Abstract
Carboxymethyl chitosan (CMCH) from different chitosan sources (shrimp, crab, and squid) and molecular sizes (polymer and oligomer) were synthesized via carboxymethylation reaction. The CMCH films were prepared by solution casting. All the CMCH films had high water solubility, higher than 85% of the dry matter of the films. The sorption isotherm of the CMCH films was evaluated at several values of relative humidity (0% RH, 23% RH, 34% RH, 43% RH, 65% RH, 77% RH, and 86% RH) at 25 ± 1°C. The equilibrium moisture content values of all the CMCH films were low at lower aw but increased considerably above aw = 0.65. The sigmoidal moisture sorption isotherms of this product can be classified as type II. Understanding of sorption isotherms is an important prerequisite for the prediction of moisture sorption properties of films via moisture sorption empirical models. The experimental data were analyzed and fitted by the nine sorption models. The various constants determined by linear fitting of the sorption equation with r2 values were in the range of 0.7647 to 0.999. The GAB model was found to be the best-fitted model for CMCH films (aw = 0.23–0.86, 25 ± 1°C), and the model presented the optimal root-mean-square percentage error (%RMS) values when compared with other models. In conclusion, it can be stated that the GAB model was found to be better estimated for predicting the CMCH films than other models. Therefore, the constant derived from different sorption models were applied for use in terms of information and for the determination of the stability of CMCH packaging films for specific end uses.
Highlights
Chitosan is a deacetylated derivative of chitin that is a major component of crustacean shells such as crab, shrimp, and squid pen
Chitosan is insoluble in aqueous solutions with pH above 6.5, which limits the practical utilization of chitosan. erefore, the requirement of water solubility of chitosan has led to several research studies attempting to convert chitosan into chitosan derivatives such as carboxymethyl chitosan (CMCH) [2,3,4,5]
Structure of Chitosan and CMCH. e structural changes of chitosan and its derivatives were confirmed by Fourier transform infrared (FTIR) spectroscopy
Summary
Chitosan is a deacetylated derivative of chitin that is a major component of crustacean shells such as crab, shrimp, and squid pen. Carboxymethyl chitosan (CMCH) is soluble in water and has unique chemical, physical, and biological properties such as high viscosity, large hydrodynamic volume, low toxicity, biocompatibility, biodegradability, and gel-forming capabilities, all of which make it an attractive option in Advances in Materials Science and Engineering connection with its use in food products and cosmetics [2, 3]. Rachtanapun and Tongdeesoontorn [12] studied the sorption isotherm of carboxymethyl cellulose from papaya peel/corn flour blended films and discovered that knowledge regarding sorption isotherms was important for predicting the moisture sorption properties of films via moisture sorption empirical models. In 2011, Rachtanapun and Tongdeesoontorn [13] reported the effect of NaOH concentration on sorption isotherm of carboxymethyl rice starch films and prediction models. There has been plenty of research on chitosan films in which the researchers examined the moisture sorption [14,15,16,17], but a little attention has been focused on the isotherm of CMCH
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