Preparation And Properties Of Modified Sodium Alginate Composite Hydrogel

Hydrogels based on natural polymer are widely used in agriculture,food,medicine and other fields because of their safety,non-toxicity,good biocompatibility and easy degradation.The modification of the hydrogel matrix can make the hydrogel more functionalized to meet its specific needs in real-world applications.In this paper,sodium alginate was modified through a mild and efficient Ugi reaction to obtain sodium alginate derivatives with different properties.A sery of functionalized composite hydrogels with interpenetrating network structure were prepared based on them.Mechanical properties,swelling properties and sustained release properties for pesticides of the composite hydrogels and the effect of dispersibility of nanoparticle on mechanical performance of hydrogels were investigated.(1)Hydrophobically modified sodium alginate(Ugi-SA)with different molecular weights was synthesized and characterized by Fourier transform infrared spectroscopy(FTIR),nuclear magnetic resonance spectroscopy(1H NMR)and gel permeation chromatography(GPC).The stability and micromorphology of the modified sodium alginate/montmorillonite(Ugi-SA/MMT)dispersion system were analyzed by multiple light scattering(MLS)and transmission electron microscopy(TEM).The results show that the high molecular weight Ugi-SA can adsorb on the surface of MMT more efficiently and make it well dispersed,and the stability of the dispersion system is the highest when its concentration is 5 g/L.Furthermore,nanocomposite hydrogels with Ugi-SA and polyacrylamide(PAM)as matrix and MMT as reinforcing agent were prepared.The structure and micromorphology of the hydrogels were analyzed by FTIR,thermal stability analyzer(TG)and scanning electron microscope(SEM).The influence of molecular weight and mass fraction of Ugi-SA on the mechanical properties of the composite hydrogel was investigated.The experimental results show that the nanocomposite hydrogel prepared by high molecular weight Ugi-SA with a mass fraction of 0.5%exhibit the best mechanical properties.(2)The effect of MMT content on the swelling properties,tensile properties and pesticide release performances of high molecular weight modified sodium alginate/polyacrylamide/montmorillonite(Ugi-SA/PAM/MMT)nanocomposite hydrogels.The composite hydrogels consist mainly of a chemical cross-linking network formed by PAM and a physical cross-linking network formed by electrostatic interaction between Ugi-SA and Ca2+.FTIR and TG data indicate a strong physical interaction between MMT and the polymer matrix.The SEM image shows the interpenetrating network structure of the composite hydrogel.XRD data and TEM images indicate that MMT is exfoliated and embedded into the network of hydrogels.Equilibrium swelling experiments show that the addition of MMT reduces the equilibrium swelling degree(Qeq)of the composite hydrogel,and the swelling process belongs to Fickian diffusion.Tensile tests indicate that when the content of MMT added is 2.5%,the composite gel exhibit the best mechanical property.Pesticide release experiments show that the addition of MMT can increase the loading efficiency of the composite gel on hydrophobic pesticides and slow down the cumulative release rate.There are hydrophobic interaction between the hydrophobic groups on the Ugi-SA side chain and the pesticide molecules,and ?-cyhalothrin is encapsulated in the hydrophobic microdomain formed on the side chain of the polymer When the hydrophobic microdomain is destroyed,pesticide molecules can diffuse to the release media.The composite gel with MMT content of 2.5%exhibits the highest loading efficiency of pesticide,while the composite gel with MMT content of 5%show the best sustained release performance.And the sustained release curves of composite hydrogels for ?-cyhalothrin can be fitted by Weibull model.(3)The host-guest interaction of azobenzene and ?-cyclodextrin were introduced into the hydrogel system.Sodium alginate(SA-CD)grafted with cyclodextrin was synthesized by Ugi reaction,and polyacrylamide grafted with azobenzene(PAM-Azo)was synthesized by free radical copolymerization reaction.The two polymers were characterized by FTIR,1H NMR,TG and GPC.UV-Vis spectroscopy(UV-Vis)was used to prove the UV responsiveness of PAM-Azo molecules.Then,the host-guest interaction between SA-CD and PAM-Azo were further explored,and they were found to spontaneously crosslink with each other under heating condition to form hydrogel.The reversible transformation of the sol,gel state can be achieved by irradiation of ultraviolet light and visible light.Furthermore,the SA-CD/PAM-Azo interpenetrating network structure composite hydrogel was prepared.The composite gels were characterized by FTTR,TG and SEM.The self-healing properties of gels were also explored.It can be observed under the microscop that the interface between the hydrogels disappeared.The tensile test showed that the introduction of CD makes the mechanical strength and elasticity of SA-CD/PAM-Azo IPN composite gel lower than that of SA/PAM-Azo IPN composite gel.The broken gel sample could be almost healed after 48h.In addition,the irradiation of ultraviolet light significantly hinders the self-healing process of the hydrogels.The host-guest composite hydrogel with self-healing properties which can be controlled by ultraviolet light may have a good application prospect in the biomedical field.