Study On Preparation And Performance Of Tetrahydrofurfuryl Alcohol Lignin Phenolic Resin

Phenolic-formaldehyde(PF)resin is a polymer material with high bonding strength,moisture resistance,and thermal stability which is widely used in exterior grade plywood.PF resin is usually synthesized from petroleum-derived phenol and formaldehyde.Due to the gradual depletion of fossil resources,the environmental pollution,and the toxicity of phenol,it is urgent to find a renewable alternative raw material.The lignin in biomass has the basic structural unit of phenols and has great potential to replace phenol.Many studies have used it to synthesize phenolic resin in a certain proportion.However,there are still some problems such as low phenol substitution rate,poor performance and so on.To solve these problems,this thesis has carried out the research on the following three aspects:1.Optimization of lignin extraction with tetrahydrofurfuryl alcohol and phenolization modification conditions.Poplar(hardwood),pine(softwood),corn stalks(Gramineae)and walnut shells(nut shells)were chosen as raw materials for lignin extraction.After analysis with Fourier Infrared Scanning Spectrometer(FT-IR),it was found that there are G and H-type structural units in the lignin of corn stalk,while pine lignin is mainly composed of G-type structural unit.Lignin of poplar and walnut shell is mainly S-type with small amount of G unit.This structural feature makes the active sites content of lignin obtained from corn stover/pine relatively high.Gel chromatography(GPC)and nuclear magnetic resonance(~1H-NMR)analysis showed that the weight-average molecular weight of corn stover/pine lignin was lower than that from walnut shell and poplar,while the active sites were relatively higher.Finally,the lignin activity was further improved by phenolic modification.The optimized phenolic reaction conditions walnut shell lignin were obtained:15%(w/w)Na OH,120℃,90 min.Under this condition,the phenolic hydroxyl group of lignin increased to 2.4%.This will provide raw materials with higher reactivity.This will provide raw materials with higher reactivity for the subsequent synthesis of phenolic resin.2.The effects of phenol-formaldehyde ratio,catalyst concentration,and phenol substitution rate on the performance of the synthesized lignin-based phenolic resin were studied.The lignin based phenolic resin with higher bonding strength(1.34 MPa)and lower free formaldehyde content(0.27%)was synthesized under phenol and formaldehyde at ratio of 1:1.8,15%(w/w)Na OH and phenol substitution ratio of50%,which fully met the national standards(bonding strength≥0.7 MPa and phenol content≤0.3%,respectively).After comparing the curing temperature of the synthesized resin,it was found that the phenolic resin synthesized with phenol and formaldehyde as raw materials was 122℃,while the walnut shell lignin-based phenolic resin with a 50%phenol replacement rate reached 140℃.This shows that the lignin synthesis of phenolic resin could increase the curing temperature.The optimized synthesis process provides an experimental method for the subsequent synthesis of lignin phenolic resin with a high substitution ratio of phenol.3.After preparing lignin-based phenolic resins with lignin extracted from different raw materials(hardwood,softwood,and grass)and analyzing their performance,it was found that under the same 50%phenol replacement ratio,the bonding strength of corn stover/pine/poplar lignin phenolic resin reached 1.40 MPa,1.35 MPa,and 1.34MPa and the curing temperature was 135℃,138℃and 140℃respectively.The formaldehyde content in all the resins also met the national standard.Among the three lignins,only phenolic resins made from pine/corn stover lignin met the national standars with the phenol replacement ratio at 70%.Among the three lignin,only phenolic resins made from pine and corn stover lignin have reached a relatively high level in terms of the replacement rate and resin performance.Through the present study,it was found that lignin extracted from corn stover and pine with tetrahydrofurfuryl alcohol can produce lignin-based phenolic resin with a phenol substitution ratio of 70%.The resins were proved to meet the national standards in terms of bonding strength and formaldehyde content.To a certain extent,This would provide the technical support for preparing phenolic resin with high lignin addition ratio.