Grade Plywood Research Articles

Adhesion and Cohesion Performance of Polyurethane Made of Bio‐Polyol Derived from Modified Waste Cooking Oil for Exterior Grade Plywood

Adhesion and Cohesion Performance of Polyurethane Made of Bio‐Polyol Derived from Modified Waste Cooking Oil for Exterior Grade Plywood

Lignin-Glyoxal: A Fully Biobased Formaldehyde-Free Wood Adhesive for Interior Engineered Wood Products

In this study, a biobased phenolic adhesive was successfully developed by entirely substituting both petroleum-based phenol and formaldehyde with an unmodified corn stover biorefinery lignin and glyoxal (a biobased dialdehyde), respectively. Lignin-glyoxal resins were synthesized using an alkaline catalyst with a molar ratio of lignin to glyoxal of 1:2. Chemical, thermal, and mechanical properties of the lignin, lignin-based resins, and final adhesives were assessed following appropriate standard test methods. The analysis of lignins and lignin-based resin molar mass was performed using gel permeation chromatography. The lignin-glyoxal resin was found to have a 3-fold higher average molecular weight than the starting lignin, demonstrating the successful integration of lignin into the polymeric resin network. The curing of the formulated adhesives was studied using differential scanning calorimetry and dynamic mechanical analysis. Although the lignin-glyoxal resin had a higher curing temperature (167 °C) than a conventional phenol-formaldehyde resin (142 °C) and the formulated lignin-formaldehyde resin (146 °C), the rate and degree of cure were similar or better than the other two resins. The adhesion strengths of the formulated adhesives were determined using single-lap-joint veneer samples cured according to recommended press parameters for commercial adhesives. The lignin-glyoxal adhesive had a relatively high dry adhesion strength (3.9 MPa), with over 90% wood failure, but failed the wet adhesion test (boiling water test). Although the formulated lignin-glyoxal adhesive failed the boiling water test, it had excellent stability at room temperature water, remaining intact after 1 week during the water immersion test. The high dry adhesion strength makes this class of lignin-based formaldehyde-free adhesives a unique biobased glue for the production of interior grade plywood and oriented strand boards.

Low curing temperature tannin-based non-isocyanate polyurethane (NIPU) wood adhesives: Preparation and properties evaluation

Bio-sourced glycerol diglycidyl ether (GDE) has been used in appropriate proportions as an enhancer to decrease the curing temperature, and improve the bonding performance, while reducing the emission of harmful substances, such as hexamethylenediamine, in the preparation process of tannin-based NIPU adhesives. The route of suggested enhancement was investigated by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry and Fourier transform infrared spectroscopy (FT-IR). The epoxy groups of GDE easily cross-link with molecules containing amino groups, promoting the reactions proceeding and resulting in a lower curing temperature. In parallel, the esterification reaction between the C3 hydroxyl groups of the flavonoid tannin heterocyclic ring and the epoxy groups of GDE occurred as well. The reduced curing temperature, improved fracture surface morphology, and enhanced thermal stability were demonstrated by thermomechanical analysis (TMA), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA), respectively. The bonding performance was significantly enhanced, satisfying the standard requirements for interior grade plywood (≥0.7 MPa), even though under a relatively lower curing temperature compared to unmodified tannin NIPU adhesives. Therefore, this modification strategy enhanced the bonding properties, reduced the energy consumption during preparation, and decreased release of harmful substances, which is in line with the requirements for a cleaner production process.

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°C), 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°C and the other around 220°C, 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.

Plywood wood based composites using crystalline/amorphous PLA polymer adhesives

Tailored crystalline and amorphous powdered polylactic acid (PLA) bio-renewable green polymers were studied for their use as adhesive for the joining of 2 and 3-ply veneers to produce and test plywood panels for strength, substrate failure and water soak resistance properties per ANSI/HPVA standards. For 3-ply construction Douglas Fir (DF) was used for the core whereas, Southern Pine (SP) veneer was used for the faces per sponsor specifications. It was found that heat or ionizing radiation tailored crystalline and amorphous type PLA-based adhesive resin formulations can both offer adequate strength as measured by the attained shear stress [ranging through ~3.4 MPa (500 psi)], and degree of substrate failure (50–90%) for a range of adhesive loadings ranging from 85 g/m2 to 300 g/m2. Highest shear strength values approaching 500 psi were obtained with emulsion spray based application using amorphous PLA in the 125–250 μm range. For 2-ply samples prepared with either crystalline or amorphous PLA adhesive, both offered satisfactory strength and soak resistance. Successful dry shear strength and 3-cycle soak water resistance under standard conditions were possible to achieve with amorphous PLA formulation for both 2-ply and 3-ply plywood samples. 3-ply tests with panels using crystalline form PLA adhesive formulation did not meet 3-cycle resistance metrics even with 300 g/m2 adhesive loading; although, 1-cycle soak resistance was possible. The superior performance of the amorphous formulation is deemed to arise out of improved wetting and substrate penetration due to its x10 higher melt index and x3 lower relative viscosity as compared with the crystalline form polymer adhesive. Plywood samples prepared with PLA formulations (as yet without cross-linking or strength tailoring), did not survive boiling water testing metrics as would be required of Type I (exterior grade) plywood. However, the research results indicate that ANSI/HVPA metrics for Type II (interior grade) plywood are attainable using the as-formulated amorphous form PLA based adhesive and the associated application methods described in the paper.

Exterior grade plywood adhesives based on pine bark polyphenols and hexamine

The aim of this work was to formulate environmental friendly adhesives for plywood production. This adhesive is based on polyphenol extracts from Pinus radiata D. Don bark, the most important by-product from the Chilean forest industry. We focused on a bio-based formulation free of formaldehyde, phenol, and isocyanates. Hexamethylenetetramine was used as hardener. The influence of pH on gel time, rheological behaviour, and pot life was evaluated. The curing process was evaluated by differential scanning calorimetry, Fourier transform infrared spectroscopy, and automatic bonding evaluation system (ABES). For the first time, exterior grade plywood (EN 314) was manufactured with pine bark extracts obtained at pilot scale. Two alternatives for adhesive application were studied: (1) wood veneers activation using a diluted solution of the bio-adhesive, and (2) pine bark extract application as dry powder on the wood veneers. Both alternatives were not reported before and demonstrated an increase in the final plywood quality, as measured by the internal bond strength (IB). On basis of this research, pine bark from Chilean forest industry is an interesting polyphenolic source for the development of adhesives free of formaldehyde and phenol.

Plywood for general purpose (interior grade) of selected different progenies of Melia composita Benth.

The present study investigated the suitability of thirteen different progenies of Melia composita for general purpose (interior grade) plywood. Plywood were prepared using urea formaldehyde adhesives and evaluated for their suitability for general purpose interior grade plywood. It was observed that the general purpose plywood (interior grade) made out of all the thirteen progenies meet the IS specification. The plywood made of progeny no. 104 performed best in modulus of rupture and modulus of elasticity along and across the grain of plywood, followed by progeny no. 28, 75 and 76. The plywood made of progeny 28 and 76 were performed best in dry and wet state glue shear strength.

Fabrication and characterization of HDPE resins as adhesives in plywood

Demand has been growing for plywood utilizing novel formaldehyde-free wood adhesives which are more durable and require environmental protection and sustainable development during the service life. In this study, a series of HDPE film as novel adhesives in plywood due to many advantages are fabricated using hot-press process followed by cold-press process. The effects of moisture content, HDPE dosage, hot-press temperature and pressure at different levels on physical–mechanical properties were evaluated by tensile shear strength, compression ratio, water absorption and thickness swelling. The results indicated that HDPE film can independently be used as adhesive in plywood, meeting the requirement for type II grade plywood of GB/T 9846.3 (Plywood-part 3: General specification for plywood for general use. Chinese National Committee for standardization, 2004) and opening up a new way for formaldehyde-free adhesives in plywood used as interior grade. Moreover, analysis of variance showed that the most important effect factor on tensile shear strength and water absorption is HDPE layer; on compression ratio and thickness swelling it is moisture content of veneer. To study the optimal hot-press condition, optimization of preparation process for plywood was carried out by response surface methodology analysis (RSMA), and then analysis by Design-Expert software. The simulation results of tensile shear strength were validated by experimental findings, indicating that RSMA can be used as an effective method to predict optimal fabrication condition.

Preparation and performance of lignin–phenol–formaldehyde adhesives

Steam explosion lignin phenol formaldehyde (SEL–PF) adhesives were prepared by ternary gradual copolymerization. The parameters for the phenolate of steam explosion lignin (SEL) and preparation of SEL–PF adhesives were optimized. Under the optimum phenolate conditions, the phenolic hydroxyl content of lignin increased by 130%, whilst the methoxyl content was reduced by 68%. The SEL–PF adhesives were used to prepare plywoods by hot-pressing. The pH value, viscosity, solid content, free phenol content and free formaldehyde content of SEL–PF adhesives were investigated. The bonding strengths of the plywoods glued with SEL–PF adhesives were determined. The maximum SEL replacement percentage of phenol reached 70wt%, and the properties of adhesives and plywoods met the Chinese National Standard (GB/T 14732-2006) for first grade plywood.

1,3-Dimethylol-4,5-dihydroxyethyleneurea as a Potential Alternative Binder for Plywood

Two types of commercial 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) resins were used for the first time as the binders in 3-ply plywood manufacturing. The studies were aimed at the assessment of the applicability of DMDHEU as substitute for widely used urea–formaldehyde (UF) resins. Applied press platen temperature was 120°C, 140°C, and 160°C and pressing time was 300 s. The results indicate that the DMDHEU can be used as a binder for plywood. The mechanical properties: tensile shear strength, modulus of rupture (MOR), and modulus of elasticity (MOE) were determined – i.e., > 1.0, 75–90, and 11100–18000 MPa, respectively. It was found that platen temperature 120°C was sufficient for the proper cure of the binder and to obtain dry shear strength that met the requirements of EN 310 standard. Formaldehyde release was 2.8 ± 0.6 mg∙m–2∙h–1 which complied with standards for interior grade plywood.

Effect of curing technology on bonding properties of silicate wood adhesive

In order to determine the best curing conditions of silicate wood adhesive, three different curing conditions, i.e. room temperature, moderate temperature, and high temperature were chosen to prepare poplar plywood with silicate adhesive and poplar veneer as raw materials. The optimised curing technology was obtained based on a lot of experimental analysis using the single factor test method and orthogonal test method. The research results showed that the curing conditions have obvious influence on the bonding properties. Compared with the samples which were cured at moderate or high temperature, the specimens cured at room temperature have higher bonding strength and water resistance. The dry and wet bonding strength of poplar plywood prepared from optimised curing technology was 0·89 and 0·61 MPa, respectively, and 24 h thickness swelling rate was 5·6%, these properties reached the Chinese National Standard of II Grade Plywood.

Pine tannin based adhesive mixes for plywood

Pine tannin extract has never been used before as an adhesive for plywood. Interior and exterior grade plywood panels were prepared based on various adhesive formulations with pine tannin extract on both, hardwood and softwood veneers. The best performing formulations appeared to be those in which the pine tannin was added in a proportion of 20–35% to a phenol formaldehyde or a urea formaldehyde resin or to pMDI (4,4′-methylene diphenyl diisocyanate). Mixed adhesive formulations where a small amount of pMDI was added on top of 20% synthetic formaldehyde resin gave plywood with even better performance but with shorter pot life of the adhesive mix.

Potential of Tannins for Exterior Grade Plywood

ABSTRACT Resins from Uncaria gambier and Acacia catechu tannins were prepared by copolymerization with phenol and formaldehyde at 100°C. Both tannins were used to substitute up to 50 percent of the phenol using 5, 8, and 11 percent alkali concentrations. Adhesive formulations and gluing conditions were tested by preparing three-ply Shorea robusta boards (53.34 by 53.34 cm). We found that U. gambier tannin can substitute up to 50 percent of the phenol, using 8 and 11 percent sodium hydroxide as a catalyst; A. catechu tannin can substitute up to 30 percent of the phenol, using 8 and 11 percent sodium hydroxide. The resultant boiling water resistance grade plywood meets the requirements laid down in Indian Standards (IS) 303-1989 for exterior grade plywood in all respects (i.e., glue shear strength in dry, water resistance, and mycological tests).

Development a new method for pilot scale production of high grade oil palm plywood: Effect of hot-pressing time

The main objective in this study were to investigate the physical properties, mechanical properties and bonding qualities of oil palm stem (OPS) plywood pre-preg using low molecular weight phenol–formaldehyde (LmwPF). The properties evaluated were physical properties (resin uptake, weight percent gain), mechanical properties (bending strength) and bonding qualities (dry test, WPB test). The results showed that, the physical properties of OPS plywood were significant at resin concentration and veneer moisture content. Moreover, the mechanical properties and bonding performance of the pre-preg OPS plywood were influenced by the pressing time. The high grade OPS plywood with improved at least 227% MOR and 348% MOE compared to commercial OPS plywood, with greater in MOR (31%) and MOE (12%) higher compared than the commercial tropical mix light hardwood (MLHW) plywood. All the shear strength of pre-preg OPS plywood panel were achieved with their minimum requirements and satisfied all the specific testing based on the standard European Norms EN 314-1 and EN 314-2 for the interior and exterior application purposes. The output of this pilot scale study proved that high performance OPS plywood could produced through pre-preg enhancement method in the current plywood mills in which provides broader area of applications compared with conventional OPS plywood. For instant, the pre-preg OPS plywood which is suitable for structural application, concrete formwork, heavy duty interior structuring board, load bearing plywood, marine grade plywood, was obtained, thus consequently increases the price of OPS plywood panels.

Lignocellulosic ethanol residue-based lignin–phenol–formaldehyde resin adhesive

Phenol–formaldehyde (PF) adhesive is usually used to bond exterior grade plywood for high bonding strength and water resistance. However, all components are based on petrochemicals, nonrenewable materials from fossil fuel. Lignocellulosic ethanol residue (ER), as the by-product of lignocellulosic ethanol production, is rich in activated lignin and usually treated as waste. In this work, the ER was used as a renewable and valuable resource to partially replace phenol in the range of 10–70% to prepare lignin–phenol–formaldehyde (LPF) adhesive. The composition, functional groups and molecular weight of the ER were characterized. The result revealed that ER, with rich hydroxyl group and less methoxyl group as well as lower molecular weight, was suitable for the synthesis of LPF adhesive. The synthesis process parameters of ER-modified PF (ERPF) adhesives were optimized. It was found that the phenol could be replaced by ER for 50% at most, without much free formaldehyde and free phenol in the ERPF adhesives and the performance of plywood bonded by ERPF adhesives met the requirement of exterior grade according to the Chinese National Standard (GB/T 9846.3-2004). FT-IR, solid state 13C-NMR and TGA were used to characterize the PF and ERPF adhesives. FT-IR and solid state 13C-NMR spectra of the adhesives showed structural similarity between them. With the increase of substitution rate, the content of aliphatic OH group in the ERPF adhesive increased. Thermal stability of ERPF adhesives was better than that of PF adhesive in the initial thermal degradation. After scale up production, the industrial feasibility of preparing ERPF adhesives had been confirmed.

Soya based phenolic resin for plywood manufacture

Phenolic and amino resins have been the preferred adhesives for the production of weather and moisture resistant wood-based panel products. Environmental concerns and the higher cost of petroleum based resins have resulted in the development of technologies to replace phenol by bio-materials for panel production. Natural bio-materials such as Cardanol (CNSL), tannin, lignin etc., have been tried as substitutes for phenol in the development of PF for panel products at IPIRTI. Hence a study was initiated to develop phenol-soya formaldehyde adhesive for the manufacture of exterior grade plywood. In this study the condition for denaturing soya flour were optimized to maximize its incorporation into the final polymerized structure. Soya flour was made to react with phenol and formalin in presence of caustic to make durable adhesives. About 40 % substitution of phenol by soya was optimized for making exterior grade plywood having strength properties confirming to relevant specifications (IS: 848-2006 and IS: 303-1989). The adhesive developed on laboratory scale meets the requirement of IS 848: 2006 (Anon 2006) for boiling water proof grade plywood. The panels were evaluated for mechanical properties as per IS: 303:1989 (Anon 1989) and the results conforms to the requirement of relevant specifications.

Suitability of Melia dubia (malabar neem wood) for plywood manufacture

The plywood industries had been utilizing plantation timbers and other lesser known timbers for making plywood because of non-availability of conventional timbers. Melia dubia (malabar neem wood) has been identified as one of the fast growing species that would be suitable for plywood making and a study was carried out for determining its suitability for plywood manufacture. Investigations have shown that type-B surface veneers could be produced by peeling and the veneers could be dried without major degrades. Gluing and bonding properties have been studied and found that the panels made using urea formaldehyde and phenol formaldehyde adhesives meets the requirement of MR and BWR grade plywood as per relevant specification.

Preparation and Performance of Bio-Adhesive Based on Acorn Starch Graft Glycidyl Methacrylate

For improving the performance of acorn starch (AS) based bio-adhesive, AS graft glycidyl methacrylate (AS-g-GMA) adhesive was prepared in this paper. The properties of the AS-g-GMA adhesive were studied by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) measurement. The bonding strength of the plywood bonded by AS-g-GMA adhesive was measured according to Chinese National Standards methods to evaluate its water resistant. FTIR results indicated that GMA was grafted on the AS successfully. The bonding strength of the plywood bonded by AS-g-GMA adhesive showed lower curing temperature, better bonding strength, and water resistance comparing with that of control. The water resistant could reach type II grade (63°C water bath 3h) plywood requirement when the glycidyl methacrylate adding amount was 6% based on AS.

The Impact of Different Dosage of Additives on the UF Resin Used in Plywood

Through the study of the effects of different dosage of additives on the properties of urea formaldehyde resin adhesive prepared at low mole ratio of formaldehyde/urea, optimize the synthetic process of the UF resin which is used at the E0 grade plywood. The results showed that the product synthesized under the following condition: the mole ratio of formaldehyde/urea is 0.99:1, the dosage of the specific additive is 1.0% and that of melamine is 3-4%, had a good comprehensive performance and the formaldehyde emission of the plywood meets the E0 grade which is environmental-friendly.

혈장변성접착제를 사용한 내수합판의 특성

This study was carried out to examine properties of water resistant plywood by using serum protein adhesive which is natural, environment-friendly and human-friendly. For the preparation of the serum protein adhesive, pig blood from slaughterhouse was centrifuged and serum was separated from corpuscles and concentrated to 30% by dry weight basis. This concentrated serum protein was modified with PF resin (50% NVC) with the ratio of 9 : 2.5. Plywood made by this modified serum protein gave 1.21 N/<TEX>$mm^2$</TEX> of dry bonding strength, 0.80 N/<TEX>$mm^2$</TEX> of wet boil bonding strength, 0% of cyclic delamination test value, and 0.025 ppm of HCHO emission, which met the excellent super <TEX>$E_0$</TEX> grade and water resistant plywood.