Abstract
In this paper, poly(vinyl alcohol) (PVA) foils of comparable thickness were obtained by using 10 wt % PVA aqueous solutions exposed to microwave (MW) radiations for different times. The main goal of this paper is to identify the effects of MW irradiation on the induced optical birefringence of PVA stretched foils, since it is known that the changes in the chemical and physical properties of polymers induced by radiations can influence the asymmetry of their molecular structures from which the birefringence of polymers derives. The efficiency of the MW oven was estimated, and the contribution of sensible and latent heat and heat loss to the absorbed energy was discussed. The effects of MW irradiation, in terms of absorbed energy, were evidenced by using FTIR spectra analysis, contact angle measurements, scanning electron microscopy (SEM) images, and induced optical birefringence. The dehydration (cross-linking) of PVA in aqueous solution and the dependence of the anisotropy on the absorbed MW energy, stretching ratio, and the type of hydrogen bonds formed are discussed in this study.
Highlights
Poly(vinyl alcohol) (PVA) is a hydrophilic polymer with many applications in the industrial field, including its use to obtain new retarders and polarizers [1,2]
By using PVA hydrolyzed to 99%, we reduce to a minimum the influence of the remaining 1% PVAc units on the intrinsic anisotropy of the foils
PVA aqueous solutions were prepared and MW irradiated to modify the optical properties of the thin foils
Summary
Poly(vinyl alcohol) (PVA) is a hydrophilic polymer with many applications in the industrial field, including its use to obtain new retarders and polarizers [1,2]. When the polymer chains are oriented in a certain direction, the optical anisotropies no longer compensate each other, and the material becomes birefringent [3,4]. The optical birefringence of the stretched polymer foils offers important information about the order degree of the polymer chains [5]. The anisotropic PVA foils increase their birefringence in the stretching process [3,4]. The main goal of this research is to obtain PVA thin foils with improved optical properties and with high values of birefringence, without deteriorating their physical and/or chemical properties. Due to the poor dielectric properties of polymers [10], the absorbed energy from the electromagnetic field cannot directly break chemical bonds, and it cannot induce severe degradation [11]. The experimental results can be used in fundamental research on the optical properties of PVA foils, which is important for obtaining various optical devices [2,12]
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