Enhancing moisture barrier and grease resistance of paper for green-based packaging materials
University of New Brunswick
Paper made of cellulose fiber from green plants is widely used in our daily life especially in packaging industry. Cellulose fibers, as the most abundant natural resource in the world, have numerous advantages, such as renewable, low cost, biodegradable, environment-friendly and nontoxic. However, due to the hydrophilic properties of cellulose fibers, paper is far insufficient for high-barrier applications, moisture barrier, and oil/grease barrier in particular. In order to improve its barrier properties and widen its applications, extensive studies have been carried out in the current thesis work. In the first section, hydrophobic modification of cellulose fibers was conducted via plasma-induced free radical polymerization in an attempt to graft the hydrophobic polymer chains on paper surface, thus increase the hydrophobicity of paper. Two hydrophobic monomers, butyl acrylate (BA) and 2-ethylhexyl acrylate (2-EHA), were grafted on cellulose fibers on the paper surface. In the second section, various biodegradable natural materials, including zein, starch, and sodium alginate were used to enhance paper hydrophobicity, lower the water vapour transmission rate and improve the oil/grease resistant properties of paper products, through both wet-end and surface coating technologies in bench-scale. In the third section, synthesized interpenetrating polymer networks composed of hydrophilic sodium alginate and hydrophobic poly (dimethyl siloxane) were applied to enhance barrier properties of paper via coating on paper surface. The feature of this work lies in the fact that the hydrophilic and hydrophobic phases were chemically linked into one interpenetrating polymer network during the preparation process, with the aim to make the most of the advantage of the complementary characteristics from these two polymers. It was found that, the paper hydrophobic properties have been improved significantly with rather high contact angle, due to the plasma induce polymerization, zein emulsion treatment and IPNs coating. The paper treated with sodium alginate and alkali-treat starch showed excellent grease resistant properties. However, the challenges in lowering water vapour transmission rate of the resulted paper treated with all these materials still remain; although the water vapour transmission rate has been lowered to a certain extent.