Synthesis and characterization of biocompatible poly(maleic acid-co-citric acid) microparticles as a smart carrier for thiamine

Impact of Modifications from Potassium Hydroxide on Porous Semi-IPN Hydrogel Properties and Its Application in Cultivation

This study synthesized and modified a semi-interpenetrating polymer network hydrogel from polyacrylamide, N,N'-dimethylacrylamide, and maleic acid in a potassium hydroxide solution. The chemical composition, interior morphology, thermal properties, mechanical characteristics, and swelling behaviors of the initial hydrogel (SH) and modified hydrogel (SB) in water, salt solutions, and buffer solutions were investigated. Hydrogels were used as phosphate fertilizer (PF) carriers and applied in farming techniques by evaluating their impact on soil properties and the growth of mustard greens. Fourier-transform infrared spectra confirmed the chemical composition of SH, SB, and PF-adsorbed hydrogels. Scanning electron microscopy images revealed that modification increased the largest pore size from 817 to 1513 µm for SH and SB hydrogels, respectively. After modification, the hydrogels had positive changes in the swelling ratio, swelling kinetics, thermal properties, mechanical and rheological properties, PF absorption, and PF release. The modification also increased the maximum amount of PF loaded into the hydrogel from 710.8 mg/g to 770.9 mg/g, while the maximum % release of PF slightly increased from 84.42% to 85.80%. In addition, to evaluate the PF release mechanism and the factors that influence this process, four kinetic models were applied to confirm the best-fit model, which included zero-order, first-order, Higuchi, and Korsmeyer-Peppas. In addition, after six cycles of absorption and release in the soil, the hydrogels retained their original shapes, causing no alkalinization or acidification. At the same time, the moisture content was higher as SB was used. Finally, modifying the hydrogel increased the mustard greens' lifespan from 20 to 32 days. These results showed the potential applications of modified semi-IPN hydrogel materials in cultivation.

Maleic acid as an important monomer in synthesis of stimuli-responsive poly(acrylic acid-co-acrylamide-co-maleic acid) superabsorbent polymer

Poly(acrylic acid-co-acrylamide-co-maleic acid) (p(AA-co-AM-co-MA)) superabsorbent polymer was synthesized from acrylic acid (AA), acrylamide (AM), and maleic acid (MA) via free radical copolymerization. Results showed the presence of maleic acid in structure of superabsorbent has the key and superior role in creating a smart superabsorbent. The structure, morphology, and strength of the superabsorbent were characterized using FT-IR, TGA, SEM, and rheology analysis. The effect of different factors was investigated to determine the ability of water absorbency of the superabsorbent. According to optimized conditions, the water absorbency capacity of the superabsorbent in distilled water (DW) was 1348 g/g and in a solution containing 1.0 wt.% NaCl (SCS) was 106 g/g. The water retention ability of the superabsorbent was also investigated. The kinetic swelling of superabsorbent was identified by Fickian diffusion and Schott's pseudo-second-order model. Furthermore, the reusability of superabsorbent was studied in distilled water and saline solution. The ability of superabsorbent was investigated in simulated urea and glucose solutions, and very good results were obtained. The response ability of the superabsorbent was confirmed by swelling and shrinking behavior against changes of temperature, pH, and ionic strength.