【作者】 徐登伟；

【导师】 周定国；

【作者基本信息】 南京林业大学 ， 木材科学与技术， 2013， 博士

【摘要】 我国已经是全球最大的人造板生产国、消费国、出口国。2011年我国人造板产量已达到2.09亿立方米。随着产量的逐年加大，原材料短缺的状况越来越制约了行业的发展。作为农业大国，我国农作物废弃物——秸秆资源极其丰富，且据不完全统计每年有超过30%的秸秆被农民焚烧于田头，造成了严重的环境污染和交通危险，迫切需要为秸秆寻找更多的出路草/木原料混合热磨制造MDF是实现“以草代木”，缓解当今中密度纤维板生产企业原料紧张矛盾的有效途径；是寻找农作物秸秆合理利用的有效措施；是解决“三农”问题提升农民收入的有效方法。本课题通过理论分析、实验室试验，中试生产试验等方面的工作，对草/木原料混合热磨制造MDF，生产过程中原料控制、生产工艺调节、磨片齿形优化等方面进行了研究，得出以下结论：（1）草/木原料混合热磨理论上是可行的。通过比较木材及非木质原料的纤维特性、化学组成发现：秸秆类原料纤维细短、薄壁组织含量高、木素含量低。因此，相比于木材，秸秆纤维分离所需的软化温度、时间要低。根据Kerekes，Martinez，Batchelor等人的研究成果，两种原料混合热磨时，由于秸秆类原料纤维直径小，其所受的压应力和剪切应力也都比木材纤维小，与两种原料解纤所需的动力恰巧相吻合。秸秆原料由于表面的蜡质存在，其与磨齿的摩擦系数要低于木材，加之其纤维细短的特点，理论上推断，草/木原料混合热磨时应根据随着秸秆含量的提高，适当减小磨盘间隙，提高纤维的分离效果。从纤维板结构角度分析，纤维长度大的针叶材更适合与纤维细短的秸秆材料混合制造MDF。（2）草/木原料混合分离制造MDF的板材性能优于草/木原料先单独分离后混合制板的性能。混合分离一方面提高了两种纤维的混合均匀性，减弱了秸秆原料中蜡质及硅物质对于胶合的不利影响；另一方面，避免了磨齿对于秸秆的过度切削，能有效减少纤维中细粉的含量。（3）草/木原料混合热磨磨片齿形应根据原料中秸秆含量作相应调整。考虑到秸秆纤维细短、所需解纤动力相对较低的特点，草/木原料混合热磨磨片较之普通分离木片磨片应适当减小齿宽，降低齿高，增加磨齿角度，通过合理设置挡齿的数量、位置、角度控制浆料的热磨时间，确保混合纤维的良好分离。（4）调整热磨工艺，控制纤维质量。为控制好纤维中粗梗、长纤维、细粉含量的的比例，随着混合原料中秸秆含量的提升，应适当减小磨盘间隙，降低蒸煮压力，缩短蒸煮时间。三者的协调控制需要综合考虑原料配比、原料含水率、目标纤维的形态等多方面因素而决定。（5）控制制板工艺，提升物理力学性能。随着秸秆含量的提高，板材各项力学性能呈下降趋势。混合纤维长度与MOE、MOR、握钉力正相关，线性关系明显；施胶量与IB、握钉力正相关，线性关系明显；板材密度与各项物理力学性能正相关，线性关系明显。因此，草/木原料混合制板过程中，应根据不同的草/木原料比，结合板材目标物理力学性能，制定合理的原料蒸煮工艺、板材密度和施胶量，确保纤维质量和板材物理力学性能的稳定。考虑到草/木原料在蒸煮工艺、胶合性能方面的差异性，如想在现有的中密度纤维板生产线上，减少设备和工艺调试成本，实现“以草代木”制造草/木复合MDF，则秸秆添加量以重量比30%左右为宜。（6）草/木复合MDF热压工艺控制。通过改善热压工艺，可以提高板材物理力学性能。从热压角度分析，草/木原料混合应尽量以木为主或以草为主，这有利于确定合理的热压温度和热压曲线；可以通过适当提高表面含水率，降低芯层含水率的方式，提高板材的静曲强度（MOR）、弹性模量（MOE）；在控制好板坯含水率的基础上，可以适当提高压机的闭合速度，以提高板材表面密度来达到提高表面抗拉性能与抗压性能；随着草纤维含量的增加，应适当降低热压的温度，增加胶粘剂的施加量，有利于防止表面过度热解，提高板坯热传导效率，确保纤维间的良好胶合，根据实验经验，一般情况下热压温度不应超过220℃，施胶量控制在12%以内。提高板材密度有利于物理力学性能的提高，但因充分考虑热压过程中因密度的提高而导致的板材内部蒸汽压力的提高，控制好板坯的含水率和加压工艺，防止板材分层、鼓泡等缺陷的形成。本次研究在实验室和中试生产线上验证了草/木原料混合热磨制造MDF工艺的可行性，在后期工作中还可在原料成本控制、工厂化生产工艺调整、板材力学性能改善、产品应用等方面作进一步的研究，以期尽快实现产业化。更多还原

【Abstract】 China has been the world’s largest man-made panel producer, consumer and exporter. Thevolume of production has reached209million m3, in2011. The shortage of raw materialsrestricted the development of the industry, as the production increased year by year. As a bigagricultural country, the agricultural residues such as plant straw are extremely rich. Whilemore than30%of the straw has been burned in the farm, which caused serious environmentalpollution and traffic problems. It is urgent to find more ways out for the straw.Straw/wood MDF is an effective way to reduce the raw material problems of MDF factories; isa good method to rational utilize the agricultural residues; also is a good way to improve thefarmers’ income and relieve the “Three Rural Issues” problems. In study, the raw materialcontrol, production process adjustment, disc segment profile optimization, etc. of theStraw/wood MDF production are analyzied, by theoretical analysis, laboratory test, pilotproduction test. The conclusions are in the following:(1) Straw/wood raw material refine together is feasible in theory. We discovered the straw fiberis shorter and thinner, higher content of parenchyma, lower content of lignin, than wood fiber,by comparing the fiber characters of wood and straw. Therefore, the softening requirements ofcooking time and temperature for straw are lower than wood. During refining, because of thesmaller fibre diameter,the compressive stress and shear stress of straw fiber are smaller thanwood fiber, according to the research results of Kerekes, Martinez, Batchelor. This happen tomeet the two kinds of material’s different separating power need. The straw’s frictioncoefficient with the segment is lower than wood, because of the wax on the straw’s surface andthe thiner and shorter fiber character, it is necessary to reduce the refining gap to improve thefiber quality, when the straw raw material content raise. From the panel’s structure perspective,the soft wood with longer fiber length is more suitable than hard wood for refine together withstraw which has shorter and thinner fiber.(2) The panels made from the straw/wood fibers separated together performed better thanstraw/wood fibers isolated separated. Refine straw/wood raw material together has threeadvantages:1) improve the mixing uniformity of the two kinds of fiber and reduce the bondingdisadvantages of wax and silicone from the straw;2) effectively reduce the fiber powder byavoiding the segment excessively cutting straw fibers.(3)The segment of refining disc should be adjusted according to the content of straw.Considering straw fiber’s shorter and thiner character, refining disc separating straw/wood fiberis necessary to reduce the segment width, depth, increase the segment angle, compared withcommon wood chips’ separating. For fibers’ good separation, the number of resist segmentsand its’ location should be reasonable arranged to control the fibers’ refining time.(4) Adjust the refining techniques, control fibers’quality. In order to control reasonalbe contentsof stem fiber, qualified fiber and powder fiber in the compound fiber, it is necessary to narrow the disc gap, lower cooking preasure and cooking time when the straw raw material contentraising. The coordination of the three factors(disc gap, cooking preasure,cooking time) shouldbe based on the straw/wood raw material ratio, raw materials’ moisture content and the targetfiber morphology, etc.(5) Control panel-making process, improve mechanical properties of panels. Themechanical properties of composites decreased when increasing straw content.The fiber lengthis positive related to the panel’s MOE, MOR, nail holding power; The glue usage is positiverelated to the panel’s IB and nail holding power. The panel density is positive related to everymechanical property of the panel. They all have a liner relationship between the factors.Therefore, it is crucial to set a reasonable cooking process, panel density and gule usageaccording to the straw/wood raw material ratio and panel’s target mechanical properties.Considering the differences in cooking process and bonding performance between straw andwood, the straw raw material content should be around30%, in order to develop thestraw/wood MDF technique in existed wood MDF production line without additionalequipment cost and complicated process adjustment.(6) Hot-pressing process control of straw/wood MDF. The panel’s mechanical properties can beimproved by adjust the hot-pressing process. The raw material should be dominated by wood orby straw, avoid equal content, that will be benefit to work out the reasonable hot pressingprocess. The panel’s MOR and MOE can be raised by properly increasing surface moisturecontent and lowering core layers’ moisture content of the slab. The panel’s surface density canbe raised by increasing machine’s closing speed to improve the panel’s tensile and compressiveproperties, base on proper slab moisture content. To prevent panel’s surface excessive hotdestruction, improve the heat conduction efficiency, ensure good bond between fibers, we canproperly lower the hot-pressing temperature increase the glue usage when the straw rawmaterial ratio increase. According to the experiment experience, hot-pressing temperatureshould not exceed180℃, the glue usage should control within12%. Increase panel’s densitycan benefit mechanical properties, while the density increase may result in an increase ofpanel’s internal steam pressure. So when the panel density increased, the slab’s moisturecontent should be properly controlled to prevent the formation of defects such as delaminationand bubbling.In the laboratory and pilot plant, this study proved the feasibility in making straw/wood MDFwith the compound fiber refined together. In the further study the raw material cost control, thefactory production process, the panel’s mechanical properties improvement, the productapplication can be deeply researched in order to realize straw/wood MDF industrialization innear future.更多还原