Preparation And Properties Of Microcapsules Based On Lignin/urea-formaldehyde Resin And Lignin Alkyl Cross-linking

Lignin has abundant sources and can be regenerated but it has low utilization rate.Using it as a wall material to prepare microcapsules is an effective way for its high value utilization in the field of materials.In this paper,lignin/urea-formaldehyde resin microcapsules（LS/UFMC）were prepared by in-situ polymerization of sodium lignosulfonate（LS）with formaldehyde and urea.Meanwhile,alkali lignin（AL）and LS were used as raw materials.Lignin-based microcapsules（LMC）were prepared by the emulsion alkyl bridge reaction of lignin and 1,6-dibromohexane at the oil-water interface using the active site of phenolic hydroxyl groups in the lignin structure,and the LMC was applied to the encapsulation of avermectin（AVM）pesticides.The main research contents and conclusions of this study are listed as follows:1.First,the effects of stirring speed and formaldehyde addition speed were studied during the preparation of UFMC.It was found that when the rotation speed is too large,emulsion breakage is easily caused,and when the rotation speed was too slow,the microcapsules are agglomerated.When the stirring speed was 300 r/min,the prepared UFMC had good morphology and dispersibility.In addition,the effect of different formaldehyde addition speed was studied at 300 r/min.The results showed that the slower the addition of formaldehyde,the more helpful the formation of UFMC.2.LS/UFMC was prepared by in-situ polymerization using LS,urea and formaldehyde as continuous phase and toluene as oil phase.Scanning electron microscopy（SEM）and infrared analysis（FT-IR）results showed that LS was successfully introduced into UFMC,and the morphology of LS/UFMC was rough and good roundness.The effects of preparation conditions such as initial reaction pH,temperature,and amount of crosslinker on the surface morphology of LS/UFMC were systematically studied.The optimal preparation conditions were determined as follows:the ratio of oil to water was 1:9,the ratio of core to wall was2.5:1.The amounts of crosslinking agent NH₄Cl and resorcinol were 0.56%,the initial reaction pH was 3.5,and the reaction temperature was 55℃.At the same time,the LS/UFMC with different LS substitution rates was prepared.The results showed that when the substitution rate of LS was 20%,the encapsulation efficiency of LS/UFMC was 81.5%,and meanwhile the LS/UFMC had good sustained-releasing and anti photolysis performance.3.The aqueous phase was prepared by using AL or LS,respectively.The cyclohexanone containing bridging agent 1,6-dibromohexane was used as the oil phase.Tween80 was used as the emulsifier,and the alkali lignin-based microcapsules（ALMC）and sodium ligninsulfonate-based microcapsules（LSMC）were prepared via the alkyl bridging reaction at the emulsion interface.Scanning electron microscopy showed that LMC was spherical or spheroidal.The optimum conditions for the preparation of ALMC and LSMC were as fllows:reaction initial pH was 11,reaction temperature was 80℃,lignin content 10 g,AL:Bridging agent=1:0.8,LS:Bridging agent=1:0.3.The encapsulation efficiency of ALMC and LSMC were 88.7%and 79.4%,respectively.The AVM cumulative release amount of AVM@ALMC and AVM@LSMC was 61.47%and 68.38%after 48 h.The effective AVM retention rate of AVM@ALMC and AVM@LSMC were 85.05%and 82.80%under UV radiation for 72 h.