The birefringence relaxation after the cessation of flow was studied by observing the birefringence of molten polymer flowing in a thin slit in the direction normal to the shearing plane in an injection molding machine.
The birefringence at the wall |(n₁₁-n₃₃)_W(t)| monotonically decreased to zero as soon as the flow was stopped. The birefringence relaxation after the cessation of flow can be understood as the recovery of the deformation of the linear polymer conformation.
The relaxation of the birefringence can be well explained by applying a modified theory of Rouse and Zimm on the deformation and relaxation of polymer conformation in dilute solutions where the maximum relaxation time τ_M is experimentally determined. The calculated values of the relative relaxation of the birefringence |(n₁₁-n₃₃)_W(t)|/|(n₁₁-n₃₃)_W(0)| against t/τ_M give an almost identical curve with the theoretical one.

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The reciprocating plastication process in injection molding is a cyclical and dynamic phenomenon during which (factor I) the screw moves forward and backward and (factor II) the screw rotates periodically. Analysis separating these two factors is necessary to probe the causes of characteristic phenomena in the reciprocating plastication process. In this study, the reciprocating plastication process and periodic plastication process in which a screw is set at a fixed position and is rotated intermittently were analyzed visually and compared. The results are summarized below:
1) It was clarified from factor I that a solid bed (SB) containing considerable melt phase appears in the feed zone at the beginning of the process, and breaks into fragments in the compression zone in the latter half of the process. This phenomenon may be explained by the following: a low bulk density group of plastic pellets was heated from the surface of each pellet during the waiting time in the feed zone. During the subsequent gathering and compression of pellets, the SB interior melted prior to the exterior regions due to heat conduction effects.
2) It was clarified from factor II that the SB in the screw compression zone increases from the start to the end of the reciprocating plastication process. It was also confirmed that an insufficiently heated SB appeared in the latter half of the charge process as the backward movement of the screw reduced the distance from the pellet feed position to the observation point in the reciprocating plastication process.
3) Based on a summary of these results, a plastication process model of injection molding was proposed.

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Polymers form one of the most useful class of materials. In the processing of polymers, one must consider the interaction between flow behavior and temperature distribution due to their complex viscoelastic time dependent behavior. In this study, we investigated the effects of die length on the temperature distribution and the swelling ratio of capillary extrudates by using the streamline-upwinding finite element method. The non-isothermal Phan-Thien Tanner model proposed by Sugeng and Phan-Thien was used as a constitutive equation.
The temperature profile and the shape of extrudates are affected by the die length. The maximum temperature in the calculation region T_max and the swelling ratio χ_f do not change in the low shear rate region. T_max and χ_f increase with the die length in the high shear rate region. χ_f increases with T_max when the dimensionless radial position of T_max is near the centerline. However, χ_f decreases with an increase of T_max when the dimensionless radial position of T_max is near the wall.

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The effects of antibacterial agents on the antibacterial and hue properties of recycled PP were examined quantitatively. Ag-zeolite and Zinc pyrithione were used as the antibacterial agents. Virgin and recycled PP pellets containing antibacterial agents were prepared by a single pass extrusion or double pass (repeated) extrusion, respectively. Test specimens were then injection molded to evaluate the antibacterial and hue properties. Processing temperatures of 200°C and 240°C were used for both extrusion and injection processes. Antibacterial properties were of antibacterial activity. Color difference was measured to evaluate hue. It was found from the experimental results that antibacterial activity increased for PP with Ag-zeolite, compared to the decreased activity with Zinc pyrithione with increasing thermal hysteresis. The color difference of PP with Ag-zeolite was smaller than that of PP with Zinc pyrithione with increasing thermal hysteresis.

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