Low-water-permeability foils based on bio-renewable cellulose derivatives†

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. However, the properties of some of the prime candidates—e.g., cellulose and its derivatives—rapidly deteriorate already at a modest relative humidity rendering them impractical for use in packaging products. Here, we show by the example of carboxymethyl cellulose that chemical crosslinking with citric acid can be exploited to precisely control the moisture sensitivity of cellulose-based structures. Specifically, we demonstrate that the water vapor transmission rate (WVTR) of carboxymethyl cellulose can be manipulated in a controlled fashion over three orders of magnitude. Thereby, the lowest WVTR value, obtained for an optimal crosslinker content, is one order of magnitude lower than that measured for poly(ethylene terephthalate) even at a relatively humidity of up to 65%. Our work, thus, clearly illustrates that cellulose-based materials can be made insensitive to humidity, which is not only of great importance for providing a solution towards more sustainable plastic packaging but, generally, for expanding the scope of applications of cellulose and its derivatives, allowing us to leverage their natural abundance, chemical versatility, and biodegradability.