Design And Synthesis Of Lignin-Derived Hydrogels And Study On Its Application In Slow Release Fertilizer

Hydrogels are frequently employed as soil moisture retention agents and nutrient carriers in agriculture due to their excellent properties,including high elasticity,high toughness,stimulus responsiveness and high water absorption capacity.In recent years,many researchers have focused on the research of agricultural slow release fertilizers with water absorption and retention properties by combining hydrogels with fertilizers.To reduce the pollution of traditional slow release fertilizers on soil environments and production costs,a series of double-layered slow release fertilizer samples were prepared and their properties were investigated by using natural polymer lignin as the matrix material and chemical modification techniques in this paper.The specific research contents and results are as follows.（1）Firstly,polyvinyl alcohol（PVA）/methyl cellulose（MC）blends were prepared by solution blending method,and monolayer coated fertilizer（PM-SRF）was prepared by spraying the blends on the surface of urea pellets as the inner coating using a spray gun in small amounts several times.Then,alkaline lignin-based coating material（LAP）was prepared by graft copolymerization method using acrylic acid（AA）and acrylamide（AM）as functional monomers,alkaline lignin as a template carrier,N,N’-methylenebisacrylamide（MBA）as a crosslinking agent,potassium persulfate（KPS）as an initiator,and attapulgite（ATP）as an additive.The alkaline lignin water-retaining double-layer slow release fertilizer（PML-SRF）was then prepared by uniformly coating LAP on the outer layer of PM-SRF using the disc method,and the optimal synthesis conditions were explored.The water retention properties and slow-release properties of single-layer PM-SRF and double-layer PML-SRF were investigated by comparative analysis.The results showed that both single layer PM-SRF and double layer PML-SRF had better water retention and nutrient release performance compared to urea.The fertilizer nutrient release of the single layer PM-SRF reached the balance after 36 days,and the cumulative nutrient release rate could reach 92.36%.The fertilizer nutrient release of the double layer PML-SRF prepared under the conditions of n（AA）:n（AM）of 1:1,alkaline lignin dosage of4.17wt%,W_MBA/W_{（L+AA+AM）}of 4wt%,W_KPS/W_{（L+AA+AM）}of 1wt%,and ATP dosage of12.8wt%reached the equilibrium after 42 days,and the cumulative nutrient release rate could reach 85.10%.（2）Firstly,sodium alginate-zinc ammonium phosphate as the core of the fertilizer was prepared by ion exchange method.Then,polylactic acid（PLA）/cellulose acetate butyrate（CAB）blends were prepared using the solution blending method,and the PLA/CAB blends were sprayed onto the surface of the fertilizer kernel using a spray gun to prepare a monolayer coated fertilizer（PC-SRF）.Then,the graft copolymerization method was used to prepare the sodium lignosulfonate coating material（LSM）with AA,AM and lauryl methacrylate（LMA）as functional monomers,sodium lignosulfonate（LS）as a template carrier,respectively,MBA as crosslinker and ammonium persulfate（APS）as initiator.The epoxy-aminated lignin coating material（ECD）was prepared by free radical polymerization in alkaline solution with epichlorohydrin（ECH）as a crosslinking agent,homemade epoxy-aminated lignin（EAL）as a carrier substance,β-cyclodextrin（β-CD）and seafoam powder as additives.Finally,sodium lignosulfonate and epoxy-aminated lignin water-retaining double layer slow release fertilizers（PSC-SRF and PEC-SRF）were prepared by uniformly coating LSM and ECD on the outer layer of PC-SRF,respectively,using the disc method,and their optimal synthesis parameters were discussed.The water retention performance and slow release performance of PC-SRF,PSC-SRF and PEC-SRF were investigated by comparative analysis.The results showed that PC-SRF,PSC-SRF and PEC-SRF all had better water retention and nutrient release performance than that of sodium alginate-zinc ammonium phosphate.The soil water retention rate after the addition of PSC-SRF and PEC-SRF could still reach more than 5%after 45 days,showing good soil water retention performance.The release of urea and phosphorus from the monolayer PC-SRF reached equilibrium after 34 and 36 days,and their cumulative release rates could reach 87.09%and 86.19%,respectively.The release of urea and phosphorus from bilayer PSC-SRF prepared at an EAL content of 1.50 g,β-CD:ECH of 1:10,seafoam of 1.00 g,W_LMA/W_{（AA+AM+LMA）}of 8.30wt%,LS of 1.00 g,MBA of 0.20 g,and APS of 0.10 g reached equilibrium after 38 and 40 days,and their cumulative release rates could reach 83.57%and 82.07%,respectively;the release of urea and phosphorus in the double layer PEC-SRF prepared under the same conditions reached equilibrium after 38 and 42 days,respectively,and their cumulative release rates could reach 81.47%and 81.66%,respectively.