聚乙烯醇/壳聚糖膜制备及其包膜尿素特性

Preparation of polyvinyl alcohol/chitosan membranes and their envelope property for relative coating urea granules

为解决传统肥料养分利用率低,以及一般聚合物包膜肥料的膜材料难以降解、养分释放速率不可控等问题,该研究以聚乙烯醇(PVA)为膜基材,通过与壳聚糖(CS)共混、使用戊二醛(GA)交联、添加纳米SiO_(2)3种不同的方式,制备了3种膜:PVA/CS膜、PVA/CS/GA膜、PVA/CS/GA/纳米SiO_(2)膜,此外,制备了纯PVA膜作为对比。对4种膜进行了吸水率(Q)、生物降解性(De)、养分渗透系数(Ps)等表征,结果表明:CS的添加提升了膜的生物降解率,GA交联可以延缓膜在土壤中的生物降解速率,而纳米SiO_(2)的添加对膜的生物降解性影响不大,总体来说4种膜都显示出良好的生物降解性(77 d内的生物降解率在30%~60%);相比于PVA膜,PVA/CS、PVA/CS/GA和PVA/CS/GA/纳米SiO_(2)膜的吸水率分别降低43.00%、68.79%和82.73%;相比于PVA/CS膜,PVA/CS/GA和PVA/CS/GA/纳米SiO_(2)膜的养分渗透系数分别降低48.51%和57.59%,说明CS的添加、GA的交联和纳米SiO_(2)的添加都增强了PVA膜的疏水性。将4种膜液通过转鼓包衣机包覆在尿素颗粒表面制得了4种包膜尿素(PCU)颗粒(PCU-PVA、PCU-PVA/CS、PCUPVA/CS/GA和PCU-PVA/CS/GA/纳米SiO_(2)),分别使用土埋法测定和数学模型拟合了氮素释放行为,结果显示4种PCU的氮释放量达到90%时所需的时间分别为5、11、23、28 d;氮素释放行为符合一级动力学模型,释放速率常数(k)依次减小,分别为0.3654、0.2333、0.1127、0.0926,且与膜的养分渗透系数(Ps)呈线性关系,相关系数(R2)为0.9991。该研究提供了系列生物降解性能良好、养分释放速率可控的聚乙烯醇/壳聚糖膜材料,并成功地应用于包膜尿素颗粒的制备,更方便和有效地指导PCU的施用。

Fertilizer has been the ever-increasing demand in agricultural production in recent years,particularly with the escalating demand for food.Simultaneously,the low efficiency of nutrient utilization and environmental risks of fertilizers have posed substantial challenges in the world.Alternatively,polymer-coated fertilizers can play a pivotal role in nutrient utilization efficiency,thus reducing the fertilizer application rates and environmental pollution risks.This study aims to improve the membrane materials of typical polymer-coated fertilizers for the high nutrient utilization efficiency in conventional fertilizers.Polyvinyl alcohol(PVA)was also employed as the membrane substrate,in order to relieve the secondary pollution and uncontrollable nutrient release rates.Three types of membranes—PVA/CS membrane,PVA/CS/GA membrane,and PVA/CS/GA/nano SiO_(2) membrane—were prepared using three methods:blending with chitosan(CS),crosslinking with glutaraldehyde(GA),and incorporating nano SiO_(2).Additionally,pure PVA membranes were prepared for comparison.The four types of membranes were characterized using scanning electron microscopy(FE-SEM),water absorption(Q),biodegradability(De),and nutrient permeability coefficient(Ps).Results indicated that there were excellent dispersion and compatibility of nano SiO_(2) in the PVA/CS membrane solution.Furthermore,the biodegradation rates of the four membranes also exhibited gradual increments during the initial 21 days.Subsequently,biodegradation rates escalated rapidly from the 21st to the 56th day,followed by a slower growth rate after the 56th day.The CS was incorporated to enhance the membrane biodegradation rates,while the GA crosslinking contributed to the less membrane biodegradation in soil.However,the addition of nano SiO_(2) had minimally impacted the membrane biodegradation rates.Overall,all four membranes displayed favorable biodegradability,with the biodegradation rates ranging from 30%to 60%within 77 days.The water absorption of PVA/CS,PVA/CS/GA,and PVA/CS/GA/nano SiO_(2) membranes decreased by 43.00%,68.79%,and 82.73%,respectively,compared with the PVA membranes.Furthermore,the nutrient permeability coefficients of PVA/CS/GA and PVA/CS/GA/nano SiO_(2) membranes decreased by 48.51%and 57.59%,respectively,compared with the PVA/CS membranes.Therefore,the addition of CS,GA crosslinking,and nano SiO_(2) all contributed to the hydrophobicity of PVA membranes.Four types of coated urea(PCU)particles—PCU-PVA,PCU-PVA/CS,PCU-PVA/CS/GA,and PCU-PVA/CS/GA/nano SiO_(2)—were prepared,where these membrane solutions were applied to the urea particles using a drum coating machine.The nitrogen release behavior was evaluated using the soil burial.The time required for the nitrogen release of the four PCUs to reach 90%varied significantly,recorded at 5,11,23,and 28 days,respectively.On the 5th day,the nitrogen released from PCU-PVA was the highest at 90.64%,whereas the lowest was from PCU-PVA/CS/GA/nano SiO_(2) at 49.32%.The CS,GA crosslinking and nano SiO_(2) enhanced the membrane hydrophobicity,which in turn reduced the nitrogen release rate.The nitrogen release behavior of all four PCUs followed a first-order kinetic model,with the release rate constants(k)decreasing progressively—0.3654,0.2333,0.1127,and 0.0926,respectively—and correlating linearly with the nutrient permeability coefficient(Ps)of the membranes.The correlation coefficient(R2)was impressively high at 0.9991.A series of polyvinyl alcohol/chitosan coating materials were introduced with excellent biodegradability and controllable nutrient release rates,suitable for use in polymer-coated fertilizers.These materials were effectively applied in the production of coated urea particles.A first-order kinetic model of PCU nitrogen release was established with the membrane nutrient permeability coefficient as a key parameter,in order to more efficiently and effectively guide the application of PCU.