(421f) Reducing Moisture Sensitivity in Carbohydrate-Based Packaging

Packaging is one of the largest contributors to plastic waste. Hence, polymers produced from renewable sources have become attractive to substitute or fully replace petroleum-based 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, the properties of some of the prime candidates ¾e.g., cellulose and its derivatives¾ rapidly deteriorate already at a modest relative humidity limiting their use without a vapor barrier. Typical approaches to limit their moisture sensitivity, such as chemical crosslinking, are complicated by the highly variable side group chemistry, often involving ionized/ionizable moieties. This talk will contrast and compare several approaches to manage moisture transport in carbohydrate coatings and films. In one approach, polyelectrolyte complexation is shown as 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) are used as a model polyelectrolyte complex (PEC) system. 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). Secondly, we also find that this approach is easily implemented concurrently with chemical crosslinking of hydroxyl groups, resulting in reduced WVTR even at 80% RH, approaching the range of some traditional packaging plastics, such as poly(ethylene terephthalate), polystyrene, and poly(vinyl chloride) under humid conditions. In an alternate approach, this talk will also present an alternative approach where cellulose nanomaterials and chitin-based materials can be layered with poly(hydroxyalkanoate) (PHA) in order to achieve attractive oxygen barrier (from cellulose nanomaterial/chitin) and water vapor barrier (from PHA) properties. This approach is applied to coatings of cellulose and chitin materials on a variety of substrates including cellulose acetate and paper, leading to effective barrier materials composed entirely of renewably sourced, biodegradable components.