Study On Microfibrillarized Cellulose Reinforced Linear Low Density Polyethylene Composites

Cellulose is one of the most abundant natural macromolecule materials on the earth.It has high strength and modulus and is non-toxic,renewable and biodegradable characteristics.Thus,cellulose is a good reinforcement.However,the surface of cellulose contains a lot of hydroxyl groups,which make it easy agglomerates due to forming hydrogen bonds during drying process.In addition,cellulose has poor compatibility with non-polar polyolefin matrix.All of these affect the enhancement of cellulose.Therefore,reducing the agglomeration of cellulose,i.e.uniformly dispersing it into non-polar polyolefin matrix,and forming a good interface between are the key points to improve the property cellulose reinforced composites.In this study,microfibrillated cellulose(MFC)was treated by four different methods:freeze-drying,surfactant coating,acetylation and silane coupling agent treatment.The treated microfibrillarized fibers were mixed with LLDPE and melt compounded by a micro-conical twin-screw extruder.Then the composites were prepared by hot-pressing plus cold-pressing.The transmittance of MFC/LLDPE composites,dispersion of MFC in LLDPE matrix and the the mechanical properties of MFC/LLDPE composites were studied.The results are as follows:(1)Treat MFC by freeze drying(LDMFC).LDMFC can be uniformly dispersed in LLDPE matrix,and the transmittance of the composite is also improved.When the content of LDMFC is 10%,the mechanical properties of LDMFC/LLDPE composites are optimal.Compared with pure LLDPE,the tensile strength and Young's modulus of the composites increase by 60.3% and 161.9%respectively.The test results of Dynamic thermomechanical analysis show that the storage modulus and loss modulus of the composites can also be improved by adding LDMFC,and increases with the increase of the content of LDMFC.Base on the pyrolysis behavior of the composite,it is found that when LDMFC content is 14%,the LDMFC/LLDPE pyrolysis temperature increase by 14? comparing to pure LLDPE.Its thermogravimetric peak shifts toward the higher temperature.(2)Microfibrillated cellulose(MFC) was treated with complex surfactant Span 80 and Tween 80(S:T=1:1,STMFC).The binding of surfactant and cellulose was analyzed by Fourier infrared spectrum(FITR).FITR results show that the characteristic peaks of surfactant appear on MFC surface after treatment.This indicates that the surfactant is combined with MFC.It can be seen from the SEM and dispersive photos of the composites that there is no obvious agglomeration of surfactant treated MFC;STMFC can be uniformly dispersed in LLDPE matrix.However,the transmittance of STMFC/LLDPE composite film is less than that of LDMFC/LLDPE.STMFC can also improve the mechanical properties of the composites.The optimum addition of STMFC is 10%.At this time,the tensile strength and Young's modulus increase by 41.03% and 106.35%,respectively,comparing to pure LLDPE.When the content of STMFC is 14%,the maximum pyrolysis temperature of STMFC composites is 20? higher than that of pure LLDPE,and higher than that of LDMFC/LLDPE composites.The results of XRD and DSC show that the addition of STMFC has little effect on the crystallization behavior of the composites.When the content of STMFC is 14%,the maximum melting temperature of the composites increases by 6?.(3)The hydroxyl group of microfibrillated cellulose was chemically modified by acetylation treatment.It can be seen from the infrared spectrum that the stretching vibration peak of O-H on the acetylated MFC disappeared.Two new characteristic peaks were formed.They are the C=O double bond stretching vibration peak of the ester group formed by acetylation reaction and the stretching vibration peak of the new C-O bond.This indicates that the microfibrillated cellulose successfully undergoes acetylation reaction.The acetylated MFC can be well dispersed into the LLDPE matrix,and the transmittance of the YXMFC/LLDPE composite is higher than that of the previous treated methods.However,the effect of adding YXMFC on the tensile strength of LLDPE is not significant.The maximum increase in tensile strength is 21.8%comparing with pure LLDPE,and there is no significant difference compared with untreated MFC/LLDPE.It shows that uniform cellulose dispersion does not make sure to necessarily improve the mechanical properties of LLDPE composites.The interfacial bonding between matrix and reinforcement should play an important role.The storage modulus and loss modulus of YXMFC/LLDPE composites are higher than those of pure LLDPE,which is the rigidity of microfibrillated cellulose itself,but the storage modulus and loss modulus of YXMFC/LLDPE composites are both lower than that of above metioned two treatment methods.(4)Treat MFC with silane coupling agent(GWMFC).GWMFC was blended with LLDPE and melt compounded in a twin-screw extruder.GWMFC/LLDPE composites were prepared by hot-pressing and cold-pressing.The dispersibility and mechanical properties of GWMFC/LLDPE composites were tested.The results show that MFC treated with silane coupling agent can be uniformly dispersed into LLDPE matrix,and improve the mechanical properties of the composites greatly.Compared with pure LDPE,the tensile strength and Young's modulus of GWMFC/LLDPE composites increased by 45.3% and 193.6%respectively,and Young's modulus is the highest among the 4 treatment methods.From the above results,it can be concluded that the freeze-drying treatment and the silane coupling agent treatment to MFC have better reinforcing effect on the composite material.