Reinforcing Properties Of Enzymatic Hydrolysis Lignin For Acrylonitrile Butadiene Rubber

The enzymatic hydrolysis lignin (EHL) is a natural polymer extracted from residues of thebiomass enzamatic hydrolysis for producing fuel ethanol, natural gas, etc. The raw materialsinclude corn stalks, corn cobs and so on. This preparationprocess well retains EHL’s chemicalactivity, thus it can be utilized as a rubber reinforcing agent. In this paper, three physicalmethods viz. ball milling (BM), spray drying (SD), jet milling (JM) were applied in thepretreatment of two kinds of EHL including the original one (EHL) and the purified one(PEHL). The influence of these pretreatment methods on the reinforcing properties of EHLfor acrylonitrile butadiene rubber (NBR) have been investigated. And the object of thisresearch is to explore the factors from various aspects affecting the properties of the NBRblends, based on the optimal pretreatment method. These factors include the blendingconditions of NBR/lignin, using different-pretreated lignin to partly substitute carbon black(CB), and the surface (compatibility) modification of lignin particles.Among three methods, the lignin obtained from JM possesses the finest particle size,smallest bulk density, largest specific surface area, as well as the best dispersion in NBRmatrix. The average particle size of the JM lignin is just2.0~2.5μm, and its bulk density is aslow as0.30~0.34g/cm3, the BET specific surface area reaching6.3m2/g. Therefore, the JMlignin exhibits the best strengthening effect to NBR. The comprehensive performance of theNBR vulcanizate reinforced by JM lignin is remarkably superior to those by BM or SD lignin.The optimum preparation condition of the NBR/lignin blends is mixing under ordinarytemperature for25min. And the optimal lignin content incorporated in100phr (parts perhundred rubber) NBR matrix is40phr. The prapared NBR/EHL-JM displays24.44%and61.29%increase in tensile strength, respectively, comparing to the vulcanizate reinforced byEHL-BM and EHL-SD. There’s257%increase in tensile strength, compared with the pureNBR. Analysis of thermogravimetry (TG) and thermal-oxidative aging mechanical propertiesreveals that lignin can exert some thermal-stabilizing and anti-aging properties on theNBR/lignin blends. Compared with the EHL-BM and EHL-SD, the scanning electronmicroscope (SEM) images show that the EHL-JM has better compatibility with NBR matrixand stronger interfacial adhesion between the two phases.Different-pretreated EHL were utilized to substitute carbon black gradually, and then theinfluence on the reinforcing properties for NBR were evaluated. The results show thecomprehensive mechanical performance of the NBR blends decrease gradually, with EHLreplacing CB stepwisely. When50%of CB was substituted by EHL-JM, the tensile strength of the blend is20.44MPa, only22.96%lower than that of NBR/CB and the tear strengthdeclines by12.03%; however, the elongation at break increases by28.50%, reversely. Thisreveals that the blend still posesses good mechanical properties. It is observed that theremaining rates of the physical properties of the NBR/CB/EHL blends (containing noneanti-aging agents) are as high as70%~90%, after aging at100℃for72h, which indicates agood anti-thermaloxidative performance. The TG and differential scanning calorimetry (DSC)analysis exhibit that the thermal stability of the blends decrese, with EHL gradually replacingCB. Meanwhile, the intermolecular interaction forces between EHL and NBR weakensignificantly, comparing to that of carbon black and NBR. The SEM images show thetensile-fractured surfaces of the vulcanizates become irregular, and the defects inside theblends increase simultaneously, with the ratio of lignin rising in the NBR matrix.Comprehensively analyzing, there concludes CB plays a leading role in the reinforcement ofNBR, and the JM lignin can exert a subsidiary reinforcing effect on NBR.Some interface modifiers were added into lignin, then the ball milling method was appliedto mix them uniformly to complete the surface modification of lignin. The impact of theabove procedures on the reinforcing properties for NBR were investigated. It displays that theSMA550(maleic anhydride grafted styrene copolymer) has little influence on the overallreinforcing properties of this two kinds of lignin. The chosen five kinds of silane couplingagents can inhance the reinforcing effect of EHL, but have no positive impact on thereinforcing properties of PEHL. Most of the optimal dosage of A151, KH580, Si69mixed in40phr EHL-JM are1~3phr. And the tensile strength of the surface-midified EHL reinforcingNBR vulcanizates increase by10~15%, comparing to that of the unmodified (blank) one. Onthis basis, the surface-modified lignin was utilized to substitute50%of carbon black toevaluate its effect on the mechanical properties of the NBR/CB/lignin blends. Overall, theprocess does no positive impact on the mechanical properties of the NBR blends. Meanwhile,the presence of SMA550or coupling agents may even have some negative influence on thedominant reinforcing properties of carbon black.In the subsequent research, it’s a key point to explore the methods of obtaining more finelignin powders. Meanwhile, there needs to select better interface modifiers to further improvethe properties of the NBR/lignin blends. In addition, to promote the application of theNBR/CB/lignin blends in relevant fields is another valuable work. All these will contribute tofurther tapping potential of the application of lignin in macromolecular materials.