A technique to measure planar elongational viscosity and step-planar stress relaxation, by using a lubricated squeeze flow method with PS and LDPE, has been optimized and established. The effect of experimental conditions, i.e., the viscosity of silicone oil as a lubricant, appeared in the measurement of the planar elongational viscosity. The dependence of the uniform planar deformation behavior on the silicone oil viscosity was greater in LDPE than in PS. A high viscosity silicone oil (3.0×10²Pa-s) was chosen to minimize the loss of lubricant. Although the step-planar stress relaxation experiments required speeds that exceeded the testing machine specification to achieve the step deformation, this problem was successfully solved by inserting a metal spacer between the lower plate and the sample. The high viscosity silicone oil produced uniform deformation in both materials with minimal loss of the lubricant, however, the high viscosity of the silicone oil was believed to lead larger measured G⁰(t) results than the predicted values. The silicone oil viscosity was optimized at a lower value of 1.0×10¹Pa-s which minimized the influence of the silicone oil on the results while still producing substantial lubricity. The measurement of planar elongational viscosity by using this optimal silicone oil showed strain-hardening in both samples, with LDPE showing a stronger dependence. “Time-strain separability” within a certain time period was confirmed for the step planar stress relaxation modulus under the optimized conditions.

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The solid bed (SB) break-up phenomenon in which the SB in the screw channel breaks and becomes discontinuous can be observed during the single screw plastication process. An analysis of this continuous extrusion process using the visual heating cylinder described in previous reports clarified that SB break-up occurs during crystal resin plastication, and generation models were proposed. In this study, analyses of polypropylene, polyamide, and general-purpose polystyrene were added, and the validity of the generation models proposed was verified. The results are summarized below:
1) The break-up phenomenon was found to occur during the plastication process of both amorphous resins as well as crystalline resins.
2) The results of the verification of previously proposed break-up generation models-stretch-breakup type and mechanically compressed-breakup-confirmed the validity of the stretch-breakup model.
3) The mechanically compressed-breakup model was generalized as a formation mechanism of the interference between the SB and wall in the screw compression zone, and the following new model was proposed:
In the screw compression zone, unmelted pellets collide strongly with the screw and cylinder wall. This generates a large tension in the SB at the collision area due to the rise in the screw surface speed and the shear rate in the melted resin layer of the SB boundary surface along the channel that becomes shallow, resulting in the break-up of the SB.

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