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.

A Review of Basic Mechanical Properties of Bamboo Scrimber Based on Small-Scale Specimens

This review summarizes the existing knowledge about the mechanical properties of bamboo scrimber(BS)in literature.According to literature reviews,the strength of BS under different load modes is affected by a series of factors,such as the type of original bamboo,growth position,resin content,treatment method and density.Therefore,different production processes can be adopted according to different requirements,and bamboo scrimbers can also be classified accordingly.In addition,this review summarizes the changes in different factors considered by scholars in the research on the mechanical properties of BS,so that readers can have an overall understanding of the existing research and make more innovative and valuable research on this basis.This review provides and discusses the conclusive observations,the current research gaps and future research directions on the mechanical properties of BS.

Experimental Study on the Axial Compression Performance of Bamboo Scrimber Columns Embedded with Steel Reinforcing Bars

In this paper,a new type of bamboo scrimber column embedded with steel bars(rebars)was proposed,and the compression performance was improved by pre-embedding rebars during the preparation of the columns.The effects of the slenderness ratio and the reinforcement ratio on the axial compression performance of reinforced bamboo scrimber columns were studied by axial compression tests on 28 specimens.The results showed that the increase in the slenderness ratio had a significant negative effect on the axial compression performance of the columns.When the slenderness ratio increased from 19.63 to 51.96,the failure mode changed from strength failure to buckling failure,and the maximum bearing capacity decreased by 43.03%.The axial compression performance of the reinforced bamboo scrimber columns did not significantly improve at a slenderness ratio of 19.63,but the opposite was true at slenderness ratios of 36.95 and 51.96.When the reinforcement ratio increased from 0%to 4.52%,the bearing capacity of those with a slenderness ratio of 51.96 increased by up to 16.99%,and the stiffness and ductility were also improved.Finally,based on existing specifications,two modification parameters,the overall elastic modulus Ec and the combined strength fcc,were introduced to establish a calculation method for the bearing capacity of the reinforced bamboo scrimber columns.The calculation results were compared with the test results,and the results showed that the proposed calculation models can more accurately predict the bearing capacity.

Preparation of liquefied wood-based resins and their application in molding material

To investigate value in use of liquefied wood-based resin applications in molding material, Chinese fir （Cunninghamia lanceolata） and poplar （Populus tomentosa） wood meal were liquefied in phenol. The reactant was co-condensed with formaldehyde to obtain liquefied wood-based resin. For this paper, we investigated the characterization of the resin and its application in molding material. The result shows that the basic properties of liquefied wood-based resin were satisfactory; the bonding strength of plywood prepared with liquefied Chinese fir and liquefied poplar resin can reach 1.54 and 1.00 MPa, respectively. The compression strengths of the molding material prepared with two kinds of liquefied wood resin were 73.01 and 73.58 MPa, almost the same as that of PF resin molding material. The limiting volume swelling of molding material made with liquefied Chinese resin and liquefied poplar resin were 8.5% and 8.3%, thickness swelling rates of water absorption were 3.3% and 4.2%, and the maximum weight ratios of water absorption were 25.9% and 26.2%, respectively. The soil burial test result shows that the weight loss rate of the molding materials made with liquefied Chinese resin and liquefied poplar resin were 8.3% and 9.1% and that of the PF resin molding material was 7.9%. After the soil internment test, the reduction ratio of compression strength of the two kinds of molding material achieved 16.9% and 17.7%, while that of the PF resin molding material was 15.4%. The test results of wood fungi inoculation on the three surfaces of the molding material indicate the breeding rate of molding material prepared with liquefied Chinese resin and liquefied poplar resin were at level 4 and that of PF resin molding material was at level 1 of the ISO standard.

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.

Dynamic Testing of Elastic Modulus,Shear Modulus,and Poisson’s Ratio of Bamboo Scrimber

The bamboo scrimber is an anisotropic material.The elastic constant values of the bamboo scrimber specimens measured by the dynamic and static methods are consistent,and the dynamic test method has the advantages of rapidity,simplicity,good repeatability,and high precision.Bamboo scrimber has strong potential as a building material,and its elastic constant is an important index to measure its mechanical properties.To quickly,simply,non-destructively,and accurately detect the elastic constant of the bamboo scrimber,they were dynamically tested by the free plate transient excitation method and cantilever plate torsional vibration method.The static four-point bending method was used to verify the accuracy and reliability of the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber.The mechanism analysis and evaluation of the quality grade,homogeneity,and size effect of the bamboo scrimber whole board were carried out.The main results show that the dynamic elastic modulus,shear modulus,and Poisson’s ratio of the bamboo scrimber are 12 GPa,1500 MPa,and 0.31,respectively,which meet the requirements of GB/T 40247-2021 for structural bamboo scrimber.

我国木质重组材料研究现状与发展

木质重组材料是一种新型的高性能木质复合材料,在定向重组过程中,木、竹材在湿-热-力和树脂聚合反应作用下发生了一系列复杂的物理和化学变化,木、竹材原有构造特征发生了显著变化,形成了木质重组材料全新的多维构造,这种新构造特征的形成使得重组材料的物理力学性能与木材、竹材等原材料性能相比有了显著改善,并且重组过程中可通过添加不同添加剂赋予木质重组材料阻燃、防腐、防霉、耐候、防虫等新功能,克服了人工速生林木材材质软、强度低、材质不均、易开裂等缺陷,解决了竹材径级小、易劈裂、材质不均等问题,可用于替代优质木材、钢铁、水泥、塑料等建筑材料,具有广泛的应用前景,是实现人工林木材和竹材高效利用的有效途径之一。本文对木、竹材在重组过程中宏观、微观等构造演变,木质重组材料多尺度构造、多层次胶合界面等多维结构形成机制以及多维结构对木质重组材料物理力学性能影响进行了综合评述,提出了木质重组材料细胞选择性增强的观点,归纳了木质重组材料亟待解决的科学问题,建议加强在细胞和分子水平层面,对木质重组材料的理论基础、制造基础和应用基础等进行研究,构建木质重组材料理论体系,从而为人工速生林木材资源高效利用这一国家重大战略需求提供基础理论和技术支撑。

重组竹内置钢筋后受弯性能有限元分析

重组竹是通过将竹束热压胶合而成的新型工程材料,具有强度高、韧性好以及固碳能力强等优点,为提高重组竹的受弯性能,通过热压工艺在重组竹中内置钢筋形成增强重组竹受弯构件。在四点弯曲试验的基础上,通过ABAQUS有限元模拟研究配筋率及配筋形式对重组竹受弯性能的影响。分析结果表明,与纯重组竹相比,内置钢筋后重组竹的受弯力学性能得到明显提高;当配筋形式相同时,随配筋率的增加,重组竹的承载力及抗弯刚度逐渐提高,与纯重组竹相比,配筋率为1.0%~8.2%的单筋重组竹承载力和抗弯刚度分别提高5.6%~48.36%和10.57%~71.81%;当钢筋直径相同时,重组竹顶部和底部同时配筋的双筋重组竹与重组竹底部配筋的单筋重组竹相比,其承载力及抗弯刚度分别提高21.78%和95.98%。

新型CFRP网格-重组竹复合板力学试验研究

为提高重组竹的力学性能并减轻其各向异性缺陷,设计了一种新型CFRP网格-重组竹复合板(CBCP).分别对8组CBCP拉伸试样和18组CBCP拉拔试样进行单轴拉伸试验和拉拔试验,以分析其力学行为并评估复合方法的影响.选择3个相似的构成模型对拉拔试样的黏结应力-滑移曲线进行拟合,根据试验结果确定CFRP网格和重组竹的临界锚固长度及计算方法,并分析讨论了CFRP层数、横向CFRP束特性和锚固长度对CFRP网格与重组竹黏结性能的影响.结果表明,复合CFRP网格可使重组竹的顺纹和横纹抗拉强度分别提高35.77%和135.20%,从而改善了重组竹的各向异性缺陷.增加网格层数和间距可提高CBCP的拉伸性能.随着锚固长度的增加,平均界面黏结强度呈幂函数递减,而峰值载荷滑移则线性递减.

单板厚度对杨木重组木性能的影响

以杨木单板为原料制备高性能特种重组木,重点探讨单板厚度对重组木性能的影响。结果表明,单板越薄,重组木及其内部单板表芯层密度差异越小,耐水性能也越好,但是垂直层向的抗压强度越低;0.7 mm单板制备重组木的静曲强度最高,为203.3 MPa,0.7 mm和1.0 mm单板制备重组木的弹性模量高于1.3 mm和1.8 mm单板制备重组木。

基于响应面法的菌草重组材制备工艺优化

菌草资源是目前世界上最丰富的农业资源之一,具有广阔的发展前景。以菌草绿洲一号为原料,制备菌草重组材,采用响应面Box-Behnken试验设计方法研究不同浸胶时间、热压时间、热压温度对菌草重组材主要物理力学性能的影响。在响应面试验结果基础上增加碱处理和帚化处理,探究改性对菌草表面结构及物理力学性能的影响。结果表明,菌草重组材的较佳制备工艺参数为浸胶时间33 min,热压时间1.12 min/mm,热压温度155℃。帚化制备的菌草重组材浸胶时间降低至15 min,其静曲强度(MOR)136.56 MPa和弹性模量(MOE)14.80 GPa比未帚化制备的菌草重组材分别提高154%和14%;吸水厚度膨胀率(TSR)5.84%和吸水宽度膨胀率(WSR)0.93%分别比未帚化制备的菌草重组材降低7和1.82个百分点,均达到GB/T 40247—2021《重组竹》的要求。碱处理试验结果显示,在NaOH质量分数为2%时MOR和MOE最佳,分别143.13 MPa和15.05 GPa;在NaOH质量分数1%时TSR和WSR最低,分别为1.85%和0.30%。通过扫描电镜分析可知,碱处理后菌草表面蜡质层出现降解,粗糙度增加;帚化处理产生的裂隙有利于酚醛树脂胶黏剂渗透到菌草内部,有利于菌草重组材的胶合,提高了力学性能和耐水性。本研究制备的菌草重组材为菌草新材料的开发提供新途径,对加快推进菌草重组材产业发展具有重要意义。

高密度重组竹的物理力学性能研究

分析了高密度重组竹的孔隙率、微观结构、耐水性和力学性能,并通过构建性能参数与密度的关系,探究密度对物理力学性能的影响规律。结果表明:随着密度的增大,孔隙率逐渐降低。当密度为1.37 g/cm3时,孔隙率仅为5.52%,竹材细胞基本实现了密实化;薄壁细胞和导管细胞发生严重变形,但纤维细胞的形态几乎未受影响。经4 h水煮-20 h 60℃干燥-4 h水煮处理后,吸水率、厚度膨胀率和宽度膨胀率均随密度的增大而下降,分别低至9.67%、7.62%和1.47%。水平剪切强度、顺纹抗压强度、静曲强度(MOR)和弹性模量(MOE)则随密度的增大而增大,分别高达28.83、215.53、354.00 MPa和28.75 GPa。所有重组竹的性能参数均达到了户外用重组竹的性能要求,且部分参数远超国标中规定的最高等级要求。此研究结果可为重组竹性能的调控与应用提供理论依据和数据参考。

压缩率对杨木重组木表面硬度的影响

【目的】以速生人工林杨木为试验材料,利用定向重组技术制备高硬度重组木,揭示压缩率对杨木重组木表面硬度的影响规律,为杨木表面改性及其重组木制备工艺优化提供可靠的方法和科学依据。【方法】利用定向重组技术制备压缩率50%、55%和59%共3种杨木重组木,选取杨木、红榉和俄罗斯柞木为对照样,采用万能力学试验机测定3种木材和3种不同压缩率杨木重组木样品表面的金氏硬度;应用超景深三维显微镜(UDTM)、场发射扫描电镜(SEM)观察样品表面的宏观和微观形貌以及样品金氏硬度测试过程中破坏面的宏观和微观形貌;运用压汞法(MIP)测试样品孔隙率;使用激光共聚焦显微镜(LSCM)和透射电子显微镜(TEM)表征酚醛树脂在重组木中的分布情况。【结果】杨木重组木的金氏硬度随压缩率增大而增大,与杨木相比,压缩率59%杨木重组木的金氏硬度增加12.63倍,其硬度高于俄罗斯柞木和红榉。金氏硬度测试过程中的应力-应变曲线显示,压缩率越大,重组木的比例极限应力越大。场发射扫描电镜(SEM)和超景深三维显微镜(UDTM)观察可知,杨木原木的破坏面呈韧性断裂,制备的重组木随压缩率增大其破坏模式逐渐变为脆性断裂。压汞法(MIP)测试样品孔隙率可知,定向重组可显著降低杨木的孔隙率,压缩率越大,重组木的孔隙率越低。激光共聚焦显微镜(LSCM)和透射电子显微镜(TEM)观察可知,随压缩率增大,酚醛树脂沿胶层带分布的宽度和深度逐渐增加,且渗透到导管、木射线和纤维细胞的细胞腔中。通过纳米压痕测试重组木细胞壁力学性能,当重组木压缩率为55%、施胶量为15%时,其细胞壁硬度和弹性模量相较原木分别提高54.65%和20.14%。重组木表面硬度增大主要是因为杨木经定向重组后,其导管和木纤维细胞被压缩密实,孔隙率降低,单位体积内的细胞实质密度增加,细胞之间的结合面积增大,连接更紧密;同时,引入的酚醛树脂不仅将压缩的细胞结构固定,而且通过形成的胶钉可提高细胞之间的连接强度,浸入细胞壁的酚醛树脂还能够增强其硬度和弹性模量,从而赋予重组木表面较高的硬度。【结论】定向重组技术可有效解决速生人工林杨木木材材质软、表面硬度低的问题,且可通过控制压缩率调控重组木硬度,以满足不同应用场景对材料硬度的需求。

压缩率和施胶量对毛白杨重组木干状和湿状表面粗糙度的影响

表面粗糙度是评价木质材料表面质量和加工性能的重要指标之一。以毛白杨(Populus tomentosa)单板和酚醛树脂为原料,采用单因素试验制备重组木,探讨压缩率(50%、55%、59%)和施胶量(10%、15%、20%)对重组木干状和湿状表面粗糙度的影响。结果表明,压缩率对干状和湿状表面粗糙度影响显著,且对干状表面粗糙度的影响大于湿状;随着压缩率的增大,重组木的干状表面粗糙度逐渐降低,湿状表面粗糙度逐渐增大;施胶量对干状和湿状表面粗糙度影响显著,且对湿状表面粗糙度的影响大于干状;随着施胶量的增加,重组木干状和湿状表面粗糙度均逐渐降低。与毛白杨单板相比,在压缩率为59%和施胶量为15%时,重组木干状粗糙度参数Ra和Rz分别降低了79.64%和73.07%,湿状粗糙度参数Ra和Rz分别降低了62.85%和50.00%。在实际生产过程中,可通过控制压缩率和施胶量调控重组木干状和湿状表面粗糙度,以满足不同应用场景对重组木材料表面粗糙度的需求。

施胶方式和单板厚度对重组木物理力学性能的影响

采用不同树种的不同厚度单板制备重组木,考察了单板施胶方式、厚度和树种对重组木耐水性能与抗弯性能的影响。结果表明:在0.7~2.2 mm范围内,树种和单板厚度相同时,采用单板表面喷胶制备重组木的吸水厚度膨胀率低于单板浸胶制备的重组木,静曲强度高于后者。树种相同时,单板越厚制备的重组木耐水性能越差。单板厚度和树种对重组木的静曲强度影响较大。单板厚度相同时,桉木重组木的耐水性能和弹性模量高于杨木重组木,但静曲强度低于后者。本研究可为薄单板制备重组木原料和施胶工艺的选择提供重要参考依据。

辊压树脂浸胶法对桉木重组木尺寸稳定性影响机理

【目的】为解决重组木制备过程中重组单元施胶不均匀导致的尺寸稳定性差的问题,通过辊压树脂浸胶工艺制备重组木,探究辊压树脂浸胶工艺对桉木重组木尺寸稳定性的影响机理。【方法】分别通过吊笼式浸胶法和辊压树脂浸胶法制备桉木重组木,采用超景深显微镜、扫描电子显微镜、微计算机断层扫描仪和激光共聚焦显微镜观察重组单元和重组木表面形貌、微观结构和胶液分布情况,并采用X射线光电子能谱仪、粗糙度仪、接触角测定仪以及63℃水泡24 h和28 h循环法(沸水煮4 h,63℃烘20 h,沸水煮4 h)研究重组木表面化学成分、表面粗糙度、表面润湿性和耐水性能。【结果】与吊笼式浸胶法制备的重组木(CWS)相比,辊压树脂浸胶法制备的重组木(RWS)表面裂隙减少,粗糙度降低,表面润湿性减弱,耐水性能显著增强。RWS表面粗糙度R_(a)和R_(z)相比CWS分别下降了34.38%和72.75%。接触角测试结果表明,第20 s时RWS的表面接触角相对于CWS增大幅度为283.95%。63℃水泡24 h测试结果显示:RWS的吸水厚度膨胀率和吸水宽度膨胀率分别为5.47%和1.11%,与CWS相比降低幅度分别达到52.16%和50.09%。28 h循环测试结果显示:RWS的吸水厚度膨胀率和吸水宽度膨胀率分别为6.24%和1.17%,与CWS相比降低幅度分别为51.45%和58.51%。辊压浸胶过程对重组单元产生了二次破坏,增加了胶液进入的通道;同时,辊压使细胞在被压缩到恢复原貌的过程中产生的负压,增加了胶液的渗透深度,形成网状胶合结构,加强了重组木的胶合性能,抑制了木材细胞在吸水后的回弹。【结论】辊压树脂浸胶法提高了重组木内部胶液分布的均匀性,降低了桉木重组木表面的粗糙度和润湿性,显著提高了重组木的耐水性能,改善了重组木的尺寸稳定性,对重组木的工艺优化和连续化生产具有重要的参考和指导意义。

人工林柏木重组木的结构与性能

【目的】采用定向重组技术制备人工林柏木重组木,分析其结构与性能,揭示柏木制备成重组木后性能变化的内因,为人工林柏木高值化利用提供技术参考和理论依据。【方法】制备80%、100%和120%不同压缩率柏木重组木,探究压缩率对重组木耐水性能、力学性能(抗弯性能和水平剪切性能)的影响规律;应用超景深显微镜(UDM)、冷场发射扫描电子显微镜(SEM)、激光共聚焦显微镜(LSM)和透射电镜(TEM)观察重组木微观结构变化以及重组木中胶液分布情况;使用剖面密度测量仪测量垂直于板面表面方向的密度梯度,分析重组木剖面密度。【结果】随着压缩率增大,重组木表面纹理颜色加深,剖面密度逐渐均匀,吸水率(WAR)、吸水厚度膨胀率(TSR)和吸水宽度膨胀率(WSR)逐渐减小,静曲强度(MOR)和水平剪切强度(HSS⊥)逐渐增大。压缩率120%时重组木WAR最小,相比原木降低34.73%,同时重组木MOR和HSS⊥达到最大,分别为125.77和17.05 MPa,相比原木分别提升53.47%和84.32%。剖面密度测量仪、冷场发射扫描电子显微镜、激光共聚焦显微镜和透射电镜观测结果显示,重组木耐水性能和力学性能提升主要是因为随着压缩率增大,木材细胞压缩密实、胶液分布范围更广,在更多的细胞腔和胞间层形成胶合位点,减少吸水时水分进入通道,抑制细胞腔回弹,增强胞间层薄弱结构。【结论】采用定向重组技术将人工林柏木制备成高性能重组木后,其力学性能显著提升;随着压缩率增大,重组木的耐水性能显著增强,压缩率120%时重组木性能达到最优。

环保型家具用重组竹的制备及性能研究

本研究采用低温固化环保型酚醛树脂为胶黏剂制备重组竹板材,探索热压温度、施胶量和板材密度对重组竹物理力学性能的影响。结果表明:当热压温度为125℃时,板材芯层温度即能达到胶黏剂的固化温度范围,且此条件下的板材密度均匀性、理化力学性能以及各项性能的稳定性更优。然而,热压温度升高对性能的改善不明显。当施胶量达到8.6%以上时,重组竹的密度可达到1.00 g/cm^(3),物理力学性能较优。

疏解工艺对簕竹重组材力学性能及尺寸稳定性的影响

本文以簕竹为原料制备重组材,研究了不同疏解工艺对簕竹重组材力学性能和尺寸稳定性的影响,并通过与毛竹重组材对比,探讨其利用价值。结果表明:随着疏解程度的增加,竹束的载胶量增大,竹青竹黄的存在使竹束对胶黏剂的吸附能力下降;相同条件下,簕竹重组材与毛竹重组材水平剪切强度相当,弹性模量及静曲强度约为毛竹的2倍左右,经28 h循环水处理吸水厚度膨胀率约为毛竹的1/2;带青带黄疏解有利于提高簕竹重组材的抗弯性能,制备的重组竹静曲强度达215 MPa,弹性模量达28 GPa,分别高于常规疏解的8.64%和12.92%,但其水平剪切强度略有下降。竹青的存在可以提高簕竹表面的耐水性,簕竹青黄宽疏解在60 s时接触角仍能达到60°,较其余条件耐水性高。以簕竹开发制备重组材在工程应用上具有较大潜力。

高密度重组竹的漆膜附着性能研究

为阐明高密度重组竹的表面涂饰性能,分析了不同密度重组竹的表面形貌、粗糙度、润湿性和漆膜附着力,考察了密度对漆膜附着力的影响。结果表明:重组竹的密度越高,其表面越光滑,粗糙度越小,Ra最低仅为1.71μm。同时,随着重组竹密度的增大,蒸馏水、甲酰胺和二碘甲烷三种极性不同的液体的接触角变大,表面自由能也随之降低。受表面粗糙度和润湿性的影响,低密度的重组竹与高密度的相比,具有更高的漆膜附着性能。然而,根据GB/T4893.4—2013对漆膜附着力的分级,所有重组竹对水性和油性木器底漆的表面漆膜附着力均为2级,表明密度对重组竹表面的漆膜附着力无显著影响。研究结果可为高密度重组竹的表面涂饰处理提供理论支持。