玉米秸秆基纤维素保水缓释肥制备及应用

为解决农业生产中秸秆废弃物不合理的使用导致资源浪费和农业污染问题,探讨秸秆基纤维素保水缓释肥的生产成本、在农业上应用的可行性,对秸秆基保水缓释肥的特性及性能进行了试验研究。以玉米秸秆为主要原料,利用硝酸-水溶液一步提取玉米秸秆纤维素,采用溶液聚合法将玉米秸秆纤维素与丙烯酸、丙烯酰胺单体进行接枝共聚反应,并利用半互穿网络技术制备具有保水功能的缓释肥(MS-CPPC),引入聚磷酸铵作为氮、磷营养物质。运用正交试验对制备条件进行优化,并利用扫描电镜(scanning electron microscopy)、红外光谱(flourier transform infrared spectroscopy)、X射线光电子能谱(X-ray photoelectron spectroscopy)、热重分析技术(thermo gravimetric analysis)对制备的产品进行表征;研究了MS-CPPC的吸水性以及在水和土壤中的氮磷缓释性。结果表明,制备的最优工艺为:纤维素与丙烯酸质量比为1:6、交联剂与纤维素质量比为1:20、引发剂与纤维素质量比为5:1、聚乙烯醇共聚物与纤维素质量比为5:2。该保水缓释肥有良好的吸水性,吸水率为443.2 g/g;混施到土壤中对水分入渗率和累积入渗量都有明显的促进作用,在实际应用中可以防止土壤表层滞水;同时,该产品具有氮磷缓释特性,24 h和30 d的氮、磷累计释放量分别为14.69%、13.01%和67.11%,55.74%,氮磷释放性能符合符合缓释肥料国家标准;土柱试验表明,添加MS-CPPC可以显著减少氮磷淋溶损失。利用玉米秸秆制备的保水性缓释肥具有制造成本低、环境友好等特点,并且可以实现秸秆资源高效利用。

Preparation and application of corn straw cellulose-based fertilizer with integration of water-retaining and slow-release

Abstract: Recycling of crop straws has been practiced in every conventional agriculture. The increase in the yield of crop straws annually has given rise to a series of serious environmental problems for leaving them to decay or burning on the field surfaces after the harvest. In order to solve these recycling problems of resource wastes during the utilization of crop straws, an experimental study was conducted on the properties and performance of water-retaining concurrently slow-release straw-based cellulose fertilizers, further to discuss their production cost and applicability to the modern agriculture. In this study, the aqueous solution of nitric acid was used to extract the required cellulose from corn straws. A novel semi-interpenetrating polymer networks (semi-IPNs) superabsorbent resin with slow-release fertilizers (MS-CPPC) were prepared through solution polymerization based on corn straw cellulose polymer and linear polyvinyl alcohol copolymer (PVA-APP). Ammonium polyphosphate (APP) was also introduced to supply the nutrients of nitrogen and phosphorus. The design of orthogonal test has been used to optimize the fabrication parameters of the obtained products, as well as the water absorbency of MS-CPPC and the slow-release performance of nutrients in water and soil. The prepared products were also characterized using scanning electron microscopy, flourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermos-gravimetric analysis. The experimental results indicated that acrylic acid (AA) acrylamide(AAm) were grafted onto the chain of corn straw cellulose, and PVA-APP was also involved by semi-interpenetrating with them in the synthesis process of fertilizers. This finding demonstrated that the formation of semi-interpenetrating networks can greatly improve the stability of raw materials. Orthogonal experiments showed that the MS to the acrylic acid mass ratio of 1:6, the MBA to MS mass ratio of 20:1, the initiator to MS mass ratio of 5:1, the PVA-APP to MS mass ratio of 5:2.The fertilizer based on the semi-IPNs superabsorbent resin (SAR) showed excellent water absorbency with the water absorption of 443.2 g/g, while significantly reduced the leaching losses of fertilizers in comparison to traditional fertilizers. Therefore, the application of this products would provide an effective way to solve the leaching loss of fertilizers that often occurred in agricultural fields. The results from the infiltration test showed that MS-CPPC that applied in soil could enhance water absorbency during the infiltration, and effectively inhibit the formation of the soil crust during the rainfall due to the increase in the infiltration rate of soil water. The accumulated release rates of nitrogen and phosphorus in distilled water for one day and 30 days were 14.69%, 13.01% and 67.11%, 55.74%, respectively, indicating the sustained release of nutrients. The release behavior of MS-CPPC was also in good agreement with the National standard on sustained-release fertilizers (GB/T 23348-2009), confirming excellent property of slow release in soil. The slow release behavior of the products can attributed that to a porous structure of the semi-interpenetrating polymer networks, which can restrict the diffusion rate of water molecules into the hydrogel network to delayed dissolution of the encapsulated fertilizer. In the Korsmeyer-Peppas model, the release patterns of nitrogen and phosphorus in the MS-CPPC both follow Fick diffusion and polymer chain relaxation according to the n value. The superabsorbent resin with straw-based cellulose fertilizers become therefore expected to share the combined properties of water-retaining and slow-release, further to provide reducing the production costing while promoting comprehensive utilization of crop straws.