Research In Expansion Impurities Removing Technology And Mechanisms Of Quercus Variabilis Cork

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.