EVALUATION OF MONOCLINIC CRYSTAL BIREFRINGENCE OF ISOTACTIC POLYPROPYLENE

Abstract

The monoclinic crystal birefringence of isotactic polypropylene was evaluated on a basis of the simple addivity as given by where Δn is measured birefringence, Δn*c is an intrinsic birefringence of monoclinic crystal, Δn*a is that of amorphous chain, Fc is uniaxial orientation factor of the c-axis of monoclinic crystal to the fiber axis, Fa is that of the amorphous chain also to the fiber axis, Xv is degree of crystallinity (volume faction), and ΔF is form birefringence.The value of Fc was evaluated by means of Wilchinsky's method from the azimuthal intensity distributions of the (110) and (040) X-ray reflections. The values of Δn and Xv were measured by Berek's compensator and density gradient tube techniques, respectively. The specimens used were sufficiently annealed so that the crystalline phase consisted wholly of monoclinic crystals.When assumed that the value of Fa is equal to zero for the low oriented specimens having the value of Δn less than 10×10-3, the value of Δn*c is estimated as 41.5×10-3, while assumed that the value of Fa is identical to that of Fc and Δn is inversely proportional to the density, the value of Δn*c is estimated as 39.0×10-3 for the highly oriented specimens having the value of Δn from 24×10-3 to 35×10-3.