Studies on Development of Molecular Composites Directed to Substitution of High-Performance FRP

玻璃钢纤维强度有限，质地不均匀。由刚性棒状分子和柔性卷曲状分子组成的分子复合材料有望是单相的、无缺陷的。本研究主要以聚对苯二甲酸乙二酯(PPTA)/尼龙6(Ny6)体系为研究对象，得出以下结论：(1)大分子量的基质聚合物阻碍了刚性棒状分子在MC中的扩散和相分离，得到了稳定的单相MC；(2)棒状分子的聚集降低了MC的应力传递效率，降低了MC的模数和屈服应力；(3)棒状分子的相对分子质量增加，MC的模数和屈服应力增加，这与FRP理论预测的结果类似。如果仅利用杆和柔性分子之间的分子间力进行应力传递，则MC的伸长率很小。通过棒状和柔性链段的嵌段共聚，由于棒状和柔性分子之间的应力传递作用，MC的延伸率得到了极大的提高。在玻璃纤维增强纤维的情况下，棒状分子的化学修饰是不可能的。用相对分子质量为26万的Ny6制备的MC，在高于Ny6熔融温度的温度下热压后，在偏光显微镜下显示出完全暗的图像，表明MC是单一的、稳定的MC。N-H伸缩谱带的FTIR显示明显的单一吸收，表明PPTA和Ny6的酰胺基团之间存在交叉氢键。在DSC曲线上没有发现结晶峰和熔融峰。这些观察结果支持MC的分子分散性。

FRP has disadvantages of limitation in fiber strength and heterogeneous texture. Molecular composite(MC) composed of rigid rodlike molecule and fexible coil-like molecule is expected to be single-phase and free from defects. This research project mainly placing target to the system of poly(p-phenyleneterephthalamide)(PPTA) and nylon 6(Ny6) revealed the following conclusions: (1) a stable single-phase MC is obtained by using a matrix polymer with huge molecular weight, with which diffusion and phase separation of rigid rodlike molecules in MC are hindered, (2)clustering of rod molecules reduces the efficiency of stress transfer and the modulus and yield stress of MC are decreased, (3) the increased molecular weight of rod molecules increases modulus and yield stress of MC, which can be similarly explained as the theory of FRP predicts, and (4) the elongation of MC is small if only the intermolecular force between rod and flexible molecules is employed for stress transfer. By block copolymerization of rod and flexible chain blocks, the elongation of MC is highly improved due to the effect of stress transfer from rod to flexible molecules. Such a chemical modification of rod molecules is impossible in case of reinforcing fiber in FRP.A MC prepared by using Ny6 with molecular weight of 260,000 showed entirely dark image under polarization microscope with crossed polars after hot-pressed at temperature above the melting temperature of Ny6 indicating a single phase, stable MC. FTIR of N-H stretching band showed a sharp, single absorption, indicating cross-hydrogen bonding between amide groups of PPTA and Ny6. No crystallization and melting peaks in DSC curves were found in this case. Molecular dispersity of MC was supported with these observations.