Preparation Of Temperature/pH-Sensitive Hydrogels With Core-Shell Structure And Its Application Study

Environmental-responsive hydrogels are environmentally friendly polymeric materials that rapidly change their volume or strength in response to the external environment such as temperature,pH,light,and magnetism when the environment changes.Environmental-responsive hydrogels,with their unique flexibility and sensitivity,enable them to be used in various fields and are now a hot topic in polymer science research.Scholars have studied more environmental-responsive hydrogels in biomedicine,detection sensors,and drug release,and less on their research and applications in agriculture are outlined.Since the soil environment is greatly affected by rainfall and light,conventional hydrogels are not effective in ecological remediation in terms of sensitivity and reproducibility.Therefore,in this thesis,hydrogels with temperature/pH-responsive core-shell structures are prepared to evaluate their applications in dry farming.Specific studies were conducted as follows:1.pH-responsive core-layer hydrogels were synthesized from popcorn(PCP),acrylic acid(AA)monomer,and PCP-g-PAA with temperature/pH-responsive core-shell structure were prepared by static template polymerization using temperature-sensitive monomer dimethylaminoethyl methacrylate(DMAEMA)polymerized with 2-acrylamide-2-methylpropanesulfonic acid(AMPS)as a temperature-sensitive shell.PCPg-PAA/P(DMAEMA-co-AMPS)hydrogels with temperature/pH-responsive core-shell structure were prepared by static template polymerization.The chemical structure,thermal stability,and morphology of the core-shell structure hydrogels were characterized by infrared spectroscopy(FTIR),X-ray diffraction(XRD),thermogravimetric analysis(TG),BET specific surface area test(BET),scanning electron microscopy(SEM)and atomic force microscopy(AFM),respectively,and the pH responsiveness and temperature responsiveness of the core-shell structure were tested.The results showed that AA was successfully grafted onto the PCP backbone and a core-shell structure existed.the PCP-g-PAA/P(DMAEMA-co-AMPS)hydrogels had a rough surface and pore structure with a specific surface area of 1.34 m~2/g and an average pore size of 4.09 nm.the lowest critical solution temperature(LCST)of the core-shell hydrogels was 43 °C,with a 25-55°C and good temperature responsiveness in the range of pH=4 to pH=13.The design of the core-shell structure enhances the stability performance of the hydrogel,which retains 80.7% of the original best performance after repeated immersion in distilled water 7 times.2.Based on SAP1(PCP-g-PAA/P(DMAEMA-co-AMPS))hydrogel,urea(urea)was loaded by in situ polymerization of SAP2(PCP-g-PAA/P(DMAEMA-co-AMPS)/urea),encapsulation of SAP3(PCP-g-PAA/urea/P(DMAEMA-co AMPS)),immersion SAP4(PCP-g-PAA/P(DMAEMA-co-AMPS))/urea 3 ways for loading.The structural characterization and performance tests of the four hydrogels were performed by FTIR,XRD,SEM,and TG,and the N-element release of the four hydrogels was tested using a fully automated interrupted chemical analyzer.The results showed that the immersion hydrogel had the best effect on urea coating,and the water absorption rate of SAP3 hydrogel was 193.45 g/g.The SAP4 hydrogel showed excellent reusability,and its water absorption rate could reach 150.35% of its previous weight after 17 repetitions,and the hydrogel prepared by the SAP4 immersion type had the highest N element release.All three hydrogels loaded with urea performed better than the SAP1.3.Four homemade hydrogels,SAP1,SAP2,SAP3,and SAP4,were applied to soil for germination and seedling growth experiments of Artemisia desertorum and Brassica campestris L.ssp.chinensis Makino seeds by simulating high-temperature and saline environments.The evaluation of the application of hydrogels with different urea loading methods was studied based on parameters such as seed germination rate,germination potential,water consumption,rootstock length,and fresh and dry weight.The results showed that the seed germination rate and germination potential of SAP1,SAP2,SAP3,and SAP4 were higher than the blank(CK)during the growth of Artemisia annua and Brassica juncea,and the advantage of SAP3 and SAP4 was more significant for seed germination rate.The three plants of SAP2,SAP3,and SAP4 consumed the least amount of water,which was also consistent with their water absorption properties.SAP1,SAP2,SAP3,and SAP4 had the lowest water consumption,SAP3,SAP4 rhizome length was significantly higher than CK,and SAP2,SAP3,and SAP4 chard fresh weight dry weight were significantly higher than SAP1.Therefore,the four laboratory homemade hydrogels are suitable for high temperatures and saline environments,and SAP2,SAP3,and SAP4 can promote plant growth and biomass accumulation while promoting seed germination.