| Sodium lignosulphonate is a natural soluble polymer with advantages such as hydrophilichydrophobic property, adsorbability, dispersibility, chelating property and so on. Though sodium lignosulphonate is widely used in many industrial fields, its application performance is poor and it is used as a kind of low-end product. Therefore it is necessary to have it modified by chemical way in order to improve its performance.In this study, aminated sodium lignosulphonate(ASL) was synthesized by Mannich reaction. Results shown that amine groups went susccessfully grafted into ASL and amino content increased from 0.1514 to 4.462 mmol·g-1 after being characterized by hydrogen nuclear magnetic resonance, infrared spectroscopy and elemental analysis. The optimum technical conditions were that nHCHO:nDETA≈1.2, mNa OH/mSXSL=0.05, reaction temperature was 75 °C and reaction time was 3h.The pH-responsive solution behaviors of ASL were further studied by fluorescence spectra, ultraviolet spectrum, Zeta potential, particle size and electron microscope. Results shown that its critical aggregation concentration slightly decreased from 0.099 to 0.088 g·L-1 with increasing amino content. When pH dropped, its absolute value of Zeta potential, particle size and ultraviolet absorbance firstly reduced and then increased, while ASL aggregations reversibly transformed from small aggregations to network structure shown by transmission electron microscope. Based on these results, the pH-responsive aggregation model of ASL was built, showing its remarkable pH-response as ASL molecules extended, shrank, aggregated and then partly disaggregated when pH reduced gradually. Effects of surfactant and polar solvent on aggregation behavior of ASL were studied subsequently. Results shown that cetyl trimethyl ammonium bromide had electrostatic shielding effect and stimulated the aggregation of ASL while polyoxyethyleneoctylphenyl-10 had dispersion effect and restrained the aggregation. Since dimethyl sulfoxide could strengthen the solubility of aggregated ASL in water, ASL molecules formed near-spherical structure in dimethyl sulfoxide-water system and the critical water content was 52 wt%.Abamectin/aminated sodium lignosulphonate(AVM-ASL) microcapsule was prepared by complex coacervation. Drug loading, entrapment efficiency and release rate were considered to measure the preparation technics and the optimum technical conditions were that the AVM solvent was ethanol, the ASL concentration was 4 g·L-1, Vethanol/Vwater=0.2, mASL/mAVM=2, reaction temperature was 35°C, encapsulated pH was 6.5, rotated rate was 600 rpm, mglutural/mASL=0.05~0.1, crosslinking temperature was 10°C, mCTAB/mASL=0.05 and mOP-10/mASL=0.05. Under the suitable condition, the drug loading and entrapment efficiency rate were 50% and 90%, respectively. And the controlled release capacity was favorable and corresponded to the AVM microcapsule product. Scanning electron microscope and energy dispersive spectrometer results shown that AVM particles were encapsulated by aggregated ASL and formed microcapsules. As the AVM-ASL microcapsule presented good stability, its particle size and release ability changed little after keeping in dark place for 30 days. And it shown obvious anti-photolysis capacity, its AVM retention rate was still 90% after ultraviolet radiation for 50 h.In this study, pH-responsive ASL was synthesized by amino reaction and pH responsive aggregated model was built after studying its solution behavior, and that provided certain theoretical basis for its application in nano materials and microcapsules fields. Based on this, AVM-ASL microcapsule with favorable performance was prepared by using ASL as wall material. The AVM-ASL microcapsule realized higher value applications of both lignin and pesticides and shown certain practical application value. |
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