α-1,3-Glucan-Palmitate: A Thermoplastic Biomaterial with Potential Use in Packaging

Packaging materials are increasingly scrutinized for their environmental persistence, which has developed renewed interest in reducing material utilization, recycling, and the environmental impact of products at their end-of-life. Persistent, nonbiodegradable plastics typically used in packaging and their attritted forms, “microplastics,” have prompted research toward more benign, biodegradable, or compostable plastic alternatives, including thermoplastic polysaccharide esters, that reduce the risk of bioaccumulation in land and aquatic species. In this work, α-1,3-glucan (a linear, semicrystalline polysaccharide, biomanufactured through enzymatic polymerization) has been converted into α-1,3-glucan palmitate (GP) using a process aligned with green chemistry principles. The GP synthesis has been developed with minimal solvent use, resulting in a low process mass intensity (PMI = 7) metric. To promote and enable the potential use of GP as material with an end-of-life disposal through composting, the degree of substitution (DS) was controlled between 0 and 2.7 palmitates per anhydroglucose unit (AGU). These materials exhibit melting points in the range 140–260 °C; mimicking conditions of current hot-melt extrusion processes, especially of typical polyolefins which are commonly used as transparent flexible packaging resins. Melt-pressed films of GP yielded a maximum stress of 2.7 MPa under 5.7% strain. Oxygen and water vapor transport properties for GP films have been measured (4.98×10−5cmSTP3mm2dayPa and 2.60×10−10gmm2sPa, respectively), suggesting the potential utility for food packaging applications where oxygen and water permeance are needed.