Abstract
The presence of the crystalline regions in poly(vinyl alcohol) coating films acts as barrier clusters forcing the gas molecules to diffuse in a longer pathway in the amorphous region of the polymer, where diffusivity and solubility are promoted in comparison. Evaluating the influence of crystalline regions on the oxygen barrier property of a semi-crystalline polymer is thus essential to prepare better coating films. Poly(vinyl alcohol) coating films with varying induced crystallinity were prepared on a polyethylene terephthalate (PET) substrate by drying at different annealing temperatures for 10 min. The coating films were first delaminated from the PET substrate and then characterized using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), and X-ray diffraction (XRD) techniques to determine and confirm the induced percentage of crystallinity. The barrier performance of the coating films, i.e., the oxygen transmission rate (OTR), was measured at room temperature. Results showed a decrease in the OTR values of poly(vinyl alcohol) film with an increase in the degree of crystallinity of the polymer matrix. Tortuosity-based models, i.e., modified Nielsen models, were adopted to predict the barrier property of the semi-crystalline PVOH film with uniform or randomly distributed crystallites. A modified Nielsen model for orderly distributed crystallites with an aspect ratio of 3.4 and for randomly distributed crystallites with an aspect ratio of 10.4 resulted in a good correlation with the experimental observation. For the randomly distributed crystallites, lower absolute average relative errors of 4.66, 4.45, and 5.79% were observed as compared to orderly distributed crystallites when the degree of crystallinity was obtained using FTIR, DSC, and XRD data, respectively.
Highlights
Poly(vinyl alcohol) (PVOH, [-CH2-CHOH-]n) is the largest volume of synthetic polymer produced worldwide
poly(vinyl alcohol) (PVOH) is a semi-crystalline polymer well-known for its low oxygen permeability, good thermal resistance, excellent adhesive properties, and resistance to organic solvents, in addition to its attractive biocompatibility and biodegradability properties [1,2]
The gas barrier property of PVOH is partially attributed to the crystalline regions/phases within its matrix
Summary
Poly(vinyl alcohol) (PVOH, [-CH2-CHOH-]n) is the largest volume of synthetic polymer produced worldwide. It is a water-soluble, linear, and non-halogenated aliphatic polyhydroxy polymer. PVOH is a semi-crystalline polymer well-known for its low oxygen permeability, good thermal resistance, excellent adhesive properties, and resistance to organic solvents, in addition to its attractive biocompatibility and biodegradability properties [1,2]. These desirable properties of PVOH have resulted in a wide range of practical applications, mainly in food packaging, biomedical materials, ultrafiltration membranes, ion exchange membranes, gas separation membranes, protective/binding coatings, etc. These crystalline regions are comprised of the platy-like lamellae (single crystals) with the thickness of 10 to 20 nm bound to each other by disordered chains [8]
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