【作者】 漆楚生；

【导师】 郭康权； Micheal P.Wolcott； Vikram Yadama；

【作者基本信息】 西北农林科技大学 ， 农业生物环境与能源工程， 2013， 博士

【摘要】 我国2012年秸秆总产量预计超过7亿吨，充分利用丰富的秸秆资源，增加生物质秸秆的经济附加值成为关注的热点问题。本研究以棉秆、甜高梁秆生物质秸秆为原料,以热塑性塑料高密度聚乙烯（HDPE）为胶合剂，采用热压工艺制备了生物质秸秆-HDPE定向秸塑板，研究了生物质秸秆的热稳定性以及秸塑板热压过程中的热传导和秸秆热解问题，探讨了热压法制备定向秸塑板的成材机理，取得的主要结论如下：1.使用高效液相色谱仪分析了甜高梁秆的化学成分，结果表明甜高梁秆的纤维素、半纤维素、木质素和水溶性糖的含量分别为24.58%，21.07%，19.08%和10.38%。2.使用TGA分析了棉秆、甜高梁秆及其表皮和髓芯的热稳定性，得到其热解温度分别为236.0℃、185.8℃、199.9℃和179.2℃；在秸塑板热压过程中，甜高梁秆中水溶性糖和木质素受热最先热解，其次是半纤维素，纤维素受热最稳定。3.分别以HDPE粉末和HDPE薄膜为胶合剂，开发了棉秆-HDPE定向秸塑板和甜高梁秆-HDPE定向秸塑板。研究了秸秆长径比、热处理温度和HDPE塑料含量对秸塑板物理力学性能的影响，得到：秸秆长径比越大，棉秆-HDPE秸塑板的力学性能越好；棉秆热处理温度为103℃和140℃时，制备的秸塑板力学性能最优，热处理温度为170℃时，秸塑板的吸水厚度膨胀率最低；添加10%的HDPE的甜高梁秆-HDPE定向秸塑板的力学性能、耐水性能和断面密度均匀性，比未添加HDPE的甜高梁秆定向板有较大改善，但HDPE添加量从10%增加到40%时，板材的力学性能有下降趋势；添加的MAPE、PF和pMDI偶联剂增强了生物质秸秆与HDPE塑料之间的界面结合力，提高了生物质秸秆-HDPE秸塑板的物理力学性能。4.通过热压压力测试、红外光谱分析、微观结构和板材失效形式观察等手段，研究了生物质秸秆-HDPE定向秸塑板的热压成型机理，得到塑料含量越高，热压时获得相同密度的板材需要的压力越小，板坯断面密度变化越大；在HDPE和偶联剂的作用下，在秸秆和HDPE接合界面形成局部机械啮合和化学接合，提高了板材性能；秸塑板的失效发生在生物质秸秆髓芯、生物质秸秆之间以生物质秸秆与HDPE塑料之间。5.利用独立平行反应模型模拟了生物质秸秆在秸塑板热压成型过程中的热解程度，计算了甜高梁秆中的水溶性糖、半纤维素、纤维素和木质素的热解动力学参数，得到其活化能分别为：101，110，202和26kJ/mol，指前因子分别为1.2×10¹¹，5.0×10⁹，3.0×10¹⁷和20min¹；预测了热压过程中甜高梁秆在板坯的表层、1/4处和中心层的热解量分别为5.4%,2.8%和2.0%。6.建立了甜高梁秆和HDPE比热容随温度变化的数学模型，甜高梁秆和熔化之前的HDPE的比热容随温度的增加而增加；在熔化过程中，使用Gauss方程和Lorentz方程拟合了由HDPE熔化吸热引起的表观比热容。7.建立了包含HDPE含量、板坯密度和温度三个参数的秸塑板导热系数数学模型。在稳态条件下测试了秸塑板的导热系数，甜高梁秆-HDPE秸塑板的导热系数随密度和温度的增加而线性增加，随HDPE含量的增加而非线性增加。8.建立了包含HDPE熔化吸热在内的秸塑板热压过程中的一维热传导模型，通过Matlab求取了热传导模型的数值解，并对模拟结果进行了实测验证，得到板坯热压过程中，随着HDPE含量的增加，当温度达到塑料熔化温度时，由HDPE熔化吸收的热量增多，在热压后期板坯的温度越低。更多还原

【Abstract】 China has very abundant biomass resources, and the total production of biomass stalks isover0.7billion ton in2012and is expected to increase in the future. It is a big challenge toutilize those abundant biomass stalks and increase their economy values. This study usedcotton stalk and sweet sorghum stalk as raw materials to fabricate composites with high-density polyethylene （HDPE） using hot pressing process. The fabrication process ofcomposites was investigated, besides the thermal stability of biomass stalks, heat transfer andthermal degradation of mat during hot press were also analyzed. The results are concluded asfollowing:1. High performance liquid chromatography （HPLC） was used to analyze the chemicalcomponents of sweet sorghum stalk, and the results showed that cellulose, hemicellulose,lignin and water-soluble sugar content of sweet sorghum were24.58%,21.07%,19.08%and10.38%, respectively.2. Thermal stability of cotton stalk, sweet sorghum stalk and sweet sorghum rind and pithwas analyzed by thermogravimetric analyze （TGA）, and showed that their degradationtemperatures were236℃,185.8℃,199.3℃and179.2℃at mass loss of2%, respectively.3. Cotton stalk-HDPE oriented composites （CSHC） and sweet sorghum stalk-HDPEoriented composites （SSHC） were manufactured using powdered HDPE and film-formedHDPE as adhesive. The effects of stalk length-to-diameter ratio, thermal treatmenttemperature and HDPE content on the physical and mechanical properties of composites wereinvestigated. The results showed that the CSHC had better mechanical performance at greaterlength-to-diameter ratio of cotton stalk and had optimal mechanical properties at thermaltreatment temperatures of103℃and140℃with best thickness swelling property at thethermal treatment temperature of170℃. The SSHC with10%HDPE content had bettermechanical properties, water resistance property and vertical density distribution than thosewithout HDPE content. The mechanical properties of SSHC had a downward trend whenHDPE content increased from10%to40%. The addition of MAPE, PF and pMDI couplingagents in the composites increased the interfacial adhesion between the biomass stalks andHDPE, which resulted in physical and mechanical increase of composites.4. The molding mechanisms of biomass stalk-HDPE composites were investigated using pressure testing duing hot pressing process, infrared spectroscopy, microstructure andcomposite failure observation. The results showed that the higher the HDPE content ofcomposite mat, the smaller the pressure of hot press to obtain the same mat density and thegreater the variation of vertical density profile of resulted composites. Mechanicalinterlocking and chemical bonding that produced by HDPE and coupling agents improved theinterfacial adhesion between biomass stalk and HDPE and contributed to the increase ofphysical and mechanical properties. The composites failure occurred at stalk pith, interfacebetween stalks and between stalks and HDPE.5. Independent parallel reaction model was employed to predict the thermal degradationof biomass stalks during hot pressing process. The reaction energies of water-soluble water,hemicelluloses, cellulose and lignin of sweet sorghum stalk were101，110，202and26kJ/mol respectively, and their pre-exponential factors were1.2×10¹¹，5.0×10⁹，3.0×10¹⁷and20min¹, respectively. Thermal degradation of sweet sorghum stalk at composites with10%HDPE content under the hot-press temperature of160℃for10minutes was predicted andfound to be5.4%,2.8%and2.0%at surface, one quarter thickness position and core of mat.6. Mathematical models for predicting specific heat capacity of sweet sorghum andHDPE were created based on experimental testing data. The specific heat capacity of sweetsorghum and HDPE before melting increased with temperature. Gauss equation and Lorentzequation were used to fit the apparent specific heat capacity of HDPE caused by heatabsorption during melting.7. Mathematical model including HDPE content, density and temperature for predictingthermal conductivity of biomass stalk-HDPE oriented composites was established based ontesting data at steady-state condition. The results showed that thermal conductivity of SSHClinearly increased with composite density and temperature, and non-linearly increase withHDPE content.8. One-dimensional heat conduction model including heat absorption of HDPE duringmelting was created and numerically solved using Matlab. Simulation results of the modelwere compared with experimental testing data and found had good consistency. Thesimulation and testing results showed that the heat absorption caused by HDPE meltingincreased with HDPE content when the mat temperature reach the melting temperature ofHDPE, and resulted in lower temperature of mat during final stage of hot press processing athigher HDPE content.更多还原