Preparation Of Alginate Hydrogel Slow/Controlled Release Pesticide Carrier And Research On Its Properties

With the continuous development of pesticide formulations as well as more attention to environmental protection, that how to improve the utilization of the carrier material and release properties, thus, to protect the economic value, improve the utilization of pesticides and reduce pesticide residues has become the focus on the development of new pesticide formulation. The goal of this study focuses on the utilization and release properties of slow/controlled release pesticide carrier material. The following formulation studies were carried out according to the project objectives, which used polysaccharide polymers alginate hydrogel as pesticide carrier material.(1) The acetamiprid hydrogel beads, which used bentonite as an adsorbent based on film-forming properties of chitosan, were prepared by the extrusion-exogenous gelation method.(2) The intercalation of CTAB into Montmorillonite and the surface modification with Poly(methyl hydrosiloxane)(PMHS) by using grinding method were considered to be a novel and green chemistry technique. Subsequently immobilization of acetamiprid into modified clay was carried out by freeze-drying technology. And the drug-loaded clays were encapsulated in alginate-chitosan beads by extrusion into calcium chloride solution.(3) Cholesterol modified alginate (CSAD) was prepared by DCC/DMAP covalent attachment of hydrophobic cholesterol onto the nature polysaccharide alginate. And the nanocapsules loaded with cyhalothrins were obtained by emulsification method.(4) Pickering emulsions loaded with cyhalothrins were prepared by SiO2nanoparticles whose surface were activated by using amphiphilic alginate derivative hydrophobically modified by cholesterol under the conditions of high speed stirring.Their structure, morphology and performance were characterized by Fourier transform infrared spectroscopy (FT-IR), scanning electron micrograph (SEM), thermogravimetry (TG), water-up tests and release studies. Experimental results showed that the obtained hydrogel beads were1.42～1.71mm in diameters. Bentonite could improve the hydrogel beads’ size and sphericity and make the drug loading rate and encapsulation efficiency of acetamiprid upgrade from4.16%and36.36%to4.91%and63.01%, respectively. Chitosan and sodium alginate had formed the polyelectrolyte complexes by electrostatic interactions assisting in crosslinking with calcium ion and made the drug loading rate and encapsulation efficiency of acetamiprid upgrade from4.16%and36.36%to5.23%and54.29%, respectively. Bentonite contains a lot of hydroxyl groups on the surface that can form hydrogen bonds with the sodium alginate and chitosan, which can effectively inhibit calcium alginate large swelling to improve the performance of their release; The grinding process effectively reduced the particle size, increased the specific surface area, enhanced the hydrophobic of the modified clay and improved its affinity to the hydrophobic organic pesticide. The drug-loading and release properties of drug-loaded composite hydrogel beads were greatly improved; the degree of substitutions of CSAD were5.3%～7.9%and their critical aggregation concentration were reduced from1.23mg/L to0.26～0.63mg/L. With the increasing degree of substitution, the hydrophobic group increased and the critical aggregation concentration reduced. The d50of the drug-loaded nanocapsules was576.4±7.4nm, and the Zeta potential value of drug-loaded nanocapsules was-32.3±0.6mV, which could exhibit excellent stability in aqueous solution. Compared with conventional microemulsions, the hydrogen bonds were key to CSAD to possess the Slow-Release properties; Alginate derivative (CSAD) and surfactant CTAB could be also adsorbed on the surface of SiO2nanoparticles with the corresponding Zeta potentials which were+16.4mV and-30.7mV, respectively. And their particle sizes were583.3nm and438.4nm, respectively. The release rate of the Pickering emulsions prepared by the SiO2particles and activated by CSAD was slower. That may be the cross-linking action of CSAD that made the activated SiO2particles adsorbed on the oil-water interface to form the relatively stable network structures or the interface membranes.