Developing Hydrophobic Alginate-Amine Derivatives as a Coating for Food Packaging

In recent years, there has been an increased interest in developing biopolymers from seaweed carbohydrates such as alginic acid. However, to provide the necessary water barrier properties, derivatization is required. In this study, hydrophobic alginate derivatives were synthesized through amidation with alkyl amines and further investigated for their properties as a coating material for food packaging. The length of the carbon chain in the alkyl amine feedstock is important both for the degree of functionalization and in achieving the required hydrophobicity, with a minimum of 12 or more carbon atoms necessary. The results also indicate that selecting the appropriate activator during synthesis significantly improves the degree of substitution (DS) and therefore the water barrier of the alginate polymers. For example, derivatization with a C12 amine chain and employing 2-chloro-1-methylpyridinium iodide (CMPI) as the activator resulted in a DS of 79% and a notable enhancement in the alginate polymer hydrophobicity compared to only 36% for the product obtained using 1-3-(dimethylamino)propyl-3-ethylcarbodiimide hydrochloride (EDC-HCl) and no water barrier enhancement. The TGA results confirm that the modified polymer with an 18-carbon chain length contains 86% less water retention than the original alginic acid compound. These functionalized alginate derivatives were then utilized to develop coatings and evaluate their water barrier properties for potential packaging applications. The optimal coating system was composed of a 10% w/v polymer concentration and a 10% w/w acetyl tributyl citrate (ATBC) plasticizer in Cyrene. The formulation exhibited consistent hydrophobicity over the testing time, maintaining its effectiveness until water evaporated from the coating. Therefore, amidation of alginate offers a promising route to improve the water barrier properties of naturally occurring carbohydrates to serve as coating materials for food packaging.