Synthesis Of Hindered Amine Grafted Sodium Lignosulfonate And Its Application In Avermectin Formulation

Sodium lignosulfonate(SL)is a kind of anionic macromolecule surfactant from liquid waste of papermaking industry.It has the advantages of rich source,low price and environment friendly.SL can be used as dispersant in many fields such as pesticides,coal water slurry and dyes.However,unmodified SL is usually regarded as a low-end product.Therefore,how to improve its added value by chemical modification is a research hotspot of this field.In this study,the monomer of hindered amine light stabilizer was introduced into SL molecule to improve its photostability and anti-oxidation performance,and used as a functional watersoluable polymer dispersant to expanding the application of SL in photosensitive pesticide filed.In this research,hindered amine grafted sodium lignosulfonate(SL-Temp)was synthesized by Mannich reaction using SL and amion-2,2,6,6-tetramethylpiperidine amine(Temp)as material.The successful grafting of Temp group was proved by hydrogen nuclear magnetic resonance,infrared spectroscopy,electron paramagnetic resonance and elemental analysis.The thermogravimetric analysis also showed that it had better thermal stability than the small molecular light stabilizer HALS-770.The effect of pH and the content of Temp group on solution aggregation behavior of SLTemp were studied by Zeta potential,particle size,ultraviolet absorption spectrum and atomic force microscope(AFM).The results showed that the solubility of SL-Temp decreased with the increase of Temp group content when pH<7.This is mainly due to the introduction of secondary amine groups into SL and the ionization of amine group weakens the electrostatic repulsive force between SL-Temp,then SL-Temp forms aggregate with large particle size.The AFM diagram also showed that SL-Temp will change from small aggregate to large network aggregates with the decrease of pH.Cetyltrimethylammonium bromide(CTAB)will promote the aggregation of SL-Temp in aqueous solution because of its electrostatic shielding effect.The addition of tristyrene phenol polyoxyethylene ether phosphate monoester will reduce the solution aggregation behavior of SL-Temp due to the dispersion for the aggregate of SL-Temp.Use SL-Temp as a functional dispersant to prepare 5% avermectin(AVM)suspension concentrate(SC),and the average particle size of AVM SC was less than 5 μm after sloppy sanding for 2 h.The application properties of AVM SC were studied by QCM-D absorption test,rheological test,thermal storage test and photolysis test.The results showed that the adsorption capacity of SL-Temp on AVM was increased and the electrostatic repulsive force was weakened with the increase of Temp group content.Also,the apparent viscosity of AVM SC increased with the increase of Temp group content of SL-Temp,which leads to the decrease of fluidity of AVM SC.The thixotropy of AVM SC was enhanced and improved the storage stability of SC.The suspension rate of AVM SC that prepared by different SL-Temp dispersants all kept above 99% after thermal storage,and there was no increase of particle size.The increase of Temp group content of SL-Temp can improve the chemical stability of AVM in thermal storage process and the anti-photolysis property of AVM SC.The decomposition rate of AVM in thermal storage decreased to 0% when SL-Temp was used as dispersant.The retention rate of AVM was 87.1% after 60 h UV irradiation,and the retention rate of AVM was only 73.6% when SL was used as dispersant.Lignin-based functional emulsifier(SL-Temp-CTAB)was prepared by electrostatic selfassembly with CTAB and SL-Temp,using ethanol and N,N-dimethylacetamide as solvent to prepare 1.8% AVM green emulsifiable concentrate(EC).Through the analysis of storage stability and diluted emulsion of EC,it was conclued that the AVM EC has good storage stability and emulsifying dispersibility when SL-Temp-CTAB content was 2%.Compared with commercial AVM EC,the drug-loaded microspheres with a size distribution of 190~275 nm could be obtained when the AVM EC prepared by SL-Temp-CTAB was dispersed in water.However,the O/W emulsion droplets with a size distribution of 125~700 nm could be obtained after the commercial AVM EC was emulsified in water.Therefore,the AVM EC prepared by SL-Temp-CTAB had controlled release property and the release equilibrium time of AVM was 5.3 times longer than that of the commercial AVM EC.The anti-photolysis of AVM EC was improved by grafting Temp into SL.The AVM retention rate of the dispersion suspension that use SL-Temp-CTAB as emulsifier was 75.8% after 70 hours irradiation,which was higher than 0.4% of commercial AVM EC and 31.4% of unmodified lignin-based AVM EC.In this work,two new functional lignin-based adjvants were obtained,which can be used as dispersant and emulsifier in AVM SC and AVM green EC,respectively.The anti-photolysis property of AVM was significantly improved and the utilization of lignosulfonate surfactants in green pesticide formulations was increased.