In this study, carbon fiber reinforced Liquid Crystalline Polymer (CF-LCP)/polypropylene (PP) blend materials were extruded in order to develop plastic materials with superior specific rigidity and processability for thin plates. Injection molded CF-LCP/PP thin plates were manufactured with two types of gates; film and side gates. The fiber orientation, morphology and bending properties of CF-LCP/PP thin plates were investigated. The morphology of the CF-LCP/PP thin plates depended on the type of gate. The bending modulus of the LCP/PP thin plates increased with an increase of LCP content in both gates. Delamination occurred in CF-LCP plates during the bending test. The density of CF-LCP/PP was lower than that of CF-LCP. It was clear that the blend ratio of CF-LCP/PP can be optimized for the required performance, weight and cost from the specific rigidity.

View full abstract

During the injection molding process, the surface of the flowing resin that is in contact with the mold surface is cooled first and followed by the inner part. It is reported that these phenomena result in a layered structure through the injection molded part. Particularly, because of the rapid rate of crystallization, poly (butylene terephthalate) injection moldings have a well-defined layered structure. The purpose of this study is to investigate the relationship between the structure and properties of PBT injection moldings in the thickness direction. Tensile tests were carried out using dumbbell specimens that were stamped from the sliced specimens of moldings. The necking start point was delayed with increasing depth from the surface. The tensile modulus and strength increased with increasing depth from the surface and eventually became constant in the inner layer. In order to discuss these results from a structural viewpoint, the microstructure of each layer was evaluated by differential scanning calorimetry, density, WAXD and Fourier Transform Infrared measurements.
The delay in neck propagation with increasing depth from the surface is due to the increased crystallinity of the inner layer compared to the layer near the surface. Both the α and β crystal forms were distributed through the thickness direction in PBT injection moldings. The α form with a lower crystal modulus was preferentially found in the surface layer and the content of the α and the β form became constant in the inner layer.

View full abstract

Glass-fiber reinforced PP (GFPP) shows high tensile strength, high heat resistance, high chemical resistance and good fluidity, thus it is a very important industrial material. GFPP has a weak point, however-low impact strength. Recently long-fiber reinforced PP (L-GFPP) has been developed to improve impact strength. Generally the improved impact strength of L-GFPP over short-fiber reinforced PP (S-GFPP) has been attributed to the higher resistance to long fiber pull out. In this paper, the influence of glass-fiber length and interfacial strength on the impact strength of GFPP was studied by an instrumented impact tester. Plastic deformation was observed in the stress-strain curve of L-GFPP but not in S-GFPP. This plastic deformation was observed by a polarizing microscope and an electron microscope. Moreover as the interfacial strength of GFPP was weakened, plastic deformation occurred more easily. This plastic deformation prevented the propagation of cracks and absorbed large amounts of energy and therefore imparted high impact strength to L-GPPP. With injection molding, it is possible to gain a high impact strength equivalent to that of stampable sheet.

View full abstract