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.