Preparation Of Photo-thermal Responsive Hydrogel Based On The Structure Transition Of Gelatin And Its Application In Sustained Release Of Pesticide

The excessive use of agrochemicals has serious adverse effects on soil,water and atmosphere,and even endangers human health.Controlling release of pesticide is an effective approach to improve pesticide utilization and reduce environmental pollution.Based on the helix-coil structure transition of gelatin(Gel),this paper studied the changes of physicochemical property in gelatin caused by structural transition under the photothermal stimulation.This structural transition was integrated into different hydrogel systems.By combining the excellent photothermal conversion property of polypyrrole(PPy)with the thermal response capacity of gelation,different types of photothermal responsive slow-release materials were prepared to achieve the stimuli-responsive release of pesticide.The main research contents are as follows:1.The pyrrole monomer was dispersed in the gelatin solution and oxidized in situ by the ammonium persulfate to form Gel/PPy hydrogel for controlling release of carbendazim.The results showed that PPy could effectively compound with gelatin to enhance the mechanical strength of the hydrogel.At the same time,environmental temperature and external light irradiation had obvious effects on the pesticide release of Gel/PPy.Increasing temperature could promote the release of carbendazim.Under light and dark conditions of 3 h,the release rate of carbendazim under light was about 2.6 times than that under dark.And the cumulative release of carbendazim under light gradually increased with the decrease of the crosslinker content.It shows that the light absorption of PPy can cause the structural transition of Gel,which is beneficial to the release of carbendazim.2.The PPy/Ca-alginate/Gel composite microspheres with a semi-interpenetrating network structure were prepared by uniformly dispersing pyrrole into two inexpensive biomass materials,Gel and Ca-alginate.The structure of the PPy/Ca-alginate/Gel microspheres was characterized by SEM,FTIR,TGA,Zeta potential and UV-vis-NIR.The experimental results showed that the PPy/Ca-alginate/Gel microspheres had high photothermal conversion efficiency which could be increased by 17 ℃ after 600 s and effectively loaded drug molecular.In addition,the microspheres had both temperature and light-controlled responsive release properties.At each temperature/light interval,the stimulation of light and heat could significantly accelerate the release of pesticide,while the release rate slowed down when it turned to low temperature or no light.The release of carbendazim in PPy/Ca-alginate/Gel reached 91.8% after the 8 h of light,however it was only 13.3% in the dark.As a photothermal agent,PPy can convert the absorbed light into heat energy,causing a helix-coil structure transition of Gel,changing the pore size of the hydrogel,and promoting the release of carbendazim.3.Using gelatin,PPy and acrylic acid(AA)as raw materials,a novel PPy@Gel/PAA hydrogel with semi-interpenetrating network structure was synthesized by chemical oxidation.The hydrogel that combined water retention and light sensitivity could control the release of carbendazim.The structure of PPy@Gel/PAA was characterized by SEM,FTIR,TGA and UVvis.And its photothermal conversion efficiency,water adsorption and controlled-release were systematically studied.Under the optimum content of crosslinker(0.05%),Gel/PAA could absorb a large amount of water and the water absorbency reached to 197.0 g/g.After adding PPy,PPy@Gel/PAA had light-controlled slow release performance,and the release of carbendazim could be increased by 3 times with 8 h of photo-assistance.From the experimental data,it can be known that PPy triggers the structure transition of Gel and changes the microstructure of the hydrogel through the photothermal effect which promotes the release of carbendazim.Consequently,excellent controlled-release capacity and water retention performance enable PPy@Gel/PAA hydrogel to be a potential candidate in agricultural application.Based on the photothermal conversion of PPy and the thermal responsiveness of gelatin,the three photothermal responsive sustained release systems have shown excellent performance in the controlled release research using carbendazim as a template molecule.The structure transition of gelatin in controlling and sustaining release of pesticides is expected to provide a new data support for developing new controlled release materials,and also has a certain reference effect for improving the pesticides utilization and environmental pollution.