Preparation And Evaluation Of Lignin-plastic Composite

Lignin is the second largest abundant renewable biopolymer. Preparing lignin-plastic composite using lignin and plastic is one of the ways to efficiently utilize thisabundant renewable resource in large scale. The utilization of lignin in plastic fieldcan save large quantities of fossil resource and reduce the environmental pollution,which promotes the utilization of biomass resources, environmental protection andsustainable development of society.In this work, the polyethylene and polypropylene are used as substrate material.The wheat straw alkaline lignin(AL), enzymatic lignin(H)(EL(H)) and enzymaticlignin(NY)(EL(NY)) are used as lignin raw material to prepare lignin-plasticcomposite. The effect of different raw lignin types and the different pretreatmentmethods on the properties of composite including elongation at break, tensile strength,tensile modulus of elasticity, morphology, water absorption, the melt index ofcomposites and additives on the performance of lignin/polypropylene composites arestudied. The obtained results can give some theoretical guidance and basic parametersfor the processing and application of lignin-plastic composites.The addition of lignin reduces the elongation at break of polyethylene orpolypropylene composites significantly. The EVA can improve the elongation at breakof polyethylene or polypropylene composites.The addition of lignin can improve the tensile strength of the lignin/polyethylenecomposite. AL(spray drying), AL(air jet mill) can improve the tensile strength oflignin/polyethylene composite higher than others. AL(spray drying) improve thetensile strength of lignin/polyethylene to12.88MPa, which is higher than the purepolyethylene by40.28%. The addition of lignin make the tensile strength ofpolypropylene composites decrease, EL (NY)(air jet mill) is better than the other twotypes of lignin. The lignin pretreated by air jet mill is better than that pretreated byball mill for strength of the composite. The addition of MAH-G-PP(PC-1) cansignificantly improve the tensile strength of lignin-polypropylene composites. At5% dosage of MAH-G-PP(occupy PP), when lignin weight are30%,40%,50%of thelignin-polypropylene composites, the strength are35.33MPa,31.40MPa and25.67MPa, improved by29.46%,36.88%and28.35%, respectively.The addition of lignin makes the tensile modulus of elasticity increase no matterpolyethylene than polypropylene composites, and increase with the increase of lignincontent.The effect of lignin on the lignin-plastic composite's water absorption is studied.The results show that the water absorption of composite increases with the increase ofthe lignin content. The30-days water absorption of composites is lower than1.0%when the lignin quality content is less than30%except AL(spray dried). The waterabsorption of the AL composites is lower than that of the EL composites.The dispersed state of lignin disperses in lignin-plastic composite is studied bythe morphology of the composites. For polyethylene-based composites, the―matrixdestruction‖is observed on the section when the AL and EL (NY) are added, but the―interface destruction‖is observed when the EL(H) is added. The interaction of theformer two lignins with the base materials is larger than the third. The―Fiberdestruction‖is observed when the AL(spray dried) is added, which shows stronginteraction between lignin and polyethylene based. The―Interface destruction‖isobserved when the lignin is added to polypropylene, which shows a small interactionbetween them.The melt index increases then decreases with the increase of the lignin contentfor the lignin/polyethylene composite and it is lower than the pure polyethylene. Themelt index decrease with the increase of the lignin content increase for thelignin/polypropylene composites and it is higher than pure polypropylene when thelignin content is less than30%. The smaller particle size of lignin in lignin-plasticcomposite is good for the melt index.