【作者】 常亮；

【导师】 王正；

【作者基本信息】 中国林业科学研究院 ， 木基复合材料科学与工程， 2014， 博士

【摘要】 人工速生林杨木是我国北方最重要的人造板用材树种，对于我国人造板行业的迅猛发展具有重要意义。随着环境安全意识的提高，人们更加重视人造板材的环保性。通过提升杨木人造板产品的环保性能，增加产品竞争力和附加值，成为推动杨树产业和人造板产业持续健康发展的重要途径。本文以高密度聚乙烯（HDPE）作为胶黏材料，基于热压-冷压生产工艺，与杨木单板复合制备无游离甲醛释放的HDPE杨木复合胶合板。考察热压-冷压成板复合因子对板材主要性能的影响，分析胶合界面的形成过程，评价复合因子对HDPE界面渗透的影响，分析HDPE在胶合板体系中的结晶行为，建立HDPE杨木复合胶合板的成板机制，评价分析HDPE在复合界面中的渗透和结晶性质。本论文的主要研究内容和结论如下：（1）以板材胶合强度为响应值，建立热压复合因子的响应面回归方程，考察复合因子及交互作用对胶合强度的影响，筛选和优化热压复合因子。结果表明：单一复合因子显著度大小依次为树脂加入量>热压时间>热压温度>热压压力，其中树脂加入量达到极显著，热压时间达到显著；热压温度和热压时间的交互作用影响达到极显著。优化复合因子水平：热压温度160℃，树脂加入量308g/m2，热压压力1.0MPa，热压时间为0.8mm/min，优化胶合强度达到和超过GB/T9846.3-2004中II类胶合板的胶合性能要求。（2）基于上述响应面的复合因子显著度分析和优化，建立单因子试验分析单板含水率、树脂加入量、热压温度、热压压力、冷压温度和冷压压力等热压-冷压成板复合因子对胶合强度、压缩率、吸水率和吸水厚度膨胀率等物理力学性能的影响。随着单板含水率的升高，胶合强度和压缩率性能逐步下降，吸水率和吸水厚度膨胀率性能逐步上升；树脂加入量对于以上4项性能的影响趋势与单板含水率因子恰好相反。伴随热压温度和热压压力的提高，胶合强度均呈现先升高后降低的趋势，在热压温度160℃、热压压力1.0MPa获得最高值，压缩率均逐步降低，吸水率也都呈现先降低后升高的趋势；然而两者的吸水厚度膨胀率变化趋势不同，前者呈现先降低后上扬趋稳的态势，最低水平效应值出现在优化因子水平160℃上，而后者则呈现逐步增加的走势。冷压温度在30℃-90℃区间，压缩率和吸水厚度膨胀率随着冷压温度的提高而逐步降低，两者均在120℃时获得最大值；冷压温度对于胶合强度和吸水率影响不显著。考察热压-冷压压力的协同作用，对比不同热压条件下冷压压力因子对板材性能的影响发现，提高冷压压力，有助于减小因热压压力产生的性能差异，二者具有协同作用。（3）利用光学显微镜和扫描电镜（SEM）分析了HDPE在胶合界面的渗透分布、路径以及界面结合状态发现，HDPE与木材之间胶合界面存在明显间隙，二者结合完全依靠机械互锁作用。采用胶线宽度、平均渗透深度（AP）和有效渗透（EP）等3个指标评价了HDPE在复合界面的渗透状况，分析成板复合因子对其渗透状态的影响。随着单板含水率增大，胶线宽度增加，AP和EP逐步减小；树脂加入量增加，3项指标均随之升高；热压温度和热压压力对于HDPE渗透影响近似，随着因子水平的提高，胶线宽度逐步减小，而AP和EP逐步升高。冷压温度仅对AP影响达到显著。低热压压力条件下，冷压压力对胶线宽度和AP影响均极显著，对EP影响显著；而高热压压力条件下，冷压压力对AP和EP影响均达到极显著，对胶线宽度影响显著。两个热压压力条件下的AP和EP均随着冷压压力的提高整体呈现上升趋势，但是低热压压力状态下的各冷压压力的渗透效应值均低于高热压压力状态，两者之间的水平效应值差距随着冷压压力的增大而呈缩减趋势。对比成板复合因子对于渗透深度和胶合强度的影响发现，单板含水率、树脂加入量、冷压温度以及冷压压力等因子，对胶合强度和渗透深度的影响趋势基本一致，但热压压力和热压温度因子对两者的影响趋势存在差异，增加渗透深度能够有效提高宏观胶合强度，渗透过度增加反而引起胶合强度的下降。综合比较发现，EP更适宜作为HDPE杨木复合胶合板界面渗透性能的考察指标。（4）利用示差扫描量热仪（DSC）考察HDPE在胶合板复合界面体系中结晶行为，以结晶温度（Tc）、熔融温度(Tmpeak)和结晶度（Xc）评价HDPE结晶状态，基于Avarami方程结晶动力学分析，考察Avarami指数（n）、结晶速率常数对数（logK（T））和半结晶时间（t1/2）等参数，分析HDPE在胶合界面体系中的结晶过程。针对实际制备过程中冷压温度、冷压压力和树脂加入量因子对HDPE界面体系中结晶行为的影响，发现提高树脂加入量、冷压温度或者降低冷压压力等措施均能提高HDPE的结晶度，但对于Tc几乎没有影响。随着树脂加入量和冷压温度的提高，n逐步增加；而增加冷压压力，n逐步减小；HDPE结晶过程是以低维数的结晶生长方式为主。通过DSC模拟不同降温速率下HDPE的非等温结晶过程可知，降温速率对于Tc几乎没有影响，Xc随着降温速率升高而逐步下降；随着降温速率的增加，结晶生长受到限制，晶体生长维度减小，整体结晶速率变慢。对比不同树脂加入量胶合板界面层和纯HDPE的等温结晶分析可知，胶合板复合界面体系中HDPE的Tc、Tmpeak和Xc均低于纯HDPE，且除了1层树脂加入量水平，其他水平n和logK（T）也都低于后者，t1/2时间更长。胶合板界面体系对于HDPE的结晶成核、结晶稳定性和规整性方面均存在阻碍作用。更多还原

【Abstract】 Fast-growing poplar is the most important timber species of wood-based panel in northChina for the rapid growing wood-based panel industry.With the rising of environmental safetyawareness, people pay more attention to environmental performance of man-made panelproduct. Through improving environmental performance, increasing competitiveness andvalue-added of poplar plywood products, it has become an important way to promote sustainedand healthy development of poplar plywood industry.In this paper, high-density polyethylene (HDPE) film was selected as an adhesive materialto maunfacture formaldehyde free poplar/HDPE composite plywood based on a specificalhot–cold pressing process.In order to establish poplar/HDPE composite plywood formationmechanism, as well as to the HDPE penetration and crystallization properties of bondinginterface status, screening and optimization of hot composite factors with bonding strength byResponse Surface Methodology, effect of hot and cold pressing composite on bonding strength,compression ratio, water absorption (WA) and thickness swelling (TS), HDPE penetration inbonding interface influenced by composite factors, the crystallization behavior of HDPE inplywood interface system were studied.The main contents and conclusions are as follows:(1) Bonding strength as the response value, Response Surface Methodology was used tooptimize the processing factor. Results showed that bonding strength was significantly affectedby HDPE dosage, hot-pressing time, hot-pressing, temperature and pressure. HDPE dosagereached the very significant level as well as interaction effects between pressing temperatureand time；hot-pressing time reached a significant level.When plywood was manufactured under following conditions: HDPE dosage of276g/m2,hot-pressing temperature of161℃，hot-pressing pressure of1.05MPa, hot-pressing time of0.83mm/min, the bonding strength reached1.68MPa which met the requirement of Type IIplywood according to the National Standard of GB/T9846.3-2004. (2) Based on the resluts of Response Surface Methodology, experiments were carried outto analyze the effect of factors (such as moisture content of veneer, HDPE dosage, hot-pressingtemperature, hot-pressing pressure, cold-pressing temperature and cold-pressing pressure) onphysical and mechanical properties (such as bonding strength, compression ratio, waterabsorption(WA),thickness swell (TS)).With increasing of veneer moisture content, bonding strength and compressionperformance declined but WA and TS gradually increased; meanwhile, the factor of HDPEdosage showed an oppsite influence. Under the optimal parameter(hot-pressing temperature at160℃, hot-pressing pressure at1.0MPa), bonding strength increased but then declined as theincreasing of hot pressing temperature and pressure. Compression ratios decreased gradually;the value of WA also rised firstly and then decreased, both of them also reached the minimumlevel in the optimal factor levels.However, the effect trend of TS was diffient between them,theformer increasing firstly and then decreased with the lowest value presenting on the160℃level,while the effect of latter factor showed a increasing trend. Within the temperature rangefrom30℃to90℃，compression ratio went down with cold-pressing temperature rising，whileTSincreasedfirstlyandthendecreased,bothofthemreachedthemaximumvalueon120℃level.Inparticular,coldtemperaturewasnotasignificantfactorforbondingstrengthandWA.Inordertostudysynergisticeffectbetweenhot-pressingandcold-pressingpressure,theeffectsofcold-pressingpressureonpanelperformanceunderdifferenthot-pressingconditionswerecompared.ReslutsshowedIncresingcold-pressingpressurewasbenefittoreducethedifferenceofplywoodperformancecausedbyhot-pressingpressure.There wasasynergisticeffectbetweenthem.(3)Byopticalmicroscopeandscanningelectronmicroscopy(SEM),permeabilitydistributionandpathofHDPEinbondinginterfacewerestudied.ThereslutsshowedtherewasagapinbondinginterfacebetweenHDPEandpoplarveneer,theircombinationdependedonmechanicalinterlockentirely.Using guleline width,average penetration depth (AP) and effective permeability (EP) toevaluate the penetration status of HDPE in the composite interface, the impacts of composite factors on penetration position were analyzed. As the veneer moisture content increasing,glueline width increased,but the value of AP and EP gradually decreased. With the increase ofHDPE dosage, value of all these three indicators increased.Effects of hot-pressing temperature and pressure on penetration in the bonding interfaceare similar: with hot-pressing time and pressure increasing, the glueline width decreased, APand EP increased gradually. However cold-pressing temperature only affected AP significantly.Under high pressure conditions, effects of cold-pressing pressure on AP and EP reachedextreme significant level,while the impact on glueline width only reached significant level.With the increasing of cold-pressing pressure, both of AP and EP went up under differenthot-pressing pressure conditions. The levels of penetration depth in low hot-pressing pressurewere lower than high hot-pressing pressure conditons. With cold-pressing pressure decreasing,the level difference between different hot-pressing pressure declined.Comparison with effects of composite factors on AP,EP and bonding strength, the effectsof veneer moisture content, HDPE dosage, cold-pressing temperature and cold-pressingpressure on the performance of bonding strength and penetration depth had the similar trend.But there were an obvious difference of factor’s impact on them between hot-pressing andcold-pressing pressure. The result indicated that increasing penetration depth couldeffectively enhance bond strength,however excessive penetration would cause the decrease ofbonding performance.By comparing the correlation of bonding strength and permeability, EPwas more suitable as an interface penetration indicator of poplar/HDPE composite plywood.（4）HDPE crystallization behavior in bonding interface system of composite plywood wasstudied by DSC.Using crystallization temperature(Tc), melting temperature(Tmpeak) andcrystallinity(Xc) to evaluate HDPE crystallization performance. Based onAvaramicrystallization kinetics equation, the crystallization processs was analyzed by Avaramiindex (n), crystallization rate constant (logK (T)) and half of crystallization time (t1/2).Effects of cold-pressing temperature, pressure and the dosage on the crystallizationbehavior in interface system in preparation process were studied. Results showed increasing of HDPE dosage and cold-pressing temperature or reducing cold-pressing pressure could increasethe crystallinity of HDPE,while there was little effect on Tcby composite factors. With theincreasing of HDPE dosage and cold-pressing temperature, the value of n increasedgradually,while the value of n decreased by the improvement of cold-pressing pressuredecreased. As the crystal growth of HDPE had been in small dimension mode.Effect of cooling rate on the non-isothermal crystallization in plywood sample preparedunder the optimal parameters was studied by DSC. Results showed the cooling rate had littleeffect on Tc, while Xcdeclined gradually with improving the cooling rate. With increasingcooling rate, crystal growth of HDPE was restricted, so crystal size was smaller andcrystallization rate slowed down.Isothermal crystallization of pure HDPE and plywood samples with different HDPEdosage were studied. In a full isothermal crystallization, Tc, Tmpeakand Xcof HDPE in bondinginterface system were lower than pure HDPE, expect the level of1layer HDPE, the value of nand logK (T) were also lower than the latter,the number of t1/2increasdgradully.It was obviousthat bonding interface system of plywood would hinder HDPE crystallization behavior innucleation, stability and regularity of crystallization.更多还原