Study On Enzymatic Lignin Hydroxymethylation And Preparation Of Phenolic Resin

Phenolic resins are widely used in outdoor artificial board production because of it's better resistance to water,higher bonding strength and other excellent characteristics.With the development of people's awareness of environmental protection and the growing shortage of fossil resources,the natural renewable resources will be utilized instead of fossil resources becoming an important direction of the modern industry.Lignins have the most abundant phenolic compounds in nature.With a large number of activity groups,the enzymatic hydrolysis lignin is the residual to prepare bioethanol and butanol.It is slightly similar molecular structure to phenol structure that could contain a segment of substitute phenol to synthesis lignin-phenolic-formaldhyde resin.In this thesis,enzymatic lignin as raw materials were methylolated when used the divalent metal oxides as catalysts.By comparing the reactivity of lignin after adding catalysis,the optimum preparation process of lignin methylation was determined.The lignin-phenolic resin?MLPF?was prepared by adding phenol and formaldehyde on the basis.The chemical structure and curing properties of the synthetic resin were comprehensively analyzed by means of FTIR,DSC,¹³C-NMR and other methods and by using the orthogonal experiment analysis method to optimize the experimental parameters,which in order to prepare the lignin phenolic resin with excellent physical and chemical properties.For the further study,based on the MLPF resin optimal synthesis process by adding urea to achieve the resin rapid curing and effectively reduce the free formaldehyde content,which provided scientific theoretical basis and technical route for preparing the fast curing lignin-phenolic resins.The main results were sum marized as follows:?1?Based on the study of lignin hydroxymethylation products,the catalytic effect of divalent metal Mg2 + on the methylation of lignin was studied for the first time.The study found that the reaction time was 2h,the methylation reaction rate is not added doubled.The discovery of Mg²⁺ catalyst by ¹³C-NMR favors the methylation of the hydroxyl side of the lignin phenolichydroxyl group.The total amount of hydroxymethylphenol in the reaction system is three times that of the unmodified,in which a small amount of hydroxymethylphenol is self-methyl bond and methylene ether bond.?2?MLPF resin and MLPUF resin were researched for the first time.The MLPF resin was optimized by orthogonal experiment that had high bonding strength.The ratio of F/P was 1.9,the amount of MgO was 1.5% and the ratio of NaOH/P was 0.9.The bonding strength is 0.81 MPa.In order to acheive the rapid curing of the resin and reduce the content of free formaldehyde,the MLPUF fast curing resin was prepared on the basis of the optimal process.When the urea content was 6%,the resin has better properties that wet glue strength was 1.1MPa,the gel time was 160 s,the storage period was 30 days,viscosity was 654 mps,free formaldhyde and free phenols were 0.2% and 0.25%.?3?By studying the chemical structure and curing properties of the LPF,MLPF and MLPUF resins,the contents of monomethylol,dimethyloxyphenol and methylene bond in MLPF resin were higher than that of LPF resin,methylene ether bond Content is low;MLPF resin curing faster.With the urea content increased,the methylene bond,co-polymerized polymethylene bond and hydroxymethyl content in MLPUF resin were increased and the curing rate was further accelerated.When the amount of urea was 6%,the resin performance is optimalthe which content of phenol hydroxymethyl was 1.63.?4?The structure of MLPF and MLPUF showed that the surface of MLPF resin had a graininess after curing.The MLPUF resin cross section had no large particles and a large number of small holes similar to honeycomb,even distribution on the surface compared with MLPF resin.