Plywood Adhesives Research Articles

Natural organic-inorganic hybrid structure enabled green biomass adhesive with desirable strength, toughness and mildew resistance

Plant based proteins are green, sustainable, and renewable materials that show the potential to replace traditional formaldehyde resin. High performance plywood adhesives exhibit high water resistance, strength, toughness, and desirable mildew resistance. Adding petrochemical-based crosslinkers is not economically viable or environmentally benign; this chemical crosslinking strategy makes the imparted high strength and toughness less attractive. Herein, a green approach based on natural organic-inorganic hybrid structure enhancement is proposed. The design of soybean meal-dialdehyde chitosan-amine modified halloysite nanotubes (SM-DACS-HNTs@N) adhesive with desirable strength and toughness enhanced by covalent bonding (Schiff base) crosslinking and toughened by surface-modified nanofillers is demonstrated. Consequently, the prepared adhesive showed a wet shear strength of 1.53 MPa and work of debonding of 389.7 mJ, which increased by 146.8 % and 276.5 %, respectively, due to the cross-linking effect of organic DACS and toughening effect of inorganic HNTs@N. The introduction of DACS and Schiff base generation enhanced the antimicrobial property of the adhesive and increased the mold resistance of the adhesive and plywood. In addition, the adhesive has good economic benefits. This research creates new opportunities for developing biomass composites with desirable performance.

Cate Levey

In 2014, with a bachelor’s degree in chemistry and about a year of professional experience working on plywood adhesives, Cate Levey sent an email to Patrick Brown, the CEO of Impossible Foods , which at the time was a buzzy start-up in the early stages of developing a plant-based meat substitute . She told Brown that she wanted to work at Impossible Foods, where she thought she could make an impact on climate change and public health. He responded, telling her that the company would soon be hiring. She landed a job there shortly afterward. “I know very well how much a motivated person who starts with very little specialized experience can accomplish and learn if they’re motivated by what they’re doing,” Brown tells C&EN in an email. “We prioritize raw potential, curiosity, imagination, initiative and desire to learn and take on hard challenges. . . . Those were all

Development and investigation of a two-component adhesive composed of soybean flour and sugar solution for plywood manufacturing

ABSTRACT In this study, soybean flour (SF) and various sugar solutions were utilized as raw materials to prepare eco-friendly plywood adhesives. First, the optimal preparation conditions were investigated by testing the bond performance. When SF was mixed with synthesized sucrose-ammonium dihydrogen phosphate (SADP) solution with 50% solid content in a 1: 4 mass proportion, the wet shear strength of the plywood achieved a maximum value of 0.83 MPa. This value exceeds the minimum limit of China National Standard GB/T 9846-2015. Second, the curing behavior of the SF/SADP adhesive was studied by measuring the insoluble mass proportion and thermal analysis. The results showed that the curing reaction of this adhesive occurred near 170 °C. In addition, the curing mechanism was studied by ATR FT-IR and Py-GC/MS analysis. Based on the results, it was concluded that the cured adhesive formed a network structure via a polycondensation reaction between small-molecule compounds derived from the SADP solution and the products of the caramelization and soy flour. Dimethylene ether bridges were the main linkages of the final polymer. SEM microstructure analysis showed that the cured SF/SADP adhesive exhibited a more compact crosslinked structure than cured SADP.

Quebracho Tannin Bio-Based Adhesives for Plywood.

Wood-based products are traditionally bonded with synthetic adhesives. Resources availability and ecological concerns have drawn attention to bio-based sources. The use of tannin-based adhesives for engineered wood products has been known for decades, however, these formulations were hardly used for the gluing of solid wood because their rigidity involved low performance. In this work, a completely bio-based formulation consisting of Quebracho (Schinopsis balancae) extract and furfural is characterized in terms of viscosity, gel time, and FT-IR spectroscopy. Further, the usability as an adhesive for beech (Fagus sylvatica) plywood with regard to press parameters (time and temperature) and its influence on physical (density and thickness) and mechanical properties (modulus of elasticity, modulus of rupture and tensile shear strength) were determined. These polyphenolic adhesives presented non-Newtonian behavior but still good spreading at room temperature as well as evident signs of crosslinking when exposed to 100 °C. Within the press temperature, a range of 125 °C to 140 °C gained suitable results with regard to mechanical properties. The modulus of elasticity of five layered 10 mm beech plywood ranged between 9600 N/mm2 and 11,600 N/mm2, respectively, with 66 N/mm2 to 100 N/mm2 for the modulus of rupture. The dry state tensile shear strength of ~2.2 N/mm2 matched with other tannin-based formulations, but showed delamination after 24 h of water storage. The proposed quebracho tannin-furfural formulation can be a bio-based alternative adhesive for industrial applicability for special plywood products in a dry environment, and it offers new possibilities in terms of recyclability.

Eco-Friendly Adhesives Based on the Oligomeric Condensed Tannins-Rich Extract from Alder Bark for Particleboard and Plywood Production.

Toxic formaldehyde emissions, and the necessity to reduce the consumption of petrochemicals, stimulates the development of environmentally friendly adhesives. The aim of this research was to study, for the first time, the possibility of using condensed tannins (CTs)-rich extracts from grey alder (Alnus incana) and black alder (Alnus glutinosa) bark in the production of particleboards and plywood adhesives. The chemical structure, composition, and molecular weight of the CTs were identified by a 13C-NMR and TOF-MS analysis. Three innovative adhesive systems were studied: CTs-phenol-formaldehyde (CTs-PF) resin; a CTs-polyethyleneimine (PEI) adhesive system; and CTs–PEI combined with an ultra-low emitting formaldehyde resin (ULEFR)—CTs–PEI–ULEFR. The results showed that CTs-PF resin has properties close to commercial PF resin, and the formaldehyde emission was twice lower. CTs–PEI bonded particleboards corresponded to the requirements of the EN 312:2010 standard for particleboards in dry conditions (Type P2). CTs–PEI–ULEFR, with a 40–60% substitution of ULEFR by CTs–PEI, had adhesive properties very close to ULEFR; the plywood shear strength fit the requirements of the EN 314-2:1993 standard for application in internal and external system conditions. The introduction of extracted alder bark residues microparticles into the composition of the adhesive system showed their positive potential for application as a filler.

Influence of Lignin Content and Pressing Time on Plywood Properties Bonded with Cold-Setting Adhesive Based on Poly (Vinyl Alcohol), Lignin, and Hexamine

The sustainability, performance, and cost of production in the plywood industry depend on wood adhesives and the hot-pressing process. In this study, a cold-setting plywood adhesive was developed based on polyvinyl alcohol (PVOH), high-purity lignin, and hexamine. The influence of lignin content (10%, 15%, and 20%) and cold-pressing time (3, 6, 12, and 24 h) on cohesion, adhesion, and formaldehyde emission of plywood were investigated through physical, chemical, thermal, and mechanical analyses. The increased lignin addition level lowered the solids content, which resulted in reduced average viscosity of the adhesive. As a result, the cohesion strength of the adhesive formulation with 10% lignin addition was greater than those of 15% and 20% lignin content. Markedly, the adhesive formulation containing a 15% lignin addition level exhibited superior thermo-mechanical properties than the blends with 10% and 20% lignin content. This study showed that 10% and 15% lignin content in the adhesive resulted in better cohesion strength than that with 20% lignin content. However, statistical analysis revealed that the addition of 20% lignin in the adhesive and using a cold-pressing time of 24 h could produce plywood that was comparable to the control polyurethane resins, i.e., dry tensile shear strength (TSS) value of 0.95 MPa, modulus of rupture (MOR) ranging from 35.8 MPa, modulus of elasticity (MOE) values varying from 3980 MPa, and close-to-zero formaldehyde emission (FE) of 0.1 mg/L, which meets the strictest emission standards. This study demonstrated the feasibility of fabricating eco-friendly plywood bonded with PVOH–lignin–hexamine-based adhesive using cold pressing as an alternative to conventional plywood.

Plant Polyphenol‐Inspired Crosslinking Strategy toward High Bonding Strength and Mildew Resistance for Soy Protein Adhesives

AbstractSoybean protein adhesives are environmentally friendly biomass‐based aldehyde‐free adhesives that have good economic value for the wood industry; however, it remains challenging to produce soybean protein adhesives with excellent water resistance, toughness, and mildew resistance through a simple modification method. In this work, inspired by plant polyphenols, a novel crosslinked soybean meal adhesive (SMPT) is obtained using a facile economic method. Polyamidoamine‐epichlorohydrin (PAE) and tannic acid (TA) are combined with a soybean meal matrix to form a tough co‐crosslinked network through strong intermolecular forces (covalent bonds, ionic bonds, and hydrogen bonds) in adhesive system. The results show that the wet bonding strength of SMPT adhesives for plywood is 134.1% higher than the unmodified soybean meal adhesive. The adhesion properties met the standard requirements for interior‐use plywood. And the compact cross‐linking network structure is accelerated the greater energy dissipation, which improves the toughness of adhesive. Moreover, cationic azetidinium groups in PAE and phenol hydroxyl groups in TA synergistically not only exhibit the good antibacterial activities but also improve mildew resistance for SMPT adhesives. This facile strategy provides an economic sustainable method to prepare high‐performance environmentally friendly wood adhesives.

Modification of Oxidized Starch Polymer with Nanoclay for Enhanced Adhesion and Free Formaldehyde Emission of Plywood

This study is aiming of developing eco-friendly wood adhesive based on oxidized starch (OS) modified by nanoclay to enhance their adhesion and no formaldehyde emission. Two types of nanoclay such as pristine-bentonite (P-BNT) and transition metal ion modified-pristine-bentonite (TMI-P-BNT) at three levels (i.e., 1, 3, and 5%) were used for the modification of OS adhesive. Basic properties, chemical properties and thermal properties of the modified OS adhesives were examined with various analysis techniques to understand the influence of nanoclay modification on OS polymer. As the nanoclay level increased, the modified OS adhesives had greater solids content and viscosity but the gelation time decreased, indicating a faster curing of the modified OS adhesive. X-Ray diffraction of the modified OS adhesives resulted in a decrease in the 2θ value and enlarged d-spacing value, showing that the nanoclay had been intercalated within OS polymer molecules. Two peaks at 526 cm−1 and 461 cm−1 detected by FTIR were assigned to Si–O–Al and Si–O–Si vibrations, respectively, and confirmed the presence of nanoclay in the OS polymer. Thermogravimetric analysis showed that the added nanoclay improved thermal stability of OS adhesives. The modified OS adhesives with 5% TMI-P-BNT enhanced their adhesion strength from 0.9 to 1.25 MPa, and resulted in free formaldehyde emission (near to 0.01 mg/L) from plywood panel. These results indicated that the modification of OS adhesives with 5% TMI-P-BNT could be used as bio-based and environmentally friendly plywood adhesive with zero formaldehyde emission.

Effect of Nano-additive on the Bonding Strength and Formaldehyde Emission of the Plywood Adhesive during Manufacturing of Wood Based Panel Products

Nano science and nano technology provides numerous opportunities for enhancing the properties of wood based panel products. In this study an extender was made using nano silicon dioxide ( Sio2), nano calcium carbonate( CaCo3) with some specialty chemicals at a certain reciprocal proportion. Efficacy study was carried out with both phenolic and amino resin in terms of rheological and formaldehyde emission test using reinforcement of nano additive as extender at different concentration level. The plywood panels has been tested as per IS: 1734-1983 for mechanical properties. The rheological and adhesive properties has been tested as per IS 848: 2006. The test data reveals that enhancement of rheological, bonding and mechanical properties have been achieved after reinforcement of synthetic resin. The increase in the percentage of nano-additive caused an increase of viscosity, glue shear strength and minimizing the formaldehyde emission than using individual nano silicon dioxide ( Sio2), nano calcium carbonate( CaCO3) instead of the extender made by combination of above. Using nano additive extender at 5%, there is an increase in glue shear strength in the glue line and enhanced rheological properties in amino resin based adhesive was observed.

Effect of Nano-additive on the Bonding Strength and Formaldehyde Emission of the Plywood Adhesive during Manufacturing of Wood Based Panel Products

Effect of Nano-additive on the Bonding Strength and Formaldehyde Emission of the Plywood Adhesive during Manufacturing of Wood Based Panel Products

A sustainable bio-based adhesive derived from defatted soy flour and epichlorohydrin

This study reports on the preparation and application of bio-based adhesive derived from renewable defatted soy flour (DSF) and epichlorohydrin (ECH), aiming at substituting formaldehyde-based adhesives in the wood industry. DSF was treated with Viscozyme® L to hydrolyze plant cell wall carbohydrates and then adjusted to an extremely low pH with hydrochloric acid containing ferric chloride to unfold the tertiary and/or quaternary structure of soy protein and expose its functional groups. The treated DSF was then glycidized with ECH to obtain the bio-based adhesive. The resulting adhesive contained epoxy groups, which were evidenced by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and 1H nuclear magnetic resonance. After curing, the epoxy groups contributed to good thermal stability and gluability of the adhesive. The grafting ratio of ECH decreased by 37.8% as the mass fraction added was increased from 5 to 25%, whereas the viscosity increased sharply by 2889.5% and the solid content increased slowly by 10.5%. Wet shear strength of Pinus massoniana plywood bonded with the bio-based adhesive with an ECH mass fraction of > 10% of the DSF mass was higher than 0.93 MPa, which met the requirements of the Chinese National Standard for plywood for interior/exterior applications. These results support the use of soy flour-based adhesives for plywood and provide data for evaluating their use as sustainable materials for other applications.

Preparation of isocyanate microcapsules as functional crosslinking agent by minimalist interfacial polymerization

Isocyanate is an extremely high activity compound that has been extensively used in the chemical materials. In this study, we employ microcapsules in preserving the activity of isocyanates and controlling their release in wood adhesives for plywood. Isocyanate microcapsules were synthesized by a one-step interfacial polymerization in an oil-in-water (O/W) emulsion. The particle size distribution, chemical structure, morphology, activity and stability of the obtained isocyanate microcapsules were characterized by laser particle size analyzer, n-dibutylamine titration, FTIR, SEM, and a universal strength testing machine. The as-synthesized microcapsules had approximately 25% active –NCO group and the core accounted for 77% of the total weight. The isocyanate microcapsules demonstrated satisfactory stability by preserving majority of the active –NCO group and core weight during 180 days of storage. These isocyanate microcapsules were used as functional crosslinking agent for making plywood. The resultant plywood showed higher tensile shear strength than the strength mandated in the Chinese National Standard (GB/T 9846-2015). Furthermore, the wet strength was greatly improved to meet the Class I and II plywood standards. Additionally, the stability of isocyanate microcapsules in wood adhesives were significantly enhanced for a prolonged application time. Their excellent bonding properties and stability make isocyanate microcapsules an ideal additive for use in chemical and manufacturing materials.

Development of mainly plant protein-derived plywood bioadhesives via soy protein isolate fiber self-reinforced soybean meal composites

Self-reinforced composites (SRCs) exhibit excellent interface compatibilities and have similar constituents for easy recycling, thereby making them competitive with traditional polymeric composites in various industrial areas. However, there is still a lack of research regarding the biodegradable plant protein-based SRCs plywood adhesives with rigid strength. In this study, the “self-gluing” concept of the binding of the soy protein isolate fibers (SPFs) network skeleton with the soybean meal (SM) matrix was explored. To avoid the SPFs’ aggregation and to improve their dispersity, a batchwise feeding of SM was applied before and after the SPFs were added. The 1,2,3-propanetriol-diglycidyl-ether (PTGE) was the cross-linker, which readily formed dense physicochemical interactions with the multiple side groups (COOH/NH2/OH) in both the SPFs reinforcement phase and the SM matrix. A set of SPFs addition amounts (0.5%–2.0%) were employed in order to manufacture the self-reinforced SPFs/SM/PTGE plywood adhesives, and their bonded three-layer plywood was produced for testing. The wet shear strength of the plywood bonded with the SPFs/SM/PTGE adhesives fulfilled China’s interior furnishing requirements (≥0.7 MPa, GB/T 9846-2015). The SPFs/SM/PTGE adhesive bonded plywood reached its highest wet shear strength of 1.12 MPa (1.5 wt.% SPFs addition), which was a 70% increase compared to the unmodified SM/PTGE-bonded plywood sample. The morphology, the infrared spectra, the crystallinity observations, and the thermal behaviors of the SPFs/SM/PTGE adhesives showed fine SPFs-to-SM interfacial bonding and a dense crosslink network in the SPFs/SM/PTGE adhesive systems. In this study, the “self-reinforced” concept of biodegradable plant protein-based composites was evaluated and showed a great potential to apply into the plywood adhesive systems.

Development of bark-based adhesives for plywood: utilization of flavonoid compounds from bark and wood. II

Although many conventional adhesives for plywood are formulated with tannins (polyflavanoid compounds) extracted from bark or wood, adhesives using tannin directly without extraction from the bark have also been made. In 2003, the first bark particle (< 63 μm) adhesive was developed from radiata pine bark. In this present study, the quality of the bark adhesive has been improved by fibrillating the bark. Finely ground bark was fibrillated using a disc mill and formulated into plywood adhesives, which consisted of fibrillated bark, phenol–formaldehyde (PF) resin and water in different ratios. The gluability of the fibrillated bark adhesives was evaluated according to the Japanese Agricultural Standard for Plywood (JAS) and was found to be excellent. These bark adhesives have a number of advantages in that there is no tannin extraction, there is a total use of the bark, a low-level requirement of PF resins, no other components required and there is a high glue bond quality. Considering that very small amounts of fibrillated bark adhesives produced high-quality wood bonding, the bark components such as tannin, hemicellulose, lignin, cellulose nanofibers and other components may well be contributing to produce such a good bonding.

Effects of typical soybean meal type on the properties of soybean-based adhesive

In order to effectively apply soybean meal for the preparation of water-resistant soybean-based adhesives for plywood, the effects of three typical soybean meal products, namely, low-temperature soybean meal (LM), high-temperature soybean meal (HM), and physical soybean meal (PM), on the properties of soybean-based adhesive were investigated. The results indicated that the number of reactive groups in the three soybean meals followed the order LM > HM > PM, which in turn led to various crosslinking densities when these soybean meals were crosslinked by epichlorohydrin-modified polyamide (EMPA) during the curing process. The LM soybean adhesive had 6.6% higher soaking bond strength and 16.5% higher boiling-dry-boiling bond strength than the HM soybean adhesive, and 19% higher soaking bond strength and 33% higher boiling-dry-boiling bond strength than the PM soybean adhesive, respectively. These three soybean meals could be used to prepare soybean adhesives for interior-use plywood because all plywood panels bonded with their adhesives passed a water-soaking test at 63 °C for 3 h, but only the LM soybean adhesive achieved the desired water resistance for floor-base plywood. Among the three evaluated soybean meals, LM was the most promising raw material for the preparation of soybean-based adhesive because of a greater number of reactive groups, higher crosslinking density, and superior bond strength. Plywood panel bonded with HM soybean adhesive had a water resistance lower than, but very close to, the standard required value (>0.8 MPa) for floor-base plywood.

Activation of Cellulosic Ethanol Lignin by Laccase and its Application as Plywood Adhesive

To reuse biorefinery waste, cellulose ethanol lignin was treated with a laccase system and used as an adhesive for plywood panel preparation. The effects of the amount of laccase, the pH of the reaction system, the reaction temperature, and the reaction time on the bonding strength were studied. The reaction characteristics of the lignin were analyzed by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR). The results showed that the amount of laccase and the pH value of the reaction system had a significant effect on the bonding strength, and the addition of Tween-80 and polymeric diphenylmethane diisocyanate (PMDI) could improve the wet strength of the cemented system. FT-IR indicated that the lignin had been etherified and NMR analysis showed the partial ether bond in the β-O-4 structure was cleaved so that the lignin fragment was involved in the gluing of the small molecules. Microscopically speaking, the SEM analysis did not observe the activation of lignin adhesives infiltrating the wood substrate, indicating a weak mechanical gluing.

Effect of Extraction Solvent on Tannin-Formaldehyde Adhesives for Plywood Production

Pine bark is a good source of natural polyphenolic compounds for wood adhesives. The objective of this study was to obtainthe most suitable solvent for extracting pine tannins in the preparation of tannin-formaldehyde plywood adhesives. Aqueousacetone, aqueous ethanol, aqueous NaOH and water as solvents were used to obtain crude tannins from pine bark. Thetannin content, sugar content and Stiasny number of the extracts were determined. Using the extracts from the solventextractions, synthesis of tannin-formaldehyde resin was carried out. Plywood panels were made using the synthesized resinsand the quality of the resins in plywood application determined. The quality of tannin-formaldehyde resins produced from thetannins were generally in close agreement with the chemical characteristics of the extracts obtained from the various solventextractions. The aqueous NaOH extraction although gave very high tannin yield (16.1%), its associated high sugar content(33.8%) and very low Stiasny number (49) resulted in poor quality resin. Similarly, although aqueous extraction gave a veryhigh Stiasny number (91), its low tannin yield (8.7%) might not be of commercial interest. The extraction process that gave ahigh tannin yield (12.9%) and a very good Stiasny number (81.5) with a corresponding good quality resin (shear strength =1.9 MPa, 22% delamination) was found for 60% aqueous ethanol extraction.

Optimum Process Parameters for Plywood Manufacturing using Soya Meal Adhesive

In view of the environmental concern and the adverse health effects with the use of formaldehyde-based plywood adhesives, there is a renewed interest to develop bio-based adhesives alternate to the petroleum-based adhesives. Current efforts are towards the development of adhesives by using soya meal powder as a major composition. This adhesive is applied on the eucalyptus veneers which are hot pressed within the specified range of temperature and pressure for manufacturing plywood. The manufactured plywood samples are tested for the flexural strength using three-point bend test. The Taguchi approach is adopted and ANOVA analysis is performed for identifying the optimum plywood manufacturing parameters (viz. temperature and pressure) to achieve the optimum Modulus of Rupture (MOR). The flexural strength estimates using the additive law and the developed empirical relation are matching well with test results.

Plywood adhesives derived from distillers' dried grains with solubles (DDGS) incorporating 2‐hydroxyethyl acrylate

ABSTRACTDistillers' dried grains with solubles (DDGS), a byproduct of corn ethanol production, are currently used primarily as an alternative animal feed thanks to its high protein content and low cost. Previous research has developed a protein‐based bioadhesive from DDGS. However, the adhesive does not possess the appropriate properties to compete with synthetic adhesives and other bio‐based adhesives. In this study, a bioadhesive is prepared from DDGS and hydroxyethyl acrylate (HEA) is incorporated to improve the bonding strength and moisture resistance. The greatest increase in lap‐shear strength was observed in the adhesive containing 50% of the acrylic resin. Water resistance was absent from the original DDGS adhesive, but established upon the inclusion of HEA. HEA was found to self‐polymerize under the hot‐pressing conditions and form a co‐continuous phase with the protein adhesive derived from DDGS. The strength of the adhesives was adequate for bonding plywood panels. More work must be done to further enhance the performance of the adhesives for wider applications. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45689.

Physico-mechanical properties of plywood bonded with ecological adhesives from Acacia mollissima tannins and lignosulfonates

The objective of this research was to develop ecological adhesives for bonding plywood panels using lignosulfonates, a common waste product of the wood pulp industry, and natural tannin extracted from Moroccan bark of Acacia mollissima using different process. Natural tannin and lignin were used in wood adhesives formulation to substitute resins based on phenol and formaldehyde. To achieve this, the lignosulfonates were glyoxalated to enhance their reactivity and the used tannins obtained by three different extraction methods were compared with commercial mimosa tannin. The proportion of Acacia mollissima tannins and lignosulfonates, the pressing time, the pressing temperature, and the pressure used were studied to improve mechanical properties, and bonding quality of plywood panel. The properties of plywood panels produced with these adhesives were tested in accordance with normative tests. Thus, the tensile strength, and the shear strength were measured. The results showed that the performance of the plywood panels made using biobased tannin adhesives was influenced by physical conditions such as pressure, press temperature as well as by chemical conditions, such as the tannin-lignin ratio. It exhibited excellent mechanical properties comparable to commercially available phenol-formaldehyde plywood adhesives. This study showed that biobased adhesives formulations presented good and higher mechanical performance and no formaldehyde emission.