Graduation date: 2007
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.