The Extraction Of Silica In Biomass And Application In Poly (Ethylene Terephthalate)

With the rapid development of world economy, a large number of fossilresources are consumed, which led to a series of problems such as energy depletionand environmental pollution.Therefore, how to use fossil resources more efficiently,reduce the rate of consumption becomes an important issue for human beings'survival and development.Biomass, as a kind of renewable resourcescan store solarenergy and be used as a complement and substitute for fossil resources. We canextract renewable biomass materials instead of fossil resources raw materials, increaseaccession to polymer and reduce the ratio of the polymer in products, thus can reducethe rate of consumption of oil and coal indirectly, and create the conditions for humanto develop new energy and new resources.Poly (ethylene terephthalate)(PET) as a petrochemical derivative, is aversatile production of polymer materials, which has good mechanical and physicalproperties, wear resistance, heat resistance, chemical resistance, insulation and lowprice, has been widely used in the field of polyester fiber, film, beverage packaging,textile and garment production, so the demand is huge.In this dissertation, PET was prepared by direct esterification with terephthalicacid and ethylene glycol using self-designed continuous reactor. The optimumreaction conditions and technological process were determined by experiment. Theresults showed that the productions had large viscosity, high molecular weight anddegree of crystallinity. By the tests of infrared spectroscopy, intrinsic viscosity andcontent of carboxyl end group showed that the intrinsic viscosity of PET could reachup to0.75dL g^-1, the molecular weight was21100g mol^-1, the carboxyl end groupcontent was39.5mol t^-1. The indicators were meet national standards. Crystallizationkinetics and the mechanism of hair color of PET were discussed by the tests of TGA,DSC, and the color, which provided a theoretical basis and experimental conditionsfor the follow-up of modified work.In this thesis, silica was extracted from the rice husk ash with ammoniumfluoride which was the by-product in fertilizer production as dissolved silicon agent by a recyclable method. It was found that silica could be synthesized at reactiontemperature of393K for2h, with NH4F concentration of4mol/L. All the chemicalreagents used in the reaction process were recycled to reduce costs and environmentalpollution. Transmission electron microscopy (TEM), X-ray diffraction (XRD),infrared spectroscopy (FTIR), elemental analysis and other analysis results showedthat the final product SiO₂is spherical with the diameter of50to60nm, the yield ofproduct could reach up to94.6%. The final product has fine features of high purity,small particle size and uniform distribution. Compared with the traditional process,the process got rid of the drawbacks of high energy consumption, high carbon dioxideemissions and the lack of high grade silica sand, which greatly reduced the cost ofproduction and investment. Therefore, it was more suitable for large-scale production.On the basis of this process, the rice husk as raw material, improve theacid-catalyzed hydrolysis of the sugar acid, in situ polycondensation charringpreparation of colloidal carbon, and then the use of ammonium fluoride preparation ofsilica and lignin. The nano-SiO₂and lignin products were high purity, small particlesize and size distribution, the utilization of raw materials was more than90%. Thewhole experimental process had optimized and simplified the methodof the comprehensive utilization of rice husk.PET/SiO₂nanocomposites and PET/lignin composites were prepared via in situpolymerization. Composites containing SiO₂nanoparticles and lignin showed a gooddispersion from SEM results. Lignin and PET can produce cross-linked structure toform the elastomer. Porous materials were prepared when the material comes out.Lignin played the role of crosslinking agents and fillers in the material. DSC, TGAresults showed that the addition of SiO₂nanoparticles obviously increased thermalstability and crystallization rate of PET. In situ polymerization method can be furtherextended to lignin and other organic materials. The method can also be extend theapplications of inorganic nanoparticles by changing the polymer system. This greatlyextended the comprehensive utilization of rice husk.Finally, the SiO₂extracted from rice husk ash were modified in situ byhexadecanol under moderate water. SiO₂particles were prepared withdifferent hydrophobic properties by different heat treatment methods.PET/SiO₂nanocomposites were prepared by in situ polymerization. According to theexperimental results, we proposed a simple model, SiO₂were modified byhexadecanol and the mechanism of dispersion in the PET matrix was studied. The hexadecanol could reduce the surface energy and surface tension of SiO₂nanoparticles through the formation of organic silicon structure, which reduced theinteraction between the particles, resulting in better compatibility in thecomposite. SEM results also showed that there was no phase separation phenomenonbetween PET and modified SiO₂nanoparticles. The interaction between PET,hexadecanol and SiO₂was not the main reason for disappear of phaseseparation. DSC, TGA results showed that adding of SiO₂nanoparticles modified byhexadecanol significant increased thermal stability and crystallization rate ofPET. This method of modification and polymerization in situ could be furtherextended to surface modification of other inorganic nanoparticles, the surfacewettability of inorganic could be changed by changing the alcohol carbon chain lengthof modifiers. Application of inorganic nanoparticles could be expanded by changingthe polymer system. The entire experimental process optimized the preparation ofnano-SiO₂, surface modification and preparation of composite materials. ModifiedSiO₂composites with polymer materials showed good dispersion compared to theunmodified SiO₂, which greatly extended the application of technology research forcomprehensive utilization of rice husk.