It was found that the impact resistant property of polyvinylchloride (PVC) could be improved by the addition of fine powdery calcium carbonate (CC) in a sufficient dispersed state, that is, an ultrasonic wave was employed in order to disperse CC into tetrahydrofuran (THF) solvent, next the THF solution of dissolved PVC was added into this dispersed solvent. After THF was evaporated, the residual mixture was blended by a heat twin roller. Through such procedure, composite materials consisting of PVC and CC were prepared. These composite materials exhibited excellent property on impact resistance. The effect was similar to that for addition of a rubber component to PVC. It could be presumed that fine powdery CC was dispersed sufficiently into PVC matrix. It was also shown that the composite materials had increased the modulus of elasticity, slightly decreased the bending strength and decreased the melting viscosity.

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From the viewpoint of work efficiency, the post-fusion cooling time of EF joints should be reduced. However, insufficient cooling time can lead to poor joint performance. To estimate what is a sufficient cooling time, this study evaluates three types of gas pipes, buried after three different cooling times following fusion, and studies the relationship between the cooling time and the EF joint performance. Evaluation items include the deformation, degree of crystallinity, polarized microscope observation, tensile strength, tensile creep strength, TEM observation, and fusion simulation. The results show only a slight difference regarding the degree of crystallinity, tensile strength, and TEM observation, while a distinct difference was observed regarding tensile creep strength. The fused zones were subjected to a temperature profile during the cooling process determined by simulation. The results showed that these three fused zones have different states (melting state, semi-solid, or solid state) at the moment when the weight of soil acts on the fused zones. By the deformation of the fused zone during the cooling process, the crystal condition changed. It is said that the difference of the crystal condition of the fusion zone is the main factor affecting the tensile creep strength.

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