纳米SiO2–聚乙烯醇–γ聚谷氨酸复合膜材料制备及其性能研究

Preparation and properties of nano-SiO2–polyvinyl alcohol–γ-polyglutamic acid composite film materials

【目的】聚乙烯醇(polyvinyl alcohol,PVA)作为缓释肥包膜材料具有价格低廉、透性好、环保、少残留的优点,但耐水性能差,制成包膜肥料进入土壤后缓释效果不持久。γ聚谷氨酸(γ-PGA)是一种原料易得的肥料增效剂,利用纳米二氧化硅(nano-SiO2)和γ-PGA对聚合物PVA进行改性,并用改性后的PVA制备了缓释材料,优化nano-SiO2、γ-PGA和戊二醛的配比参数。【方法】试验采用三因素三水平L9(33)正交设计,三因素三水平是PVA浓度(因素A)4%、6%、8%,γ-PGA与PVA的质量配比(因素B)0.8∶3、1∶3、1.2∶3,戊二醛占PVA与γ-PGA体积之和比例(因素C)0.1%、0.2%、0.3%,以不添加戊二醛的9个处理做对照。用有机高分子聚合法制备复合膜,分析了不同原料配比制备的膜材料的吸水性和渗透性能,找出最优原料配比。在此基础上,在上述包膜材料中分别加入5、10和20 g/kg的nano-SiO2和少量无水乙醇制成复合膜,测定复合膜材料的吸水率、渗透率,分析了膜的红外光谱特征和表面微观结构变化,探讨其改性成膜机理。【结果】加入交联剂戊二醛后,复合膜材料的吸水率和渗透率均显著降低。当PVA浓度为4%,γ-PGA与PVA质量比为1.2∶3,戊二醛体积分数为0.3%时,复合膜材料的吸水率最低,为118%,铵离子和水的渗透率分别比对照降低了46.8%和23.0%。添加nano-SiO2后,各处理膜的吸水率均随nano-SiO2添加量的增加呈现先升高后降低的变化,当添加量为20 g/kg时,复合膜材料吸水率和NH4+渗透率最低,与不加nano-SiO2相比,复合膜材料吸水率和NH4+渗透率分别降低了6.8%~38.2%和23.8%~53.2%,而水渗透率增加了38.4%~67.7%。红外分析光谱结果表明,PVA和γ-PGA反应生成醚键;添加nano-SiO2处理的―OH伸缩振动峰变宽,透过率增加,并且出现了Si―O―Si摇摆振动和反对称伸缩振动;同时,从官能团特征看出复合膜中仍存在未反应的γ-PGA。扫描电镜结果显示纳米SiO^2-聚乙烯醇-γ聚谷氨酸复合膜材料的表面更光滑,致密均一,这可能是包膜材料能减缓氮素释放的主要原因。【结论】nano-SiO2与PVA、γ-PGA、戊二醛分子结合生成的交联纳米复合膜材料亲水基团数目减少,膜材料吸水率降低,提高了包膜材料的缓释性能,更适用于颗粒肥料包膜。膜材料中存在的游离γ-PGA可以继续发挥肥料增效剂的作用。

【Objectives】Polyvinyl alcohol(PVA),as a coating material of slow-released fertilizer,has advantages of low price,good permeability and friendly to environment.However,the water resistance of PVA film is poor.The slow-released effectiveness of fertilizer coated with the PVA does not last long in soil.γ-polyglutamic acid(γ-PGA)is a kind of environmental-friendly fertilizer synergist and easily obtained.In this study,we modified PVA properties by adding nano-SiO2,γ-PGA and glutaraldehyde,then prepared composite coating films using the modified PVA.The processing parameters were optimized.【Methods】The experiment adopted L9(33)orthogonal experimental design.The concentrations of PVA(factor A)were 4%(A1),6%(A2),8%(A3);the mass ratios ofγ-PGA to PVA(factor B)were 0.8∶3(B1),1∶3(B2),1.2∶3(B3);the volume fractions of glutaraldehyde inγ-PGA and PVA(factor C)were 0.1%(C1),0.2%(C2),0.3%(C3).Meanwhile,nine treatments without cross-linker were conducted as blank control.Organic high molecular polymerization method was used to prepare the composite materials,and the hydrophilism and permeability of composite materials were tested.Then composite films were prepared by adding 5,10 and 20 g/kg of nano-SiO2 and anhydrous ethanol.The hydrophilism,permeability,infrared spectrum characteristics and surface microstructure of composite materials were measured.【Results】The hydrophilism and permeability of the composite materials were significantly reduced after adding crosslinking agent.Under condition of factor A 4%,B 1.2∶3 and C 0.3%,the hydrophilism of composite materials was the lowest(118%),and the NH4+and water permeability were reduced by 46.8%and 23.0%,compared with the control.With increasing of nano-SiO2 addition,the hydrophilism of each treatment showed an up-and-down trend.When adding 20 g/kg of nano-SiO2,the hydrophilism and NH4+permeability of composite films were the lowest,which were decreased by 6.8%-38.2%and 23.8%-53.2%,respectively,compared with no nano-SiO2 treatment.However,the water permeability was increased by 38.4%-67.7%.The results of infrared spectroscopy indicated that new ether bonds between PVA andγ-PGA were generated during the reaction.With nano-SiO2 addition,the stretching vibration peak of―OH was widened,the transmittance was increased,new rocking vibration of Si―O―Si and antisymmetric stretching vibration of Si―O―Si appeared.Additionally,unreactedγ-PGA still existed in composite films according to the functional groups characteristics.The surface of the nano-SiO2-PVA-γ-PGA composite film material was getting smoother and more uniform.【Conclusions】In the composite film materials,which is prepared by crosslinking nano-SiO2 with PVA,γ-PGA and glutaraldehyde,the number of hydrophilic groups is significantly decreased,resulting in the decreased water absorbency and improved sustained-release property.Thus,the composite film materials become more suitable for fertilizer coating materials.Besides,the residualγ-PGA could still play the role of fertilizer synergist.