Evaluation of NADES for Pectin Films Reinforced with Oxalic Acid-Modified Chitin Nanowhiskers

Abstract

The effect of three NADESs as pectin film plasticizers was evaluated at 10%, 30%, and 50% w/w by using the casting method. Two hydrophilic (choline chloride with glycerol or citric acid) and one hydrophobic (thymol–camphor) NADESs were used as replacement for glycerol. Oxalic acid-modified chitin nanowhiskers (oCNWs) at 1% w/w were used to evaluate the effect of the NADESs on the nanofiller. The resulting films using the hydrophobic NADES were difficult to handle and prone to cracking and performed similarly to or worse than pure pectin films. As a result, they were not further evaluated. In contrast, the hydrophilic ones showed characteristics comparable to glycerol. It was found that films containing glycerol and choline chloride–glycerol NADESs showed a decrease in opacity and tensile strength and an increase in WVP, Young’s modulus, and maximum elongation. In contrast, those that contained citric acid exhibited a different behavior: opacity was less affected, and a decrease in WVP and an increase in tensile strength and Young’s modulus (at 10% and 30% plasticizer) were found. oCNWs tended to decrease WVP and increase Young’s modulus but not in a very significant way. Our findings demonstrate that NADESs can be used as plasticizers in pectin films without the need to include glycerol and that the nature of NADESs is relevant to tuning the final properties.