Selecting Hydrogel Films Composed of Carboxymethyl Cellulose and Microcrystalline Cellulose From OPEFB With Citric Acid as a Green Crosslinker for Fruit Wrapping.

Abstract

Cellulose-based hydrogel films are promising alternatives to plastic for wrapping. Hydrogel films based on carboxymethyl cellulose (CMC) and microcrystalline cellulose (MCC) must exhibit high mechanical strength and be capable of absorbing moisture. Crosslinking increases the absorption capacity and mechanical strength of hydrogel films. As a filler, MCC can synergize with citric acid, which acts as an environmentally friendly crosslinker to enhance mechanical strength. This research aimed to develop a suitable CMC/MCC formulation and citric acid as a crosslinker, resulting in a hydrogel with high water absorption and mechanical strength. CMC/MCC formulations were combined with citric acid concentrations of 5%, 7.5%, and 10%. The results showed that the MCC and citric acid will affect absorption and mechanical strength. The addition of MCC up to 50% tends to produce a brittle hydrogel film, and this phenomenon is also correlated with increased citric acid. A 90:10 CMC/MCC formulation with 5% citric acid (w/v) resulted in a water uptake of 222.72 ± 9.32 at pH 7.0. In contrast, the 80:20 CMC/MCC formulation resulted in a water uptake of 603.02 ± 26.98. They both showed higher rehydration of the dry gel than the others. FTIR confirmed the sharpening of the peak wave number at 1705 cm^-1, which is identical to the protonated carbonyl group and correlates with the water absorption capacity. The morphology of hydrogel films containing a CMC/MCC ratio of 90:10 exhibits a smoother surface than that of those with a CMC/MCC ratio of 80:20, which feature bubbles on the surface cracks of the hydrogel film due to the presence of more water absorption channels. Hydrogel films with a CMC/MCC ratio of 90:10 and 5% citric acid (w/v) can be developed for wrapping by modifying their hygroscopic properties. In contrast, hydrogel films with an 80:20 ratio and 5% citric acid are suitable for use as absorbents.