(601f) Making Cellulose-Based Films Work in High Humidity

Petroleum-based plastics are ubiquitous in society, but their limited recyclability and slow degradation present significant environmental concerns. In fact, most plastic waste is not recycled but instead discarded to landfills or accumulated uncontained in the environment where they persist for many years. Thus, solid waste accumulation, energy consumption, and CO₂ emissions associated with virgin plastic manufacturing have driven extensive research efforts to develop more sustainable alternative materials to traditional plastics. Cellulose is an obvious candidate to substitute or replace petroleum-based plastics due to its natural abundance, renewability, and biodegradability. Consequently, cellulose-based materials have been widely studied for applications such as packaging, composite materials, and printed electronics. However, the physicochemical properties of cellulose and its derivatives are sensitive to moisture and relative humidity, limiting their performance in many applications. Here, we discuss approaches to control swelling and water vapor transmission rates (WVTR) in cellulose-based films including crosslinking with renewable polyacid, coordination with soluble metal oxide hydrates, and polyelectrolyte complexation. We find that crosslinking with polyacid reduces swelling of cellulose-based films, and the WVTR of crosslinked films can be tuned over approximately four orders of magnitude by varying the crosslinker content. The WVTR of crosslinked films is one order of magnitude lower than that of poly(ethylene terephthalate), but increases when the RH is above 65% due to hydrophilic moieties of the polymer and crosslinker. Promisingly, the hydrophilicity of the crosslinker can be reduced by coordination with a metal oxide hydrate, preventing interaction with water. Similarly, polyelectrolyte complexes of cellulose and chitosan are less hydrophilic than the neat materials, demonstrated by their insolubility and high resistance to swelling. The approaches explored here to control moisture sensitivity in cellulose-based films are therefore promising for expanding the application space of cellulose as a sustainable alternative to petroleum-based plastics.