(297e) Polyelectrolyte Complexation As a Method to Manage Moisture Sensitivity in Renewable Cellulose and Chitin Barrier Materials

Packaging is one of the largest contributors to plastic waste, and its production is a significant contributor to global greenhouse gas emissions. To address these problems, polymers produced from renewable sources have become attractive to substitute or fully replace conventional plastics in packaging materials. Polysaccharides are the most abundant class of natural polymers, making them attractive starting materials to design renewable alternatives to petroleum-based plastics for high volume applications such as packaging. Results have already demonstrated that commercially relevant oxygen barrier properties are achievable with these materials. However, these properties rapidly deteriorate already at a modest relative humidity, limiting their use without a vapor barrier. Typical approaches to limit polysaccharide moisture sensitivity, such as chemical crosslinking, are complicated by the highly variable side group chemistry, often involving ionized/ionizable moieties. Here, we show that polyelectrolyte complexation is a promising approach to limit the hydration of ionized side groups and design moisture-resistant polysaccharide-based barrier films. Carboxymethyl cellulose (CMC) and chitosan (CH), two commercially available polysaccharides, are used as a model polyelectrolyte complex (PEC) system. We find that the degree of ionization of CMC and CH in PEC films depends on the processing pH and the specific acid or base used to control pH. Increasing the number of intrinsic ion pairs by varying the processing conditions or film composition leads to properties consistent with increased moisture resistance including decreased water vapor transmission rate (WVTR). We also find that this approach is easily implemented concurrently with chemical crosslinking of hydroxyl groups, resulting in a WVTR as low as 6.6 g-mm/m²-day at 23 °C and 80% RH, approaching the range of some traditional packaging plastics, such as poly(ethylene terephthalate), polystyrene, and poly(vinyl chloride) under humid conditions.