【作者】 宋孝周；

【导师】 郭康权；

【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， 2008， 博士

【摘要】 为了充分利用农作物秸秆，生产可替代木材、强度高、环境友好的重组材，本文以几种农作物秸秆(棉秆、豆秆、辣椒秆、烟秆及玉米秆)为原料，围绕原料特性、秸秆重组材的制板工艺、成板机理及关键技术展开研究。首先通过显微镜观察、纤维离析、化学成份分析等方法研究五种秸秆的理化特性，为原料的合理利用提供基础理论和数据；其次，研究了秸秆的软化处理方法及梳解工艺，通过正交试验、单因素试验研究了秸秆重组材的制板工艺及改善棉秆重组材防水性能的措施；第三，检测了板坯中心层温度的变化，采用非稳态法测量秸秆重组材的导热系数、比热和导温系数，建立了秸秆重组材板坯的传热模型。利用显微照相观察成板过程中棉秆组织结构的变化规律，应用傅立叶变换红外光谱、扫描电镜分析了脲醛胶棉秆重组材的胶接机理；最后，分析了秸秆重组材工业化生产的流程，并对工业化生产中关键的梳解设备和铺装设备进行了深入研究。主要结论如下：(1)棉秆、豆秆、辣椒秆和烟秆均由韧皮部、木质部和髓心组成，玉米秆是由表皮层、维管束组织和薄壁细胞组成；五种秸秆纤维的化学成分与木材相似，但也存在着各自的特点，可以作为木材的替代原料。在五种秸秆中，棉秆是优良的重组材制备原料。(2)在实验室条件下，含水率为12％左右的棉秆、豆秆、辣椒秆以及烟秆木质化程度较高的实心部位采用90℃热水常压蒸煮3h，可以取得较好的梳解效果，烟秆中空部位和玉米秆只需在常温下用冷水浸泡1～2h即可达到软化的目的。(3)利用脲醛胶压制10mm厚的棉秆重组材，在实验室条件下较佳的工艺参数为：密度0．7g／cm~3、施胶量12％、热压温度150℃、热压时间为14min，除2h吸水厚度膨胀率(2hTS)外，棉秆重组材的其它性能指标均超过刨花板国标GB／T4897．2-2003(以下国标均指此标准)的要求；参照此工艺参数，压制豆秆和辣椒秆重组材，测试结果和棉秆重组材相似，烟秆重组材的内结合强度和2hTS没有达到国标要求，利用脲醛胶无法压制玉米秆重组材；利用酚醛胶压制秸秆重组材，除了玉米秆外，棉秆、豆秆、辣椒秆和烟秆重组材的各项性能均达到或远远超过国标的要求。(4)在较佳工艺参数条件下，施加石蜡乳液能够降低棉秆重组材的2hTS，但施加量即使达到2．5％，仍未达到国标的要求；将热压温度分别提高到180℃和200℃，在添加1．5％的石蜡乳液的条件下制板，棉秆重组材的2hTS均能达到国标的要求；当混合胶料中脲醛胶和酚醛胶的重量比为4：2时，棉秆重组材的2hTS也达到国标的要求。(5)秸秆重组材板坯热压时中心层温度的变化曲线可以分为三段，即水分开始气化前的快速升温段、水分气化时的恒温段和水分气化之后的慢速升温段；在热压过程中，施胶量、含水率、热压温度、目标密度和厚度对棉秆重组材板坯中心层的升温速度、水分气化所需时间以及板坯中心层达到玻璃化反应温度的时间均有不同程度的影响。(6)对秸秆重组材的导热系数、比热和导温系数进行测定；在试验条件下，含水率和密度与棉秆重组材的导热系数和比热均呈显著正相关，与导温系数的相关性不显著；板材厚度变化对棉秆重组材热学性能各指标没有明显的影响。(7)在合理假设下，建立了秸秆重组材板坯中心层温度随时间变化的数学模型，模型曲线基本反映了秸秆重组材板坯热压时中心层温度的变化规律，提出了模型修正的思路。(8)棉秆重组材在成板过程中，原料存在径向和弦向的压缩，组织结构发生了变形，木射线变弯曲了，导管由原来的近似圆形明显被压扁了，木纤维也被压缩成不规则的形状。压力是细胞发生变形的主要因素，同时，细胞变形与温度和含水率也有一定关系。(9)红外光谱分析表明：脲醛胶棉秆重组材在成板过程中，羟基缔合形成氢键，使得游离羟基的数量减少；半纤维素羰基吸收峰的位置和形状发生了变化，说明半纤维素在成板中可能参与了化学反应；木质素羰基的吸收峰位置发生变化，表征苯环的特征峰吸收强度相对减弱，说明木质素在成板过程中可能参与了化学反应。(10)扫描电镜显示在用脲醛胶压制棉秆两片的横面和纵面及周围细胞中，能够明显看到固化的胶层，说明棉秆重组材中存在着“胶钉”接合。(11)从机械胶接理论、吸附胶接理论、化学键理论、弱界面层理论及流变学理论的角度分析了脲醛胶棉秆重组材的胶接机理。(12)秸秆重组材工业化生产可分为预处理、梳解、干燥、施胶及铺装、热压和完成共6个工段，据此制定了工业化生产的工艺流程，绘制了厂房工艺平面布置图。(13)提出了棉秆梳解机主要参数的设计原则、限定条件以及用撕裂系数表示梳解质量，完成了梳解机的结构装配设计；设计了一种新的板坯铺装方法和设备，可实现秸秆重组材的机械化铺装。更多还原

【Abstract】 Crop straw is a reproducible resource,whose effective utilization has drawn more andmore attention worldwide.In order to produce high strength and environmental safereconsolidated timber which would be used as an alternative to wood,the five raw materialsused in this experiment were cotton-stalks,soybean-stalks,capsicum-stalks,tobacco-stalksand corn-stalks.The main research of the dissertation was conducted in the areas of raw materialcharacteristics,processing technologies,forming mechanisms and key technologies ofreconsolidated crop-stalks.First of all,the characteristics of five crop stalks were analyzed inthe paper through observation via optical microscopy,fiber isolation,analysis of chemicalcomponents and so on.Secondly,through single factor and orthogonal experiments,theprocessing technologies of reconsolidated crop-stalks and the methods of improving waterresistance of reconsolidated cotton-stalks were studied in the article after determining theoptimum softening process and scrimming technology.In the third place,the temperature ofthe center layer of mat was measured continuously and automatically by advanced instrumentin the hot-pressing process.Thermal conductivity,specific heat and thermal diffusivity ofreconsolidated crop-stalks were measured with non-steady state conditions.Under fivesuppositions,mathematic model of thermal transfer in the process of hot-pressing wasdeduced.Variation of cotton-stalks cells before and after the hot-pressing were observed withoptical microscopy.By means of fourier transform infrared spectroscopy(FTIR)and scanningelectron microscope(SEM),mechanisms of adhesive joints of reconsolidated cotton-stalksbonded with urea-formaldehyde(UF)resin were analyzed.Lastly,the process for industrialproduction of reconsolidated crop-stalks was given and scrimming equipment and layingequipment were studied in the dissertation.The main results of the dissertation are as follows:(1)Cotton-stalks,soybean-stalks,capsicum-stalks and tobacco-stalks are all consist ofxylem,phloem and pith.Corn-stalks is consist of epidermis,vascular bundles andthinner-walled cells.The chemical components of fiber of five crop stalks are similar to woodfiber.Five crop stalks can substitute for wood as raw materials of reconsolidated timber.Among five crop-stalks,cotton-stalks is an excellent raw material of reconsolidated timber. (2)The optimum scrimming technology under the current conditions is that cotton-stalks,soybean-stalks,capsicum-stalks and the solid part of tobacco-stalks,whose moisture contentare all 11%,are cooked 3 hours(90℃)and then crushed.Corn stalks and the hollow part oftobacco-stalks soaked 1～2 hours(20℃)and then crushed can also obtain the betterscrimming effect.(3)Manufacturing UF reconsolidated cotton-stalks with the size 350mm×350mm×10mm,the optimum technological parameters obtained under the lab conditions are:0.7g/cm~3density,150℃press temperature,12% UF and pressing time of 12min.The mechanicalproperties of the UF reconsolidated cotton-stalks can meet the requirements of industrialstandard(GB/T4897.2-2003)except for 2h thickness swell(2hTS).Under the sametechnological conditions,the mechanical properties of the UF reconsolidated soybean-stalksand capsicum-stalks are similar to reconsolidated cotton-stalks and the internal bond strengthand 2hTS of UF reconsolidated tobacco-stalks can not meet the requirements of industrialstandard.The bunch of corn stalks can not be bonded with UF.Under the same technologicalconditions,the mechanical properties of reconsolidated cotton-stalks,soybean-stalks,capsicum-stalks and tobacco-stalks bonded with phenol-formaldehyde(PF)resin can alsomeet or exceed the requirements of industrial standard except for PF reconsolidatedcorn-stalks.(4)As the increasing of paraffin latex consumption,2hTS of UF reconsolidatedcotton-stalks can reduce gradually on the condition of optimum technological parameters.Even if the value of paraffin latex consumption is up to 2.5%,the 2hTS of the panel can notreach to the standard value.When the temperature of hot-pressing reaches to 180℃or 200℃and add 1.5% paraffin latex,or the weight ratio of UF to PF is up to 4:2 in the mixture ofadhesive,2hTS of UF reconsolidated cotton-stalks can all meet the requirement of industrialstandard.(5)The curves of temperature changing of mat’ center layer can be divided into threestages:the fast temperature rising stage in which the moisture in the mat is not vaporizing,theconstant temperature stage in which the moisture is vaporizing,and the slow temperaturerising stage in which the moisture vaporizing process is near to the end.During thehot-pressing process of reconsolidated cotton-stalks,glue spread rate,moisture content,hot-pressing temperature,density and thickness have an effect on velocity of elevatedtemperature of mat’ center layer,the times of moisture vaporizing process and the times thattemperature of mat’ center layer is up to glass transition temperature.(6)Moisture content and density are all significantly correlated with thermalconductivity and specific heat of reconsolidated cotton-stalks,and are not closely related with its thermal diffusivity.The thickness change no long has an impact on thermal properties ofreconsolidated cotton-stalks.(7)Mathematic model is established in the paper,which can basically reflect the rule forthe changes of mat’ center layer temperature varying with time,and whose improvingthoughts are also presented.(8)Raw materials are compressed in radial and tangential section during the hot-pressingprocess.Hot-pressing technology makes the wood rays bent,makes the vessels crushed,andmakes the wood fibers compressed into irregular form.Compress is the main factorinfluencing deformation of tissue structure.There are some other factors,such as temperatureand moisture content.(9)The results of FTIR show that free hydroxyls form hydrogen-bonding duringhot-pressing of UF reconsolidated cotton-stalks,resulting in strengthened fiber self-bonding,that the position and shape of carbonyl’ absorption peak of hemicellulose have changed afterhot-pressing which indicates that hemicellulose may take part in chemical reaction,and thatthe position of carbonyl’ absorption peak of lignin has changed and the relative absorbingintensity of peak of benzene ring has reduced after hot-pressing which indicates that ligninmay take part in chemical reaction.(10)The result of SEM shows that there are adhesive joints of glue nail in the UFreconsolidated cotton-stalks.(11)The mechanism of adhesive joints of UF reconsolidated cotton-stalks are analyzedin the aspects of mechanical bonding,absorption theory,chemical bond,weak bonding layerand rheology.(12)Industrial production of reconsolidated crop-stalks is divided into six sections thatare pretreatment,scrimming,drying,glue blending and lay-up,hot pressing andafter-treatment.Technological process of industrial production is made.The technologicalplane layout chart of reconsolidated crop-stalks is also drawn.(13)The design principles and limited conditions of main parameters of scrimmingmachine and scrimming quality expressed by tearing coefficient are proposed.Assemblingdesign of scrimming machine has been finished.A new laying equipment is developed,whichcan realize mechanized mat forming.更多还原