EFFECTS OF MOLECULAR-ORIENTATION AND CRYSTALLINITY ON MEASUREMENT BY X-RAY-DIFFRACTION OF THE CRYSTAL-LATTICE MODULUS OF POLY(VINYL ALCOHOL) PREPARED BY GELATION CRYSTALLIZATION FROM SOLUTION

The crystal lattice modulus of poly(vinyl alcohol) was measured by X-r ay diffraction using films which were prepared by gelation/crystalliza tion from solution and elongated in a silicon oil after evaporating so lvent. The measured crystal lattice modulus of specimen with Young's m odulus 13-20 GPa was in the range 200-220 GPa. These values were lower than that for polyethylene measured by using ultradrawn films. To che ck the morphology dependence of the measured crystal lattice modulus o f poly(vinyl alcohol), a numerical calculation was carried out by cons idering molecular orientation and crystallinity. In this calculation, a three-dimensional model was employed, in which oriented crystalline layers are surrounded by oriented amorphous phase and the strains of t he two phases at the boundary are identical. The theoretical results i ndicate that the difference between the crystal lattice modulus as mea sured by X-ray diffraction and the intrinsic value becomes less pronou nced and Young's modulus of a sample becomes lower when a series coupl ing between crystalline and amorphous phases is predominant. A series of numerical calculations for the system with low crystallinity and or ientational degree of amorphous chain segments indicates that the real value of the crystal lattice modulus is slightly higher than 200-220 GPa measured by X-ray diffraction.