The behavior of fibers in flow of concentrated short fiber composites is quite different from that in flow of dilute or semi-dilute suspensions. When fiber volume fraction is large, fiber-fiber interaction becomes very strong, and it introduces anisotropy in suspension structure and change in velocity distribution. When fiber length (l) is of the same order of cavity thickness (2H), fiber-wall interaction cannot be neglected.
In this paper, numerical analysis is used to calculate the fiber orientation distribution and to predict the melt flow in a slit channel cavity, in which the motion of each fiber is given from equilibrium conditions of forces in consideration with fiber-fiber interaction and fiber-wall interaction. Results are summarized as follows: (1) Distribution of fiber orientation and melt flow becomes approximately steady after a flow distance of X=20∼30mm (2H=2mm). Pressure gradient decreases gradually with temperature in-crease due to shear heating. (2) Fiber-wall interaction makes fibers shift away from the mold wall and concentrate at ξ/l=1/2 (ξ: distance from the mold wall). The peak of fiber orientation distribution is made at (θ, φ)=(90°, 165°). (3) As flow rate increases, shear heating concentrates in a layer of low fiber volume fraction near the mold wall, and the pressure gradient decreases. As the fiber length increases, the thickness of the low fiber volume fraction layer increases. This causes pressure gradient decrease. (4) As the fiber-fiber interaction parameter nl³ (n: fiber number density) increases, the melt flow approximately becomes a plug one.

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It is known that the crystallization behavior of crystalline polymers are influenced by the pressure during the solidification process. Therefore, it should be possible to control the crystallinity by changing the loading pressure. In general injection molding, the holding pressure does not play a role in controlling the pressure in the cavity after gate-freezing. Therefore, it is impossible to control the pressure during the entire crystallization process, whereas the injection compression molding is able to control the cavity pressure throughout the compression process even after gate-freezing. In order to investigate the possibility of crystallinity control in the crystalline polymer molded by the injection compression molding, we have examined experimentally about the relationships among crystallinity, crystal structure and molding conditions for polypropylene. The results obtained were as follows: (1) Crystallinity of the molded parts decreased with increasing the compression pressure, (2) It was possible to control the crystallinity distribution in the thickness direction by changing the compression pressure during the process of polymer solidification. Controlling crystallinity is useful for an improvement in quality of the molded parts, and it should be possible to produce new molded parts with special characteristic such as functionally graded materials.

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