Dynamic Mechanical Properties and Interaction at the Interface in Poly (p-Phenylene Terephthalamide) Fiber Reinforced Poly (Methyl Methacrylate) Composite

The dynamic mechanical properties of the composites of poly (p-phenylen terephthalamide) (PPTA) fibers (rigid molecules) and poly (methyl methacrylate) (PMMA) matrix (flexible molecules), were investigated as a function of the surface area of the fiber and temperature. These composites showed reinforcing effect indicated by the storage modulus (E') over the whole temperature range. At the temperature region of glassy state, E' was influenced by both the elastic modulus and the surface area of reinforcing fiber. However, at the temperature region of rubbery state, E' depended mainly on the surface area. Disappearance of beta -relaxation, that is attributed to rotation mode of the side-chain, and the shift to the higher temperature side of alpha -relaxation of main-chain of PMMA were observed in the PPTA composite with larger surface area. These results are attributed to an interaction at the PPTA/PMMA interface. Furthermore retardation of thermal decomposition of PMMA was observed in the presence of PPTA. It can be shown that the higher activation energy for the thermal decomposition of PMMA is equivalent to higher interaction energy in the PPTA composites. The shift of -NH, > C=O IR absorption band of benzanilide, a model compound of PPTA, with change in the PMMA composition proved that the interaction is chemically originated from the formation of hydrogen bond between PPTA and PMMA.