AN X-RAY POLE FIGURE ANALYSIS ON BIAXIALLY DEFORMED POLYETHYLENE FILM

The orientational states induced upon two-step biaxially stretching lo w-density polyethylene at 25-degrees-C have been investigated. A pole figure analysis of the (200), (020), and (002) crystalline planes has been employed to elucidate the evolution of the molecular crystalline orientation as a function of biaxial stretching. The initial uniaxial- like orientation induced along the extrusion direction of the films wa s gradually lost upon transverse stretching and, consequently, replace d by a biaxial orientation as suggested by the orientation functions. In these cases, the a crystallographic axis was observed to be strongl y oriented along the film normal, thus confining the c and b axes to t he film plane. The pole figures clearly indicate that the c and b axes are preferentially aligned 45-degrees with respect to the stretching directions. This unique orientational state of the orthorhombic unit c ell of polyethylene has been termed a biaxial-double orientation. Bire fringence measurements on the biaxial samples indicated that the amorp hous and crystalline regions are simultaneously biaxially oriented. Th e evolution of the crystalline orientation as a function of stretching was conveniently followed on a White/Spruiell orientation triangle. Q uantification was hindered, however, by the presence of different crys tal populations in the biaxially stretched samples. (C) 1994 John Wile y & Sons, Inc.