| In this thesis,corn straw,new rape straw and old rape straw were used as raw material to prepare glueless biomass board in wet process.Self-bonding mechanism was researched using x-ray diffractometer,Thermogravimetric instrument and Fourier Infrared Spectrometer.Furthermore,Density Functional Theory method was also used to analyze the effect of hot pressing pressure on hydrogen bond and covalent bond.The conclusions are as follows:(1)Benzene-Alcohol extractive content,lignin content and pentosan content of corn straw were more than rape straw while ?-cellulose content and holocellulose content were less than it.Lignin content and ?-cellulose content of corn straw and rape straw were less than that of the woods while pentosan content was larger than them.Lignin content,?-cellulose content and pentosan content of old rape straw were larger than new rape straw while Benzene-Alcohol extractive content was less than it.The cellulose,hemicellulose and lignin decomposed after one year so the quantity of monosaccharide rose that was the reason Benzene-Alcohol extractive content became larger for the old rape straw.For rape and corn straw,the most length segmentation was 0.5mm~1mm and the average length of the fiber were 1.4mm and 1.14 mm separately.For rape straw,ratio of length to width was51 which could reach to wood s' and for corn straw,that is 80 which could exceed many kinds of the woods'.As far as fiber Morphology and chemical contents were concerned,these two kinds of straw could be use as a substitute of wood for board producing.Rape straw was more suitable for board making because of its ?-cellulose content and the length of the fiber.(2)The process of board making was four steps: soaking,refining,shape recovery and hot-pressing,through which the biomass board was successfully produced.For corn straw and rape straw,the range of the density is from 0.93g/cm3 to 1.15g/cm3,which could be classified as hardboard according to Japanese Industrial Standard(JIS).Under the same hot pressing condition,the density of board made from the new rape straw was larger than the one from the old rape straw.There was little difference of Moisture Content among boards from these three kinds of raw material under the same hot pressing condition.Under the hot-pressing temperature of 110?,the range of Moisture Content was from 7% to 8%,while Moisture Content kept 4% if the range of hot pressing temperature was from 130?to 190 ?.Under such hot-pressing pressure which changed from 2MPa to 6.5MP,the density of the boards rose with the pressure rising.When the hot pressing pressure attain to8 MPa,the density would not rise any longer.The bending strength of rape straw changed from 32.87 MPa to 55.41 MPa which performed well enough to be qualified as 30-type board according to JIS and tensile strength from 16.72 MPa to 29.45 MPa.For corn straw,the bending strength changed from22.90 MPa to 49.33 MPa which could be satisfied with 15-type board according to JIS and tensile strength from 20.77 MPa to 33.31 MPa.So the bending strength of rape straw was higher than corn straw while tensile lower than it.For these two kinds of new straw,the bending strength rose with the hot pressing pressure rising before it attained to 6.5MPa and the bending strength didn't rose any more after attaining to this pressure.For these two kinds of straw,the tensile strength was the largest when the hot pressing temperature was150?.Under 110? hot pressing temperature,compared old rape straw with the new one,the bending strength(28MPa)is lower than the new one(55.4 MPa)a lot.With the hot pressing temperature rising,the difference between new rape straw board with the old one became very little.Combined mechanical data with density data,it could be found that density,hot pressing pressure and bending strength had strong correlation;to corn straw and rape straw,the best hot pressing condition were 150 ? hot pressing temperature and 6.5MPa hot pressing pressure;the chemical composition of old straw was not helpful for board-making but raising temperature properly could improve the mechanical property of the board made from the old straw.(3)After hot pressing,cellulose content and hemicellulose content became smaller while Benzene-Alcohol extractive content and lignin content became larger.The reason was that hemicellulose decomposed and the ramification of which(furfuralcohol and furfural)could reacted with lignin to generate lignin adhesive which can not dissolve in Benzene-Alcohol.For rape straw,board under 170? and 190? hot pressing temperature,the Pyrolysis temperature in the second stage advanced a little than board under 110??130??150?.Perhaps hemicellulose decomposed into monosaccharide with Low-molecular-weight in170? that made pyrolysis become easy.For corn straw,board under 150?,170? and190? hot pressing temperature in the second stage,the Pyrolysis temperature advanced a little than board under 110 ? and 130 ?.Perhaps hemicellulose decomposed into monosaccharide with Low-molecular-weight in 150 ? hot pressing pressure that made pyrolysis become easy.Weight loss ratio of the boards reduced with hot pressing pressure rising till 6.5MPa that means raise hot pressing pressure properly can improve Bondingforce between the molecules.Crystallinity of rape straw boards ranged from 0.57 to 0.63 under different hot pressing conditions and crystallinity of corn straw boards ranged from 0.56 to 0.60.For these two kinds of straw,crystallinity of the boards made under 2MPa,3.5 MPa and 5 MPa hot pressing pressure are larger than which under 6.5MPa and 8MPa,that could be explained that much higher pressure could destroy crystalline region of the cellulose.For these two kinds of straw board,much more hydrogen bonds formed under higher hot pressing pressure till 6.5MPa.For rape straw board,that the absorption peak of the hemicellulose(carbonyl,1730cm-1)enhanced when hot pressing temperature rising up to170? meants hemicellulose began to decompose from this temperature.For corn straw board,that the absorption peak of the hemicellulose enhanced when hot pressing temperature rising up to 150 ? means hemicellulose begin to decompose from this temperature.That the absorption peak of the hemiacetal enhanced with the hot pressing temperature rising means much more C-O-C bond formed by the much more hydroxyls condensation.Using x-ray diffractometer,Thermogravimetric instrument and Fourier Infrared Spectrometer,the factors affecting self-bonding mechanism could be concluded as follows:(1)quantity of hydrogen bond;(2)condensation of ramification from hemicellulose composing;(3)The glass transition of the lignin[84].(4)With the hot pressing pressure increasing,The Gibbs free energy for combination processes of hydrogen bond formed from hydroxy of different sites of cellulose,hemicellulose and lignin became small(the smallest free energy formed from lignin),which could show better mechanical property in the macroscopic scale.At the same time,with the hot pressing pressure increasing,the Gibbs free energy had a tendency of convergence that means much higher pressure was not useful for hydrogen bond forming.The Gibbs free energy of condensation reaction was also considered when the hot pressing temperature was high enough for hemicellulose decomposing.The result was negative showed that the covalent bonds were more stable than hydrogen bond.For this reason,the mechanical property of the straw board was good when hot pressing pressure rose up to some extent.The result from DFT method and the result from mechanical property are consistent means DFT method could explain how the hot pressing pressure and the hot pressing temperature effect the mechanical property of the biomass board in the microscopic scale. |
PDF Full Text Request