Fully Biobased, Biodegradable Superabsorbent Polymers Based on Citric Acid and Sorbitol

Abstract

This study presents the development of a series of fully biobased, biodegradable superabsorbent polymers (SAPs) from citric acid, its sodium salt, and sorbitol. An approach combining polycondensation and subsequent thermal cross-linking in the absence of any externally added cross-linker is utilized for the fabrication of these SAPs, followed by comprehensive characterization to analyze their composition and structure and to assess their water absorption capacity and biodegradability. An optimized synthesis of superabsorbent polymers (SAPs) is achieved at a 1:1 molar ratio of the combined citric acid (CA) and its sodium salt to sorbitol. This specific formulation is found to be critical for producing a precursor polymer with the maximum molecular weight, which, in turn, yields SAPs exhibiting the highest water absorption capacity. Furthermore, when the neutralization degree (ND) of CA in the monomer feed is 70%, the resulting extracted SAPs exhibit the highest water absorption capacity of approximately 18 ± 2 g/g SAPs with an approximate yield after an extraction of 75%. Most importantly, the resulting SAPs exhibit superior biodegradability under mild conditions in activated sludge. The findings underscore the possibility of the production of synthetic, renewable, and biodegradable SAPs from citric acid and the biobased sorbitol monomer. The observed biodegradability, thereby avoiding the formation of persistent microplastics, is extremely important with respect to environmental concerns and the advancement of sustainable material development.