Performance evaluation of a natural based adhesive derived from Irvingia wood species kernel extracts on wood panel production

Abstract

Irvingia seed kernels have been identified as potential raw materials for a wide range of applications such as biodiesel, cosmetics, perfume, and soap. As a result, the Irvingia wood species is earmarked for domestication globally in order to commercially exploit these potential benefits. This study investigated the physical and mechanical properties of experimental panels made with pine (Pinus elliottii) wood particles, using modified Irvingia gabonensis (IG) and Irvingia wombolu (IW) extracts as a binder. The mean values of modulus of rupture (MOR) and modulus of elasticity (MOE) for the panels produced with this Irvingia-based adhesive were 5.8 and 1251?MPa, respectively. These values are within the minimum requirement for MOR and MOE (5.5 and 1034?MPa, respectively) for panel grade 1-L-1 as specified by the American National Standards Institute A208.1. The results from the study show that Irvingia kernel extracts may be considered as a potential environmentally friendly adhesive for wood composite manufacture.     

传统木材胶粘剂的改性研究进展

本文介绍了脲醛胶、酚醛胶、三聚氰胺一甲醛胶和白乳胶等传统胶种的低醛改性研究进展，并对木材胶粘剂的发展进行了展望。     

Synthesis and properties of polyurethane wood adhesives derived from crude glycerol-based polyols

Crude glycerol, a waste stream of the biodiesel production process, is low-cost renewable feedstock for the production of chemicals and polymers. In this study, polyurethane (PU) adhesives were synthesized from crude glycerol-based polyols (CG-based polyols) for wood bonding applications. Effects of different variables, including hydroxyl values of CG-based polyols, chain extenders, and the molar ratio of NCO/OH on the properties of PU adhesives were investigated. The chemical structures of PU adhesives were characterized, and their thermal, mechanical, and chemical resistance properties were evaluated. The experimental results indicated that an increase of the NCO/OH molar ratio (1.3) substantially improved bonding strength by up to 38 MPa. Higher thermal stability and stronger chemical resistance to hot and cold water and to alkali and acid solutions were observed comparing to vegetable oil-based adhesives. However, the effect of the hydroxyl value of polyols on bonding strength was not significant. Additionally, bond strength of crude glycerol-based PU adhesives was comparable to that of some commercial PU wood adhesives. All these properties demonstrated the potential of CG for PU wood adhesive applications, particularly for fast-curing uses.     

Characterization of canola oil based polyurethane wood adhesives

A novel bio-based poly (ether ester) polyol containing both primary and secondary functional groups was synthesized from canola oil using a low cost and efficient procedure. In this work, use of the new canola oil derived polyol for the production of polyurethane (PU) adhesives was demonstrated. The canola oil based PU adhesives had similar or better adhesive properties in terms of lap shear strength than three commercial PU adhesives. The effect of NCO/OH ratio and temperature on adhesive characteristics on wood bonding was also evaluated by lap shear tests. It was found that the use of an elevated curing temperature (i.e. 100 °C), as well as optimized NCO/OH molar ratio (higher than 1.5/1.0), improved the wood adhesive properties. The overall chemical resistance of bio-based PU adhesives to cold water, acid and alkali was comparable to that of commercial PU adhesives whilst its resistance to hot water was superior.     

Phenolic resol resin adhesives prepared from alkali-catalyzed liquefied phenolated wood and used to bond hardwood

Wood-based resol resins were prepared from both water- and sodium hydroxide (NaOH)-catalyzed liquefied phenolated wood. The effects of various reaction parameters, e.g. the concentrations of phenol and formaldehyde, temperature, and time, on the extent of yield, free phenol content, molecular weight as well as the gluability of the resol resins have been evaluated. As far as the yield, free phenol content, and molecular weight are concerned, the optimum conditions of resol resin preparation were found to be a phenol : wood weight ratio of 4 : 6, a formaldehyde : phenol mole ratio of 1.5 : 1, a temperature of 82.5°C, and time 3 h. However, these optimum conditions changed when the performance of the adhesives was considered in terms of the adhesive bond strengths for plywood joints. The yield, molecular weights, polydispersity, and gluability of resol resins prepared from water-catalyzed liquefied wood were lower compared with those prepared from NaOH-catalyzed ones. In most cases, the dry-bond strengths of the experimental plywood joints exceeded the minimum Japan Agricultural Standard (JAS) values. On the other hand, except at a higher formaldehyde: phenol ratio (i.e. 2.0 : 1 mole ratio), the plywood joints of all samples delaminated during 'boil-dry-boil' cyclic treatments. However, both dry- and wet-bond strengths of the plywood joints could be improved to exceed standard values by using an additional crosslinking agent, e.g. poly(methylene (polyphenyl isocyanate)) (polymeric MDI). The adhesive perfomance of the wood-based resol resins was explained on the basis of the adhesion between wood veneers and resol resin adhesives.     

Effects of phosphorus-containing additives on soy and cottonseed protein as wood adhesives

Soy and cottonseed proteins appear promising as sustainable and environment-friendly wood adhesives. Because of their higher cost relative to formaldehyde-based adhesives, improvement in the adhesive performance of proteins is needed. In this work, we evaluated the adhesive properties of soy and cottonseed protein formulations that included phosphorus-containing acids and esters. For cottonseed protein isolate, most of these additives improved dry adhesive strength, with methylphosphonic acid, phosphorous acid, and phosphoric acid increasing the dry strength by 47, 44, and 42%, respectively, at their optimal concentrations. For soy protein isolate, these additives did not show significant benefits. The phosphorus-containing additives also improved the hot water resistance of the cottonseed protein formulations but showed either no effect or a negative effect for the of soy protein formulations. Thus, the combination of cottonseed protein with phosphorus additives appears to be attractive as wood adhesives.     

木材胶粘剂的研究现状和发展趋势

本文综述了木材胶粘剂的国内外现状；论述了各种木材胶的结构及作用机理，结合各胶种的优缺点介绍了其应用情况，重点讨论了水性聚氨酯胶粘剂作为木材胶的特点及优势：指出了我国木材加工领域用胶存在的问题和发展趋势。     

Soy-oil-based waterborne polyurethane improved wet strength of soy protein adhesives on wood

Soy-oil-based waterborne polyurethane (WPU) is used to improve wet strength in shear test of wood bonded with an adhesive of soy protein isolate (SPI) by dispersing WPU into SPI slurry. WPU׳s effects on the physiochemical properties of WPU-SPI adhesives are characterized through Fourier transform infrared spectrum, transmission electron microscopy, thermal analysis, contact angle, and mechanical strength. Wet strength of the WPU-SPI adhesives increases by 65% compared to SPI control. Moreover, the microstructure of WPU has effects on the interactions between WPU and SPI. In this study, smaller and more uniform distributed WPU0002 is easier to interact and form stronger crosslinking network with protein than WPU0500. The stronger interaction between WPU0002 and protein results in increased viscosity and bond strength. The WPU-SPI blended adhesives show significantly improved wet strength, demonstrating their potential as wood adhesives.     

Properties of paper sheets prepared from in-situ synthesis of cuprite in wood pulp fibers

Wood pulp-cuprite paper sheets were prepared from in-situ synthesis of copper(I)-oxide in wood pulp fibers, to study its effect on fire retardant property. Factors such as the amount of copper sulfate, amount of reducing carbohydrate, pH-value, temperature and the amount of carboxymethyl cellulose were studied to derive the optimum conditions for the formation of Cu(I)O with maintaining or improving the strength properties of the prepared paper sheets. The X-ray diffraction was used to identify the formation of Cu(I)O inside the fibers; while FTIR-spectroscopy analysis was used to clarify the behaviour of Cu(I)O inside the fibers. The electrical properties of the prepared paper sheets, e.g., AC-conductivity ( σ ), dielectric constant ( l ') and dielectric loss ( l ") were also examined. The thermal degradation behaviour of some prepared paper sheets has been studied by means of non-isothermal thermogravimetric analysis, and the kinetic parameters were estimated by using Coats and Redfern equation. The results obtained show a good relation between the amount of formed cuprite with the mechanical and electrical properties of the produced sheets. The formation of cuprite in wood pulp fibers improves the fire retardants property of the paper sheets; while the addition of CMC during cuprite formation diminishes this effect.     

Synthesis and characterization of lignin-polyurethane based wood adhesive

The present work aims to evaluate the influence of addition of kraft lignin in moisture curing polyurethane (PU) based wood adhesives. The mechanical, thermal properties and chemical structure of the adhesive were studied. The lignin-PU adhesives were obtained by replacing 1%, 3% and 5% of polypropylene glycol (PPG) by Kraft lignin and further reacted with monomeric diphenylmethanediisocyanate (MDI). The aliphatic hydroxyl level of lignin was not taken into consideration in the stoichiometry, in order to find out effect on % free NCO of the final product. The chemical structure of the synthesized lignin-PU adhesives were analyzed by Fourier transform infrared spectroscopy (FTIR). The lap shear strength of the adhesives was tested by bonding canarium wood substrates. The results illustrated that by increasing the weight % of lignin in such lignin-PU adhesives, a decrease in the free isocyanate content, leading to slower setting time but higher shear strength values, were observed. Similarly, the thermal properties of lignin-PU adhesive were also studied, showing an increase in glass transition temperature (Tg) with increase in lignin content.     

Comparative study of zein- and gluten-based wood adhesives containing cellulose nanofibers and crosslinking agent for improved bond strength

Many of the currently used wood adhesives contain chemicals that are harmful to human health and the environment. Increasing environmental and human health concerns have made the development of safe biobased adhesives a priority. In this study, two plant proteins, i.e., zein and wheat gluten, were used to develop wood adhesives and their performance was compared through simple lap shear tests and plywood flexural/internal bond tests in dry and wet conditions. To increase their bond strength, cellulose nanofibers were added to create nanocomposite adhesives and glutaraldehyde was also used to crosslink the proteins. Single-lap shear test was performed to measure the bond strength of different adhesive formulations and determine the optimal formulations and processing conditions. Fractured bond surfaces were studied using optical observation and scanning electron microscopy to determine bond failure mechanisms. Thermal and chemical properties of the adhesives were evaluated using thermogravimetric analysis and Fourier transform infrared spectroscopy, respectively. The bond strength of both zein and gluten adhesives was significantly increased by the addition of the cellulose nanofibers and/or glutaraldehyde, although the two adhesives responded differently to the two reinforcement materials due to the different solvents used to prepare the adhesives. The bond failure mode changed from cohesive failure of the adhesive to structural failure of the adherent for the gluten adhesive containing CNFs and glutaraldehyde. Potential zein and gluten adhesive formulations were used to produce plywood samples and their performance was assessed under different conditions. The formulations with industrial potential were discovered through this study.     

我国木材胶粘剂用量的估算和预测

据《中国林业统计资料》和已发表的有关数据推算 ,现在木材胶粘剂的用量约为 92万吨(干 )。预测 2 0 0 5年和 2 0 1 0年的人造板用胶量分别为 1 41万吨 (干 )和 1 69万吨 (干 )。     

葛根淀粉基胶黏剂制备与性能研究

研究开发以淀粉为主要原料的环保型胶黏剂替代"三醛类"木材胶黏剂,对彻底解决人造板及其制品的甲醛释放问题具有重要意义。以野生葛根淀粉为原料,通过降黏处理,并与聚醋酸乙烯酯和异氰酸酯复配,制备出胶合强度达到国家Ⅱ类要求的淀粉基木材胶黏剂。研究了降黏剂用量、降黏时间、聚醋酸乙烯酯和异氰酸酯用量对淀粉基木材胶黏剂胶合强度的影响。优化工艺条件下制备胶黏剂胶接胶合板的胶合强度为1.89 MPa,能够满足国家Ⅱ类胶合板强度要求。     

Fabrication of nontoxic natural dye from sappan wood

The use of natural dyes has attracted increasing worldwide attention as the carcinogenicity and environmental pollution problem of synthetic pigments are becomes a great concern. A nontoxic natural dye was fabricated from an extract from Caesalpinia Sappan (sappan wood). Oily natural dye for industrial application was made from extracted sappan wood by using a micro-emulsion method. The absorbance of the dye extracted from sappan wood by distillation was measured with an Ultraviolet/Visible spectrometer. The highest absorbance was obtained from the mordant containing 2 wt% Al. The emulsification conditions were controlled by changing the mixing ratios of TEOS (tetraethyl ortho-silicate), DC3225C (cyclomethicone and dimethicon copolyol) and extracted dye. A W/O (water in oil) type dye was obtained with a TEOS concentration ranging from 19.9 to 50.0 wt% when the DC3225C concentration was fixed to 10 wt%. The W/O type emulsion was verified by optical microscopy. The fabricated dye was applied to colored paper. The applicability of the nontoxic natural dye was verified by analyzing the heavy metals and color fastness of the colored paper.     

Adhesive distribution related to mechanical performance of high density wood fibre board

In a full-scale mill experiment two groups of high density wood fibre boards were produced. While one group was bonded with a standard melamine reinforced urea-formaldehyde adhesive, a second group was bonded with a modified adhesive yielding systematically improved board properties at identical amounts of adhesive applied. By means of a novel fluorescence-microscopic method using the dye Acriflavine to colour the cured adhesive after board production, adhesive distribution within the industrial produced boards was evaluated and quantified. Very clear differences in the size distribution of the two adhesives were found, leading to the conclusion that a relationship exists between adhesive distribution and mechanical board performance.     

Flammability of wood plastic composites prepared from plastic waste

The flammability of wood plastic composites manufactured from recycled plastics was investigated by using the cone calorimetry technique. The peak of the heat release rate was 12% to 25% lower compared to references produced from pure polyethylene‐ and polypropylene‐based composites. The total heat capacity and mass loss rate were also smaller for recycled material compared to the references. The stability of the composites was improved due to the presence of various thermally stable compounds, eg, traces of fire retardants, pigments, and other additives and impurities that can be present in recycled material. Incorporation of carbon black into the secondary materials did not reduce the peak of the heat release rate, but the total heat capacity and mass loss rate decreased further.     

Bond strength/disbonding behavior and dimensional stability of wood materials with different adhesives

In this study, we aimed to describe the effects of adhesives [poly(vinyl acetate) (PVAc), Desmodur vinyl trie ketonol acetate, and urea formaldehyde (UF)] on wooden materials (Scotch pine and oriental beech) cut tangentially and radially impregnated with Protim Solignum, chromate copper arsenate (CCA), and Celcure AC 500 and exposed to humidity and water and heat‐resistance, heating, and cooling tests. For the adhesives, the highest swelling (4.3%) was obtained for oriental beech bonded with UF and cut radially, and the lowest swelling (1%) was obtained for Scotch pine bonded with PVAc and cut radially. For the control samples, the humidity‐resistance, water‐resistance, heat‐resistance, and heating and cooling tests decreased the bonding strength. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and properties of novel dentin adhesives with esterase resistance

A new methacrylate monomer, trimethylolpropane mono allyl ether dimethacrylate (TMPEDMA), was synthesized and evaluated. This branched methacrylate was designed to increase esterase‐resistance when incorporated into conventional HEMA (2‐hydroxyethyl methacrylate)/BisGMA (2,2‐bis[4(2‐hydroxy‐3‐methacryloyloxy‐propyloxy)‐phenyl] propane) dental adhesives. The new adhesives, HEMA/BisGMA/TMPEDMA in a 45/30/25 (w/w) ratio were formulated with H₂O at 0 (A0T) and 8 wt % water (A8T) and compared with control adhesives (HEMA/BisGMA, 45/55 (w/w), at 0 (A0) and 8 wt % (A8) water). Camphoroquinone (CQ), 2‐(dimethylamino) ethyl methacrylate and diphenyliodonium hexafluorophosphate were used as photoinitiators. The new adhesives showed a degree of conversion comparablewith the control and improved modulus and glass transition temperature (T_g). Exposure of photopolymerized discs to porcine liver esterase for up to eight days showed that the net cumulative methacrylic acid (MAA) release in adhesives formulated with the new monomer and 8% water (A8T: 182 μg/mL) was dramatically (P < 0.05) decreased in comparison to the control (A8: 361.6 μg/mL). The results demonstrate that adhesives made with the new monomer and cured in water to simulate wet bonding are more resistant to esterase than conventional HEMA/BisGMA adhesive. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

淀粉基生物质胶粘剂的固化与性能研究

将淀粉在硫酸作用下水解的产物用于替代甲醛与苯酚进行缩聚反应生成淀粉基酚醛树脂,然后以六次甲基四胺为固化剂进行交联固化。研究了淀粉基酚醛树脂的凝胶时间、固化反应表观活化能、冲击强度、热失重性能与断面形貌,并与甲醛基酚醛树脂性能进行比较。结果表明,淀粉基酚醛树脂的固化反应表观活化能为19.8kJ/mol,冲击强度为741J/m2,600℃质量残留率为40%,具有良好的耐热性能,游离甲醛质量分数仅为0.4%,大大低于常规酚醛树脂的甲醛含量。     

Thermoplastic polymers as modifiers for urea‐formaldehyde (UF) wood adhesives. II. Procedures for the preparation and characterization of thermoplastic‐modified UF wood composites

Wood composites were prepared by using wood flour (sugar maple, Acer saccharum March) and thermoplastic‐modified urea‐formaldehyde (UF) suspensions. Thermoplastic (5–10% w/v) was introduced into the UF suspension as an aqueous solution, a self‐stabilized dispersion in water, or as a surfactant‐stabilized latex. The modified suspension was blended with wood flour, and the blend was cured by using a cure cycle that was suitable for all the thermoplastic‐modified UF formulations and unmodified UF controls. The wood flour composites were tested by using a notched Izod impact strength test. All formulations containing surfactant decreased the impact strength by ～ 30–40% relative to the unmodified UF control, whereas the water‐soluble thermoplastic had no effect on the impact strength. The formulations with self‐dispersed thermoplastics all increased the notched Izod impact strength, with the greatest increase being 69% more than the UF control, except in a single instance when the molecular weight of the thermoplastic was very high, which decreased resin flow. Increasing the thermoplastic content from 5 to 10% w/v did not further improve the impact test results. Scanning electron microscopy of the fracture surfaces showed morphological differences in the systems that varied with the thermoplastic and method of thermoplastic addition to the UF suspension.© 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 898–907, 2003