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

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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.