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Study on Mechanical Properties of Plant Fiber Foamed Material Composite with Sodium Silicate Gel

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Tutor: XieYongQun
School: Fujian Agriculture and Forestry University
Course: Wood Science and Technology
Keywords: Plant fiber,Foamed materials,Response surface methodology,Sodiumsilicate gel,Com
CLC: TS653
Type: Master's thesis
Year:  2013
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Abstract:
The plant fiber foamed material was a lightweight material used plant fiber of thebamboo or wood class or Poaceae stem to puff and then molded the fiber through theliquid foaming process. Its physical and mechanical performance parameters closed tothe polystyrene foam material, the flame retardant grade could up to the nationalstandard of flame retardant B1level, and could replace polystyrene foam in the fieldof construction and packaging. However, the mechanical properties of the plant fiberfoamed material were weak. In order to improve the mechanical properties of thematerial, this article used the sol-gel method and mechanical foaming method tomanufacture sodium silicate gel and plant fiber composited foamed material, thenused the Box-behnken mode in statistical software Design-Expert to study influencingfactors and optimized technological parameters, and tested verification. By usingenvironmental scanning electron microscope, X-ray photoelectron spectrometer,fourier transform infrared spectrum analyzer, thermo gravimetric analyzer, the articleanalysis and discussing the macroscopic morphology, microstructure and mechanicalproperties of the plant fiber foamed material, the fiber morphology, valence bond andchanges in functional group of the plant fiber, revealed the relationship between themechanical properties and influencing factors.First of all, the optimization of sol-gel process parameters of plant fiber foammaterial gel by the response surface method showed that:1. When the pH values stayed the same, the higher the concentration of silicaincreased, silicate gelled faster. The pH of waterglass solution was more near neutral,the shorter the gelled time of the waterglass, i.e. waterglass gelled faster; As thealkalinity or acidity of the sodium silicate solution gradually increased, sodiumsilicate gelled time relative increased and sodium silicate gelled speed relativelyslowed;2. The viscosity of the solution was first increased and then leveled along withthe rise of pH; 3. Sodium silicate gelled time became shorter as the silica concentrationincreased. When the concentration was0.5mol·L-1, the sodium silicate gel time wasonly6s, the water glass polymerize faster at this time;4. By analyzing surface micro-structure diagram sodium and photoelectronspectroscopy valence bond distribution of silicate gel we could see: when the pHvalue was7, the volume of the gel was the largest, colloidal structure was more stable,the gel surface was more smooth, the performance was better; Gel valence bond totalintensity was highest at pH value of7, the binding energy intensity was minimum inthe pH value of2.5;5. From contour map of two interoperable factors in the analysis of the responsesurface we could see: these three factors, the added amount of water glass, silicaconcentration and pH value, had a strong interaction. The primary and secondaryfactors influence on the compressive strength of the order as follows: added amountof water glass, silica concentration, pH value;6. Used Design-Expert to investigated the three key parameters affected thecompressive strength of sol-gel method enhanced plant fiber foamed material, andstudies had shown that the relationship between the silica concentration, pH value andsodium silicate added amount were more close to quadratic polynomial model. Thismodel could be expressed as:Y=46.61+4.17×A-0.30×B+2.78×C-0.60×A×B-0.73×A×C-0.720×B×C-2.57×A2-0.89×B2-0.77×C2.The correlation coefficient between the inferred and the experimental values of themodel reached up to98.87%, the model could explain97.42%of the experimentalvalues, thus the simulate similarity of model was good;7. Used response surface methodology to calculate the optimized processparameters of the plant fiber foamed material: silica concentration of0.69mol·L-1,sodium silicate dosage of55.05%and the pH value of6.39, the predictive value ofcompression strength is50.087KPa. Took into account the actual test conditions,corrected the respective conditions to: silica concentration of0.7mol·L-1, thewaterglass addition amount of55%, a pH value of6. The verification test on the test results in the correction condition obtained a compressive strength of50.1KPa, itbasically matched the values inferred by equations that indicated a good accuracy ofthe model.Secondly, the study of waterglass gel composited plant fiber foamed materialshowed that:1. A result could be seen from the single factor test. These four factors, foamingagent dosage, adhesives dosage, waterglass addition amount, the proportion ofchemical pulp, had a larger impact on compressive strength and density of the plantfiber foamed material. The four factors had a strong interaction through analysis ofresponse surface, and the order of the four factors that impacted on the compressivestrength was, in descending order: waterglass addition amount, adhesives dosage,foaming agent dosage, the proportion of chemical pulp;2. Used Design-Expert to investigated the four key parameters affected the plantfiber foamed material, and studies had shown that the relationship between them weremore close to quadratic polynomial model. This model could be expressed as:Y=55.87+0.77×A-0.47×B-0.72×C+0.41×D-2.9×A×B+0.21×A×C+2.14×A×D-3.15×B×C-0.7×B×D+1.86×C×D-0.36×A2-0.57×B2-0.50×C2-1.09×D2.The simulate similarity of model was good;3. Used response analysis to calculate compressive strength maximumoptimization of process parameters was: waterglass addition amount of43.28%,foaming agent dosage of57.31mL, the proportion of chemical pulp was2.06%,adhesives amount of34.09mL. The predictive value of compression strength was59.57KPa. Took into account the actual test conditions, corrected the respectiveconditions to: waterglass addition amount of43%, foaming agent dosage of57mL,the proportion of chemical pulp was2%, adhesives amount of34mL. The verificationtest on the test results in the correction condition obtained a compressive strength of60.1KPa, it basically matched the values inferred by equations that indicated a goodaccuracy of the model;4. Before the addition of the gel and after adding waterglass and optimizing theprocess parameters, the comparison of test results of the physical and mechanical properties of the plant fiber foamed material showed: when did not add the waterglass, the inside bonding strength of the plant fiber foamed material was56.01KPa,the modulus of elasticity was5.01MPa, the static bending strength was493.8kPa, thecompressive strength was48.35kPa, the density was0.0763g/cm3. After addingwaterglass and optimizing the process parameters, the density and mechanicalproperties of the sample increased. Contrast to not add water glass, the strength of theinternal bond strength of the material enhanced by19.5%, to66.93KPa; Elasticmodulus enhanced by23.6%, to6.19MPa; Static bending strength enhanced by22.1%, to602.9KPa; compressive strength enhanced by24.3%, to60.1KPa; densityincreased by21.0%, to0.0923g/cm3.Finally, the characterization and analysis of sodium silicate gel composited plantfiber foamed material showed that:1. The drying temperature and the addition amount of aluminum sulfate had agreater impact on morphology of waterglass gel. The higher the drying temperature,the waterglass gel surface rougher. The more the adding amount of aluminum sulfate,the more opaque of silicate gel. The fracture might be caused by Si-O-Al bondcleavage due to the evaporation of the moisture;2. According to the analysis of X-ray photoelectron spectroscopy of the gel, wecould see that start from the pH of2.5, with increasing pH value, C1s photoelectronspectroscopy wide spectral peak first widened and then narrowed, while the maximumspectral peak gradually increased from low intensity to high intensity state. As can beseen from the XPS spectra of the O1s peak, with the pH value increased, the numberof oxygen atoms bonded to carbon atoms increased;3. As could be seen from the environmental scanning electron micrographs, theconnection between the fiber and the fiber was interactive non-directional, andpresented a three-dimensional network structure; Fiber morphology varies, some thick,some relatively slender; With the increased of the added amount of the waterglass gel,the films and gels on the surface of the fiber increased. These films and gels had acertain effect on the increase of the compressive strength of the plant fiber foamedmaterial; 4. Fir fluff pulp fibers thicker and more solid than fir unbleached chemical pulpfibers; the length of most fir fluff pulp fiber was longer than fir unbleached chemicalpulp fiber length, the width of most fir fluff pulp fiber was wider than fir unbleachedchemical pulp;5. Silicate gel could inhibit heat transfer, reduce the loss of quality of thematerial, improve the thermal stability of the plant fiber foamed material, and play acertain insulation flame retardant effect;6. With waterglass gel added, before the addition of the gel and after addingwaterglass and optimizing the process parameters, the peak positions of the plant fiberfoamed material in the two infrared spectrum of the absorption curve had substantiallyno change, so there was a need for much deeper researches to understand thecondition of specific functional groups.
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