In order to determine the P (pressure)-v (specific volume)-T (temperature) properties of general-purpose polymers, we have constructed a plunger type of apparatus. It is used to investigate experimentally the temperature and pressure dependence the specific volume of various polymers, and the relaxation of loading pressure for molten polymer. Furthermore, P-v-T properties of polymers were discussed in connection with thermal constants such as thermal conductivity, thermal diffusivity and specific heat. The results show that the specific volume of PE at 150∼200°C is about 18∼22% larger than that of one at room temperature because of thermal expansion. The compressibility of the specific volume with increasing loading pressure was measured and the degree of compaction Δv/ΔP (ratio of specific volume to pressure) of the molten polymers was measured to be 8.9∼9.1×10^-7 in the PE, 8.5∼9.9×10^-7 in the PP and 6.4∼6.9×10^-7m³/kg/MPa in the PS, respectively. The volume compressibility of the crystalline polymers are larger than that of the amorphous polymer. The pressure relaxation of the molten polymer in a closed barrel under isothermal-constant volume conditions is dependent on the diffierence between the plunger loading pressure and the pressure produced by thermal expansion of the polymer itself. Using a=1/ρ·λ/C_p, and if thermal conductivity λ and specific heat C_p are known at each temperature, the thermal diffusivity a can be calculate as a function of specific volume v (=1/ρ). Thus the P-a-T properties of polymers can be determined experimentally. The behavior of thermal diffusivity a in a P-a-T diagram of polypropylene (PP) was found to resemble that of specific volume v in a P-v-T diagram.

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Thermoforming (Vacuum forming) originally found most of its applications in the packaging industry. Recently this method is being used increasingly in the automotive and computer industries. In this paper we discuss the effects of forming conditions on the thickness distribution in products made with modified PVC which is often used for computer housings. The forming conditions studied are heating temperature, mold temperature, vacuum speed and sheet direction (anisotropy of sheet). A three step forming process is adopted; blowing process, stretching process and vacuuming process. The effects of heating temperature, mold temperature, and vacuum speed on thickness distribution are small. On the other hand anisotropy of sheet is the biggest factor.

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The technique of introducing an initial crack in the specimen for fracture toughness tests has a significant effect on the fracture toughness. This study is mainly concerned with the technique of pressing a razor blade to make a pre-crack in PMMA, GPPS and PC which were commercial grades. A pre-crack of 5mm depth was introduced using a home-made notching machine at various temperatures. Then, three point bending tests were carried out to obtain the fracture toughness. For PMMA and GPPS, the crack length was difficult to be control at room temperature and 50°C. When the temperature was raised near T_g a pre-crack of 5mm length without crazes could be introduced which reduced fracture toughness. In such a case, the shape of the pre-crack was like a natural crack, but residual stress remained around the crack. A pre-crack of 5mm length could be introduced in PC even at room temperature. However, plastic deformation and residual stress were also generated around the crack. The fracture toughness was increased by the presence of this plastic deformation around the crack.

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