淀粉基赋钾保水剂的制备表征与保水释钾性能优化

为优化合成一种兼具吸水和释钾功能的淀粉基赋钾保水新材料，该研究通过单因素和正交试验，比较分析了不同反应条件对淀粉基赋钾保水剂吸液释钾性能的影响；并通过红外光谱和扫描电镜表征了原矿白云母、活化白云母和赋钾保水剂的结构和形貌特征。结果表明：反应温度950 ℃，助熔剂NaCl和白云母质量比2:1，煅烧2 h时对白云母的活化效果最好，释钾率和释钾量分别达到92%和32.4 mg/g。淀粉、交联剂、引发剂、丙烯酰胺添加量和中和度分别为20%、0.02%、0.4%、25%和80%，活化白云母用量20%时，赋钾保水剂达到最大吸液倍率358 g/g（蒸馏水）和155 g/g（自来水），且重复吸水倍率也明显大于纯淀粉基保水剂；40 ℃下，25 h后赋钾保水剂仍能维持40%以上的初始水分。该赋钾保水剂吸水溶胀过程符合非Fickian扩散，由水分子扩散和高分子链段松弛过程共同决定。赋钾保水剂的累积释钾量随活化白云母用量的增加而增大，静水浸提9 d后，钾释放量和释放率分别增加2.59和3.64倍。活化白云母除了部分以物理填充形式存在于淀粉基保水剂中外，还有部分粉末在聚合过程中与有机物发生了反应。赋钾保水剂粗糙的表面有利于其吸水释钾性能的发挥。分析认为，该研究中合成的淀粉基赋钾保水剂兼具保水持水和重复吸水性能，而且对钾素具有缓释和促释作用。

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.