Preparation and characterization of lignin polyols
Lignin polyols were prepared using lignin as raw material,a mixture of small molecule alcohols as liquefaction agent,and concentrated phosphoric acid as catalyst.The influences of liquefaction agent ratio,liquid solid ratio(mass ratio of liquefaction agent to lignin),reaction temperature on liquefaction rate were investigated.The optimal process for preparing lignin polyols has been determined as follow:the mass ratio of liquefied agent 1,2-propanediol to glycerol of 5∶5,the liquid-solid ratio of 13∶1,the reaction temperature of 170 ℃,and the liquefaction rate could reach 99.69％.Under the optimal conditions,the hydroxyl value,acid value and viscosity of lignin polyol were 2 213.74 mg/g,40.07 mg/g and 947 mPa·s,respectively.The structure and properties detected by infrared spectroscopy and SEM showed that lignin was degraded during the liquefaction process.The rheological performance analysis results indicated that lignin polyols exhibited a phenomenon of shear thinning.
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