Production of cellulose-based superabsorbent polymers for soil water retention
Abstract
Superabsorbent polymers (SAPs) have attracted tremendous attention, with researchers noting that their high water absorption capacity (AC) is valuable for various applications, especially in agricultural contexts. Two types of materials can be used to produce SAPs: fossil-based (which are harmful to the environment) and bio-based (which are significantly more environmentally friendly, given their biodegradability and minimal toxic side effects). Although bio-based SAPs (Bio-SAPs) are preferable due to their environmental merits, their preparation tends to be time consuming and labour intensive, and their AC is still far below expectations. To address these problems, a novel, eco-friendly, cellulose-based superabsorbent polymer (Cellulo-SAP) was developed in this study through facile preparation via free radical synthesis using esterified pure cellulose. First, pure cellulose was esterified with maleic anhydride to evaluate the effects of the catalyst, solvent, and cellulose–maleic anhydride molar ratio. Second, an approach for graft copolymerization of esterified pure cellulose with acrylic acid was developed; this involved free radical synthesis using polyethylene glycol diacrylate as the crosslinker, resulting in the production of Cellulo-SAP. Third, the absorbency, thermal/pH stability, reusability, and biodegradability of Cellulo-SAP were evaluated. This new polymer demonstrated reusability as a water reservoir, in addition to high thermal and pH stability. More importantly, Cellulo-SAP achieved an AC of 475 g/g and exhibited superior biodegradability compared to a commercial, fossil-based SAP (Sigma-Aldrich sodium polyacrylate). These results suggest that Cellulo-SAP can be used in agriculture as an effective alternative to fossil-based SAPs. Finally, crude cellulose was obtained via organosolv fractionation with a mixture of acetic acid, formic acid, and water added to the biomass from cornstalk residues. The crude cellulose consisted of 13.87% lignin, 27.58% hemicellulose, and 57.46% a-cellulose, and it had a 0.41 degree of esterification after fractionation. This crude cellulose was used as a raw material to obtain a Bio-SAP (CrudeCellulo-SAP) via the methodology developed for graft copolymerization and crosslinking of Cellulo-SAP. CrudeCellulo-SAP demonstrated an AC of 369 g/g.