The phenomenological and structural aspects of biaxial drawing of a vinyl alcohol-rich ethylene/vinyl-alcohol copolymer is studied as a function of temperature. For draw temperature above the crystalline mechanical relaxation, T,, sharp necks accompanied with catastrophic fissures develop during simultaneous biaxial drawing as well as in the first step of sequential biaxial drawing. For draw temperature below T,, simultaneous biaxial drawing can be successfully achieved via propagation of diffuse necking so that a minimum macroscopic draw ratio of about 3 X 3 is required to obtain a uniform plastic strain. The strong interaction anisotropy of the sheet-like structure of the monoclinic phase is responsible for the fissuring trend at T > T,. In contrast, the isotropic mesomorphic phase that is strain-induced at T < T, enables simultaneous biaxial drawing. The development of a planar texture suggests that the transformation results from transverse crystal slip. However, the random distribution of the H-bonds in the mesomorphic phase is rather consistent with an accumulation process of conformational defects that remain frozen in the crystal
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Tensile drawing of ethylene/vinyl-alcohol 3. Biaxial orientation copolymers: 3. Biaxial orientation / Roland Seguela, Karina Djezzar, Laurence Penel, Jean-Marc Lefebvre, Yves Germain // Polymer. – 1999. – N 40. – P. 47–52.