結晶性高分子の微細構造と粘弾性吸收

Abstract

Locations of absorption maxima, intensities of absorptions (or magnitudes of dispersions) and values of elastic moduli, obatined from the temperature characteristics of dynamic modulus E' and dynamic loss E at a constant frequency for crystalline high polymers, were interpreted in terms of their crystalline texture.The series model of crystalline (C) and amorphous (A) region corresponds to the fringed micell model adopted heretofore as the crystalline texture of crystalline polymers, since the stress applied is transferred from the crystalline to the amorphous region along the molecular chains. It can be predicted for the AC-series model that there exists only one absorption maximum between the two absorption maxima corresponding to the pure crytstalline and pure amorphous regions. On the other hand, when the spherulitic texture with lamella structure, recently verified morphologically, is adopted, the AC-parallel model is to be assumed, because the lamella forms a continuous crystalline phase with a thickness of about 100 A and a portion of the stress applied is transferred along this phase from one end to the other of the specimen. With respect to the AC-parallel system, it can be predicted that, (1) there exist two characteristic absorption maxima, the αc-and the αa-absorption, corresponding to the crystalline and the amorphous region and their locations do not depend on the degree of crystallinity, and (2) the intensity of each absorption maximum is proportional to the volume fraction of the corresponding phase.Unoriented crystalline polyethylene specimens (Marlex 50 and Alkathene 7F) with various degrees of crystallinity were prepared by controlling the temperature of the crystallization bath. Temperature characteristics of E' and E at the constant frequency of 100cps were measured with the direct reading dynamic viscoelastometer. The αa-and the αc-absorption were observed separately, and their intensities were approximately proportional to the corresponding volume fractions of crystalline and amorphous region. From these relations, the AC-parallel model can be applied to the viscoelastic behavior of an unoriented polyethylene, while, as the secondary effect, the αc-absorption tends to shift to the lower temperature side and the αa-absorption to the higher temperature side for the specimens crystallized at the lower temperature. This tendency is caused by the increase of defects in the crystal lattice and the increased restriction of molecular chains in the amorphous region.The dynamic modulus of Marlex 50 at the temperature after completion of the αa-absorption is (1.5-3)×1010dynes/cm2, which value agrees with the tensile modulus of molecular crystals of low molecular weight compounds, (1-2)×1010dynes/cm2. The deformation of lamellae takes a mechanism of enlarging the distance between the lattice planes combined by the van der Waals' force, because the molecular chains stand normally to the plane of lamella and perhaps are folded between the thin thickness of about 100 A, and thus the stress cannot be transferred along the direction of the molecular chain (its modulus is expected to be 2×1012dynes/cm2).The dynamic modulus of polyethylene terephthalate with crystallinity 50% and a distinct spherulitic texture takes a value of about 5×109dynes/cm2 at the temperature after completion of the αa-absorption. The modulus of the pure crystalline region of this polymer can be estimated again as 1×1010dynes/cm2, after correction of crystallinity by assuming the AC-parallel model.