Preparation And Properties Of Microbial Foaming Porous Hydrogel Based On Yeast

In this paper,the yeast as microbial foaming agent was introduced into polyvinyl alcohol/cellucose composites.The foaming system was formed by the blending of polyvinyl alcohol which was one of macromolecular polymer and natural polymer such as carboxymethyl cellulose(CMC),hydroxyethyl cellulose(HEC).Then,PVA/CMC and PVA/HEC porous composite hydrogels were prepared by cyclic freeze-thaw process.Single factor test and orthogonal test were used to select the best foaming condition.The structure and performance of porous hydrogels were characterized and measured by fourier transform infrared spectrometer(FTIR),thermogravimetric analyzer(TG),scanning electron microscopy(SEM)and universal tensile test machine.Finally,the adsorption performance of two kinds of porous composite hydrogels were analyzed by using methylene blue as adsorption model,its adsorption process were analyzed by isothermal adsorption models and kinetic models.The main results are as follows:(1)The porous structure of the PVA/CMC and PVA/HEC porous composite hydrogels were formed by the yeast foaming method,and the pore opening structure of large pores and small pores was showed inside.PVA/CMC porous composite hydrogel is best in foaming condition of which temperature is 31 ℃,yeast and glucose ratio is 2.8/1,foaming time is 60 min and PVA/CMC is 1/0.7.PVA/HEC porous composite hydrogel is best in foaming condition of which temperature is 32 ℃,yeast and glucose ratio is 2.8/1,foaming time is 60 min,PVA/HEC is 1/1.4 and PVA polymerization degree is 1700.The two of them have the characteristics of rapid response of water absorption and good water retention,which maximum equilibrium swelling ratio can reach 1631.9 % in 20 s.(2)Compared with PVA/CMC composites,the compressive strength and ultimate compressive stress of microbial foam PVA/CMC porous composite hydrogels were increased from 1.2 and 3.8 MPa to 2.5 and 7.6 MPa,respectively.The PVA/CMC composite exhibits two stages of weight loss.The decomposition temperature is about 260 ℃ and 430 ℃.PVA/CM C porous composite hydrogels exhibit a stage of thermal decomposition,which maximum temperature is 319 ℃.Compared to PVA/CMC composites,the compressive strength and ultimate compressive stress were increased from 9.7 and 4.8 MPa increased to 13.2 and 6.4 MPa,respectively.The thermal weight loss stage from 3 to 2 in the first stage.The decomposition temperature from 280 ℃ to 335 ℃.The results show that the mechanical and thermal properties are improved.(3)By using the method of cyclic freezing-thawing,the two kinds of hydrogels can be used to fix the pores and crosslinking.In the foaming process,the yeast was dispersed in the foaming system,and after a short period in 10 min of adjustment and adaptation.The SEM of hydrogel was observed that the yeast had begun to foam at 10 min and have formed the porous structure of the large pore surrounded by small cells at 30 min.Through the freezing-thawing process,the yeast fermentation of the fixed holes into the hydrogels.The physical gelation of hydrogels are based on the physical entanglement between PVA and CMC,PVA and HEC,the hydrogen bond and the microcrystalline region.(4)The adsorption properties of these two kinds of hydrogels were studied by methylene blue adsorption model.According to the results of FTIR,SEM and XPS,PVA/CMC and PVA/HEC porous composite hydrogels foamed by yeast inside which the keyhole wall is attached by yeast,illustrating the methods not only to the successful introduction of hydrogel porous structure,and the yeast is fixed on the hole wall.As the yeast itself non-toxic harmless,has certain adsorption performance,therefore,the PVA/CMC,PVA/HEC porous composite hydrogel did not introduce a new source of pollution,and increased the adsorption properties of hydrogels.The experimental results show that compared with the single PVA hydrogel,PVA/CMC and PVA/HEC composites,the adsorption performance is improved obviously.The adsorption kinetics of methylene blue by the two groups is in good agreement with the pseudofirst-order kinetic model.The adsorption equilibrium is in 360 min.The Langmuir model can well describe the isothermal adsorption behavior,and R squre is greater than 0.99.