ポリエチレン分子の音響的配向評価

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In recent publications, it has been proposed by Moseley and others that the velocity of sound propagation along oriented polymeric system of mono-phase can be sued as direct measurement of the degree of molecular orientation in a similar manner to the derivation of the optical orientation factor, f. Samuels has demonstrated that the semi-crystalline polymers, such as polypropylene, can not be derived as a mono-phase but is best represented by a two-phase system of crystalline and non-crystalline regions, and he formulated the sonic modulus as: 3/2(ΔE)^<-1>=(xf_c/E_<tc>+[(1-x)f_a/E_<ta>], (1) where (ΔE)^<-1>=(E_u)^<-1>-(E_0)^<-1>, x is the fraction of crystalline phase, and E_0 and E_u are the measured sonic moduli of the oriented and unoriented specimens, respectively. For a given x, the difference in the sonic moduli between an oriented and unoriented specimens depends upon the orientation factors, f_c and f_a of the two phases in the the specimens. Birefringence for a uniaxially oriented system may be given in the followings expression. Δ/xf_c=Δ_c+Δ_a{[(1-x)/x](f_z/f_c)} (2) Where Δ is the measured birefringence, Δ_c and Δ_a are the intrinsic birefringence of the crystalline and non-crystalline phases, respectively. A combination of the sonic modulus measurement with birefringence one gives a rapid determination of the orientation factors, when the values of E_<tc>, E_<ta>, Δ_c and Δ_a for the given semi-crystalline polymer are known from other sources. Polyethylene films of various density high and low have been used to check the above relation s for the two-phase system, where the values of Δ_c, Δ_a, and E_<tc> are accepted from reports made by several authors and the values of f_c and f_a are determined from the simultaneous measurements of birefringence and X-ray diffraction of the stretched specimens. The intrinsic sonic modulus of the non-crystalline phase, E_<ta> may be evaluated from Eqs. (1) and (2), giving that the lateral forces between the amorphous chain molecules in these system would be expected to be constant value independent of the degree of orientation. The agreement among the evaluations of E_<ta> for highly stretched specimens (150-400%) is good, while that for low stretched specimens is very bad, suggesting that the propagation mechanism of sonic wave in low stretched polyethylene would be more complicated than that proposed by the above relations.
社団法人日本材料学会の論文
1967-07-15

ポリエチレン分子の音響的配向評価

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