Mechanical characterization of industrial particleboard panels glued with cornstarch–mimosa tannin–urea formaldehyde resins

The aim of this work was to validate the utility and performance of optimal laboratory cornstarch–mimosa tannin-based resins in the industrial particleboard production. In this way, the cornstarch and mimosa tannin was introduced in the classic adhesive formulation in order to supply a part of urea-formaldehyde (UF). Our results show that industrial particleboard panels (8.2?m?×?1.85?m?×?19?mm) bonded with optimal cornstarch–mimosa tannin–UF (10:4:86; mass ratio) resins exhibited comparable mechanical properties to those of boards bonded with commercial UF resins and largely satisfied the exigencies of European norms EN 312. The formaldehyde emission levels obtained from panels bonded with cornstarch–mimosa tannin–UF were lower to those obtained from panels bonded with control UF. Finally, the addition of cornstarch and mimosa tannin improves markedly the water resistance of UF resins.     

Properties of plywood panels bonded with ionic liquid-modified lignin–phenol–formaldehyde resin

The aim of this research was to investigate the physical and mechanical properties of plywood panels bonded with ionic liquid-modified lignin–phenol–formaldehyde (LPF) resin. For this purpose, soda bagasse lignin was modified by 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) ionic liquid, and then, various contents of modified lignins (10, 15, and 20 wt%) were added as a substitute of phenol in phenol–formaldehyde (PF) resin synthesis. The properties of the synthesized resin were compared with those of a control PF resin. The changes in curing behavior of the resins prepared were analyzed by differential scanning calorimetry (DSC). The physical properties of the resins prepared, as well as the water absorption, thickness swelling, shear strength, and formaldehyde emission of the plywood panels bonded with these adhesives, were measured according to standard methods. DSC analysis indicated that in comparison with PF resins, curing of the LPF resin occurred at lower temperatures. The physical properties of the synthesized resins indicated that viscosity and solid content increased, while gel time and density decreased by addition of treated lignin to the PF resin. Although the panels containing resins with modified lignin yielded low formaldehyde emission, their dimensional stability was worse than those bonded with a commercial PF adhesive. The plywood prepared using IL-treated lignin PF resins has shear strength, which satisfy the requirements of the relevant standards specifications and significantly better than that of panels prepared with the control PF resin. The mechanical properties of the panels could be significantly enhanced with increased percentage of treated lignin content from 0 to 20 wt%.     

Improving the properties of ionic liquid-treated lignin-urea-formaldehyde resins by a small addition of isocyanate for wood adhesive

The aim of this research was to investigate the effect of polymeric 4, 4 diphenyl methane diisocyanate (pMDI) on the physical and mechanical properties of plywood panels bonded with an ionic liquid (IL)-treated lignin-urea-formaldehyde resin. Soda lignin modified by 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) IL was added to a urea formaldehyde (UF) resin during resin synthesis to prepare a lignin-urea-formaldehyde (LUF) resin. pMDI at various contents (2, 4, and 6% on resin solids) was then added to prepare a LUF resin. The thermal and physicochemical properties of the resins prepared as well as the water absorption, shear strength, and formaldehyde emission of the plywood panels bonded with them were measured according to standard methods. DSC analysis indicated that the addition of pMDI decreases the gel onset and curing temperatures of the LUF resin. According to the results obtained, the addition of pMDI significantly increased the viscosity and solid content and accelerated the gelation time of LUF resins. Based on the findings of this research, the addition of pMDI dramatically improves the performance of LUF resins as a new adhesive for wood-based panels. The LUF resins with isocyanate added yielded panels presenting lower formaldehyde emission and lower water absorption content when compared to those bonded with the control LUF resins. Greater dry and wet shear strength can be obtained by a small addition of pMDI to LUF resins.     

紫胶改性酚醛树脂胶粘剂的研究

紫胶是一种具有多种用途的天然树脂,利用紫胶改性酚醛树脂胶粘剂,有利于扩大紫胶的应用范围,提高对可再生资源的综合利用。研究了对紫胶改性酚醛树脂胶粘剂的固化时间、粘接胶合板的粘接强度和甲醛释放量进行了测定。结果表明:紫胶改性酚醛胶的固化时间与普通酚醛胶接近,粘接胶合板的粘接强度达到Ⅰ类胶合板的要求,胶合板的甲醛释放量降低。因此,用紫胶改性酚醛树脂胶粘剂是可行的。     

The effect of soda bagasse lignin modified by ionic liquids on properties of the urea–formaldehyde resin as a wood adhesive

The aim of this research was to investigate the influence of lignin modified by ionic liquids on physical and mechanical properties of plywood panels bonded with the urea–formaldehyde (UF) resin. For this purpose, soda bagasse lignin was modified by the 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) ionic liquid and then the various contents of unmodified and modified lignins (10, 15, and 20%) were added at pH=7 instead of second urea during the UF resin synthesis. The physicochemical properties of the prepared resins as well as the water absorption, shear strength, and formaldehyde emission of the plywood panels made with these adhesives were measured according to standard methods. According to Fourier Transform Infrared (FTIR) Spectrometry, by treatment of lignin, the C=O, C–C, and C–H bonds decrease while the content of the C–N bond dramatically increases. Based on the finding of this research, the performance of soda bagasse lignin in UF resins dramatically improves by modification by ILs; as the resins with modified lignin yielded lower formaldehyde emission and water absorption when compared to those made from unmodified lignin and commercial UF adhesives, respectively. The shear strength as well as wood failure percentages are lower for the panels produced with modified lignin than for the panels produced with UF resins alone.     

低甲醛释放量人造板用改性脲醛树脂制备及应用研究

为了降低脲醛树脂的游离甲醛含量及其胶接制品的甲醛释放量,本研究在脲醛树脂合成过程中加入改性剂代替部分甲醛,通过尿素-甲醛-改性剂发生共缩聚反应,合成了改性脲醛树脂。研究了改性剂取代甲醛的摩尔比对改性脲醛树脂固化速度、游离甲醛含量的影响,以及在不同的热压条件下,对胶接胶合板的胶合强度和甲醛释放量的影响。研究结果表明,改性剂的加入不仅能有效降低改性脲醛树脂的游离甲醛含量及其胶合板的甲醛释放量,还能提高胶合板的胶合强度和耐水性。     

Eco-Friendly Adhesives Based on Tannin and N,N-Bis(2-Hydroxy-Ethyl) Fatty Amides (HEFAs) from Non-Traditional Oils for Wood Bonding

Abstract

Wood adhesives were formulated using tannin and N,N-bis(2-hydroxyethyl) fatty amides (HEFAs). The natural tannin-based adhesives can be used to replace formaldehyde-based adhesive systems and thereby reduce formaldehyde and volatile organic compound (VOC) emissions from adhesives used for plywoods. Performance properties of the adhesively bonded wood joints viz., tensile strength, impact strength and chemical resistance were measured. N,N-bis(2-hydroxyethyl) fatty amides (HEFAs) from non-traditional oils were mixed with a pure tannin-based adhesive as a crosslinker, and this increased the tensile strength, impact strength and chemical resistance of wood joints. The results revealed that a high performance and eco-friendly adhesive system for wood can be successfully formulated using tannin and HEFA.     

Effects of natural-resource-based scavengers on the adhesion properties and formaldehyde emission of engineered flooring

In this study we investigated the effects of using four additives, wheat flour (WF), tannin, rice husk (RH) and charcoal, to melamine-formaldehyde (MF) resin for decorative veneer and base plywood in engineered flooring in order to reduce the formaldehyde emission levels and improve the adhesion properties. We determined the effects of variations in hot-press time, temperature and pressure on the bonding strength and formaldehyde emission. Blends of various MF resin/additive compositions were prepared. To determine and compare the effects of the additives, seven MF resin blends were prepared with the four different additives: four with a wt ratio of 8:2 (MF/WF, MF/tannin, MF/RH and MF/charcoal), and three in the wt ratio of 8:1:1 (MF/WF/tannin, MF/WF/RH and MF/WF/charcoal). The desiccator and perforator methods were used to determine the level of formaldehyde emission. The formaldehyde emission level decreased with all additives, except for RH. At a charcoal addition of only 20%, the formaldehyde emission level was reduced to nearly 0.1 mg/l. Curing of the high WF and tannin content in this adhesive system was well processed, as indicated by the increased lap-shear strength. In the case of WF, the lap shear strength was much lower due to the already high temperature of 130°C. The adhesive layer was broken when exposed to high temperature for extended time. In addition, both WF and tannin showed good mechanical properties. With increasing WF or tannin content, the initial adhesion strength increased. The MF resin samples with 20% added tannin or WF showed both good lap shear and initial adhesion strengths compared to the pure MF resin.     

弱酸性条件合成脲醛树脂工艺的探讨

探讨了在弱酸性条件下合成低甲醛释放量的脲醛树脂工艺的可能性。同时,对不同pH值条件下合成脲醛树脂的工艺及其性能进行了研究,并采用傅立叶红外光谱和化学方法对脲醛树脂的官能团进行了分析,同时定性分析了不同pH值条件下合成树脂的热学性能。研究表明在弱酸性条件下合成脲醛树脂的树脂性能和其胶合板的力学性能达到国家标准并且其胶合板甲醛释放量达到GB／T17657—1999中的E,级标准。弱酸性条件下合成脲醛树脂的工艺不仅能降低生产成本,还能生产性能优异的脲醛树脂胶黏剂。     

A comparison between lignin modified by ionic liquids and glyoxalated lignin as modifiers of urea-formaldehyde resin

The aim of this research was to compare the influence of modified lignin by ionic liquid (IL) on the physical and mechanical properties of wood-based panels bonded with urea-formaldehyde (UF) resin with the effect of glyoxalated lignin (GL) on UF properties. For this purpose, soda bagasse lignin was respectively modified by 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) IL and glyoxal and then the various content of modified lignins (10, 15, and 20%) were added at pH=7 during the UF resin synthesis instead of the second urea . The changes in the structure and thermal properties of lignin, after and before modification with glyoxal and IL, were analyzed by Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry (DSC). The physicochemical properties of the prepared resins as well as the water absorption, shear strength, and formaldehyde emission of the plywood panels made with these adhesives were measured according to standard methods. According to the FTIR spectra, the content of C=O bond increased in GL while in the IL-treated lignin the content of C–N bond markedly increased. DSC analysis indicated that lignin modified by IL had lower glass transition temperature (T_g) value compared to those modified with glyoxal and unmodified lignin, respectively. The UF resins containing IL-treated lignin exhibit a faster gel time compared to those prepared with GL. Equally, the plywood panels prepared with an IL had lower formaldehyde emission and higher mechanical strength compared to those made from UF resin containing GL. There were no significant differences in dimensional stability of the panels bonded with UFs modified with GL and those with IL-modified lignin.     

Adhesive Properties of Medium-Density Fiberboards Fabricated with Rapeseed Flour-Based Adhesive Resins

This study examined the adhesive properties of adhesives formulated with rapeseed flour (RSF), a by-product of edible oil and bio-diesel manufacture, for medium-density fiberboards (MDFs). The RSF was hydrolyzed by sulfuric acid (AC-RSFH) and sodium hydroxide (AK-RSFH) solutions of 3%, 5%, and 7%. Phenol–formaldehyde (PF) prepolymers were prepared with formaldehyde to phenol molar ratios of 1.5, 1.8, and 2.1 (1.5-, 1.8-, and 2.1-PF). RSF-based adhesives were formulated by cross-linking 35% AC-RSFH, 35% AK-RSFH, and 30% PF prepolymers on a solid weight basis. The mechanical strength and dimensional stability of the MDFs were improved by decreasing the concentration of RSF-hydrolytic agents. The properties of the MDFs bonded with RSFH/1.8-PF resins were superior to those of RSFH/1.5- or 2.1-PF resins. These results suggest that RSF can be used as a raw material for environment-friendly adhesives used in MDF production.     

Influence of acrylamide copolymerization of urea–formaldehyde resin adhesives to their chemical structure and performance

To lower the formaldehyde emission of wood‐based composite panels bonded with urea–formaldehyde (UF) resin adhesive, this study investigated the influence of acrylamide copolymerization of UF resin adhesives to their chemical structure and performance such as formaldehyde emission, adhesion strength, and mechanical properties of plywood. The acrylamide‐copolymerized UF resin adhesives dramatically reduced the formaldehyde emission of plywood. The ¹³C‐NMR spectra indicated that the acrylamide has been copolymerized by reacting with either methylene glycol remained or methylol group of UF resin, which subsequently contributed in lowering the formaldehyde emission. In addition, an optimum level for the acrylamide for the copolymerization of UF resin adhesives was determined as 1%, when the formaldehyde emission and adhesion strength of plywood were taken into consideration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Use of organosolv lignin in phenol-formaldehyde resins for particleboard production: II. Particleboard production and properties

The objective of this work was to demonstrate the utility of lignin-based resins designed for application as an adhesive in the production of particleboard. Bond qualities of lignin-phenol-formaldehyde resins, phenolated-lignin-formaldehyde resins and commercial phenol-formaldehyde (PF-com) resin were assessed by using an automatic bonding evaluation system, prior to production of particleboards. In order to evaluate the quality of lignin-based resins, particleboards were produced and physical and mechanical properties were investigated. These physical properties included internal bond, modules of rupture and modulus of elasticity. Thickness swell and water absorption properties of particleboards bonded with lignin-based resins were also determined. The lignin-based resins have been reported previously in Part I of this study. The results showed that particleboards bonded with phenolated-lignin formaldehyde resins (up to 30% lignin content) exhibited similar physical and mechanical properties when compared to particleboards bonded with PF-com. The work has indicated that phenolated-lignin formaldehyde resins (up to 30% substitution level) can be used successfully as a wood adhesive for constructing particleboard. The performance of these panels is comparable to those of boards made using PF-com resin.     

Kraft lignin in phenol formaldehyde resin. Part 1. Partial replacement of phenol by kraft lignin in phenol formaldehyde adhesives for plywood

The objective of this study was to investigate the potential for partially replacing phenol with kraft lignin in the phenol formaldehyde (PF) resin designed for application as an adhesive in the production of plywood. The kraft lignin, considered to be an environmentally friendly alternative to phenol, was precipitated from black liquor recovered from kraft pulping of softwood. Kraft lignin phenol formaldehyde (KLPF) resin was prepared in a one-step preparation with different additions of lignin. Replacing 50 wt% of the phenol with kraft lignin (50KLPF) was, under the conditions used, considered to be optimal with respect to resin viscosity, storage stability, and bonding ability. The resin consists of an integrated kraft lignin-phenol network. The hot-pressing time in the plywood manufacturing had to be increased by approximately 30% at 150°C for the 50KLPF resin compared with that normally used for PF resin, in order to comply with plywood standard demands. The mechanical properties of test samples made from KLPF resins were equal to or better than those of test samples made from PF resin only.     

尤戎(Uron)树脂及其用法对脲醛树脂性能的影响

以不同工艺制备了三种含尤戎结构的脲醛树脂(Uron树脂),通过其与普通脲醛树脂的混合制得多种混合脲醛树脂。研究了Uron树脂及其使用方法对降低脲醛树脂胶粘剂游离甲醛含量及胶接胶合板甲醛释放量的作用与效果。结果表明:1)三种不同摩尔比的Uron树脂对脲醛树脂游离甲醛含量及胶接胶合板甲醛释放量都有明显的降低作用,游离甲醛含量最多可降低43％,甲醛释放量最多可降低61％;2)Uron树脂的添加量在10％-20％时对胶合强度的提高有利,强度最大可提高29％;3)低摩尔比Uron树脂对脲醛树脂的改性效果优于高摩尔比Uron树脂。     

丙二酸二乙酯改性酚醛树脂胶粘剂的制备与性能研究

以甲醛和苯酚为主要原料、丙二酸二乙酯为改性剂,制备碱催化水溶性酚醛树脂(PF)胶粘剂;采用DMA(动态力学分析)法、DSC(差示扫描量热)法、FT-IR(红外光谱)法和TGA(热失重分析)法等对改性PF的性能进行了表征。结果表明:适量改性剂的引入,能有效提高改性PF胶粘剂的韧性,但其固化温度和胶合板的胶接强度下降;当w(改性剂)=0.015%(相对于苯酚质量而言)时,改性体系的固化温度下降了4℃,相应胶合板的胶接强度(>0.80 MPa)仍满足GB/T 9846—2004标准中I类胶合板的指标要求。     

Using Renewables in Panelboard Resins to Influence Volatile Organic Compound Emissions from Panels

Technical lignin and condensed tannins have been combined with soy flour as model of no-added-formaldehyde adhesive binders for veneer wood products to understand their impacts on volatile organic compounds (VOCs) produced during panel manufacture. VOC emissions captured on manufacturing lauan hardwood plywood at 170?C were dominated by acetaldehyde, hexaldehyde, acetone, and terpenes in both the condensate and gaseous fractions of press emissions. Other aldehydes including formaldehyde, valeraldehyde, and propionaldehyde were produced in relatively lower quantity during panel manufacture. Compared to using soy flour alone, lignin, and tannin reduced the formaldehyde and acetaldehyde contents in press emissions. These reductions in VOCs had a dependency on adhesive resin pH with an alkaline formulation proving to also decrease longer chain aldehydes such as valeraldehyde and hexaldehyde. Chamber testing plywood panels found the composition of VOC emissions initially released from panels to be prominent compounds released in press emissions formed on panel manufacture. Use of soy flour alone as binder produced relatively high acetaldehyde emissions from panels, whereas incorporating lignin and tannin with soy flour as adhesive binders reduced both acetaldehyde and formaldehyde emissions from panelboards post-manufacture.     

Reduction of Formaldehyde Emission from Particleboard by Phenolated Kraft Lignin

The aim of this study was the reduction of formaldehyde emission from particleboard by phenolated Kraft lignin. For this purpose, the lignin was extracted from black liquor and then modified by phenolation. During the urea formaldehyde (UF) resin synthesis different proportions of unmodified and phenolated Kraft lignins (10%, 15%, and 20%) were added at pH = 7 instead of the second urea. Physicochemical properties and structural changes of resins so prepared, as well as the internal bond (IB) strength and formaldehyde emission associated with the panels bonded with them were measured according to standard methods. The Fourier transform infrared (FTIR) analysis of lignin indicated that the content of O–H bonds increased in phenolated lignin while the aliphatic ethers C–O bonds decreased markedly in the modified lignin. Since both synthesis of UF resins and lignin phenolation are carried out under acid conditions, phenolation is an interesting way of modifying lignin for use in wood adhesive. The panels bonded with these resins showed significantly lower formaldehyde emission compared to commercial UF adhesives. The UF resin with 20% phenolated lignin exhibited less formaldehyde release without significant differences in internal bond strength and physicochemical properties compared to an unmodified UF resin. XRD analysis results indicated that addition of phenolated lignin decreased the crystallinity of the hardened UF resins.     

Physico-mechanical properties of particleboards bonded with pine and wattle tannin-based adhesives

This study investigated the physical and mechanical properties of particleboards made using two types of tannin-based adhesives, wattle and pine, with three hardeners, paraformaldehyde, hexamethylenetetramine (hexamine) and TN (tris(hydroxyl)nitromethane), by measuring the physical (thickness swelling, linear expansion and water absorption) and mechanical properties (bending strength and internal bond strength). The performance of the particleboards made using tannin-based adhesives was influenced by physical conditions such as press time and temperature as well as by chemical conditions, such as the chemical structure of the tannin and the hardener. Wattle tannin-based adhesive being a thermoset, the wattle tannin-based particleboards were more influenced by physical conditions, while the pine tannin-based particleboards were influenced by the chemical structure of the pine tannin nuclei, which include phloroglucinolic A-rings. The reactivity of the hardener toward the tannin was in the order: paraformaldehyde > hexamine > TN for wattle tannin, while for pine tannin the order was hexamine > paraformaldehyde > TN.     

Influence of nanoclay on urea–glyoxalated lignin–formaldehyde resins for wood adhesive

In this research, the influence of nanoclay on urea–glyoxalated lignin–formaldehyde (GLUF) resin properties has been investigated. To prepare the GLUF resin, glyoxalated soda baggase lignin (15 wt%) was added as an alternative for the second urea during the UF resin synthesis. The prepared GLUF resin was mixed with the 0.5%, 1%, and 1.5% nanoclay by mechanically stirring for 5 min at room temperature. The physicochemical properties of the prepared resins were measured according to standard methods. Then the resins were used in particleboard production and the physical and mechanical properties of the manufactured panels were determined. Finally, from the results obtained, the best prepared resin was selected and its properties were analyzed by differential scanning calorimetry (DSC), Fourier transform infrared spectrometry (FTIR), and X-ray diffractometry (XRD). Generally the results indicated that the addition of sodium-montmorillonite (NaMMT) up to 1.5% appears to improve the performance of GLUF resins in particleboards. The results also showed that nanoclays improved mechanical strength (modulus of elasticity (MOE), Modulus of Rupture (MOR), and internal bond (IB) strength) of the panels bonded with GLUF resins. The panels containing GLUF resin and nanoclay yielded lower formaldehyde emission as well as water absorption content than those made from the neat GLUF resins. XRD characterization indicated that NaMMT only intercalated when mixed with GLUF resin. Based on DSC results, the addition of NaMMT could accelerate the curing of GLUF resins. The enthalpy of the cure reaction (ΔH) of GLUF resin containing NaMMT was increased compared with neat GLUF resin. Also the results of FTIR analysis indicated that addition of NaMMT change the GLUF resins structures.