Synthesis Of PH-responsive Zwitterionic Copolymers And Their Application In Cellulase Recycle

Enzymatic saccharification of lignocellulose into fermentable sugars is a critical step in biorefinery.Recycling the cellulase left in hydrolysate and enhacing enzymatic saccharification reaction are main ways to reduce enzymatic saccharification cost.In this dissertation,several linear pH-responsive zwitterionic copolymers were synthesized from functional monomers through free radical polymerization.The pH-responsive zwitterionic copolymers could dissolve in aqueous buffer and enhance enzymatic saccharification of lignocellulosic substrate.When lowering the hydrolysate pH,the pH-responsive zwitterionic copolymers could co-precipitate with cellulase.The recycled cellulase will be reused in the next enzymatic saccharification of new substrate to reduce the cost.First,three kinds of linear pH-responsive zwitterionic copolymers were synthesized from anionic monomer?-methacrylic acid,cationic monomer 2-(dimethylamino)ethyl methacrylate,hydrophobic monomers benzyl methacrylate,hexyl methacrylate and initiator ammonium persulfate.The hydrophobicity of copolymer was controlled via monomers feed ratio.The molecular weight of copolymer was controlled via concentration of initiator and functional monomers.FT-IR and ~1H-NMR characterization indicated that pH-responsive zwitterionic copolymers were successfully synthesized.The UV-turbidity and isoelectric point(pI)experiments showed that zwitterionic copolymers exhibited sensitive pH-responsiveness.The dissolution-precipitation?pH was around 1 pH unit and the precipitation rate was over 90%in the vicinity of pI(3.3-3.7).Increasing the hydrophobicity or molecular weight of pH-responsive zwitterionic copolymer could increase its pH-responsiveness and precipitation rate.Then the effect of pH-responsive zwitterionic copolymers on the enzymatic saccharification of lignocellulose and its ability to recycle cellulase were investigated.The results showed that pH-responsive zwitterionic copolymers had little effect on the enzymatic saccharification of pure cellulose however it could enhance the enzymatic saccharification of lignocellulose.The enhancement was about 10-25%when adding 2 g/L zwitterionic copolymer solution.The pH-responsive zwitterionic copolymers could recycle cellulase in hydrolysate.Increasing the hydrophobicity or molecular weight of pH-responsive zwitterionic copolymer could increase its ability to recycle cellulase.The enzymatic saccharification efficiency of recycled cellulase was 64.3%of the initial cellulase.SDS-PAGE analysis showed that pH-responsive zwitterionic copolymers could recycle 100%?-glucosidase.The recycle rates of cellulase components increased with the increase of hydrophobicity or molecular weight of zwitterionic copolymers.Therefore pH-responsive zwitterionic copolymers could recycle cellulase through hydrophobic affiliation.Increasing the hydrophobicity of copolymer could increase its bonding with cellulase.Increasing the molecular weight of copolymer could increase the bonding sites with cellulase.The pH-responsive zwitterionic copolymer that do not contain hydrophobic monomer had prior ability to recycle cellulases with high pI.And its recycle ability was strongly influenced by pH and ionic strength which indicated that it can recycle cellulase through ion attraction.A novel approach using pH-responsive zwitterionic copolymer to recycle cellulase and enhacing the enzymatic hydrolysis was established in this dissertation.The results will provide theoretical foundation for synthesizing pH-responsive zwitterionic copolymer which exhibit good cellulase recycle ability.