Study On Mechanism Of Ultrasonic Assisted Dissociation Technology And Its Applications Of Non-Wood Fiber

In view of the waste of resources and environmental pollution caused by the waste and incineration of agricultural straw in China,to solve the shortage problem of raw materials in papermaking industry,and to widen the source of fiber raw materials,the ultrasonic dissociation of non-wood fiber and its properties and application were studied in this paper,and the technical parameters of ultrasonic oxidation-assisted dissociation of fiber raw materials were optimized.As a typical fiber raw material,the wheat straw fiber properties made by ultrasonic oxidation-assisted dissociation technology were investigated by means of scanning electron microscope(SEM),infrared spectroscopy(IR),thermogravimetric analyzation(TG),X-ray spectroscopy(XRD),Raman spectroscopy and nuclear magnetic resonance spectroscopy(NMR),ect.The mechanism of ultrasonic oxidation-assisted dissociation and research on papermaking and fiberboard preparation was discussed.The findings are as follows:According to the basic principle of ultrasonic synergy and auxiliary oxidation,the process of ultrasonic oxidation-assisted dissociation of wheat straw fiber raw material were researched.Then the ultrasonic oxidation-assisted dissociation technology suitable for wheat straw was explored,and the performance of ultrasonic wheat straw pulp was analyzed.The findings are as follows:ultrasonic frequency is 20 kHz,ultrasonic power density is 3W/cm3,reaction temperature is 20 ?,material concentration is 15%,reaction time is 2 hours and heat preservation is 0.5 hours.The stirring speed is 500 rms,the amount of potassium hydroxide is 2%,ammonia water is 6%,sodium dodecyl sulfonate is 0.5%,sodium silicate is 8%,and magnesium sulfate is 1%.Under these conditions,the yield of ultrasonic pulp was 71.3%,and whiteness and strength properties were both exceed the national standard of bleaching alkali wheat straw pulp(GB/T 26188-2010).Simultaneously,ultrasonic oxidation-assisted dissociation experiments were also carried out on other non-wood materials,such as reeds and bamboos.In order to explore the mechanism of wheat straw ultrasonic oxidative-assisted dissociation pulping and study the related properties of wheat straw pulp,various instruments were tested and analyzed on ultrasonic wheat straw pulp and chemical wheat straw pulp.Results from the fiber properties show that the average fiber length is 0.809mm.And the whiteness and strength properties of ultrasonic wheat straw pulp is better than chemical wheat straw pulp,which the tensile index is 32.49N m/g,the folding resistance is 45 times and tear index is 3.98 mN m 2/g.Results from the analysis results of wheat straw pulp components reveal that the contents of ash,holocellulose and lignin are respectively 24.92%,69.04%and 4.31%.In addition,from the results of SEM,TG and XRD,The fiber of ultrasonic oxidation-assisted wheat straw pulp is relatively complete,with coarse and hard surface,particle matter on the surface.Ultrasonic oxidation-assisted wheat straw pulp has higher crystallinity than chemical wheat straw pulp,and it is speculated that a crystalline filler material was formed due to a sharp diffraction peak at 2?=26.5° on the XRD diagram.At the end of heat loss of TG,the final residual amount of wheat straw pulp is about 30%,cellulose is about 10%,and lignin is about 22%,which indicates that ultrasonic oxidation-assisted has caused a large change in the structure and properties of lignin.In view of the generation of reactive oxygen species and the influence on fibers in ultrasonic oxidation-assisted pulping,we successfully demonstrated that in the process of ultrasonic oxidation-assisted dissociation pulping,the reactive oxygen groups such as hydroxyl radicals(HO·),hydrogen peroxy radical(HOO·)are indeed present in the liquid medium through alizarin violet colorimetry and sea fluorescein analog(FCLA).And the generation mechanism of reactive oxygen groups such as hydroxyl radicals(HO·)and the degradation mechanism of functional groups such as aromatic rings and double bonds in lignin are described.Therefore,the mechanism of ultrasonic oxidation-assisted dissociation is as follows:under the synergistic action of ultrasonic mechanical effect,thermal effect and cavitation effect,the intercellular layer of the raw material fiber cells is divided at first,which causes the chemical medium to enter the fibroblasts rapidly and fully.Then some of the lignin small molecule in the middle lamella(ML)and corner layer(CC)were dissolved in solution with degrading,and then wheat straw raw material were dissociated to form pulp.Ultrasonic oxidation-assisted produces reactive oxygen group,hydroxyl radical(HO·)and hydrogen peroxy radical(HOO·),and oxidizes with lignin to form non-chromogenic substances.Ultrasonic wheat straw pulp fiber has good bonding force during sheet forming.First,the pulp produces a beating effect under the action of ultrasonic waves and raw material fiber was more fully wetting,swelling and soft.And then the strengther fine fibrosis and bigger fiber surface area,cause more exposure of hydroxyl,which can form more hydrogen bond.Additionally,under the effect of hydroxyl radicals(HO·)and hydrogen peroxy radical(HOO·)produced by ultrasonic,residual lignin in pulp generated more hydroxyl,carboxyl and active sites.Then more hydrogen bond and cross-linking produced,which could improve the bonding strength of the fiber.The paper blending experiment with ultrasonic wheat straw pulp was carried out,and the parameters such as the ratio of blending,the amount of additives were studied.The paper types included offset paper,newsprint,multilayer food card,monolayer food card and ordinary food wrapping paper,etc.The preparation of medium density fiberboard(MDF)with 100%ultrasonic wheat straw fiber was studied and the compound properties of flame retardant and water repellent were optimized.Each index of the product reaches or exceeds the value of the state or industry standard.In conclusion,the ultrasonic oxidation-assisted dissociation technology of non-wood fiber has a good development prospect,the strength and optical properties of ultrasonic-assisted wheat straw pulp fiber are excellent,and it can be used as a useful supplement to the traditional pulp.It could also be used to prepare green buiding or indoor fiberboard.