Overview of the Synthesis, Characterization, and Application of Tannin-Glyoxal Adhesive for Wood-Based Composites

More than a century after its initial synthesis,urea-formaldehyde(UF)resins still have dominant applications as adhesives,paints,and coatings.However,formaldehyde in this industry produces formaldehyde emissions that are dangerous to health.Scientists have spent the last decade replacing formaldehyde and phenol with environmentally friendly substances such as glyoxal and tannin to create bio-based adhesives.This review covers recent advances in synthesizing glyoxal tannin-based resins,especially those made from sustainable raw material substitutes and changes made to synthetic processes to improve mechanical properties.The efficacy of using tannin-glyoxal adhesives in producing wood-based composites has been proven.The glyoxylate reaction forms cross-linked bridges between the aromatic sites of the tannin and glyoxal molecular structures.Glyoxal tannin adhesive with a greater percentage of glyoxal than tannin will produce an adhesive with better characteristics.The gel time reduces as the hardener concentration rises from 7.5%to 15%when glyoxal is used in adhesives.However,excessive amounts of glyoxal will result in a decrease in viscosity values.Glyoxal exhibits faster delivery degradation when it reaches a maximum temperature of approximately 130°C,although it initiates the curing process slightly slower at 110°C.Adding glyoxal to tannin-based adhesives can improve the mechanical properties of composite boards.The wet shear strength of the resulting plywood is increased by 105.4%with the addition of 5-weight percent tannin-based resin with glyoxal as a cross-linker in Soy Protein Adhesive.With glyoxal as a hardener,the panels produced showed good internal bond strengths(>0.35 MPa)and met the international standard specifications for interior-grade panels.

Termite Resistance of Heat-Treated Eucalyptus OSB Bonded with Eco-Friendly Castor Oil Adhesive

Over the last decade,the oriented strand board(OSB)market presented meaningful growth.However,as a woodbased product,because of its anatomical structure and chemical composition,OSB can be damaged by biodeterioration agents.Given that,the biodeterioration of OSB panels must be investigated to improve its durability.In this way,this work analyses the biological resistance against termites(Cryptotermes brevis and Nasutitermes corniger)of heat-treated OSB panels made with Eucalyptus wood glued with vegetable-based polyurethane-an ecofriendly and sustainable adhesive derived from castor oil.Various panels were produced with different layers compositions(face:core:face of 25:50:25 and 30:40:30)in wood mass proportion and were submitted to postproduction heat treatment(at 175℃ and 200℃)replacing the use of chemical insecticides.The influence of the layers variation and heat treatment temperature were evaluated,and these results were compared with commercial panels(made from pinus wood with insecticide).The results showed that the heat treatment did not improve the resistance against termite attack.However,all the experimental panels presented a satisfactory performance that was compatible with the commercial panels produced with insecticide available in the Brazilian market.The combination of Eucalyptus wood and castor oil adhesive to produce OSB,in any variation of layer composition,demonstrated natural resistance against termite attack compatible with the commercial panels,even without using chemical additives to increase durability.

Little Secrets for the Successful Industrial Use of Tannin Adhesives:A Review

This brief article reviews a very particular and quite narrowfield,namely what has been done and what is needed to know for tannin adhesives for wood panels to succeed industrially.The present fashionable focus on bioadhe-sives has led to producing chemical adhesive formulations and approaches for tannin adhesives as a subject of academic publications.These,as good and original they might be,are and will still remain a rather empty aca-demic exercise if not put to the test of real industrial trials and industrial use.They will remain so without the“little”secrets and techniques outlined here that show that there is a great gap between developing an adhesive formulation in the laboratory and the hard reality to make it work where it does really count,in its industrial application.It outlines the fact that even more modern and excellent,newly developed bioadhesive formulations might well miserably fail once tried in the industry if the problems that always arise in their upgrading are not identified and solved,and solved well.It also outlines the fact that not only must costs always be taken into account and that a practical and possibly easy-to-handle approach must always be used,but too expensive or complex and unyielding adhesive systems are also often shown to be unusable or unsuitable in industry.

Study on the Preparation Process Optimization of Plywood Based on a Full Biomass Tannin-Sucrose Wood Adhesive

Biomass adhesive is conducive to decreasing the dependence of the wood adhesive industry on synthetic resin based on fossil resources and improving the market competitiveness of adhesives.It is also a critical breakthrough to realize the goal of carbon peaking and carbon neutrality in the wood industry.In this study,a full biomass wood adhesive composed of tannin and sucrose was developed and applied successfully to the preparation of ply-wood.The preparation technique of plywood was optimized,and the chemical structure,curing performance,crystallization property and thermal performance of the adhesive were investigated.Results showed that:(1)hot-pressing temperature played a decisive role in the performances of tannin-sucrose composite adhesives and it also had a very significant influence on the water resistance of plywood.(2)The preparation of tannin-sucrose composite adhesive was a process in which sucrose was transformed into furan aldehydes and then made cross-linking reaction with tannin.These composite adhesives could only get good bonding performances when the curing temperature was above 210℃.(3)The optimal plywood preparation technique was:hot-pressing tem-perature of 220℃,hot-pressing time of 1.2 min/mm,m(tannin):m(sucrose)of 60:40,and adhesive loading of 160 g/m^(2).The wet bonding strength in boiling water of the prepared plywood was 0.83 MPa,meeting the strength requirements of Type-I plywood in the standard of GB/T 17657-2013.(4)The curing temperature of tannin-sucrose composite adhesive was further decreased by lowering the temperature during the transformation of sucrose into 5-HMF,which was a key in subsequent research.

A design and application of compound multi-functional sensor in wood-based panel processing

A compound multi-functional sensor was designed by the study on the on-line testing technology of wood-based panels, and its properties of shape, functions, size, resistance to special environment were studied in details. The operational principles of different sensors, technical flow of manufacturing, development of software systems of special functions, and the assessments of technical specification were also be introduced. This sensor adopted many new technologies, such as the applications of piezoresistant effect and heat sensitive effect can effectively measure the pressure and temperature, digital signal processing technology was used to extract and treat signals, and resist interference, encapsulation technology was used to keep the normal run of sensor under a harsh environment. Thus, the on-line compound multi-functional temperature/pressure sensor can be applied better to supervise the production of wood-based panels. All technical specifications of the compound multi-functional sensor were tested and the results met the requirements of the equipments.

Soy Protein Isolate Non-Isocyanates Polyurethanes(NIPU)Wood Adhesives

Soy-protein isolate(SPI)was used to prepare non-isocyanate polyurethane(NIPU)thermosetting adhesives for wood panels by reacting it with dimethyl carbonate(DMC)and hexamethylene diamine.Both linear as well as branched oligomers were obtained and identified,indicating how such oligomer structures could further cross-link to form a hardened network.Unusual structures were observed,namely carbamic acid-derived urethane linkages coupled with lactam structures.The curing of the adhesive was followed by thermomechanical analysis(TMA).It appeared to follow a two stages process:First,at a lower temperature(maximum 130℃),the growth of linear oligomers occurred,finally forming a physically entangled network.This appeared to collapse and disentangle,causing a decrease of MOE,as the temperature increases.This appears to be due to the ever more marked Brownian movements of the linear oligomer chains with the increase of the temperature.Second,chemical cross-linking of the chains appeared to ensue,forming a hardened network.This was shown by the thermomechanical analysis(TMA)showing two distinct MOE maxima peaks,one around 130℃ and the other around 220℃,with a very marked MOE decrease between the two.Plywood panels were prepared and bonded with the SPI-NIPU wood adhesive and the results obtained are presented.The adhesive appeared to pass comfortably the requirements for dry strength of relevant standards,showing to be suitable for interior grade plywood panels.It did not pass the requirements for wet tests.However,addition of 15%of glycerol diglycidyl ether improved the wet tests results but still not enough to satisfy the standards requirements.

Lignocellulosic Micro and Nanofibrillated Cellulose Produced by Steam Explosion for Wood Adhesive Formulations

The reinforcing impact of Lignocellulosic micro and nanofibrillated cellulose(L-MNFCs)obtained from Eucalyp-tus Globulus bark in Urea-Formaldehyde UF adhesive was tested.L-MNFCs were prepared by an environmentally friendly,low-cost process using a combination process involving steam explosion followed by refining and ultra-fine grinding.Obtained L-MNFCs showed a web-like morphology with some aggregates and lignin nanodroplets.They present a mixture of residual fibers and fine elements with a width varying between 5 nm to 20μm,respec-tively.The effects of the addition of low amounts of L-MNFCs(1%wt.)on the properties of three different adhe-sives(Urea-Formaldehyde UF,Phenol-Formaldehyde PF,and Tannin-Hexamine TH)were studied by the evolution of the pH,the viscosity,and the mechanical properties.Results showed that the viscosity of PF and UF adhesives increased with the addition of L-MNFCs,unlike TH.Meanwhile,the addition led to better mechan-ical behavior for the three adhesives.Particleboards were then prepared using modified UF with L-MNFCs and tested.Results showed that an amount of 1%wt.of L-MNFCs was sufficient to increase the internal bonding by≈67%,the modulus of elasticity by≈43%,and the modulus of rupture by≈29%.

生物质基胶黏剂的研究进展

我国的木材胶黏剂消耗量巨大,以丰富的生物质资源制备生物质基胶黏剂作为传统三醛树脂胶黏剂的补充具有重要的现实意义。本文综述了生物质原料在三醛树脂中的应用及生物质基胶黏剂的研究进展,展望了生物质基胶黏剂的发展趋势及研究方向,为我国生物质基胶黏剂行业未来发展提供参考。

木质素及其衍生物在木材胶黏剂中应用研究进展

以天然可再生资源替代传统化石资源开发绿色环保、性能优异的木材胶黏剂是人造板行业研究的热点。木质素来源广泛、价格低廉,且分子结构中含有羟基、甲氧基、羧基等活性基团,易于功能化修饰,是合成木材胶黏剂的理想原料。本文重点综述了木质素及其衍生物在酚醛树脂、脲醛树脂、环氧树脂、聚氨酯等合成树脂木材胶黏剂中的应用与研究现状,介绍了化学改性、降解、溶剂分级纯化等预处理方式对木质素化学反应活性及合成树脂胶黏剂力学性能的影响,探讨了木质素基木材胶黏剂目前发展面临的困难和挑战,并展望了未来应用及研究方向,以期为木质素资源的高效、高值化综合利用及高性能生物基木材胶黏剂的开发提供理论与技术参考。

电子显示屏幕用光学胶粘剂的研究进展

手机、平板电脑、智能手表等电子产品的触摸显示屏幕由许多具有不同结构和功能的复杂薄层组成,光学胶粘剂在其中起着重要的作用。随着屏幕技术的迭代,触摸显示屏幕向着全面屏、折叠屏以及卷曲和可拉伸屏幕方向发展,对光学胶粘剂提出了更高的要求。本综述介绍了3C产品屏幕中聚氨酯光学胶粘剂、环氧树脂光学胶粘剂、丙烯酸酯光学胶粘剂以及有机硅树脂光学胶粘剂的特点和研究现状,讨论了各类光学胶粘剂的发展和问题。对丙烯酸酯光学压敏胶的制备和性能进行深入探讨,总结了近年来对于柔性可折叠屏幕的光学压敏胶最新研究进展。对电子显示屏幕用光学压敏胶的应用、挑战和未来发展方向提出了展望,为后续研究工作提供参考。

建筑墙体环保装饰板用酯溶型复合胶粘剂的制备与性能测试

以聚氨酯树脂、丙烯酸酯单体结合引发剂(CHP)、促进剂(TMTU)等主要材料,通过热溶解法制备了建筑墙体环保装饰板用酯溶型复合胶粘剂。选择异佛尔酮二异氰酸酯作为固化剂,测试了不同制备温度、引发体系的物质用量、引发剂用量、丙烯酸酯类单体/聚氨酯树脂比例、固化温度和固化剂含量等条件下,胶粘剂的拉伸剪切强度、绝对黏度、涂膜性能、固化时间、断面形貌、热稳定性等性能。研究结果表明:(1)制备温度在45~55℃之间,胶粘剂的制备效果相对最好。选择由CHP-TMTU共同组成的引发体系,当w(CHP)=5%、w(TMTU)=4%时,胶粘剂的拉伸剪切强度可达到6.48MPa。(2)引发剂用量对胶粘剂的绝对黏度有显著影响,适当增加引发剂用量可以提高聚合反应速率和固含率,从而增加胶粘剂的黏度。(3)丙烯酸酯类单体/聚氨酯树脂比例对胶粘剂涂膜性能有显著影响,丙烯酸酯类单体的引入增加了交联度和硬段含量,从而提高了涂膜的硬度和耐冲击性。(4)固化温度和固化剂比例对胶粘剂的固化时间有明显的影响。添加固化剂后,胶粘剂具有更为韧性的断面特点,且胶粘剂在高温条件下表现出更高的热稳定性。

人造板用三醛树脂胶黏剂改性研究进展

介绍了甲醛系树脂胶黏剂的改性方式及机理,通过改性脲醛树脂、酚醛树脂和三聚氰胺甲醛树脂胶黏剂,来改善人造板板性能并且降低游离甲醛的释放量。改性后的甲醛系树脂胶黏剂在人造板制造中表现出优异的性能,降低甲醛释放量,提高环保性能,且胶合强度优异。

人造板胶黏剂储罐防火技术措施研究

以人造板胶黏剂储罐的防火设计为研究对象,开展工程设计应用研究。通过对现行建筑设计防火规范及相关行业标准深入解读,综合分析人造板生产工艺需求、胶黏剂储罐安全性及建筑消防措施等因素,提出了胶黏剂储罐位置及容量设置要求及相应的防火技术措施,为人造板厂房的设计者与管理者提供参考。

铝合金温成型工艺对与铝合金表面电泳性能的影响研究

本文介绍了国内汽车行业首款批量应用铝合金温成型工艺实现更高冲压深度的车门内板在开发过程中使用温合金温成型工艺生产的零件对于后续电泳性能的影响。通过对温成型工艺过程使用的润滑脂成分分析,门内板预处理工艺研究和验证,从机理层面揭示了铝合金温成型工艺过程使用含硅油润滑脂成分的关键性以及对于后续电泳工艺问题影响。最后通过增加酸洗等改善措施解决了铝合金温成型工艺使用的含硅油润滑脂造车的零件电泳附着力不足的难题,保证了车型顺利批量生产,对铝合金温成型工艺在汽车行业进一步的推广和应用具有一定指导意义。

人造板用无机胶黏剂研究现状

随着人造板产业的快速发展,胶黏剂的无甲醛化受到人们的广泛关注,而在人造板行业中,常用的胶黏剂为“三醛类”有机胶黏剂,在使用过程中会释放甲醛,危害人们的身体健康。因此,无甲醛化的无机胶黏剂研究引起了研究者的兴趣。本文主要介绍了人造板工业中常用的硅酸盐胶黏剂和氯氧镁胶黏剂及其改性研究现状,并且对无机胶黏剂生产人造板的研究与应用现状进行了阐述,以期为无机胶黏剂生产人造板提供参考。

油料饼粕基木材胶黏剂研究应用进展

在食用油和生物柴油的提炼过程中,不可避免地产生大量的富含蛋白质和碳水化合物的油料饼粕副产物,利用其研发木材胶黏剂是油料饼粕利用的一条新途径。本研究对大豆饼粕、油菜籽饼粕、花生饼粕、棉籽饼粕、小桐子饼粕和油茶饼粕等油料饼粕制备木材胶黏剂的研究及应用现状进行了简要总结,指出目前存在的问题并进行了客观分析,展望了油料饼粕木材胶黏剂的发展前景。

阻尼复合板粘黏剂涂抹区域隔声优化

研究一种基于划分粘黏剂涂抹区来实现的阻尼复合板隔声优化方法。首先,以铝板和木质胶合板为基板,基于混合有限元-统计能量分析(Hybrid FE-SEA)法建立其阻尼复合板隔声量预测模型;随后,通过模态贡献度分析与振型分析相结合,划分出粘黏剂涂抹区域。与传统的全区域涂抹粘黏剂相比,优化后两组复合板的计权隔声量提升0~0.1 dB,平均隔声量上升0.05 dB~0.2 dB,且粘黏剂使用量下降55%~70%,符合成本节约及轻量化设计原则,具有工程实用意义。

T型长桁加筋壁板胶层厚度的影响因素研究

胶层厚度对加筋壁板胶接强度至关重要。以四筋T型长桁加筋壁板为对象,采用三坐标机测量了T型长桁的回弹变形,对壁板进行胶接面剖切观察并测量了胶层厚度,研究了T型长桁回弹变形、缘条宽度和缘条边缘倒角对加筋壁板胶层厚度的影响。同时,采用有限元软件ABAQUS对T型长桁回弹变形和缘条受压变形进行了仿真计算。结果表明,本试验中的T型长桁的回弹变形约0.4°~0.5°,回弹变形对胶层厚度具有明显影响。当缘条宽度22mm时,长桁边缘到长桁腹板胶层厚度呈现由厚再到薄的变化趋势;当缘条宽度73 mm时,长桁边缘到长桁腹板胶层厚度呈现由薄到厚再到薄的变化趋势。长桁边缘倒角可以有效地改善长桁边缘附近的胶层厚度,避免该位置由于蒙皮褶皱导致的胶层厚度突变,进而提高胶接质量。在实际零件研制过程中,可以从以上几个方面进行控制,改善胶层厚度,保证零件胶接强度。

石膏基瓷砖胶粘剂施工质量问题浅析

贵州某项目内隔墙采用磷石膏空心条板,墙裙粘贴瓷砖,投入使用3个月后墙裙瓷砖出现脱落、开裂等质量缺陷。现场查勘石膏空心条板上的墙裙做法不符合设计要求。XRD分析了不同缺陷处瓷砖胶粘剂的化学成分,判定瓷砖脱落区域瓷砖胶粘剂为石膏基胶粘剂,瓷砖开裂位置瓷砖胶粘剂为水泥基胶粘剂。粘结试验结果显示,石膏基胶粘剂粘结强度最大值为0.2 MPa,且数值离散性大,粘结强度低是墙裙瓷砖脱落的原因;XRD分析结果显示,在水泥基胶粘剂与石膏空心条板界面产生大量的钙矾石,导致瓷砖胶粘结层起鼓、瓷砖开裂。

CFRP车身胶粘螺母的胶接工艺与应用

为验证碳纤维复合材料(CFRP)上胶粘螺母的连接可靠性,研究和对比聚丙烯酸酯(PA)和聚氨酯(PU)结构胶的固化速率和对胶粘表面处理要求的敏感性,发现PA结构胶具有较好的施工工艺性能。然后以B柱中加强板上的M6和M8两种胶粘螺母为研究对象,采用PA结构胶制作试样,通过测试胶粘螺母的破坏扭矩和横向振动轴向力,考察胶粘螺母安装可靠性和电泳烘烤后的性能。测试结果表明,胶粘螺母的连接性能均满足产品的设计要求。研究充分论证碳纤维复合材料胶粘螺母的连接可靠性,设计的胶粘螺母连接工艺对于碳纤维复合材料在车身上推广应用具有现实指导意义。