Reduction of formaldehyde emission from plywood

The aim of this work is to evaluate performances of tannin-based resins designed as adhesive in the plywood production. For this purpose, a part of phenol formaldehyde (PF) and melamine formaldehyde (MF) in the classic adhesive formulation was replaced by tannin. The physical properties of the formulated resins (rheological characterization, etc.) were measured. In order to analyze the mechanical performance of tannin-based resins, plywood panels were produced and the mechanical properties including tensile strength wood failure and three-point bending strength were investigated. The performance of these panels is comparable to those of plywood panels made by commercial PF and MF. The results showed that the plywood panels bonded with tannin–PF (PFT) and tannin–MF (MFT) resins exhibited better mechanical properties in comparison to the plywood panels made of commercials PF and MF. The introduction of small properties of tannin in PF and MF resins contribute to the improvement of the water performance of these adhesives. The formaldehyde emission levels obtained from panels bonded with tannin-based resins were lower than those obtained from panels bonded with control PF and MF. Although there are no actual reaction at all between PF, MF, and tannin, addition of tannin significantly improves the water resistance of PF and MF resins. This is a novel finding that manifests the possibility of replacing a convention PF and MF resins by tannin. Modified adhesive is one of the goals in the plywood production without changing any of their production conditions with improvement to their overall properties.     

A Formaldehyde-Free Water-Resistant Soy Flour-Based Adhesive for Plywood

The phasing out of the use of urea–formaldehyde adhesive in the fabrication of interior‐used hardwood plywood requires development of environmentally friendly bio‐based wood adhesives. We recently reported that phosphorylation of soy flour (SF) using phosphoryl chloride (POCl₃) greatly improved the moisture resistance of soy flour adhesive. In the present study, we investigated the effects of inorganic oxidizing agents, such as NaClO₂ and Ca(NO₂)₂, to further improve the wet bonding strength of phosphorylated SF (PSF) wood adhesive. We report that addition of 1.8 % (wet weight basis) Ca(NO₂)₂ to phosphorylated SF (PSF) adhesive formulation containing 25 % soy flour solids increased the wet bonding strength to greater than 3 MPa at 140 °C hot‐press temperature. The water resistance testing of the glued three‐ply hardwood plywood panels passed the three‐cycle soak/dry test recommended by the American National Standard for Hardwood and Decorative Plywood/Hardwood Plywood and Veneer Association protocol (ANSI/HPVA HP‐1‐2004). Since the process involves only inorganic chemistry and no petroleum‐based chemicals such as formaldehyde or polyamidoamine–epichlorohydrin are used, the PSF + Ca(NO₂)₂ adhesive is non‐toxic and environmentally safe.     

木质素改性酚醛树脂的研究进展

人造板工业用的酚醛树脂胶,虽然粘接性能好,但在制造和使用的过程中都会释放出污染物甲醛,而木质素分子中有酚羟基和醛基,使用木质素,既可改善胶粘剂的性质,又可节约苯酚的用量,降低甲醛释放量,达到废物利用与保护环境的目的本文综述了木质素磺酸盐、碱木质素、甘蔗渣木质素、酶解木质素等代替部分苯酚应用于环保树脂胶的制备工艺及研究发展现状,并对其发展前景作了展望     

Soy-based,tannin-modified plywood adhesives

In this research, two different types of commercial tannins, namely a hydrolysable tannin (chestnut) and a condensed flavonoid tannin (mimosa), were used to prepare two types of soy-based (soy flour (SF) and soy protein isolate) adhesives for making plywood. Thermogravimetric properties (TGA) and its derivative as function of temperature (DTG) of different soy-based adhesive were measured in the range 40°C–300°C. Thermomechanical analysis (TMA) from 25°C to 250°C was done for the different resin formulations. Duplicate three-ply laboratory plywood panels were prepared by adding 300 g/m² of the adhesives’ total resin solid content composed of SF or isolated soy protein (ISP), urea, chestnut, and mimosa tannin extracts with hexamine as hardener. Based on the results obtained, tannins can improve SF adhesion properties. The TMA showed that chestnut tannin extract appeared to react well with SF, while mimosa tannin extract appeared to react well with ISP. Matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry also showed that among other reactions, the soy protein amino acids reacted with the tannins. Furthermore, delamination and shear strength test results showed the good water resistance of plywood bonded with soy-based tannin modified adhesive.     

Environmentally friendly mixed tannin/lignin wood resins

We obtained lignin‐based wood adhesives satisfying the requirements of relevant international standards for the manufacture of wood particleboard. These were based on two different low‐molecular‐mass lignins. These lignin‐based wood adhesives did not use any formaldehyde in their formulation; formaldehyde was substituted with a nonvolatile nontoxic aldehyde, namely, glyoxal. The last formaldehyde present, contributed by a fortifying synthetic phenol–formaldehyde resin, was also eliminated by the substitution of the phenol–formaldehyde resin with a natural, vegetable polyflavonoid tannin extract to which no aldehyde was added. This substitution brought the total content of natural material up to 80 wt % of the total adhesive. The adhesives yielded good internal bond strength results of the panels, enough to pass relevant international standard specifications for interior‐grade panels. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

苯酚改性豆基蛋白胶黏剂的制备及胶接强度的研究

通过对大豆粉采用碱处理使大豆蛋白质大分子结构展开,暴露出的官能团进一步与甲醛反应生成稳定的蛋白质,这种物质与苯酚共聚反应生成改性豆基蛋白胶黏剂。采用单因素实验方法,探讨了改性豆基蛋白胶黏剂压制杨木三层胶合板的胶合工艺。分析了热压温度、热压时间和涂胶量对胶合板胶合性能的影响。结果表明：采用改性后的豆基蛋白胶黏剂,在压力为1．4MPa,温度为165℃左右,热压时间为1．4～1．6min·mm^-1,涂胶量为220g·m^-2,压制的杨木胶合板胶合性能较佳且达到Ⅰ类胶合板的标准。     

Combination of lignin polyol–tannin adhesives and polyethylenimine for the preparation of green water‐resistant adhesives

In this study, a green adhesive from renewable lignin and tannin was developed with polyethylenimine (PEI) with a method to improve the water resistance of the lignin/tannin adhesive. Lignin polyols were prepared through the liquefaction of oil‐palm empty fruit bunches. The characteristics of the adhesive samples were compared with those of a commercial phenol–formaldehyde resin. Three plywood specimens bonded with the new adhesive showed a very high tensile strength (63.04 MPa) and were very water resistant. The effect of the solid content of the adhesives on the tensile strength and gel time and various weight ratios of PEI on the tensile strength and water resistance of the plywood specimens were evaluated. Thermal stability tests revealed that the lignin polyol–tannin/PEI adhesives had a high heat resistance (360 °C). © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43437.     

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.     

Cold weather installation of wood flooring by adhesive bonding and its impact on indoor air quality

This study discusses the effect of installation of wood flooring by adhesive bonding under cold weather conditions on indoor air quality (IAQ) and analyzes an onsite strategy that can ensure the adhesion strength of the wood flooring and improve IAQ. To examine the temperature effects of adhesive bonding on volatile organic compound (VOC) emissions from wood flooring, the emission rates from flooring composites were compared with those from adhesive and plywood flooring as individual materials under temperature variations in a small-scale chamber. In addition, the effect of strategies, including room heating to enhance adhesion performance, and the ventilation on material emissions and indoor concentrations, were examined in onsite apartment units equipped with a radiant floor heating system. The results of the small-scale chamber test showed that VOC emissions increased notably when the temperature was elevated, particularly in the adhesive-bonded plywood flooring compared to plywood flooring alone. The results of the onsite field test showed that the flooring bonded onto the radiant floor heating system, which supplied direct heat to the flooring, caused emission of a large amount of VOCs due to the combined effects of the bonding installation and temperature-dependent characteristics. Overall, the results indicate that heating the room in conjunction with ventilation is an effective strategy to ensure adhesion strength and to improve IAQ under cold weather adhesive bonding conditions when the material temperatures can be properly maintained.     

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%.     

耐水胶合板用环保乳清蛋白基水性胶粘剂

乳清蛋白是干酪加工过程中所产生的一种副产品,除被用作食品添加剂外,仍有相当数量乳清蛋白并未得到有效利用。为了实现乳清蛋白的高附加值利用,本文以乳清蛋白为原料,研制了具有良好耐久性和环保的乳清蛋白基胶合板用水性胶粘剂,并评价了变性处理、改性剂种类及其用量对乳清胶粘剂的胶合性能及游离甲醛释放量的影响。结果表明,热变性使乳清蛋白胶粘剂的胶接耐久性提高;不同改性剂对乳清蛋白胶粘剂的性能影响不同。采用1％多异氰酸酯改性胶接耐久性最好;采用0．15％戊二醛／1％乙二醛改性胶接强度最高。中试结果表明,所研制的耐水性环保乳清蛋白基胶合板胶粘剂的干胶接强度达到1．98MPa,煮－烘－煮28h后湿胶接强度为1．14MPa,游离甲醛释放量仅为0035mg／L（干燥器法）,达到了1ISK6806--2003环保结构胶合板用胶粘剂要求。     

A New Soy Flour-Based Adhesive for Making Interior Type II Plywood

In this study, we developed a formaldehyde-free adhesive from abundant, renewable, and inexpensive soy flour (SF). The main ingredients of this adhesive included SF, polyethylenimine (PEI), and maleic anhydride (MA). The optimum formulation of this adhesive and the optimum hot-press conditions for making plywood were investigated. A three-cycle soak test and a boiling water test (BWT) were employed for evaluating the strength and water-resistance of plywood bonded with this adhesive. Results showed that SF, PEI, MA and sodium hydroxide were all essential components for the adhesive and the SF/PEI/MA weight ratio of 7/1.0/0.32 resulted in the highest water-resistance. When the hot-press temperature was in the range of 140–170 °C, both water-resistance and shear strength of plywood bonded with the adhesive remained statistically the same, except that the dry shear strength of plywood at 170 °C was statistically lower than that at 160 °C. When the hot-press time ranged from 2 to 6 min, the plywood panels at 5 min had the highest boiling water test/wet (BWT/w) shear strength. The plywood panels made at 5 min had a higher dry shear strength than those made at 3 min. Plywood panels bonded with this SF/PEI/MA adhesive exceeded the requirements for interior applications.     

Low Formaldehyde Emitting Biobased Wood Adhesives Manufactured from Mixtures of Tannin and Glyoxylated Lignin

Abstract

Kraft (LN-T-CO₂-2) and wheat straw (CIMV) glyoxalated lignin mixed with mimosa tannin and hexamine as a hardener were used as wood adhesive resins in particleboard fabrication. The adhesive systems proportion used were 40/60 and 50/50 w/w for lignin and tannin, respectively. The gel time test was determined by knowing the polymerization time between the different mixes under the controlled conditions. The results showed a slower polymerization with the kraft lignin/mimosa tannin blending than with the wheat straw lignin/mimosa tannin one. Thermomechanical analyses (TMA) tests were carried out as an indication of the final strength of the adhesive systems revealed by the elasticity modulus (MOE). The MOE results have demonstrated the best mechanical resistance values in 40/60 lignin/mimosa tannin proportion with respectively 3.422 and 3.347 (MPa), for CIMV and LN-T-CO₂-2, and 2.122 (MPa) for 50/50 proportion. Particleboards were prepared and the internal bond (IB) tests were carried out according to the European Standard EN 312. The IB tests confirmed the TMA results. The higher mechanical results of the IB were .43 and 0.53 (MPa), for CIMV and LN-T-CO₂-2 lignin in a 40/60 lignin/mimosa tannin proportion. They were classified as interior panel P2 in according with the standard request EN-312. Free-formaldehyde was determined through the flask method EN 717-3. Particleboards prepared with these natural adhesive resins registered emissions at least 87 and 75% lower than the commercial UF and MUF dhesive resins. The panels were classified as E0.     

基于改性橡子淀粉制备的UF胶粘剂用填料性能研究

以改性橡子淀粉、茶叶废料粉和无机矿物粉组成的复合无机填料作为面粉的替代物,配制胶合板用脲醛树脂(UF)胶粘剂。着重探讨了复合无机填料的种类及含量对UF胶粘剂和胶合板的固化速率、预压性能、热稳定性能、胶合强度及其甲醛释放量等影响。结果表明:以复合无机填料替代面粉制成的胶合板用UF胶粘剂,具有预压性能良好、胶合板胶合强度更高且甲醛释放量更低等优点,其应用前景良好。     

An All‐Natural Adhesive for Bonding Wood

A novel adhesive that is solely based on natural materials of defatted soy flour (SF) and magnesium oxide (MgO) has been investigated for preparation of five‐ply plywood panels. The resulting plywood panels met the industrial water‐resistant requirement for interior plywood. In this study, mechanisms by which an aqueous mixture of SF and MgO served as a strong and water‐resistant adhesive for bonding wood were investigated. SF was first fractionated into soy protein isolates (SPI), a water‐soluble fraction, and insoluble carbohydrates (ICs) that were mixed with MgO, respectively, for preparation of maple laminates. The water resistance of the resulting maple laminates was evaluated by a three‐cycle water‐soaking‐and‐drying (WSAD) test and a two‐cycle boiling‐water test (BWT). The mixture of MgO and the soluble fraction was not able to bond maple veneers together. The shear strengths of the resulting maple laminates before and after WSAD and BWT all had the following order: MgO–SPI > MgO–SF > SF only > MgO–IC. The water solubility of SF in the heat‐cured SF–MgO mixture was much lower than that of the heat‐cured SF. We believe that the low water solubility of SF–MgO and close interactions between MgO and soy proteins instead of soy carbohydrates were responsible for the superior strengths and high water resistance of the soy‐MgO adhesive.     

A new formaldehyde-free wood adhesive from renewable materials

A formaldehyde-free adhesive that consists of soy flour (SF) and a new curing agent (CA) was developed and evaluated for making interior plywood. Three types of plywood panels (seven-ply maple/white fir/pine/white fir/pine/white fir/maple, five-ply yellow poplar, and five-ply aspen) were prepared with the SF–CA adhesives and evaluated for their water resistance. The CA was derived from the reaction of epichlorohydrin (ECH) and ammonium hydroxide in water. Effects of the reaction time, reaction temperature, NaOH usage, heat treatment of CA, addition order of reactants in the preparation of the CA, and storage time of the CA on the water resistance of plywood panels bonded with SF–CA adhesives were investigated. The reaction time required for the completion of the reaction significantly decreased as reaction temperatures increased. The addition of NaOH to the SF–CA adhesive improved the water resistance and dry shear strength of the five-ply aspen panels. All plywood panels met the requirements for interior plywood when the CAs were prepared at 45–60 °C no matter whether the CA was heat-treated or not. Mixing ECH and ammonium hydroxide all at once resulted in better water resistance of the resulting plywood panels than adding either of ECH or ammonium hydroxide to the other dropwise. The viscosity of heat-treated CA was comparable to that of untreated CA when the CA was prepared at 50 °C. Both heat-treated and untreated CAs could be stored at room temperature for at least two months without compromising the water resistance of the resulting plywood panels.     

Soybean meal-based adhesive enhanced by MUF resin

Soybean meal flour, polyethylene glycol (PEG), sodium hydroxide (NaOH), and a melamine-urea-formaldehyde (MUF) resin were used to formulate soybean meal/MUF resin adhesive. Effects of the adhesive components on the water resistance and formaldehyde emission were measured on three-ply plywood. The viscosity and solid content of the different adhesive formulations were measured. The functional groups of the cured adhesives were evaluated. The results showed that the wet shear strength of plywood bonded by soybean meal/NaOH adhesive increased by 33% to 0.61 MPa after adding NaOH into the adhesive formulation. Addition of PEG reduced the viscosity of the soybean meal/NaOH/PEG adhesive by 91% to 34,489 cP. By using the MUF resin, the solid content of the soybean meal/MUF resin adhesive was improved to 39.2%, the viscosity of the adhesive was further reduced by 37% to 21,727 cP, and the wet shear strength of plywood bonded by the adhesive was increased to 0.95 MPa, which met the interior plywood requirements (≥0.7 MPa). The formaldehyde emission of plywood bonded by the soybean meal/MUF resin adhesive was obtained at 0.28 mg/L, which met the strictest requirement of the China National Standard (≤0.5 mg/L). FTIR showed using the MUF resin formed more  CH₂ group in the cured adhesive. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

无甲醛聚合物胶粘剂的合成与应用研究

将尿素与两种活性化合物在一定条件下进行共缩聚反应,合成了尿素-化合物L-化合物R共缩聚(ULR)初期树脂。通过胶合板制造实验、力学性能测试以及甲醛释放量测试,初步探讨了ULR树脂作为胶粘剂应用于胶合板制造的可能性。结果表明:一定反应条件下,反应时间对ULR树脂的粘度影响不大;面粉添加量对ULR树脂胶接胶合板的胶合强度影响较大;当反应时间为120min、面粉添加量为15%时,ULR树脂胶接胶合板的胶合强度能够满足国家标准(≥0．7MPa),甲醛释放量接近0。因此,ULR树脂作为胶粘剂应用于胶合板制造是可行的。     

Preparation of a New Type of Polyamidoamine and Its Application for Soy Flour-Based Adhesives

The most commonly used curing agents for soy-based adhesives are polyamines, which have the problem of low solid content and/or high viscosity. To overcome this problem, a new type of polyamidoamine (PADA) resin was synthesized and applied to soy flour-based adhesives to improve their water resistance. The PADA solution obtained had a high solid content of 50 wt% and low viscosity of 270 cP. The optimum weight ratio of soy flour/PADA/maleic anhydride to prepare adhesive was 40/7/1.68. The wet strength of plywood prepared at the optimum weight ratio was 0.82 MPa, which meant the plywood could be used as type II plywood according to the Chinese National Standard GB/T 9846.7-2004. The results of water-insoluble solid content measurement and SEM observation demonstrated that cured soy flour–PADA–maleic anhydride adhesive had a 16 % greater water-insoluble solid content than soy flour–NaOH adhesive. The cross-linking network formed by the reactions of PADA and MA would increase the water-insoluble solid contents and improve water resistance of cured soy flour-based adhesives.     

工艺参数对生物油酚醛树脂胶合板甲醛和TVOC含量的影响

为探究制胶阶段和压板阶段的6个因素(生物油替代率、醛酚比、热压温度、热压时间、热压压力、涂胶量)对胶合板中甲醛和总挥发性有机物(TVOC)含量的影响,在单因素试验基础上,设计L25(56)正交试验对工艺参数进行优化.采用顶空固相微萃取法(HS-SPME)和气相色谱/质谱(GC/MS)联用技术对生物油酚醛树脂胶合板(BP...