Properties Of Nano-TiO₂ Modified Wheat Straw Fiber/Polypropylene Foamed Composites

As a new type of environmental protection material,biomass fibers/thermoplastic composites have been widely used in constructions and parks.However,some problems,such as heavy weight,high volume expansion rate,and poor weatherability,have seriously hindered its development.In this study,TiO2 nanoparticles surface-modified by silane coupling agent were used to prepare wheat straw fiber/PP foamed composites as a filler by blending,the effects of surface modified TiO2 nanoparticles on mechanical properties and anti-UV performance of wheat straw fiber/PP foamed composites were investigated.On this basis,to improve the dispersion of nanoparticles and increase the possible interactions between wheat straw fiber and the PP matrix,the TiO2 nanoparticles were surface-modified by two kind of silane coupling agents respectively,then the wheat straw fibers were vacuum pressure-impregnated by nano-TiO2 suspension,and surface modified TiO2 nanoparticles were used to prepared nano-TiO2 modified wheat straw fiber/PP foamed composites as interface compatibilizer.The effects of TiO2 nanoparticles modified by different kind of silane coupling agents on the properties of wheat straw fiber/PP foamed composite were evaluated.The surface modification mechanism of TiO2 nanoparticles and the enhancement mechanism of the interface compatibility of the TiO2 nanoparticles on the interface were revealed.The aim of this study was to improve the mechanical property of biomass fiber/thermoplastic foamed composites and give them UV aging resistance,to establish and perfect the modification system of biomass fiber,to provide theoretical basis and technical support for both the large-scale efficient utilization of biomass resources and the performance optimization of biomass fiber/thermoplastic composites.The main details were summarized as follows:(1)The properties of surface-modified TiO2 nanoparticles/wheat straw fiber/PP foamed composites by direct blending preparation were studied.Ti02 nanoparticles(0,1,1.5,2,2.5,3 wt.%)surface-modified by vinyltrimethoxy silane(A171)were directly mixed with each component to prepare wheat straw fiber/PP foamed composites as a filler.The results indicated that the organic functional groups of A171 were successfully grafted onto the TiO2 nanoparticles.The thermal stability of the wheat straw fiber,the mechanical properties and anti-UV performances of the composites all reached the highest value when the surface-modified TiO2 nanoparticles content was 3%.Compared with the control group,the weight loss rate of wheat straw fiber only decreased by 8%,and the thermal stability of wheat straw fiber was improved slightly.The flexural strength,tensile strength and impact strength increased by 64.52%,104.98%,and 518.87%,respectively,and the mechanical properties were significantly improved.A higher UV stability of the samples treated with modified Ti02 nanoparticles was exhibited by the study of the color change and loss in mechanical properties.The flexural strength,tensile strength and impact strength loss rate decreased by 76.01%,65.1%,and 63.06%,respectively,and the surface color change decreased by 25.3%after ultraviolet aging treatment.(2)The surface modification of TiO2 nanoparticles by different kind of silane coupling agents and its effects on the properties of wheat straw fibers were studied.TiO2 nanoparticles were modified by two kinds of silane coupling agents,A171 and y-aminopropyl triethoxy silane(KH550),respectively.The results indicated that both silane coupling agents were grafted onto the surface of TiO2 nanoparticles by Ti-O-Si,and the grafting rate of KH550 was slightly higher than that of A171,but it did not change the crystalline structure of TiO2 nanoparticles.The smaller particle size and better dispersion of TiO2 nanoparticles(30-45 nm)were obtained after modified by silane coupling agent KH550.After vacuum pressure-impregnated by nano-TiO2 suspension(0,1,3,4,5 wt.%),some nanoparticles were penetrated into wheat straw fiber cells with hydrogen bonding,and excess nanoparticles formed a weak interfacial layer on the surface of wheat straw fibers.UV-shielding behavior of the wheat straw fiber was obtained with the TiO2 nanoparticles,the surface modified TiO2 nanoparticles reduced the light transmittance of the wheat straw fiber by about 10%when the surface modified TiO2 nanoparticle content was 5%.(3)The properties of nano-TiO2 modified wheat straw fiber/polypropylene foamed composites were investigated.TiO2 nanoparticles were surface-modified by A171 or KH550,then the wheat straw fibers were vacuum pressure-impregnated by nano-TiO2 suspension(0,1,3,4,5 wt.%),and surface modified TiO2 nanoparticles were used to prepared nano-TiO2 modified wheat straw fiber/PP foamed composites.The results showed that unmodified TiO2 nanoparticles or silane coupling agent surface-modified TiO2 nanoparticles all improved the mechanical properties of wheat straw/PP foamed composites,and the enhancement of mechanical properties was obvious for surface-modified TiO2 nanoparticles treated composites.The mechanical properties were enhanced first and then decreased with the increase of either A171-modified TiO2 or KH550-modified TiO2 nanoparticles.However,no remarkable differences were recorded among the pure TiO2 nanoparticle-incorporated samples.The mechanical strength was highest for the samples treated by KH550-modified TiO2 at 4%,and the flexural strength,tensile strength and impact strength increased by 83.05%,128.62%,and 490.91%,respectively.Besides,unmodified TiO2 nanoparticles or silane coupling agent surface-modified TiO2 nanoparticles all improved the unti-UV properties of wheat straw/PP foamed composites,and the enhancement of unti-UV properties was obvious for surface-modified TiO2 nanoparticles treated composites.After UV aging,the color change and loss in mechanical properties.of samples treated by surface modified TiO2 nanoparticles showed a decreasing tendency along with the increasing concentration of modified TiO2 nanoparticles,except for a increase at a high level of modified TiO2 nanoparticle loading.The loss in mechanical strength was lowest for the samples treated by KH550-modified TiO2 at 4%,and the loss in flexural strength,tensile strength and impact strength decreased by 84.36%,81.05%,and 86.83%,respectively,compared to control group.The color change and loss in mechanical properties.of composites were not obvious with addition amount of pure TiO2 increasing.