Aqueous processing of dense films from cellulose-based coacervates

Abstract: The non-solvent induced phase separation (NIPS) process is commonly used to manufacture films from petroleum-derived polymers using toxic, aprotic solvents, which are under increasing scrutiny due to their negative environmental impacts. In order to decrease our dependence on petroleum-derived polymers, while also increasing our fundamental knowledge in green engineering, this study explores the potential of forming free-standing, antimicrobial films from the natural polymer carboxymethyl cellulose (CMC) using all-aqueous processing. First, turbidity measurements were used to conduct a wide screening of the ability of CMC and the synthetic polycation poly(diallyldimethylammonium chloride) (PDADMAC) in the presence of salt (sodium chloride (NaCl) or potassium bromide (KBr)) and their ability to form polyelectrolyte complexes (PECs). The optimized PEC conditions were corroborated via rheological testing which indicated higher coacervate sensitivity to KBr than to NaCl. Next, the optimized hybrid coacervates were blade-cast into films using aqueous phase separation (APS). Their morphology and mechanical performance were evaluated using scanning electron microscopy (SEM) and tensile testing, respectively. Dense, robust films were formed from the “optimized” coacervates using NaCl or KBr. When high salt concentrations were used, the films morphology changed to a fractured and unstable surface, resulting in a significant decrease in mechanical strength. With the knowledge that our CMC/PDADMAC films were manufactured with an excess of PDADMAC, we hypothesized that their cationic nature would result in strong antimicrobial properties via contact killing. We suggest that these CMC-based films hold potential for the development of packing and coatings via completely aqueous processing of biopolymer-based films for enhanced sustainability.