Study On Preparation Of Low Molecular Weight Lignin And Its Application Performance In Thermoplastic Elastomer

Thermoplastic elastomers have both the high elasticity of rubber and the easy processing ability of plastics.It is gradually replacing traditional rubber in many fields and has a wide range of uses.However,the anti-aging properties of thermoplastic elastomers are insufficient,and antioxidants need to be added during its processing and application to delay the aging process.At present,the commonly used small molecule antioxidants have problems such as high cost,migration,precipitation,toxic,environmental pollution.Lignin is rich in phenolic hydroxyl,aromatic ring structure and has certain antioxidant capacity.It has the advantages of low price,non-toxic,degradable and has the potential as a green antioxidant.However,its performance is inferior to commercial antioxidants and difficult to use directly.Therefore,carrying out research on the antioxidant properties of lignin and developing high value-added natural antioxidants are of great value for the high-value utilization of lignin.Aiming at the problem of the prove antioxidant capacity of lignin,this article uses two methods to treat lignin:alkali-catalyzed depolymerization and organic solvent extraction.Alkali-catalyzed depolymerization is to partially depolymerize the enzymatically hydrolyzed lignin in an alkaline environment to reduce its molecular weight and increase the content of phenolic hydroxyl groups.The organic solvent extraction method is to extract the enzymatically hydrolyzed lignin and alkali lignin with ethanol or ethyl acetate to reduce their molecular weight and increase the phenolic hydroxyl content.The prepared low molecular weight lignin is used as an antioxidant.Lignin/SBS composites were prepared by melt blending low molecular weight lignin and polystyrene-butadiene-styrene triblock copolymer(SBS).Further use low-molecular-weight lignin as a macromonomer to partially replace petrochemical multi-component to synthesized lignin-based polyurethane elastomer.The effect of lignin on the mechanical properties and thermal oxidative aging resistance of the elastomer is systematically explored.The main conclusions are as follows:(1)After the treatment,the molecular weight of the enzymatically hydrolyzed lignin and alkali lignin decreased significantly,and the content of phenolic hydroxyl group increased significantly.The weight average molecular weight of enzymatically hydrolyzed lignin decreased from 4500 g/mol to 1700 g/mol after alkali-catalyzed depolymerization for 8 hours,and the phenolic hydroxyl content increased from 2.10 mmol/g to 3.75 mmol/g;After extraction with ethyl acetate,the molecular weight of alkali lignin decreased from 3000 g/mol to 900 g/mol,and the phenolic hydroxyl content increased from 2.88 mmol/g to 3.80 mmol/g.After the enzymatic hydrolyzed lignin and alkali lignin are processed,the free radical scavenging ability is significantly improved.The IC50 value of the alkali lignin AOE extracted with ethyl acetate is 0.023 mg/ml,which is lower than the IC50 value of Irganox1010(0.026 mg/ml).AOE showed slightly higher free radical scavenging ability than Irganox1010 in aqueous solution.(2)Lignin/SBS composites were prepared by melt blending low molecular weight lignin and SBS.The results show that under low loading,the interface compatibility between lignin and SBS is good,and lignin is uniformly dispersed in SBS,with an average particle size of 40nm.Lignin can significantly improve the antioxidant capacity of SBS,and the oxidation induction time of composite materials with 2.5%AOE is more than 60 minutes.After aging at90?for 18 days,the retention rate of the mechanical properties of the composite materials exceeded 100%,and the lignin in SBS showed better oxidation resistance than Irganox1010.(3)Low molecular weight lignin is used to partially replace petrochemical polyols to synthesize lignin-based polyurethane elastomers with good strength and toughness.The tensile strength of the sample with 10%lignin AOE addition was 35.9 MPa,and the fracture absorption energy reached 151.0 MJ/m~3.The samples have good elasticity,and the elastic recovery rate is generally above 95%.The samples have good reprocessing ability,and the retention rate of mechanical properties of the sample R1.4AOH20 after reprocessed twice exceeds 70%.Thermal oxygen aging experiments show that lignin can significantly improve the anti-aging ability of polyurethane elastomers.The tensile strength of R1.4EOH10 can still reach 69%after 18 days of thermal and oxygen aging at 100 degrees Celsius,and the retention of elongation at break can reach 75%.Polyurethane elastomers without lignin are broken after aging for 6 days.