A thermotropic liquid crystalline polymer (LCP) and its carbon fiber (CF) and glass fiber (GF) filled systems were injection-molded into dumb-bell shaped specimens in order to investigate the effects of the processing conditions on their fiber orientation and mechanical properties. Minimal damage was found for either fiber under the processing conditions in this study. Microscopic observations of the cross sections of the molded specimens for their fiber orientation showed that the orientation distribution was greatly affected not only by the molding condition, but also by the gate geometry. This, in turn, suggested that the injection rate (Q) had a great effect on the fiber orientation in the molded products. The molds used in this study were designed using two different gate geometries-gate I (with a cross section with thickness and width both less than the thickness and width of the specimen) and gate II (with a cross section with thickness slightly larger than the thickness of the specimen but a width equal to the specimen width). The CF-filled specimens obtained with the mold using gate II showed better CF orientation along the flow direction in the center (core) layer than those produced with the mold using gate I. This phenomenon, not observed with a conventional general-purpose polymer, well represents the characteristics of thermotropic liquid crystalline polymers. In addition, it was found that the specimens produced using a gate with a reduced channel shape like gate II showed better fiber orientation aligned along the flow direction than in the case of those obtained using a gate with an enlarged channel shape like gate I, although the degree of the fiber orientation was not found to always increase in proportion to the injection rate (Q). It was also confirmed that the mechanical properties of the dumb-bell shaped specimens were greatly affected by the fiber orientation and the flow pattern of the melt during its injection into the mold. More specifically, the tensile modulus (E) of the unfilled and CF-filled LCP specimens produced with gate II decreased with increasing injection rate (Q), while the relationship between E and Q was reversed for the GF-filled LCP specimen. In addition, the E value of the CF-filled specimen was approximately two times higher than those of the unfilled and GF-filled LCP specimens, showing that CF and GF are different in their effects on the E values of the resultant fiber-filled LCP specimens. CF and GF also showed a difference in their effects on the dependency of the tensile strength (σ_B) of the resultant fiber-filled LCP specimens upon the injection rate (Q). However, the unfilled LCP specimen showed higher tensile strength (σ_B) and rupture elongation (ε_B) than the CF-and GF-filled specimens when produced at a low injection rate. Both CF-and GF-filled LCP specimens gave larger values of E, σ_B and ε_B when produced using gate II than gate I both at their dumb-bell ends and parallel sections. Microscopic observations suggest that this is because of the multilayer structure for both the unfilled and fiber-filled LCP systems.

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A high content of magnesium hydroxide was filled into a polypropylene (PP)-type resin containing maleated PP-type elastomer PER (MPER) and a compound was prepared. The structure and properties of the compound were measured and compared with those of a compound without MPER, compounds with maleated soft resins besides MPER, and a flexible polyvinyl chloride (PVC) resin. This compound shows comparable or even superior properties to flexible PVC not only in flammability but also in flexibility, abrasion resistance, rubbery properties and electric properties. Since MPER is more compatible with the PP-type resin than other maleated soft resins, the compound with the former is superior to the compounds with the latter. These superior properties are assumed to come from ionic crosslinking, which is shown to exist by the observations of a carboxylic acid ion absorption peak in the infrared absorption spectrum at 1580cm^-1, of much gel remaining after p-xylene extraction, and by a high melt viscosity and low die swell ratio. Because of these excellent properties, the ionically crosslinked compound is expected to be widely used in cable coating, leather cloth, tape, etc. as a substitute for flexible PVC.

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A high content of magnesium hydroxide was filled into a polypropylene-type resin containing maleated polypropylene-type elastomer PER (MPER) and an ionically crosslinked compound was prepared. The rheological properties of the ionically crosslinked compound were measured and compared with those of a compound without MPER, MPER, PER, and a flexible polyvinyl chloride (PVC) resin. The temperature dependence of the viscosity of MPER is stronger than that of PER and the viscosity of MPER tends to rise at low shear rates, which suggests the existence of light crosslinking in MPER. The viscosity of the ionically crosslinked compound continues to increase linearly even at low shear rates. Therefore, it shows a very high value at the low shear rates encountered during drawdown of shaped molten articles. However, it scarcely differs from those of usual resins at the high shear rates of extrusion and injection molding. Although the change of viscosity with shear rate is large, the change with temperature is very small. The die swell ratio is nearly unity and the extrudate scarcely swells after leaving a die. The change of die swell ratio with temperature and shear rate is very small and the extrudate is stable at disturbances. The ionically crosslinked compound does not generate a melt fracture until high shear rates. The elongational viscosity is about one decade higher than those of other samples. The dynamic viscoelasticity shows a rubbery plateau modulus of 3×10⁴Pa. These rheological properties come from the synergy between the ionic crosslinking and the filling effect of magnesium hydroxide. From these experimental results, it may be assumed that the ionically crosslinked compound is a kind of thermoplastic elastomer and is suitable for contour extrusion, vacuum/pressure molding, big blow molding and foam molding. Flexible PVC shows similar rheological behaviors to the ionically crosslinked compound and has good processability. However, it has a very high activation energy for flow (the temperature dependence of viscosity and other rheological properties) of 3-5 times that of the ionically crosslinked compound. It also shows a large die swell ratio of 1.1-1.3 in comparison with 1.0 for the ionically crosslinked compound. It shows a considerably lower viscosity at low shear rates than that of the ionically crosslinked compound at around 190°C which is a suitable Processing temperature for flexible PVC. It also has the drawback of easy generation of melt fracture. Accordingly it may be said that the ionically crosslinked compound in this study has better processability than flexible PVC.

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One of the most important issues to guarantee high quality is the ability to predict the warpage deformation behavior of injection molded thermoplastics. This is especially true for the glass fiber (GF) reinforced thermoplastics, where anisotropy in fiber orientation can lead to the increase of warpage deformation.
In this study, we observed cross sections and measured the multi-directional thermal expansion coefficients of GF reinforced polyamide 6 (PA6) samples of varying weight fractions of glass fiber and thicknesses. In photomicrographs of cross sections, the fiber orientation showed a symmetrical structure of three layers, skin/core/skin, which depended on the weight fraction of glass fiber and the thickness of the molding. The thermal expansion coefficient showed an anisotropy that depended on the fiber orientation. In addition, numerical results obtained using a model that considered the fiber orientation distribution at each layer thickness qualitatively agreed with the experimental measurements of warpage deformation.

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This study is concerned with the analysis of the relationship between the interfacial energy of a polymer and the micro voids that are formed by stretching the composite polymer sheet having incompatible particles in the matrix. The void formation caused by the interfacial delamination between Poly (ethylene terephthalate) (PET) and dispersed incompatible polymers of varying sizes was simulated by the finite element method (FEM) and compared with experimental measurements.
The following results were obtained;
(1) Experimentally, voids increased in size with increasing surface tension difference between PET and the incompatible polymers. The aspect ratio of the voids did not depend on particle size.
(2) Theoretically, a decrease in the critical stress of delamination coincided with increasing the surface energy. The aspect ratio of the voids did not depend on particle size.
(3) Interfacial tension obtained from this experiment was qualitatively related to the critical stress calculated from the numerical analysis of void formation.

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