Poly(vinyl alcohol) / cellulose nanocomposite barrier films /
There is a continual interest in developing robust, flexible, durable, lightweight, waterborne polymer barrier coatings which are increasingly resistant towards both chemical warfare agents as well as an ever growing number of toxic industrial chemicals. In this study, barrier films were prepared with poly(vinyl alcohol) (PVOH) and varying amounts of cellulose nanocrystals (CNXLs) as filler. Poly(acrylic acid) (PAA) was used as a crosslinking agent to provide water resistance to PVOH. The films were heat treated at various temperatures (125, 150, 170, 185 °C) in order to determine the optimum crosslinking density. Heat treatment at 170 °C for 45 minutes resulted in films with improved water resistance without polymer degradation. Infrared spectroscopy (FTIR) indicated ester bond formation with heat treatment. Mechanical tests showed that films with 10%CNXLs/ 10%PAA/ 80%PVOH had the highest tensile strength, tensile modulus and toughness of all the films studied. Polarized optical microscopy and atomic force microscopy showed agglomeration of CNXLs at filler loadings of 15% CNXLs. A thermogravimetric analysis (DTGA) showed highly synergistic effects with 10%CNXLs/ 10%PAA/ 80%PVOH and supported the tensile test results. The purpose of these barrier films is to prevent the diffusion of chemical warfare agents while allowing moisture to pass through to allow breathability. Water vapor transmission indicated that all the films allowed moisture to pass. However, moisture diffusion was reduced by the presence of both CNXLs and PAA compared to pure PVOH. The crystalline nature of CNXLs causes the diffusing molecules to undergo a tortuous path, while the crosslinking forms a network structure which reduces diffusion. A standard time lag diffusion test utilizing permeation cups was used to study the chemical barrier properties. The film containing 10%CNXL/ 10%PAA/ 80%PVOH showed an improvement of 90% compared to 100% PVOH film. Surface modification of CNXLs was successful and well dispersed carboxylated CNXLs were obtained. Carboxylated cellulose nanocrystals (C.CNXLs) showed less agglomeration, improved interaction, slightly reduced flux and slightly increased time lags compared to CNXLs.
School:Oregon State University
School Location:USA - Oregon
Source Type:Master's Thesis
Keywords:protective coatings nanocrystals cellulose polyvinyl alcohol
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