| Effective utilization of the resources of agricultural and forestry residues and preparation of composite materials from renewable resources are important research areas in the field of green materials.Natural plant fiber reinforced resin composites have been widely interested due to the low cost,high strength-weight ratio and environmental friendliness.However,some limitations of natural fibers,such as high moisture absorption and incompatibility with matrix resin,limit the application in composites.In this study,poplar wood fiber(PWF)from poplar residues was prepared by chemi-mechanical pulping method and pretreated by different dehydration treatments.Then PWF was modified with silanes in ethanol-water solution by impregnation and spray methods,respectively.PWF reinforced epoxy resin composites were prepared by hot pressing molding method.The modified PWF had higher surface hydrophobicity and better interfacial compatibility with epoxy resin.It was shown that the composites had excellent mechanical properties,thermal stability and water resistance.The high performance of the modified PWF reinforced composites was conductive to expand the full utilization of renewable agroforestry residues and their application in the field of composite materials.1.PWF from poplar branches was prepared by chemi-mechanical pulping method and pretreated by direct drying,solvent replacement and vacuum freeze drying,respectively.The properties of PWF such as size,chemical composition,micro-morphology,element composition and hydroxyl content were characterized.The results showed that:(1)the aspect ratio of chemi-mechanical pulp fibers was lower than that of the mechanical pulp fibers.The length and diameter of PWF decreased and the aspect ratio increased with the increase of grinding degree.The aspect ratio of PWF treated by solvent replacement was higher than those treated by other dehydration methods;(2)compared to the mechanical pulp fibers,the chemi-mechanical pulp fibers had higher content of holocellulose and lower content of lignin;(3)the solvent replacement treatment avoided the agglomeration of the PWF in drying course,and the hydroxyl value of PWF reached 280 mg/g.2.PWF was modified with hexadecyltrimethoxysilane(HDS)and(Heptadecafluoro-1,1,2,2-tetradecyl)trimethoxysilane(FDS)in ethanol-water solution by impregnation and spray methods,respectively.The effects of solvent ratios,silane dosage,temperature and time on the surface modification of PWF were investigated.The properties of modified PWF were characterized by Fourier transform infrared(FT-IR)spectroscopy,X-ray diffraction(XRD),X-ray energy dispersive spectrometer(EDS),scanning electron microscope(SEM)and surface contact angle measurement.The results showed that the modified PWF had the properties of higher crystallinity,rougher surface,larger specific surface area,lower surface polarity and higher hydrophobicity.Compared with the impregnation method,the spray method had the advantages of small consumption of silane,simple process,cleanliness and high efficiency.3.1,1,1,3,5,5,5-heptamethyl-3-[2-(trimethoxysilyl)ethyl]trisiloxane(HTEO)was synthesi-zed by 1,1,1,3,5,5,5-heptamethyltrisiloxane(MDHM)and vinyltrimethoxysilane(VTMS)in the presence of Custer catalysts,and its chemical structure was characterized by FT-IR and nuclear magnetic resonance(NMR).Then HTEO and VTMS were used to modify PWF,respectively.The properties of the modified PWF were characterized by FT-IR,SEM,XRD,EDS and surface contact angle measurement.The results showed that the modified PWF had the properties of higher crystallinity,rougher surface,larger specific surface area,lower surface polarity and higher hydrophobicity.4.PWF reinforced epoxy resin composites were prepared by hot pressing molding method.The structure and properties of the composites were studied by mechanical properties test,thermogravimetric analysis,water absorption test and section morphology analysis.The results showed that the fiber size,content and silane modification had significant effects on the properties of composites.The mechanical properties of the composites were significantly improved after silanes modification,which was attributed to the improved interfacial compatibility between PWF and epoxy resin matrix.The impact strength,flexural strength and flexural modulus of the composites reinforced with HTEO modified PWF were 10.8 k J/m~2,101.8 MPa and 10126 MPa,respectively,which were 63.9%,100.3%and 35.0%higher than those of unmodified composites.Besides,the water resistance and thermal stability of the modified PWF reinforced composites were improved. |
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