架橋ポリエチレンの粘弾性 : 高分子レオロジー

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The effect of extension on the viscoelastic behavior and on the incipient temperature of crystallization were studied for irradiated polyethylene, Irrathen film. Dynamic modulus and tan δ were measured over a temperature range from room temperature to 150℃ at 20 cps with an apparatus, described in another paper. In undrawn sample, tan δ goes through two maxima which correspond to β and α dispersions respectively. The crosslinks between molecules introduced by irradiation cause the higher transition temperature for β and the lower transition temperature for α compared with the unirradiated polyethylene. The α dispersion shifts to lower temperature and decreases its height with extension, on the other hand β dispersion occurs at the same temperature and increases its height with extension. As it is known that α dispersion is associated with crystalline part and β dispersion with amorphous part, it can be deduced that the degree of crystallinity decreases and the numbers of imperfect crystallites increases when the specimen is highly extended. Dynamic modulus increases with extension. In a previous paper, one of us has derived a simple relationship between elastic modulus E' and degree of crystallinity x as follows : (E'-E'_0)/T=kx/(αx_0-x) where E'_0 the elastic modulus of the completely amorphous region, k the constant related to the rubber-like elasticity of molecule, α the constant expressing the effective range of crosslinkage due to crystallite, x_0 the maximum degree of crystallinity and T the absolute temperature. In this theory both crystallites and entanglements act as physical crosslinks and somewhat ordered amorphous regions between crystallites were taken into account. The same relationship was found to be applicable to this undrawn sample. E'_0 is about 2×106 dynes/cm^2 and negligible small. The effect of extension on the incipient temperature of crystallization was studied at constant temperatures, 105.5, 106.8 and 108℃ respectively. Flory's equation 1/T^0_m-1/T_m=(R/H_f)φ(α) relating incipient temperature of crystallization to elongation rate, α was applied to our results. The plot of φ(α) against inverse incipient crystallization temperature was linear, as shown in Fig. 3. The slope is proportional to the heat of fusion per segment, H_f, and the extrapolated intersection to abscissa gives the inverse incipient crystallization temperature, 1/T^0_m for undrawn sample. Assuming that number of segments between crosslinks, n's are 50, 100 and 200, the value of H_f was calculated to be about 3×10^4 R cal/mole.
社団法人日本材料学会の論文
1961-05-15

架橋ポリエチレンの粘弾性 : 高分子レオロジー

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