Preparing and charactizing starch-based potassium releasing superabsorbent polymer, and optimizing water absorption and potassium release

To prepare the cassava starch-based potassium releasing superabsorbent polymer (AM-SAP), an orthogonal experiment and range analysis were applied to optimize the synthesis conditions for the best water absorbency and potassium release capacity. A comprehensive feasibility study on the potassium release amount and release rate by activated muscovite (AM) sample was investigated as a function of cosolvent dosage, reaction temperature and reaction time. The water absorbency, repeated water absorbency, water holding capacity, water absorption swelling process and cumulative potassium release amount of AM-SAP samples were all compared with different AM dosages. The structural and morphological characteristics of the raw muscovite (RM), AM and AM-SAP samples were compared by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope analysis (SEM). The results showed that the RM samples were best activated as reaction temperature and time of 950 ℃ and 2 h, respectively, with the mass ratio of NaCl and muscovite was 2:1. Under such condition, the potassium release amount and release rate could reach by 92% and 32.4 mg/g, respectively. The maximum water absorbency of AM-SAP sample was 358 g/g in the distilled water and 155 g/g in the tap water, respectively, which was determined as the starch content, crosslinking agent, initiator, acrylamide and neutralization degree were 20%, 0.02%, 0.4%, 25% and 80%, respectively. The AM amount, that affected the water absorption and potassium release capacity of AM-SAP sample were quite different. Compared with the pure cassava starch-based superabsorbent polymer, the repeated water absorbency of AM-SAP sample was obviously larger than that of the former with the AM amount of 20%. While the cumulative potassium release amount of AM-SAP sample was increased with the increasing of AM dosage. After 9 d immersion at the temperature of 25 ℃, the cumulative potassium release amount and release rate were increased by 2.59 and 3.64 times, respectively. The AM-SAP sample could maintain more than 40% of the initial water content after 25 h later, even at the temperature of 40 ℃. The swelling process of AM-SAP sample conformed to the non-Fickian diffusion, which was determined by the diffusion of water molecules and the relaxation process of polymer chain segments. The FTIR data confirmed that AM existed in the AM-SAP in the form of physical filling, and some powder reacted with organic matter in the process of polymerization. The SEM showed that the rough surface of the AM-SAP sample was beneficial to the performance of water absorption and potassium release. It was preliminarily concluded that the AM-SAP is expected to be widely used in agricultural production due to its capacities of water retention, repeated water absorption and slow releasing and promotion of potassium.