Synthesis Of Temperature-responsive Sulfobetaine Copolymers And Its Application In Cellulase Recovery

Enzymatic hydrolysis is an important step of lignocellulose-based sugar platform technology.The high cost of enzymatic hydrolysis is one of the key bottlenecks that must be solved in its industrialization.In this work,a new idea was proposed to synthesize sulfobetaine copolymers with the upper critical solution temperature（UCST）response,and use it to recycle cellulase and strengthen the enzymatic hydrolysis of lignocellulose,so as to achieve high efficiency and low cost enzymatic hydrolysis.In view of the problem that UCST responsive sulfobetaine homopolymer（PSPE）has no significant effect on the enzymatic hydrolysis of lignocellulose.Sulfobetaine（SPE）and isopentenol polyoxyethylene ether（TPEG）were taken as monomers.UCST responsive sulfobetaine binary copolymers P（TPEG-co-SPE）（PPSP）with different composition and molecular weight were synthesized by free radical polymerizations in aqueous solution.The effects of PPSP dosage,molecular weight and composition on UCST responsiveness,enhanced hydrolysis and cellulase recovery were investigated.The results showed that the UCST response,enhanced enzymolysis and enzyme recovery performance of high molecular weight PPSP were more significant when the two monomer structural units in copolymers were basically the same.For example,in the response temperature range of 25～50℃,when the concentration of PPSP₁₀-3 with the highest molecular weight is 0.5 g/L,the self-recovery rate is 75.1%;Under the same concentration,the hydrolysis efficiency of corn cob residue（CCR）can be increased by1.3 times,and the cellulase consumption can be saved by 20%.In the cellulase buffer system of 0.2 g/L,0.1 g/L PPSP₁₀-3 can recover 25.9%of the enzyme protein.This is attributed to the fact that PPSP with high molecular weight has a longer molecular chain and greater hydrophobicity,so it is more likely to form steric hindrance when adsorbed on lignin during enzymatic hydrolysis,thus reducing ineffective adsorption of enzymes and strengthening enzymatic hydrolysis,and more likely to hydrophobic polysink with enzymes when cooled after enzymatic hydrolysis.When the molecular weight of the copolymers are basically the same,the molar proportion of the TPEG structure units in the copolymers are higher,the UCST response of the copolymer are less sensitive,the strengthening enzyme hydrolysis performance are more significant,and the recovery enzyme performance are less significant.For example,when the concentration of PPSP₄₀-3,which has the highest molar proportion of TPEG structural units,is 0.3 g/L,the enzymatic hydrolysis efficiency of CCR can be increased by 1.3 times.This was attributed to the fact that PPSP with a high TPEG ratio had higher hydrophilicity,which was easier to form hydrophilic hydration membranes adsorbed on lignin during enzymatic hydrolysis to reduce the ineffective adsorption of enzymes and strengthen enzymatic hydrolysis,and the hydrophobic binding of enzymes were weak when cooling after enzymatic hydrolysis.In conclusion,the introduction of TPEG structure unit in copolymer can improve the enhancement effect of enzymatic hydrolysis,but can weaken the UCST response sensitivity of copolymer and its enzyme recovery performance.Then,this work aimed at the problems that UCST response performance of PPSP is not significant and recovery enzyme recovery performance is not significant.Using p-styrene sulfonate（SSS）and SPE as monomers,through aqueous free radical polymerization method,a series of sulfobetaine binary copolymers P（SSS-co-SPE）（PSSP）with UCST response.The effects of composition,molecular weight and dosage of PSSP on UCST responsiveness,enhanced hydrolysis and recovery of cellulase were investigated.The results showed that the UCST response were successfully synthesized,enhanced enzymatic hydrolysis and enzyme recovery performance of high molecular weight PSSP were also more significant when the two monomer structural units in copolymers were basically the same.For example,when the concentration of PSSP₃₀-3with the highest molecular weight is 10.0 g/L,the self-recovery rate is 96.5%in the range of 25～50℃response temperature.The enzymolysis efficiency of CCR can be increased by 1.36 times and cellulase consumption can be saved by 50%under the same concentration.In the cellulase buffer system of 0.2 g/L,PSSP₃₀-3 of 4.0 g/L could recover56.0%of the enzyme protein.When the molecular weight of the copolymers are basically the same,the molar proportion of the SSS structural units in the copolymers are higher,the UCST response of the copolymers are less sensitive,the strengthening enzyme hydrolysis performance is more significant,and the recovery enzyme performance is less significant.For example,when the concentration of PSSP₄₀-3,which has the highest molar proportion of SSS structural units,is 10.0 g/L,the enzymatic hydrolysis efficiency of CCR can be increased by 1.44 times.This was attributed to the fact that the copolymer with high SSS ratio had more sulfo-group and higher hydrophilicity,so it was easier to form hydrophilic hydration film adsorbed on the lignin during enzymatic hydrolysis to reduce the ineffective adsorption of enzymes and strengthen enzymatic hydrolysis,and the hydrophobic binding of enzymes was weak when cooling after enzymatic hydrolysis.In conclusion,the introduction of SSS structural units in copolymer PSSP can also improve the enzymatic strengthening effect,UCST response and enzyme recovery performance of copolymer PSSP.In this paper,a series of UCST responsive sulfobetaine copolymers were synthesized to strengthen the enzymatic hydrolysis of lignocellulosic acid,and were applied in the recycling of cellulase,to reduce the amount of enzyme,and the cost of enzymatic hydrolysis,so as to improve the theoretical guidance and technical support for the industrialization of lignocellulosic sugar platform technology.