ポリエチレンのレオロジー : 結晶性高分子の構造とレオロジー

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In an attempt to clarify tne mechanism of the deformation process of the crystalline polymers, measurements were carried out on the stress relaxation, the dead weight creep, and the two-dimensional extension of polyethylene films up toe the range of large deformation. In the stress relaxation within 5% extension, the anisotropy of Young's modulus was measured and it was found that the modulus in the direction parallel to the molecular chain orientation was lower than the modulus in the perpendicular direction, and that the modulus decreased with increasing initial elongation. On the other hand, in the dead weight creep test, it was found that the specimen film could be extended more easily in the direction perpendicular to the chain orientation than in the parallel direction. These facts snggest a difference exhisting between the mechanism operating in the small deformation process (as in the stress relaxation) ahd that in the large deformation process (as in the creep). The difference can also be seen directly on the inspection of the creep curves with various loads : With a load lower than a certain critical value the elongation remains within several per cent, while with a larger load the specimen elongates in definitely up to the break point. It may be conceivable that the small deformation process results from the rubber-like elongation of the amorphous chains as well as from the orientation and the plastic deformation of the crystallites. On the other hand the large deformation process may be due to the long range rearrangement of the crystallites resulting in the transformation of the spherulite structure to the fibre structure. Creep test on sevesal high density polyethylene (Marlex 50) were also performed. They, in general, exhibited different features compared with the low density polyethylene. It was found that the specimen with lower melt indices manifested larger creep. Two-dimensional stress-strain measurements were made by the inflation of the polyethylene film hydrostatically. Elongation at the break was much lower in the two-dimensional case than in the one-dimensional case. This fact can be interpreted as that the large deformation through the rearrangement of crystallites will be hindered in the case of two-dimensional extension.
社団法人日本材料学会の論文
1959-04-15

ポリエチレンのレオロジー : 結晶性高分子の構造とレオロジー

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