Curing Process of Phenol Formaldehyde Resin for Plywood under Vacuum Conditions

The study characterized the curing behaviors of phenol formaldehyde(PF)resin under different vacuum degrees and explored the properties of 9-ply plywood panels hot-pressed under both vacuum and atmospheric conditions.The changes in core temperature and moisture content of the plywood mats during hot pressing were investigated as well.It was found that the gel times and gel temperatures of PF resin decreased with the increase of vacuum degree using a self-made device.FTIR spectra indicated the degree of polycondensation of hydroxymethyl gradu-ally increased with the increase in temperature.It was also observed that a higher degree of vacuum led to a slower polycondensation reaction rate of PF resin.During different hot-pressing processes,the bonding strengths in the innermost and uppermost gluelines of the vacuum hot-pressed plywood panels were up to 30%–50%higher than their counterparts of conventional hot-pressed products.A less difference in the bonding strengths between these two gluelines was also observed for vacuum hot-pressed products.In addition,the core of vacuum hot-pressed plywood was found to have a greater heating rate and higher temperature at thefinal stage of hot pressing,which was beneficial to cure the PF resin.The results from this study indicate a promising potential of introducing a vacuum during hot pressing to improve the quality and productivity of plywood products and provide a basis for adopting vacuum to hot press wood composites.

Design and Development of Composite Plywood that Integrates Fire Resistance,Water Resistance and Wear Resistance

In order to improve the fire resistance,water resistance and wear resistance of ordinary plywood products in the wood processing industry,three composite structures of plywood products S1,S2 and S3 were designed in this paper,and a reasonable production process was proposed.Through the physical and mechanical properties and fire resistance testing and technical and economic analysis,the applicability of composite plywood was evaluated.The results of the study showed that the physical mechanics of the three kinds of composite structure plywood met the standard requirements,and their fire resistance was far better than that of ordinary plywood.Among them,the S1 structural board had the best overall physical and mechanical properties.The S3 structural board showed the best fire resistance,which was about 1.9 times more than that of ordinary plywood,and the added cost was the lowest.The thin cork board added to the S2 structural board had poor fire performance since the air in the cork board cavities had a certain combustion-supporting effect,which inhibited the fire resistance of high-pressure laminate(HPL)layer.Moreover,the additional cost of the S2 board was the highest,and its comprehensive performance was the worst.The S3 structural plywood product composed of HPL fireproof board with a thickness of about 1 mm in the surface layer and ordinary plywood with a thickness of about 12 mm in the core layer was the most cost-effective product,which could meet the needs of various fields such as construction,home furnishing,decoration and transportation.

Research on utilizing recycled plastic to make environment-friendly plywood

In our study, we replaced traditional adhesives with compounds made with recycled plastic shopping bags in order to make hot-melt plywood using various amounts of plastic film, different hot-pressing temperatures and hot-pressing times. All three variables have an effect on the intensity and water-resistance of plywood. The results show that the bonding strength of plywood does not increase with increasing amounts of plastic film. When the hot-pressing temperature is increased to 150℃, the bonding strength does not necessarily increase any further. At a hot-pressing time of 6 min, the bonding strength reaches a maximum, after which it will decrease. The optimum hot-pressing parameters are as follows： 100 g·m^-2 of recycled plastic, a hot-pressing temperature of 150℃ and a hot-pressing time of 6 min. This study puts forward a new idea of making use of plastic waste, which, ultimately, may solve the problem of formaldehyde emission without damaging the environment. It has enormous potential market applications.

Effect of moisture and fungal exposure on the mechanical properties of hem-fir plywood

Hem-fir plywood were exposed to two brown rot fungi, Gloeophyllum trabeum and Postia placenta, and one white rot fungus, Trametes versicolor, to investigate the effect of fungal decay on mechanical properties of plywood. Results showed that modulus of rupture （MOR） and modulus of elasticity （MOE） of hem-fir plywood declined significantly by inoculating fungi, and weight loss of sample had a modest decrease. The fungi also made a greater effect on MOR than on MOE. Of three fungi, Postia placenta caused a most significant weight loss, and Gloeophyllum trabeum resulted in a largest flexural properties loss. Substantial declines in MOR and MOE of hem-fir plywood were also observed when the plywood samples were stored under wet conditions over 15 weeks, even in the absence of fungal attack.

Preparation of adhesive for bamboo plywood using concentrated papermaking black liquor directly

Adhesive for bamboo plywood prepared directly using lignin existing in the black liquor as a kind of material replacing phenol was proposed on the basis of the same structural properties of lignin and phenol. The results indicate that the reaction time of black liquor methylating is 30min, when the ratio of alkali to formaldehyde is controlled at approximately 0.20, decomposition rate of formaldehyde is the lowest and the effect of black liquor methylating is the best, the optimal molar ratio of phenol： formaldehyde to NaOH to H2O of preparing phenolic resin is 1.00 ： 1.50 ： 0.50 ： 9.00, and the suitable viscosity is 27 - 30 Pa· s. At different mass ratios of methylated black liquor to phenolic resin, all terms of performance of black liquor phenolic resin are excellent and satisfy the requirement. All terms of performance of bamboo plywood prepared using this technique are hetter than that of excellent bamboo plywood of national criteria. Using this technique, the cost is depressed by 28.69% without altering the traditional adhesive producing technique flow, and without using additional equipment.

Reinforcement of Lignin-Based Phenol-Formaldehyde Adhesive with Nano-Crystalline Cellulose (NCC): Curing Behavior and Bonding Property of Plywood

The curing behavior of lignin-based phenol-formaldehyde (LPF) resin with different contents of nano-crystalline cellulose (NCC) was studied by differential scanning calorimetry (DSC) at different heating rates (5, 10 and 20&degC/min) and the bonding property was evaluated by the wet shear strength and wood failure of two-ply plywood panels after soaking in water (48 hours at room temperature and followed by 1-hour boiling). The test results indicated that the NCC content had little influence on the peak temperature, activation energy and the total heat of reaction of LPF resin at 5 and 10&degC/min. But at 20&degC/min, LPF0.00% (LPF resin without NCC) showed the highest total heat of reaction, while LPF0.25% (LPF resin containing 0.25% NCC content) and LPF0.50% (LPF resin containing 0.50% NCC content) gave the lowest value. The wet shear strength was affected by the NCC content to a certain extent. With regard to the results of one-way analysis of variance, the bonding quality could be improved by NCC and the optimum NCC content ranged from 0.25% to 0.50%. The wood failure was also affected by the NCC content, but the trend with respect to NCC content was not clear.

LARIX GMELINI TANNIN-BASED ADHESIVE FOR PLYWOOD

Larix tannin-phenol-formaldehyde (TPF) adhesive, having 60% by weight of phenol bcing replaced, was evaluated for its utilization in plywood. The kinetic characteristic of the TPF resin was investigated through differential scanning calorimetry (DSC) and the results obtained from the DSC scans show that the resin has a little bit different thermochemical behavior from that of phenol-formaldehyde (PF) resin. Two kinds of plywood panels wcre produced using the TPF adhesive in laboratory. The desired test results met the Chinese GB 9846-88 and ZB B70006-88, respectively, and the long assembly time of TPF resin in preparing plywood can be improved by mixing with the filler.All the properties of plywoods bonded with the TPF adhesive were compared with those obtaincd with synthetic PF adhesive.

Study of Burning Behaviors and Fire Risk of Flame Retardant Plywood by Cone Calorimeter and TG Test

A flame retardant composition was prepared by using phosphoguanidine,guanidine sulfamate,disodium octaborate tetrahydrate and dodecyl dimethyl benzyl ammonium chloride.Veneers were immersed in such flame retardant mixture to prepare plywood.The combustion characteristics and thermal stability of plywood were assessed using a cone calorimeter and TG.Results showed that:(1)High concentration and loading of flame retardant were beneficial for the fire resistance of the plywood.(2)The limiting oxygen index(LOI)and residual mass of plywood processed using the flame retardant was increased by 87.52%and 58.66%compared to those of the untreated plywood,while the average heat release rate(av-HRR),total heat release(THR),effective heat of combustion(EHC),total smoke release(TSR),CO yield(COY),CO_(2) yield(CO_(2)Y)and oxygen consumption were decreased by 44.3%,82.9%,47.0%,86.0%,89.9%,50.1%and 83.1%,respectively.(3)Treated plywood which had a low fire growth index(FGI)displayed a later combustion heat release rate peak and slower flame spread than observed for the untreated material.Combustion of treated plywood displayed a higher fire performance index(FPI),indicating a longer time to ignition.This suggests that burning structures from this material would be subject to a longer time for escape from the structure and would present lower fire risk than similar structures containing treated plywood.(4)TG results demonstrated that the presence of the flame retardant can decrease the pyrolysis temperature for hemicellulose and cellulose,change the decomposition and reaction progress for plywood degradation and promote dehydration carbonization and accelerated charformation.Moreover,the formed char was more stable than that combustion of untreated plywood.(5)The flame retardant contains nitrogen(N),phosphorus(P),boron(B),chlorine(Cl)and guanidine(Gu)compounds.The adhesive also contains N and P compounds.These substances display flame resistance and supplement each other to generate flame retardance than any one used alone.By changing the thermolysis and thermal decomposition processes,the heat release and smoke release from plywood,undergoing combustion was reduced.This controlled generation of combustible substances and promoted dehydration and carbonization to form char.As a result,the flame resistance of plywood was improved significantly.The probability of smoke asphyxia or poisoning death of those trapped in structures containing treated plywood during fire accidents can be decreased dramatically.

Influence of Formulation and Hot-Pressing Conditions on the Performance of Bio-Based Molasses Adhesive for Plywood

Molasses can serve as a natural adhesive for plywood and particleboard.However,several disadvantages remain,including lower dimensional stability and low bonding strength compared to other adhesives.Therefore,modifications are needed to use molasses as an adhesive for plywood.This research aims to improve bio-based molasses(MO)adhesive for plywood using citric acid(CA)adhesive.In addition,this research aims to analyze the effect of adding citric acid and to investigate the optimum hot-pressing temperature to produce the best quality plywood.In the first stage,the molasses and citric acid were combined in a ratio of 100:0,75:25,50:50,25:75,0:100 w/w%.Then,the second stage focuses on analyzing the influences of pressing temperature based on an optimum first stage.The research demonstrated that the addition of CA altered the gelation time,solid content,viscosity,and pH of the molasses adhesives.In addition,the thermal properties of molasses adhesives were changed after mixing with citric acid.These phenomena indicate changes in characteristics,such as the curing of adhesive.Overall,the characteristics of plywood showed a steady improvement as the CA ratio increased but revealed a significant decline for the 25:75 MO-CA ratio.By raising the pressing temperature from 180℃ to 200℃,the quality of plywood was effectively improved.The plywood that was bonded using adhesives with a 50:50 MO-CA ratio exhibited superior mechanical properties and improved dimensional stability compared to the plywood bonded solely with MO.Furthermore,the optimal mechanical and physical properties resulted in plywood bonded with a 50:50 MO-CA ratio when subjected to a pressing temperature of 200℃.The Thermal and FTIR measurements revealed that CA established ester bonds with both the MO and wood veneers.In conclusion,the mechanical characteristics of plywood were improved,while maintaining its excellent dimensional stability.

超低甲醛释放木质素基胶黏剂的制备及应用

针对脲醛树脂耐水、耐候性能差和潜在甲醛释放的问题,以工业碱木质素(L)为原料,通过与苯酚(P)、尿素(U)和甲醛(F)共缩聚反应制备了符合ENF级Ⅰ类胶合板要求的木质素基胶黏剂(LPUs)。考察了L、P和U质量比对LPUs凝胶时间、游离甲醛含量、储存稳定性、固化反应活性以及胶合板理化性能的影响。结果表明:mL/(mP+mU)为1∶1时制备的树脂LPU1~LPU4中,随着尿素用量的增加,LPUs树脂的凝胶时间逐渐缩短,m(P)∶m(U)=30∶70时制备的LPU4,其凝胶时间为(18±2)min,约为LPU1(m(P)∶m(U)=90∶10)的凝胶时间(30±2)min的40%,游离甲醛含量从0.05%(LPU1)升高至0.18%,储存期由127 d缩短至14 d,表现出脲醛树脂的理化特性。DSC监测固化过程焓变行为表明,LPUs树脂反应活化能仅为商业酚醛树脂和脲醛树脂的2%~7.8%。mL/(mP+mU)=1且苯酚用量不低于尿素时制备的LPU1~LPU3树脂胶合板耐沸水胶合强度和甲醛释放量满足ENF级Ⅰ类胶合板要求,其中LPU2树脂的施胶量可降低至工业生产工艺的66.7%,此时,依然可以确保胶合板的耐沸水胶合强度和甲醛释放量满足ENF级Ⅰ类要求,可有效降低胶合板生产成本。

基于AE-BP模型的杨木胶合板应力损伤识别

【目的】利用声发射(AE)技术对应力损伤全过程中的杨木胶合板进行无损检测,并利用BP神经网络对AE检测结果进行识别,以提高胶合板损伤检测精度。【方法】以市场占有量较高的托盘用杨木胶合板作为研究对象,在联合AE和应力损伤试验过程中,提取6个AE特征参数,利用声发射RA-AF联合分析法区分杨木胶合板产生裂纹的类型,采用K-均值聚类分析方法确定损伤演化程度和AE特征参数之间的对应关系,利用BP神经网络建立损伤识别模型,并对识别网络进行测试训练。【结果】AE信号幅度和上升时间可有效地表征杨木胶合板应力损伤从微裂纹萌生、产生宏观裂纹至完全断裂的损伤演化过程;通过RA-AF联合分析发现:杨木胶合板在应力损伤试验第一阶段主要为剪切破坏损伤,第二、三阶段主要为拉伸破坏损伤;通过K-均值聚类分析发现损伤类型与AE峰值频率之间的存在较强对应关系,可有效的表征不同的损伤类型:在31 kHz内为基体开裂,在31~100 kHz内为脱胶分层,大于100 kHz为纤维断裂;构建AE-BP神经网络模型对应力损伤类型训练样本的拟合优度是95.94%,测试集的拟合优度是98.89%,模型总拟合优度是96.51%,网络训练效果较好。【结论】在应力承载AE监测过程中,通过构建AE-BP模型,可对杨木胶合板产生的未知损伤进行有效检测并准确识别。

桉木单板背面裂隙率对胶合板性能的影响

为给胶合板生产过程的组坯工艺优化提供理论依据,采用图像处理技术与宏观力学性能试验相结合,分析桉木单板背面裂隙率对胶合板性能的影响,探讨桉木单板背面裂隙率与胶合板性能的相关性。结果表明,不同单板背面裂隙率下,干状、冷水浸泡24 h和热水浸泡3 h胶合板的胶合强度及顺纹静曲强度均差异极显著,横纹静曲强度、横纹弹性模量和顺纹弹性模量均差异不显著。随单板背面裂隙率增大,胶合板在3种条件下的胶合强度、顺纹静曲强度和顺纹弹性模量均呈下降趋势。相关性分析表明,单板背面裂隙率与干状胶合强度、冷水浸泡24 h胶合强度和顺纹静曲强度均呈极显著负相关,与顺纹弹性模量呈显著负相关。单板背面裂隙率对胶合板性能的影响表现为冷水浸泡24 h胶合强度>干状胶合强度>顺纹静曲强度>顺纹弹性模量>热水浸泡3 h胶合强度>横纹弹性模量>横纹静曲强度。

基于钻石模型的胶合板国际竞争力来源实证研究

出口是中国胶合板产业发展的重要动力因素,但近年来中国胶合板出口竞争呈现不利态势,分析胶合板国际竞争力来源及其动态变化,有助于中国胶合板重构竞争优势。文章利用UNComtrade、WDI数据库等相关数据,以国际市场占有率表征的实际国际竞争力为导向,以波特钻石模型的国际竞争力来源要素为指导选择代表性指标,运用多元线性回归模型实证研究胶合板国际竞争力的实际来源。结果显示:(1)劳动力、资源、资本等3个传统生产要素是胶合板国际竞争力的主要来源,影响程度分别为0.81、0.42、0.20;相关支持性产业水平也发挥着重要作用,影响程度为0.12;受刨花板、中密度纤维板替代和环保需求增强等影响,胶合板面临需求困境,需求的影响程度为-0.36;技术要素与企业战略、结构和同业竞争因素影响不显著。(2)异质性分析表明,随着时间变迁,胶合板国际竞争力对丰富劳动力的依赖程度降低,劳动力成本影响显化,资源禀赋作用上升,资本要素作用增强,工业基础水平作用显现,胶合板呈现从劳动密集型转向资本技术密集型的趋势。文章构建了国际竞争力来源的实证研究逻辑,提供了国际竞争力来源研究的时间和空间视角,弥补了胶合板国际竞争力来源计量经济研究的不足。结合中国胶合板产业实际,提出重组资本与劳动要素、夯实资源基础、改善需求条件、发挥相关支持性产业作用、促进高水平竞争等政策启示,重构中国胶合板竞争优势,再塑中国胶合板国际竞争力。

基于改进卷积神经网络的胶合板霉变检测技术研究

霉变是评价胶合板结构质量的重要指标,其直接影响胶合板的安全性、适用性和耐久性。通过对卷积神经网络进行改进,使用EfficientNetB0模型与迁移学习,提出了胶合板霉变监测模型。EfficientNetB0模型采用神经结构搜索技术设计,通过Adam优化器来更新网络参数。将提出的模型与MobileNetV2、DenseNet201和InceptionV3进行对比,结果表明,所提出的模型不仅减少了参数的数量,同时具有比较高的检测准确率,能够在不同情况下有效地进行胶合板霉变检测。这对胶合板结构质量评价具有一定的实用价值。

钢筋混凝土夹板墙加固石砌体片墙力学性能分析

为保护福州市平潭地区传统石头厝建筑的独特风格,本研究拟采用钢筋混凝土夹板墙对其进行加固并对其力学性能加以分析。为明确该加固技术对内、外墙的不同加固效果,首先,利用有限元数值分析软件ABAQUS分别建立了未加固、单侧加固和双侧加固的石砌体片墙试件的数值分析模型;然后,通过面外单向加载分析了混凝土加固层厚度及配筋率对加固墙体性的影响。结果表明,钢筋混凝土夹板墙能大幅度提高石砌体片墙的承载力,且随着加固层混凝土厚度的增加,墙体承载能力不断增大,但配筋率对加固效果的提高作用不明显。

生物基阻燃水性聚氨酯涂料的制备及对胶合板性能的影响

针对包装、建筑和家具领域使用的胶合板易燃的问题,对胶合板进行阻燃处理,利用蓖麻油、马来酸酐、异佛尔酮二异氰酸酯、季戊四醇、三乙胺、硼酸锌、丙酮、乙二胺,通过丙酮法制备生物基阻燃水性聚氨酯乳液,采用浸渍涂布法制备阻燃杨木胶合板。根据GB/T 1040.3—2006对水性聚氨酯胶膜的物理性能进行测试,采用傅里叶变换红外光谱表征硼酸锌添加量不同的乳液的官能团,采用氧指数测定仪、热重分析仪、锥形量热仪、导热系数测试仪表征阻燃处理前后杨木胶合板的阻燃性能、热稳定性、热释放速率和隔热性能,并探究了阻燃杨木胶合板的抗流失性能。结果表明:阻燃杨木胶合板具有良好的阻燃性能,当硼酸锌添加量达到7.5g时阻燃杨木胶合板的极限氧指数可达34.8%,残炭率较对照样提高了360.94%,最大热释放速率降低了24.10%,总热释放量下降了43.32%,总烟释放量下降了37.50%,导热系数下降了24.14%,同时抗流失性也有所提升。生物基阻燃水性聚氨酯乳液可以增强杨木胶合板的阻燃性能,较直接添加硼酸锌具有更好的抗流失性,可以为胶合板提供更持久的阻燃效果。

喷箱辊筒式胶合板生产连续热压机设计

根据胶合板生产的工艺要求,结合并借鉴辊筒式单板干燥机的结构,设计了一型专用于胶合板生产的、采用辊筒加压、喷箱加热的连续式热压机;说明了喷箱辊筒式连续热压机的结构组成与工作原理,设计计算了压机的分段尺寸、液压系统与辊筒驱动系统的工作参数及其年产能;利用ANSYS Fluent软件,对喷箱喷孔的热气流流速均匀性、胶合板坯的加热均匀性进行了数值分析;设计与分析结果表明,该压机在结构设计上能够满足胶合板的生产需求,可以为胶合板连续热压机的开发提供借鉴。

初始张拉力对预应力-CLT组合结构受力影响研究

正交胶合木(CLT)是一种适合于建筑工业化的人工绿色材料,具有可预制、可再生、自重轻但强度和刚度较高等特点,有较好的环境效应。如果能够在正交胶合木基础上加上预应力,则该组合结构受力性能将会得到进一步提升。主要对不同初始张拉力下预应力-正交胶合木组合结构进行试验研究:考虑预应力钢绞线的2种不同初始张拉力,设计了2个CLT剪力墙构件进行拟静力往复加载试验,得到了2个构件的骨架曲线、刚度退化曲线、等效粘滞阻尼系数、变形模式等内容;同时,通过将试验结果与国内相关研究成果进行对比分析,发现施加预应力对CLT结构整体刚度、耗能能力等有较大提升;相比于预应力-木组合结构组装于钢底梁上,预应力-木组合结构组装在混凝土底梁上在一定程度上减少了钢节点的使用,缩小了两者之间的刚度差,使得混凝土底梁情况下构件屈服荷载、屈服位移以及最大承载力方面有一定的提升。

胶合板用氯氧镁胶黏剂制备工艺的初步研究

采用正交试验优选氯氧镁胶黏剂的原料配比和胶合板制备工艺,分析优化工艺合成的氯氧镁胶黏剂及其制备胶合板的性能。结果表明:优选的氯氧镁胶黏剂可以作为一种木材胶黏剂,能够通过杨木单板孔隙渗透到木材内部孔隙中,形成机械粘接结构,但胶合板的湿态胶合强度未达到GB/T 9846—2015《普通胶合板》Ⅲ类胶合板≥0.7 MPa的要求。分析结果证明518相晶体的含量决定氯氧镁胶黏剂的强度和耐水性,胶黏剂内部结构较为疏松。518相晶体状态是重要影响因素,需通过518相晶体状态的改变或者堵塞水分子通道来阻止其与水分子接触的方法,提高氯氧镁胶黏剂的各项性能,促进工业化应用。

广西17家胶合板生产企业的主要职业卫生问题调查分析

目的:探讨广西17家胶合板生产企业存在的主要职业危害因素、职业防护设施效果以及对工人健康的影响,为减少职业性危害、保护工人身心健康提供科学依据。方法:以17家胶合板生产企业为观察对象,通过职业病危害因素检测和职业卫生调查,对主要职业卫生问题进行综合分析评价。结果:17家胶合板生产企业木粉尘、甲醛、噪声、高温的超标率分别为5.6%、28.1%、24.9%、29.1%。17家噪声超标,5家木粉尘和甲醛超标,仅2家高温超标。生产防护设施的防尘、防毒符合率为98.3%,防暑设施符合率为88.2%,噪声防护设施符合率为76.5%。个人防护用品佩戴与使用符合率为52.9%,安装洗眼喷淋装置符合率为58.8%。17家企业总体检率为42.6%(705/1654),体检异常检出率为14.6%,其中听力、胸部X线片、肺功能异常检出率分别为7.4%、2.1%、1.7%。结论:广西17家胶合板生产企业的主要职业卫生问题是木粉尘、甲醛、噪声、高温,尤以噪声较为突出。针对木粉尘、甲醛的防控效果较好,对于高温、噪声的防控措施需要进一步加强。