Highly-enhanced water resistant and barrier properties of cross-linked poly(vinyl alcohol) hybrid films
Mijin Lim, Dowan Kim, Jongchul Seo
Department of Packaging, Yonsei University
The barrier properties of polymeric films are important for their application in the various industrial fields such as microelectronics, food and pharmaceutical packaging, and solar cell . Among various barrier polymer films, poly(vinyl alcohol) (PVA) is an water-soluble synthetic polymer, which has been widely used in various industrial applications such as in paper coating agents, adhesives, drug delivery carriers, and as a component of biomedical and flexible packaging films [1-2].
Although PVA has excellent oxygen barrier properties and mechanical properties in the dry state, its applications are limited in the wet state and in moisture sensitive fields. Its poor resistance to water molecules such as high moisture uptake and fast moisture transmission, originating from hydroxyl groups in the repeating unit of PVA, restricts its potential use in many applications [1-2].
To overcome this problem, PVA should be increased by nanocomposites , polymer-polymer blending  and cross-linking [5-7]. PVA can be cross-linked by various methods such as heat treatment and UV radiation or by chemical agents such as hexamethylene diisocyanate, glutaraldehyde, and boric acid (BA) [5-7].
BA is commonly used in the cross-linking processes in PVA. The reaction between PVA and BA occurs between the hydroxyl groups to form bridge. From the reaction, the cross-linking process decreases the hydrophilic character of PVA . In previous work, the thermal, mechanical, and oxygen barrier properties of pure PVA were highly improved by introducing BA into PVA. Although those properties of hybrid films were improved, this study did not improve the moisture properties of pure PVA. Therefore, it is necessary the introduction of a hydrophobic material to improve the moisture barrier properties [6-7].
Poly(acrylic acid) (PAA), which shows high solubility in water and high miscibility with PVA, is selected as a crosslinking agent because each carboxylic acid group in PAA can react with PVA and characteristics including Strong crosslinking by ester linkage can be formed between the hydroxyl group of PVA and the carboxyl group of PAA [5,7].
In addition, to remove the OH groups from unreacted PVA, BA was added to the PVA/PAA solution. The chemical properties of the hybrid films are investigated using Fourier transform infrared (FT-IR) spectroscopy, and the morphology properties are evaluated wide angle X-ray diffractometer (WAXD) analysis and scanning electron microscope (SEM). To determine the thermal properties of the films, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) are used. The barrier properties of the hybrid films are confirmed by oxygen transmission rate (OTR), contact angles and water-pressure resistance measurement.
 S.E.M. Selke, J.D. Culter, R.J. Hernandez, Plastics Packaging; Properties, Processing, Applications and Regulations, 2nd Ed., Hanser Publishers, Munich, 2004.
 W.H. Hu, Z.H. Zhang, Q.G. Zhang, Q.L. Liu, A.M. Zhu, Pervaporation dehydration of water/ethanol/ethyl acetate mixtures using poly(vinyl alcohol)-silica hybrid membranes, J. Appl. Polym. Sci. 126 (2012) 778-787.
 M. Lim, D. Kim, H. Han, S. B. Khan, J. Seo, Water sorption and water-resistance properties of poly(vinyl alcohol)/clay nanocomposite films: effects of chemical structure and morphology, Polym. Compos. 36 (2015) 660-667.
 G. Zhu, F. Wang, S. Dong, K. Zu, Y. Liu, Thermal, mechanical and chemical properties of hydrophilic poly(vinyl alcohol) film improved by hydrophobic poly(propylene glycol), Polym. Plast. Tech. Eng. 52 (2013) 422-426.
 J.Y. Park, J.J. Hwang, S.D. Yoon, J.H. Lee, I.H. Lee, Influence of glyoxal on preparation of poly(vinyl alcohol)/poly(acrylic acid) blend film, J. Nanosci. Nanotech. 15 (2015) 5955-5958.
 T. Miyazaki, Y. Takeda, S. Akane, T. Itou, A. Hoshiko, K. En, Role of boric acid for poly (vinyl alcohol) film as a cross-linking agent: melting behaviors of the films with boric acid, Polymer 51 (2010) 5539-5549.
 K. Kumeta, I. Nagashima, S. Matsui, K. Mizoguchi, Crosslinking reaction of poly(vinyl alcohol) with poly(acrylic acid) (PAA) by heat treatment: effect of neutralization of PAA, J. Appl. Polym. Sci. 90 (2003) 2420-2427.
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