| Lignin is the second largest component in plants.The molecule’s functional groups such as aromatic rings and phenolic hydroxyl groups endow it with ultraviolet shielding and anti-aging functions.Ethylene-octene copolymer(POE)is a kind of non-polar thermoplastic Polyethylene elastomer,which has the elasticity of rubber and the ease of processing of plastic.However,POE has a low melting temperature and weak mechanical strength,so it is usually used as a toughener for plastic modification,or as a rubber phase for polyolefin thermoplastic elastomer composites.Utilizing the characteristics of high glass transition temperature and rigid structure of lignin to modify POE,thermoplastic elastomer composites with lignin as the plastic phase and POE as the rubber phase are prepared,which increases the strength of the material,reduces the use of fossil resources,and promotes the high-value utilization of lignin resources.And it can not only reduce the use of fossil resources,but also promote the high-value utilization of lignin resources.However,the direct blending of polar lignin and non-polar POE results in poor dispersibility and compatibility,which leads to poor performance of the composites.In this study,based on the rich characteristics of oxygen-containing polar groups in Enzymatic hydrolysis lignin,a strategy of in-situ construction of interfacial metal coordination bonds between lignin and polyethylene elastomer by melt blending was proposed to solve the problems of weak interfacial force and poor compatibility between lignin and nonpolar polyolefin materials and realize the simultaneous strengthening and toughening of polyolefin elastomer composites by lignin.Furthermore,lignin/POE elastomer composites were applied to polypropylene to prepare polyolefin thermoplastic elastomer composites,which explored a new path for the application of lignin in polyolefin materials.The main research results are as follows.(1)The metal coordination bonds are constructed at the phase interface of the lignin/POE elastomer composites,and the mechanical property of the composites material is remarkably improved.The abundant polar functional groups of lignin are used as natural ligands of zinc ions,3-amino-1,2,4-triazole is introduced as a reactive compatibilizer,and the interface metal coordination bonds are constructed in-situ between lignin and maleic anhydride-grafted ethylene-octene copolymer elastomer(PM)by adopting a melt blending method.A thermoplastic elastomer composite material was prepared using lignin as a plastic phase and PM as a rubber phase.The tensile strength of the sample(PM content 80 wt%and lignin content 20 wt%)with metal coordination bonds constructed is 21.4 MPa,which is 35%higher than that of pure PM.The elongation at break exceeds 600%,and the toughness reaches 70.9 J/cm3,which is 100%higher than that of PM and twice as much as that of the sample without metal coordination bonds,thereby realizing the simultaneous strengthening and toughening of PM by lignin.In addition,the sample has excellent shape memory function.(2)The strengthening and toughening mechanisms of metal coordination bonds on lignin/POE composites were further revealed by atomic force microscopy and small angle scattering.The results show that the intermolecular force between lignin and PM is increased by 45%with the construction of metal coordination bonds,and the compatibility between the two is significantly improved.The average dispersed particle size of lignin in the composites decreases from 2000 nm to 200 nm,and the dispersibility greatly improves and the phase boundary area is also increased.The test results such as stress relaxation,variable elongation and constant elongation reveal the mechanism of energy dissipation of metal coordination bonds.It also proves that the weak bond properties and reconfigurability of metal coordination bonds play a role in strengthening and toughening.Through the deformation mechanism research such as small angle scattering and x-ray diffraction,it is found that the metal coordination bond constructed by lignin synergy can greatly improve the energy dissipation under the action of external force.At the same time,due to the constraint effect of the interface metal coordination bond,the crystallizable segments and partially oriented segments are promoted to form new micelle crystals during the stretching process,and the self-strengthening of the material is achieved.(3)The effects of different nitrogen heterocyclic compounds as reactive assistants and different metal ion centers on coordination bonds were studied.The results show that the effects of using different nitrogen heterocyclic compounds to construct metal coordination bonds from excellent to poor were:3-amino-1,2,4-triazole,1,2,4-triazole,imidazole,while 3aminopyridine and pyrrole could not effectively construct interfacial coordination bonds.The 3-amino-1,2,4-triazole containing a triazole heterocycle and a nitrogen-containing branch chain could construct stronger metal coordination bonds in the composite.The tensile strength of the sample PMLAZ(PM content 80 wt%and lignin content 20 wt%)prepared by using 3-amino1,2,4-triazole as reactive assistants reaches 16.1 MPa,4.94%and 4.50%higher than that of pure PM and PML(lignin content 20 wt%)without metal coordination bond,respectively.The toughness of the sample PMLAZ is 71.5 J/cm3,which is 74.3%and 26.1%higher than that of PM and PML respectively.The metal coordination bonds constructed by ferric ions as the metal center could enhance the rigidity of the composites better than that of divalent zinc ions.The tensile strength and toughness of PMLAF1(lignin content 20 wt%)prepared by ferric ions as metal centers are 14.2%and 12.5%higher than PMLAZ at 800%strain respectively.The comprehensive properties of lignin-elastomer composites can be optimized by selecting different reactive additives or metal salts and the number of additives.(4)The application of lignin/PM composite elastomer in polypropylene(PP)was further studied,and the polyolefin thermoplastic elastomer composites were prepared by blending lignin/PM with pp,which improved the UV-shielding and thermal oxygen aging resistance.The results show that the mechanical properties of the composites prepared by the two-steps process(lignin and PM first blended to prepare composite master batch,and then blended with PP)are slightly higher than those prepared by the one-step process(lignin,PM and PP directly blended).The mechanical properties of composites with metal coordination bonds are also higher than those without metal coordination bonds.The tensile strength,elongation at break and toughness of the sample prepared by the two-step method with 90 wt%of PP,8 wt%of PM,2 wt%of lignin and metal coordination bonds are 35.7 MPa,734%and 173.3 J/cm3,respectively.The tensile strength,elongation at break and toughness of the sample with 80 wt%of PP,16 wt%of PM,4 wt%of lignin and metal coordination bonds are 31.2 MPa,725%and 145.6 J/cm3,respectively.The UV-shielding rate of PP80-P16L4A with lignin content of 4 wt%and incorporation of metal coordination bonds reaches 99.5%,which are higher than that of composites without metal coordination bonds.The UV-shielding performance is excellent.The thermal oxygen aging resistance of PP composites is improved by lignin.The construction of metal coordination bonds also contributes to the thermal oxygen stability of the composites. |
PDF Full Text Request