Fabrication and properties of a novel superabsorbent composite based on coco peat and poly (acrylic acid) cross-linked trimethylolpropane trimaleate under ultraviolet irradiation

A series of novel poly(acrylic acid)/coco peat (PAA/CP) superabsorbent composites were prepared via the ultraviolet irradiation copolymerization of acrylic acid monomer (PAA) and coco peat cellulose (CP) in the presence of the cross-linker trimethylolpropane trimaleate. The physico-chemical structures of obtained PAA/CP were characterized by Fourier transform infrared spectroscopy, thermogravimetry/derivative thermogravimetry, X-ray diffraction, and scanning electron microscopy, respectively. The critical parameters of affecting the water absorbency of PAA/CP, including the cross-linker level, amount of CP and reaction time, were studied in detailed. The experimental results showed that the PAA/CP samples exhibited the maximum swelling value of 523.09g/g in distilled water and 40.52g/g in 0.9wt % NaCl solution. The swelling behaviors of PAA/CP were significantly relied on the concentration of salt solution and the pH of external solution. The effect of ions species on the swelling performance was in the order: Na+>Ca2+>Fe3+ , and in pH 2.2 and 7.2 aqueous solutions PAA/CP composites displayed better pH-responsiveness and reversible on-off switching characteristics. Urea, as an agrochemical model, was loaded into PAA/CP substrate to supply with nitrogen nutrient. The test of their loading and releasing diffusion performance of urea suggested that the urea loading percentage of PAA/CP was remarkably dependent on the concentration of aqueous urea solutions and the release of urea from loaded PAA/CP samples in water followed a non-Fickian mechanism. Owing to their considerable good water absorption capacity, slow urea release, economical and environment-friendly merits, PAA/CP composites could be exploited for the agriculture applications. Copyright (c) 2016 John Wiley & Sons, Ltd.