It is well known that a heat-treated poly-p-phenylenebenzobisoxazole(PBO)fiber gives an anisotropic four-point scattering pattern in small-angle X-ray scattering(SAXS)indicating growth of density fluctuations during the heat treatment. Many researchers inferred that the density fluctuations originate from density difference between crystal and amorphous regions in the PBO fiber. However, it is not fully clarified and the hypothesis is never experimentally proved yet. In order to elucidate the structural entity of the density fluctuations, the superstructure was investigated by direct observation of transmission electron microscopy(TEM)using defocus contrast(DFC)method. The obtained DFC image from a PBO fiber gave an intriguing contrast in the TEM micrograph and the 2-dimensional Fourier transform of the image gave a four-point pattern which strongly suggests that the contrast can be derived from the density difference corresponding to the density fluctuations giving rise to the SAXS pattern. Moreover, it is proved that higher density regions in the density fluctuations correspond to PBO crystals in the fiber because crystalline lattice fringes of the PBO fiber in the high-resolution image were inevitably located at the darker regions in the DFC image. This must be a first experimental evidence for the hypothesis based on the crystallization enhancement of density fluctuations in PBO fiber.
Three synthetic textiles, polyester, nylon 6 and acetate fabrics, were treated by atmospheric pressure plasma(APP)jet with nitrogen gas. From the contact angle measurements using a single fiber, the wettability and the base parameter of surface free energy of the three fibers were found to increase drastically after the APP treatment. X-ray photoelectron spectroscopy and atomic force microscopy showed that the APP exposure increased the oxygen concentration and the roughness, respectively, for any fiber surface. It was confirmed from the stress-strain behavior and the visible reflection spectrum that the APP impact damage was negligibly small for any fabric. The increase in hydrophilic nature of the fiber surface resulted in promoting water wicking and soil release by laundering. Moreover, the color strength of the polyester and acetate fabrics dyed with disperse dyestuff was found to increase mainly by the topographical change in the fiber surface. Such improvement of textile performances by the APP treatment was remarkable for the polyester fabric.
Carbon fiber fabric reinforced polypropylene(CFRPP)was prepared by press molding. The mechanical properties of the CFRPP samples were measured by means of a three-point flexural test. An evaluation was carried out on how press molding conditions, maleic acid content in the PP film, and removal of sizing agent adhered to carbon fiber affected the flexural properties of CFRPP. The flexural strength and flexural modulus increased with increasing press temperature, and the impregnation of melted PP into the carbon filaments improved. However, the arrangement of carbon fiber was disarranged by the flow of melted PP when the press molding temperature was too high. Therefore, it is necessary to determine the optimal press molding temperature along with the press molding pressure. The mechanical properties of CFRPP were improved by increasing the content of maleic acid and removing sizing agent. Through observation of failure mode and apparent volume fraction of void, it was estimated that the improvement of mechanical properties was due to improvement of interfacial adherence between carbon fiber and PP. The maximum flexural strength of CFRPP was 453 MPa and the maximum flexural modulus was 58.2 GPa in this study.