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

Abstract

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).

Crystal Poisson's Ratios of Polyethylene and Poly(vinylalcohol) Estimated by X-ray Diffraction Using the Ultradrawn Films

“…18 The fourth-order factor of the amorphous chain segments was calculated by using an inversely superposed Gaussian type function with the parameter which gives the best value of the second order factor. 8 Detailed methods were described elsewhere. 4,19 Poly(viny alcohol).…”

“…The stress homogeneous hypothesis could be valid for polyethylene (PE) dry gel films with draw ratios λ > 50, 3 polypropylene (PP) dry gel films with λ > 30, 7 and poly(vinylalcohol) dry gel films with λ > 10. 8 Namely, the experimental values were almost independent of the draw ratio and were 213-229 GPa for PE, 3 40-43 GPa for PP, 7 and 200-220 GPa for PVA. 8 In spite of a number of reports for crystal lattice modulus (the crystal elastic compliance along the chain axis), [1][2][3][4][5][6][7][8] few papers for estimating the crystal Poisson's ratios by X-ray diffraction have been reported for normally-drawn polyethylene by Miyasaka et al, 9 poly(p-phenylene terephthalamide) by Nakamae et al 10 and polydiacetylene single crystal by Tashiro et al 11 Such few publications are due to the difficulty in measuring very small compressible (negative) crystal strain perpendicular to the direction of the external applied stress.…”

Understanding the Dispersion and Assembly of Bacterial Cellulose in Organic Solvents

“…3 Structurally, BCN consist of stiff crystalline regions joined by more disordered amorphous segments, where the disordered domains form weak spots along a nanofibril. 4 Young's moduli of individual BCN have been reported [4][5][6][7] to be as high as 78-160 GPa. Excellent mechanical properties and high water-holding capacity make BCN appealing for a variety of applications.…”

Mechanical Properties of Poly(ethylene terephthalate) Estimated in Terms of Orientation Distribution of Crystallites and Amorphous Chain Segments under Simultaneous Biaxially Stretching

“…19 This indicates no temperature dependence of crystal lattice modulus of PET along the chain direction, as has been reported for PE 23 PP, 24 and PVA. 10 In contrast, the other crystal moduli decrease with increasing temperature. Of course, temperature dependence of the crystal lattice moduli as listed in Table II is useful as fundamental information to analyze the temperature dependence of the present simultaneous biaxially stretching films later.…”

“…8,9 This treatment represented as a continuous body is essentially suitable, if there exist no aggregations of crystallites such as spherulites and rods within the material. The analysis has been successful for polyethylene (PE) with an orthorhombic crystal unit 5,6 and for poly(vinyl alcohol) (PVA), 10 nylon 6 11,12 and cellulose 13 with a monoclinic crystal unit. The generalized fourth order orientation factors can be obtained from the orientation factors.…”