応力-ひずみ-赤外二色性の同時測定による高密度ポリエチレンおよびポリプロピレンの変形機構の研究

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In the previous paper very efficient use was made of simultaneous measurement of stress, strain and infrared dichroism in interpreting the stress-strain curve of low density polyethylene. The stretcher employed in the previous studies has been improved so that the upper and lower crossheads can move up and down at the same rate, attaining the total stroke of 30 cm. A drawtube has also been furnished in the way of an oven to control measuring temperature by circulating air at a controlled temperature. For high density polyethylene, the dichroic ratio D(⊥/⫽) for 730 and 720 cm^<-1> bands has been measured as a function of strain at a constant rate of elongation of 30%/min, and the orientation functions of a-, b- and c-axes, F_α, F_β and F_ε, have been evaluated. These orientation functions plotted against strain give similar curves to those for low density polyethylene reported previously, indicating that quite the same explanation can be given to the stress-strain curve of the high density polyethylene sample as in the case of low density polyethylene. For polypropylene, on the other hand, the orientation function F_ε for c-axis evaluated from the dichroic ratio D(⊥/⫽) for 998 and 840 cm^<-1> bands takes negative values at first and then positive values as the strain increases, indicating that molecular chains in crystalline region orient at first perpendicularly and then in parallel in the direction of elongation. This negative dichroic ratio is consistent with negative birefringenece observed at small strains for the same material. The strain at which F_ε takes its minimum coincides with the strain at the yield point. From these observations, the following deformation processes can be considered to occur during the stress-strain measurement : Below the yield point, spherulites or superstructures consisting of lamellae show elastic deformation, in which the lamellae rotate their axes in the direction of elongation. Beyond the yield point, the spherulities or superstructures show irrecoverable deformation due to the unfolding of folded chains which can orient in the direction of stretching as the strain increases. In this case, the strain at which the necking of the sample film can be observed coincides with the strain at which the unfolding takes place.
社団法人日本材料学会の論文
1967-09-15

応力-ひずみ-赤外二色性の同時測定による高密度ポリエチレンおよびポリプロピレンの変形機構の研究

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