SAXS Studies on Structural Changes in a Poly(vinyl alcohol) Film during Uniaxial Stretching in Water

Abstract

We have investigated structural changes in a poly(vinyl alcohol) (PVA) film during uniaxial stretching in water by conducting simultaneously the tensile stress−strain measurement with small-angle X-ray scattering (SAXS) using our newly developed drawing apparatus for the in situ SAXS measurements. Below the strain of 70%, the crystalline lamellae orient to the direction perpendicular to the stretching direction and the intervening amorphous regions are elastically expanded with the film drawing in proportion to the macroscopic deformation. Beyond the strain of 70%, the molecular chains in the intermediate amorphous region are relaxed with the lamellar breakup. Above 180% strain, the structural transition of the lamellar structure to the microfibrillar one takes place, as suggested by appearance of the transversal streak with an intensity maximum on each streak and the mechanical transition. Moreover, interfibrillar interaction of the adjacent microfibrils decreases with the film stretching by the pulling-out of the tie chains, which are interpenetrating to the adjacent microfibrils, leading to the macroscopic plastic deformation of the PVA film and stress relaxation of most of the microfibrils, which is shown by the continuous longitudinal long period decrease. In the final stage of deformation, the networking with a long-range connectivity composed of the microfibrils and the interfibrillar extended amorphous chains proceeds associated with the sliding between the adjacent microfibrils with successive drawing. However, the network of the interfibrillar extended amorphous region is considered to be an origin of the strain-induced hardening, which occurs above 180% strain up to a break, because most of the microfibrils are relaxed with strain.

Poly(vinyl alcohol) films for topical delivery of S‐nitrosoglutathione: Effect of freezing–thawing on the diffusion properties

“…The increase in crystallinity of PVA films as a result of the F/T is in accordance with other works 28,29,37 The average distance of 10.5 nm between the crystallites dispersed in the amorphous phase obtained by SAXS is also in accordance with previous works 38,40 and can be assigned to long period distances of the semicrystalline PVA matrix. The loss of the correlation peak for films prepared by 1-, 3-, and 5-F/T suggests that there was an increase in the long period distances among crystallites with the increase in the number of F/T 38 .…”

“…The loss of the correlation peak for films prepared by 1-, 3-, and 5-F/T suggests that there was an increase in the long period distances among crystallites with the increase in the number of F/T 38 . Although in the first F/T only loose crosslinking networks are expected to be formed, the densification of the amorphous phase of PVA leads to an increase in the R g value from 155 nm for the non-F/T film to 176-179 nm for the 1 to 5-F/T films.…”

A real time study on drying and the mechano-optical behavior of polyvinyl alcohol films in solid and swollen state

“…This study was conducted using an off-line characterization technique at different stages. To follow the structure evolution real time, Miyazaki [21,22] used a stretching instrument that could perform stressestrain experiments coupled with small angle X-ray scattering (SAXS) or wide angle X-ray diffraction (WAXD) simultaneously to characterize the structural development of PVA film during uniaxial stretching in water. By means of WAXD and SAXS, the structural development of crystalline regions in swollen state were characterized, leading to observation of strain induced crystallization in the extended amorphous regions with increasing the strain.…”

Drying of Methanol and Methyl Acetate from Poly(vinyl alcohol) Flakes

“…[1] PVOH (with high molecular weight and high degree of saponification) is used for polarizing films for liquid crystal displays. [2,3] PVOH is a biodegradable synthetic polymer, but the biodegradation rate is extremely slow. [4,5] However, PVOH can be compounded with other cheap renewable polymers, such as starch, to improve its biodegradation rate and to improve its price competitiveness.…”