Preparation And Evaluation Of Hydrophobic Modified Sodium Lignosulfonate Coated Urea

Slow-release fertilizer is one of the most effective methods to solve the ecological and environmental problems caused by the use of chemical fertilizers in agricultural production.In this paper,sodium lignosulfonate was used as a raw material to prepare modified sodium lignosulfonate with hydrophobicity and thermoplastic film-forming ability.It avoids the dependence on solvents in traditional coating technology,realizes solvent-free coating by relying on the thermoplastic ability of modified materials,and evaluates the sustained release performance of modified lignin material coated urea.The slow-release fertilizer prepared from lignin can not only increase the humic acid content of the soil and continuously improve the soil physical and chemical environment,but also avoid the waste of resources.At the same time,the improved solvent-free coating process can also provide useful suggestions for the preparation and research of slow-release fertilizers.The main conclusions of the study are as follows:1.Through the cross-linking reaction of sodium lignosulfonate and epichlorohydrin,the molecular weight is amplified to prepare four kinds of cross-linked sodium lignosulfonate(CSL)with different molecular weights,molecular weight:CSL0<CSL-50<CSL-100<CSL-150.Four cross-linked gradient cross-linked sodium lignosulfonate and lauryl chloride are reacted to obtain four esterified modified crosslinked sodium lignosulfonate(ECSL)with glass transition temperature,Tg(ECSL-0):31.15℃,Tg(ECSL-50):65.03℃,Tg(ECSL-100):92.27℃,Tg(ECSL-150):153.92℃.The modification solves the problem of strong hydrophilicity and poor thermoplasticity when lignin is used as a coating material,making it possible for ECSL to be used as a coating material.The optimized modification conditions of cross-linked sodium lignosulfonate and lauryl chloride are:reaction time 2.5h,reaction temperature 20℃,pyridine(mL):CSL-100(g)is 6:1,acid chloride(mL):CSL-100(g)is 6:1.2.On the basis of the traditional drum coating process,using the thermoplastic ability of the prepared ECSL-100,the coating material ECSL-100 melts and adheres to the surface of the heated urea particles and is formed by heat preservation,successfully realizing a solvent-free coating.The coating layer formed by the coating process is dense and uniform,and the film-forming effect is good.Explore the influence of four factors,such as the heating temperature of urea,the rotating speed of the drum coater,the degree of sieving of the coating material,and the number of coatings,on the coating rate of the solvent-free coating process.The optimization results show that the coating temperature is≥100℃,the best coating rotation speed is 40r/min,and the coating effect is good when the sieving mesh number of the coating material is≥100 meshes.The impact of the number of coatings on the coating rate is proportional to the number of coatings.In addition,after the first coating of different coating materials,the increase of the coating rate is similar each time in the subsequent coating process.3.SR100(CSL-0:ECSL-100=0:100),SR90(CSL-0:ECSL-100=10:90),SR80(CSL-0:ECSL-100=20:80),SR70(CSL-0:ECSL-100=30:70)and SR60(CSL0:ECSL-100=40:60)have different hydrophobicity.The hydrophobicity is prepared by mixing 100 mesh ECSL-100 and 200 mesh CSL-0.The coating application of the coating material on the coated urea It exhibits good film-forming ability,and the slowrelease performance of the slow-release urea fertilizer prepared from different coating materials is adjustable.The best performance is SR100 coated urea,and the release time of 86.37%under the conditions of soil column leaching is 44 days.The first-order kinetic equation,Higuchi kinetic equation,and Ritger-peppas kinetic equation were fitted for the sustained release process of coated urea.The fitting results show that the slow release process of coated urea has a good correlation with the first-order kinetic equation,and the slow release process is stable,especially when the content of ECSL100 is high,the kinetic fitting characteristics of SR100 and SR90 are good,and the error is small,high credibility.