type bicomponent fibers consisting of polypropylene (PP) or poly (ethylene terephthalate) as a sheath component and thermoplastic liquid crystalline polymer (TLCP) as a core component were prepared by the high-speed melt spinning process. Continuous fiber reinforced thermoplastic composites, in which TLCP act as a reinforcing fiber and PP or PET as a matrix polymer, were fabricated by the compression molding of these fibers. In the melt spinning, the attainable highest take-up velocity of TLCP was improved by co-processing with PP or PET.Tensile modulus and strength of the TLCP component in the PP/TLCP and PET/TLCP bicomponent fibers increased with an increase in the take-up velocity. Comparison of the wide-angle X-ray diffraction patterns of starting bicomponent fibers and fabricated composites indicated that the niticeable orientation relaxation of TLCP did not occur in the compression molding process. Accordingly, the tensile modulus and strength of the PP/TLCP and PET/TLCP composites were similar to those of the respective bicomponent fibers. Continuous fiber reinforced thermoplastic composites with various types of structural gradient were fabricated from the bicomponent fibers prepared by gradually changing the sheath-core composition in the spinning process. In the three-point bending test of a composite with asymmetric structural gradient in the thickness direction, the yielding behavior and maximum flexural load varied but initial flexural modulus did not vary depending on the direction of load application. Composites with symmetric structure but two different types of structural gradient, one in which TLCP content is higher near the surfaces and lower in the core and the other in which TLCP content is lower near the surfaces and higher in the center, were prepared. These composites exhibited different initial modulus and yielding behavior even though the TLCP content is similar.