摘要
为提高我国软木制品的质量，改善我国软木的加工性能，为开发软木绝缘材料、软木隔音材料以及软木地板、软木装饰板等高档软木产品提供基础资料和依据，本文主要以陕西产栓皮栎软木为原材料，对软木的主要物理性能、软木的夹砂和夹杂、软木的膨化除杂工艺以及膨化机理展开研究。首先对国产栓皮栎商品软木的主要物理性能进行研究，为国产软木的合理利用提供基础数据；其次，对栓皮栎软木的夹砂和夹杂，从细胞结构和主要化学成分含量方面分析了二者与软木细胞的不同；第三，研究了软木的膨化除杂工艺，通过优化确定了较佳的膨化工艺条件；最后，通过膨化软木的性能、结构和主要化学成分含量的变化分析，进行了汽爆膨化工艺的机理探索。取得的主要研究结论如下：
（1）通过研究国产栓皮栎软木的主要物理性能，与葡萄牙栓皮槠软木比较，结果显示栓皮栎软木的皮层厚度小，密度大，硬度大，导热系数大，抗压指数大，压缩回弹率稍低，含水率、吸湿率和吸水率二者相差不大，表明栓皮栎软木质地硬、导热性差、弹性差，因而栓皮栎软木质量较差。
（2）对软木的夹砂和夹杂进行研究。发现夹砂（石细胞）的细胞壁较厚，为白色，细胞腔内也充有白色物质；夹砂的木栓脂含量少，纤维素、灰分含量多。夹杂（皮孔细胞和组织）整体上排列比较疏松，细胞间隙发达；皮孔细胞和组织的木栓脂含量也较少，纤维素含量较多。
通过比较夹砂和夹杂与软木细胞的结构和主要化学成分含量，表明其细胞结构不同，主要化学成分含量不同，因此性能不同。夹砂和夹杂的木栓脂含量低，纤维素含量高，质硬，弹性小。软木中夹杂多，夹砂大，导致其密度大，导热性差、弹性差，因而质量差，影响软木的加工和利用。
（3）对栓皮栎软木进行高温膨化除杂工艺处理，选取工艺参数进行正交试验。在试验范围内，试验因素对体积膨胀率和除杂率的影响基本一致：蒸煮方式影响最显著，其次是温度，软木块尺寸大小和加热时间2h以上影响不显著。在试验条件下，优化得到较佳的高温膨化工艺：对初生软木，为加压、加甲醇蒸煮1h、尺寸（长度×宽度×厚度）是（40-50）×（30-40）×（20-30）（mm）、温度是240℃、时间是2h，其膨化效果体积膨胀率是32.72%，除杂率是19.02%；对再生软木，为加压、加甲醇蒸煮1h、尺寸（长度×宽度×厚度）是35×35×20（mm）、温度是240℃、时间是3h，其膨化效果为体积膨胀率是29.77%，除杂率是21.54%。
（4）软木汽爆膨化的工艺流程分为预处理、加热升压、保压、卸压和收集5个阶段。据此设计了软木汽爆膨化关键设备的主要参数，研制成整套软木汽爆膨化装置。采用二次正交旋转设计进行了软木汽爆膨化试验研究。在试验条件下，优化得到各因素的较佳组合为：压力0.92MPa，时间30min，含水率20%；其膨化效果为：体积膨胀率是41.12%，除杂率是32.26%。试验结果表明，该装置工作性能达到设计要求，可以满足试验条件；汽爆膨化方法使软木体积膨大明显，除杂效果好，是一种较好的软木除杂方法。
（5）对汽爆膨化软木和未膨化软木的主要物理性能测试和分析。结果显示，膨化软木比未膨化软木，硬度减小了约27.8%~37.5%，密度减小了约31.8%~50%，抗压指数减小了约30%~50%，压缩回弹率在24h后提高了约2.0%~8.8%。因此汽爆膨化改善了软木的物理性能和加工性能。
对汽爆膨化软木和未膨化软木的结构和主要化学成分含量分析，膨化软木的扫描电镜结构显示，膨化软木细胞壁未发现分层、断裂，明显可见细胞壁上的褶皱变少，细胞壁被拉直，细胞膨胀，体积增大；膨化软木的木栓脂、纤维素和木质素的含量相对提高。表明汽爆膨化没有破坏软木的细胞结构和基本化学组成。
（6）软木汽爆膨化的机理是，软木细胞为一密闭结构，无细胞间隙，细胞壁无纹孔而存在大量褶皱，细胞壁主要由具有弹性和韧性的木栓脂组成，在高温、高压水蒸汽作用下，细胞壁软化，高压蒸汽迅速释放时，细胞腔内的水蒸汽分子迅速急剧膨胀，拉直了细胞壁上的褶皱，使软木细胞膨胀，软木体积增大。在试验的压力范围内，蒸汽膨胀所产生的膨胀力不足以破坏软木细胞壁的弹性和韧性。
This study researched the main physical properties, sclereids, lenticels, expansionimpurities removing technology and expansion mechanism of cork using Quercus variabiliscork from Shanxi province as test materials, in order to increase the products quality of cork,improve the processing properties and provide the base materials and evidences fordeveloping cork insulating material, cork sound insulation materials, cork floor board, corkdecorative material and the other slap-up cork products. Firstly, the main physical propertiesof domestic commercial cork were tested to provide the base materials for reasonableutilization of cork. Secondly, the sclereids and lenticels in Q. variabilis cork were researched.The differences of those and cork cells were studied form cell structure and main chemicalcomponents testing. Thirdly, the expansion impurities removing technology was studied andthe expansion process conditions were determined by optimization. Finally, the technologyand mechanism of steam-explosion expansion were analyzed from the properties, structureand main chemical components of Q. variabilis cork. The main research conclusions were asfollows:
(1) The main physical properties of domestic Q. variabilis cork were studied. Comparedto Portuguese Quercus surber cork, the domestic cork has lower thickness, higher density,higher hardness, higher thermal conductive and higher anti-pressure index, little lowercompression spring rate. The moisture content, hygroscopic rate and water absorption rate ofdomestic Q. variabilis cork are almost equal to Portuguese Q. surber cork. The results showedthat the hardness, thermal conductive, elasticity and qualities were worse than Portuguese Q.surber cork.
(2) The sclereids and lenticels in Q. variabilis cork were studied in this paper. The cellwall of sclereids was thick and white with whiteness in the cell lumen. The suberin ofsclereids was low and the cellulose and ash content of that were high. The cells and tissue oflenticels arranged loosely with large intercellular space. The suberin of lenticels cells andtissue were low and the cellulose was high.
The structure and main chemical components of sclereids and lenticels were compared tocork cell, and the results showed that the structure, main chemical components of the there were difference, so that the there differed from the properties. The suberin of sclereids andlenticels were low and the cellulose of those was high. So sclereids and lenticels were hardwith low elasticity. The cork with more lenticels and larger sclereids has higher density, lowerthermal conductive, lower qualities effecting the processing and utilization of cork.
(3) Q. variabilis cork was treated by high-temperature extrusion impurities removingprocess and the parameters were chose for orthogonal test. In the test, the effect of test factorson volume expansion ratio was basically identical with impurities removing ratio. The effectof boiling methods was the most significant, and the effect of temperature was the second one.The effect of the size of cork and the heating time more than2h were not significant. Underthe condition of the present experiment, the optimum processing was as follows: the primarycork were boiled adding methanol in high pressure for1h size（length×wideth×thickness）（40-50）×（30-40）×（20-30）（mm）. The treatment temperature was240℃and the treatmenttime was2h. The volume expansion ratio was32.72%, the impurities removing ratio was19.02%. The regenerative cork were boiled adding methanol in high pressure for1h size（length×wideth×thickness）（35×35×20）（mm）. The treatment temperature was240℃andthe treatment time was3h. The volume expansion ratio was29.77%, the impurities removingratio was21.54%.
(4) The technological process of steam-explosion expansion of Q. variabilis cork couldbe divided into five phases which were pretreatment, heating and g pressure increasing,pressure keeping and pressure releasing. The main parameters of the steam-explosionexpansion of cork were designed according to the technological process, the equipment wasdeveloped and the steam--explosion expansion was researched by quadratic rotating design.Under the condition of the present experiment, the more optimum processing are pressure at0.92MPa, time at30min, moisture content at20%. The result of the expansion was that thevolume expansion ratio was41.12%, the impurities removing ratio was32.26%. The testingresults showed that the equipment could reach design requirement and meat test conditions.The volume was expansed significantly and the impurities removed well by steam-explosionexpansion which was a good method for impurities removing.
(5) The physical properties of steam-explosion expanded cork and unexpanded cork wereresearched. It was showed that compared to unexpanded cork, the hardness of expanded corkdecreased27.8%~37.5%, the density of expanded cork decreased31.8%~50%, the antipressure index decreased30%~50%and the compression spring rate after24h increased2.0%~8.8%. So the physical and processing properties were improved by steam-explosionexpansion.
The structure and main chemical components of steam-explosion expanded cork and unexpanded cork were researched. The structure of expanded cork observed by scanningelectron microscope (SEM) showed that there were no layering and break on cork cell wall.The wrinkles on cell wall were decreased and the cell wall was stretched. The cell wasexpanded and the volume of cell was increased. The suberin, cellulose and lignin of expandedcork were increased relatively. The result showed that the cell structure and basic chemicalcomponents were not destroyed by steam-explosion expansion.
(6) The mechanisms of steam-explosion expansion of cork were that the cork cell was anairtight structure with no intercellular space. There were no pits but a lot of wrinkles on thecell wall which mainly composed of suberin with reach elasticity and tenacity. The cork cellwall was softening in high temperature and high pressure gas. The wrinkles were stretched,the cork cell was expanded and the volume of cell was increased by the rapid expansion ofsteam in the cell lumen when the high pressure was released rapidly. The elasticity andtenacity of cork cell could not be destroyed by the expansion force produced bysteam--explosion under the pressure of the present experiment.
引文
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