Bio-degradable, fully bio-based, thermally cross-linked superabsorbent polymers from citric acid and glycerol

Abstract

In this study, cross-linker free, fully bio-based, biodegradable superabsorbent polymers (SAPs) were synthesized from the multi-functional monomers citric acid (CA), monosodium citrate (MSC) and glycerol (GLY) by polycondensation and subsequent thermal self cross-linking. All monomers (CA, MSC, GLY） used in this study were not only bio-based but also non-toxic. All of them contain more than two hydrophilic groups in one molecule, which shows great potential to be used in the production of SAPs. The structure, water absorbance capacity and biodegradability of the resulting SAPs were investigated in detail. Upon removal of the soluble fraction, the SAPs have a gel content of approximately 60%, and exhibit a maximum absorption capacity of deionized water of 24 ± 2 g/g Moreover, the prepared SAPs show good biodegradability at 25 oC (40% biodegradability after 28 days) in an activated sludge-containing medium and are accordingly promising eco-friendly materials for potential use in our environment, not generating persistent microplastics like commercial non-biodegradable SAPs based on neutralized polyacrylic acid and polyacrylamides. Therefore, the bio-based SAPs described in this paper have a promising application potential for sustainable chemical industries including hygiene products and agricultural products, e.g. controlled-release fertilizer coatings and soil improvers.