Research Of Polyurethane Synthesized By Modified Alkali Lignin

Polyurethane adhesive with formaldehyde-free has many of benefits, such as formaldehyde-free, little of sizing quantity and higher bonding strength, that makes its usage in the lumber industry increase gradually. But due to the factor of price, the proportion of polyurethane adhesives in wood adhesives is still smaller. Lignin is the second of biological renewable resources in nature, industrial lignin is a by-product of pulping and papermaking, the recycling rate is not high, most of them discharge with waste water, it is both pollution environment and waste resources. Lignin used in polyurethane adhesives, can both reduce the production cost and solve the problem of pollution environment which is due by optional emissions of Lignin. Therefore, the research about lignin modify has an important research value in the application area of Polyurethane adhesive.In this paper, the study improved the active hydrogen content and increased the reaction activity of lignin through aminatied and epoxidatied modification, which useed straw alkali lignin as raw material. Modified alkali lignin reacts with the4,4’-two phenyl methane diisocyanate (MDI) and polyethylene glycol (PEG) to synthesize polyurethane adhesives with acetone as solvent. The research determined the best optimal reaction conditions of two modified methods through the single factor experiment:the better process condition of synthesis of aminated lignin was using water as solvent, the mass ratio of ethylamine and lignin X was1, the reaction temperature is60℃, the reaction time was2h, then the highest rate could reach to92%; the better process condition of synthesis of oxidatied lignin was using6%NaOH solution as solvent, the mass ratio of epichlorohydrin and lignin X was4.7, the quality ratio of catalyst and lignin X’was4, the reaction temperature was80℃, the reaction time was2h, then the highest rate could reach to36%.This study characterized the chemical structure and stability of two kinds of modified lignin with FT-IR, TG, GPC and Kjeldahl Nitrogen, according to calculated, the content of N in the amination modified lignin reached to3.20%. The modified products structure conformed to prospects, and the thermal stability of two modified products improved significantly. After modification, the activated hydrogen quantity in lignin increased, and the reaction activity of lignin enhanced, lignin could be applied in adhesive synthesis yield further.This paper analysised many factors which could impact properties of adhesive, such as the raw material ratio, the molecular weight of polyethylene glycol, the isocyanate index, the content of modified lignin. The results show that the optimum reaction condition of the prepolymer was that choosing PEG (400) and MDI as raw materials, acetone as solvent, the ratio of NCO and OH was2:1, the ratio of dosage was1%(mass ratio); the synthesis temperature was60℃and the reaction time was3h. The reaction could react smoothly under this conditionWhen R was2, the corresponding wet bonding performance of PU adhesive was relative maximum, and the mechanical properties decreased with the content of lignin increasing. When wIignin was25%, the wet shear strength of aminatied lignin PU adhesive (1.53MPa) was0.43MPa more than the unmodified lignin PU adhesive, and the wet shear strength of epoxidized lignin PU adhesive (1.44MPa) was0.34MPa more than the unmodified lignin PU adhesive.Aminatied lignin and epoxidatied lignin could improve the reaction activity of NCO effectively, and which could also substitute parts of PEG, when the w modified lignin was25%, the bonding strength of corresponding adhesive reached to class I of the requirements of plywood, and the thermal stability and anti degradation ability of modified lignin rised apparently. Through taking modified lignin to the PU adhesive system, this method could improve introduction of adhesive effectively.Polyurethane adhesive makes its usage in polyurethane adhesives synthesis, this method could reduce the production cost, solve the problem of environmental pollution from the lignin free pollution, and solve the problem of waste resources at the same time.