Fabrication And Properties Research Of Waste Yeast-Based Ecomaterials

With the advancement of human civilization and the rapid development of the global economy,the demand and consumption of materials and energy have increased year by year.A large number of non-renewable resources were excessive consumed,and many serious environmental problems arose increasingly.As a consequence,many researchers focus on the multi-functional and high performance ecomaterials based on renewable resources.Thereinto,the re-utilization of biomass waste resources is one of the effective ways to prepare ecomaterials.Waste brewer's yeasts are a by-product of the brewing industry,which are rich,cheap,safe and non-toxic.Additionally,the waste brewer's yeasts have unique cellular structure and physicochemical/biological properties.By using immobilized microorganism technology,the natural characteristics of yeasts can be easily and effectively introduced into the novel ecomaterials to improve their added value.Herein,we prepared a series of waste brewer's yeasts derived ecomaterials through immobilized microorganism technology,which combined the native yeast with carrier materials or crosslinked by crosslinkers to improve the comprehensive performances.The details are described as follows:?1?The fabrication and properties research of PAA-immobilized-yeast superabsorbent composites.PAA-immobilized-yeast superabsorbent composites were successfully synthesized by graft co-polymerization of monomers acrylic acid onto the surface of yeasts by using ammonium persulfate as a free-radical initiator and N,N'-methylene-bisacrylamide as a cross-linker in aqueous solution.The optional experimental conditions were selected as follows:mass ratio of acrylic acid and yeasts was 8:1,initiator dosage was 1.4 wt%,crosslinker concentration was 0.002 mol/L,and neutralization of monomer was 80%.Thus-prepared PAA-immobilized-yeast superabsorbent composites exhibited brilliant water absorbency?354.2 g/g?,saline absorbency?54.9 g/g?,and water retention?83.65%?.The maximum adsorption capacity for methylene blue was 92.2%,which was ascribed to the abundant hydrophilic functional groups,including carboxyl group,hydroxyl group and amino group on the yeast cell wall and PAA.?2?The fabrication and properties research of PAA/PVA-immobilized-yeast composites with interpenetrating network.PAA/PVA-immobilized-yeast composites with interpenetrating networks were prepared by solution polymerization reaction using ammonium persulfate as a free-radical initiator and N,N'-methylene-bisacrylamide as a crosslinker.On the basis of PAA-immobilized-yeast composites,the interpenetration of PVA improved the thermal stability?T_m=423.9oC?and mechanical stability to resist shear force.A large amount of carboxylic groups existed on the polymer scaffold and yeast cell wall with a point of zero charge at pH_PZC=4.8,which equipped the PAA/PVA-immobilized-yeast composites with pH-sensitive water absorbency,dye adsorption capacity and selective adsorption behaviors.The maximum adsorption capacity was obtained in weak base solution,and the adsorption mechanism was chemisorptions.?3?The fabrication and properties research of citric acid crosslinking-immobilized-yeast composites.The citric acid crosslinking-immobilized-yeast composites were prepared by esterification reaction using citric acid as crosslinker.The hydroxyl groups on the yeast cell wall were esterified with carboxyl groups of citric acid,resulting in the crosslinking immobilization of yeasts with a microgel state.The size was about 36 times that of yeast cell.The experimental temperature of 120oC had the best effect on the carboxyl content?483mEq/100 g?,degree of esterification?45%?and point of zero charge(pH_PZC=3.1)of the citric acid crosslinking-immobilized-yeast composites.The water absorbency was 38.1 g/g,and salt resistance and pH sensitivity were both improved.Additionally,the citric acid crosslinking-immobilized-yeast composites could be utilized as a controlled release formulation for ketoprofen by controlling the pH values of the medium solution.?4?The fabrication and properties research of chitosan embedding-immobilized-yeast composites.The chitosan embedding-immobilized-yeast composites were prepared through sol-gel method.The immobilized carrier of honeycomb chitosan crosslinked network was formed after ageing in the alkali solution with a pore diameter of about 0.2 mm.The chitosan embedding-immobilized-yeast composites integrated the toughness of yeast cell wall,water retention and tolerability of yeast itself,and the physiochemical properties of chitosan hydrogels as well.The maximum water absorbency was obtained when the yeast content was40 wt%.The excellent salt tolerance,pH sensitivity,temperature tolerance and reutilization made the chitosan embedding-immobilized-yeast composites as a pH-controlled release carrier for fertilizers.?5?The fabrication and properties research of NaAlg/PVA embedding-immobilized-yeast composites with diffusion barriers.The biodegradable NaAlg/PVA embedding-immobilized-yeast composites with diffusion barriers were prepared by ionic gelation method in CaCl₂ solution and thermal chemical modification by citric acid.The optimal mass ratio of NaAlg and citric acid at 1:1 had the best effect on the carboxyl content?498 mEq/100 g?,degree of esterification?39%?,water absorbency?23.5 g/g?,and salt resistance.The tenacity of the yeast itself combined with the interpenetration of PVA endowed the NaAlg/PVA embedding-immobilized-yeast composites with high mechanical strength to resist the damage of shear force.The diffusion barriers significantly reduced the water evaporation ratio of the soil,prevent indole-3-butyric acid from leaching loss or burst release.The NaAlg/PVA embedding-immobilized-yeast composites were an ideal slow release formulation through gradual desorption,diffusion and ion exchange.