A DYNAMIC-MECHANICAL STUDY ON UNIDIRECTIONAL CARBON-FIBER-REINFORCED POLYPROPYLENE COMPOSITES

Fiber-reinforced polymer composites show high specific strength and stiffness. The alignment of reinforcing fibers results in anisotropy of the material. This anisotropic behavior has been studied through dynamic mechanical analysis of unidirectional carbon fiber-reinforced polypropylene (CFRPP) composites measured in both parallel and transverse directions to fiber arrangement. Several parameters such as storage modulus (E'), loss modulus (E''), loss factor or damping factor (tan delta), and complex viscosity (MU*) have been determined over a wide range of frequencies and at a fixed temperature. Relaxation and retardation spectra have been constructed for these composites. Modulus enhancement occurs due to stiffness imparted by the fiber and efficient stress transfer at the interface. Relaxation of the polymer matrix ceases with increase in the volume fraction of the fibers. alpha'-relaxation is observed for the composite having a 13% volume fraction of fibers and is ascribed to relaxation in the crystalline phase where the additional crystallinity arises out of the transcrystalline growth at the fiber-matrix interface. There exists a good correlation between theoretical curves with the experimental ones. Relaxation and retardation spectra and the dynamic parameters determined for these composites show a good correlation with the volume fraction of fibers as well as the direction of the applied load. (C) 1994 John Wiley & Sons, Inc.