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ABSTRACT:The crystal lattice modulus of poly(vinyl alcohol) was measured by X-ray diffraction using films which were prepared by gelation/crystallization from solution and elongated in a silicon oil after evaporating solvent. The measured crystal lattice modulus of specimen with Young's modulus 13-20GPa was in the range 200-220GPa. These values were lower than that for polyethylene measured by using ultradrawn films. To check the morphology dependence of the measured crystal lattice modulus of poly(vinyl alcohol), a numerical calculation was carried out by considering 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 the two phases at the boundary are identical. The theoretical results indicate that the difference between the crystal lattice modulus as measured by X-ray diffraction and the intrinsic value becomes less pronounced and Young's modulus of a sample becomes lower when a series coupling between crystalline and amorphous phases is predominant. A series of numerical calculations for the system with low crystallinity and orientational 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.KEY WORDS Poly(vinyl alcohol) / Crystal Lattice Modulus / Numerical Calculation/ X-Ray Diffraction/ Series Coupling/ Since 1974, the preparation of polymeric fibers and films with high-strength and highmodulus has been extensively investigated for flexible polymers by gel-state spinning, 1 ultradrawing of dried gel films 2 • 3 ultradrawing of single-crystal mats,4 and two-step drawing of single-crystal mats. 5 This research is based on the assumption that the theoretical Young's modulus and tensile strength of polymeric materials could be realized if the chains are fully aligned and if the specimen is almost completely crystalline. Results of interest have been obtained for polyethylene and polypropylene whose Young's moduli at 20°C are higher than 200 GPa 3 • 4 and 40 GPa, 6 • 7 respectively. These values are nearly equal to their crystal lattice moduli as measured by X-ray diffraction technique. Although the theoretical Young's modulus of polyethylene is one of the highest among crystalline polymers, the range of application is limited by its low melting point. Therefore, it is important to achieve ultradrawing of other crystalline polymers such as polyamide, polyester, and poly(vinyl alcohol) (PV A).

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