Phenol-formaldehyde Adhesives Research Articles

Mechanical and Fire Properties of Flame-Retardant Laminated Bamboo Lumber Glued with Phenol Formaldehyde and Melamine Urea Formaldehyde Adhesives.

This study investigated the effects of different adhesives, phenol formaldehyde (PF) and melamine urea formaldehyde (MUF), on the mechanical and fire properties of flame-retardant laminated bamboo lumber (LBL). The results demonstrated that the flame-retardant treatment using phosphorus-nitrogen-boron compounds endowed the LBL with excellent flame retardancy and smoke suppression properties, even though the bending strength and bond shear strength were slightly reduced. The PF-glued LBL exhibited superior mechanical and shear properties to the MUF-glued ones, primarily due to its higher processing temperature and deeper adhesive penetration. In addition, the MUF-glued flame-retardant LBL displayed better heat release reduction and smoke suppression properties than the PF-glued LBL, which resulted from the synergistic flame retardancy between the melamine element in MUF and the applied flame retardant. The analysis of the influence of adhesive type on the mechanical and fire properties of flame-retardant LBL holds significant importance for the future design and production of high-performance LBL material.

Effect of Lignin Structure Characteristics on the Performance of Lignin Based Phenol Formaldehyde Adhesives.

As the second most abundant biopolymer, lignin remains underutilized in various industrial applications. Various forms of lignin generated from different methods affect its physical and chemical properties to a certain extent. To promote the broader commercial utilization of currently available industrial lignins, lignin sulfonate (SL), kraft lignin (KL), and organosolv lignin (OL) are utilized to partially replace phenol in the synthesis of phenol formaldehyde (PF) adhesives. The impact of lignin production process on the effectiveness of lignin-based phenolic (LPF) adhesives is examined based on the structural analysis of the selected industrial lignin. The results show that OL has more phenolic hydroxyl groups, lower molecular weight, and greater number of reactive sites than the other two types of lignins. The maximum replacement rate of phenol by OL reaches 70% w/w, resulting in organosolv lignin phenolic (OLPF) adhesives with a viscosity of 960 mPa·s, a minimal free formaldehyde content of 0.157%, and a shear strength of 1.84MPa. It exhibits better performance compared with the other two types of lignin-based adhesives and meets the requirements of national standards.

Nanocellulose-Phenol Formaldehyde Adhesive System for Engineered Wood Products: Review

Abstract Incorporating cellulose nanomaterials into wood adhesives has recently been considered for improving sustainability within wood composite panels. The role of nanocellulose in such an application is mainly determined by nanocellulose dimension, form, morphological and physicochemical properties, characteristics of an adhesive system, and chemical interaction of nanocellulose and adhesive, as well as the dispersion and the orientation of nanomaterials in the polymeric matrix of adhesive. Phenol formaldehyde (PF) adhesives have been extensively used in engineered wood products for decades, and concerns about their brittleness led to continued research efforts for modifying the resin. Recently, the developments in the bio-economy and the nanocellulose industry provided new possibilities for PF adhesive modification and its structural reinforcement with a renewable, biodegradable, abundant, and mechanically strengthened resource. This paper aims to review and demonstrate the available research on the development of nanocellulose-reinforced PF as an adhesive matrix for engineered wood products, in particular, plywood, particleboard, and oriented strand board.

Micro-Fibrillated Cellulose in Lignin–Phenol–Formaldehyde Adhesives for Plywood Production

Petrochemical-based phenol–formaldehyde (PF) adhesives are widely used in plywood production. To substitute phenol in the synthesis of PF adhesives, lignin can be added due to its structural similarity to phenol. Moreover, micro-fibrillated cellulose (MFC) can further enhance the bond performance, mechanical properties, and toughness of adhesive systems. Thus, the aim of this study was to evaluate the adhesion performance of lignin–PF (LPF) adhesives reinforced with MFC. In LPF formulations, three levels of MFC (0, 15, and 30 wt% based on the total solid content of adhesives) were added to the homogenous adhesive mixture. Three-layer plywood panels from birch (Betula pendula Roth.) veneers were assembled after hot pressing at 130 °C under two pressing durations, e.g., 60 and 75 s/mm. Tensile shear strength was measured at dry (20 °C and 65% RH) and wet conditions (water soaked at room temperature for 24 h). The results indicated that the addition of lignin reduced the strength of LPF adhesives in both dry and wet conditions compared to the control PF adhesive. However, MFC reinforcement enhanced the shear strength properties of the plywood. Furthermore, a longer pressing time of 75 s/mm slightly increased the shear strength.

Effect of Dilute Acid Pretreatment and Lignin Extraction Conditions on Lignin Properties and Suitability as a Phenol Replacement in Phenol-Formaldehyde Wood Adhesives.

Corn stover was subjected to dilute sulfuric acid pretreatment to assess the impact of pretreatment conditions on lignin extractability, properties, and utility as a phenol replacement in wood phenol-formaldehyde (PF) adhesives. It was identified that both formic acid and NaOH could extract and recover 60-70% of the lignin remaining after pretreatment and enzymatic hydrolysis under the mildest pretreatment conditions while simultaneously achieving reasonable enzymatic hydrolysis yields (>60%). The availability of reaction sites for the incorporation of lignins into the PF polymer matrix (i.e., unsubstituted phenolic hydroxyl groups) was shown to be strongly impacted by the pretreatment time and the recovery. Finally, a lignin-based wood adhesive was formulated by replacing 100% of the phenol with formic-acid-extracted lignin, which exhibited a dry shear strength exceeding a conventional PF adhesive. These findings suggest that both pretreatment and lignin extraction conditions can be tailored to yield lignins with properties targeted for this co-product application.

COMPARATIVE STUDY ON PHYSICAL-MECHANICAL PROPERTIES OF PLYWOOD PRODUCED FROM EUCALYPTUS GRANDIS AND POPULUS DELTOIDS VENEERS. SHORT NOTES

Nine-ply plywood panels were produced from Eucalyptus grandisand Populus deltoidsusing urea-formaldehyde (UF) and phenol-formaldehyde (PF) adhesives. The physical and mechanical properties,such as moisture content, density, modulus of rupture (MOR) and modulus of elasticity (MOE) of the eucalyptus and poplar boards, were compared in this study. Samples were tested on both,along and across the grain. Higher values of MOR and MOEwere observed foreucalyptus as compare to poplar. Density of ply board was observed as 500-560kg.m-3in plywood from poplar and 700-720 kg.m-3in plywood from eucalyptus species. These differences were attributed to the variation in properties of veneer wood species. The effect of veneer wood species on some physical and mechanical properties of plywood was found statistically different.

Теоретическое и экспериментальное обоснование характера взаимодействия модифицированных связующих с древесиной

There are numerous methods for analyzing surface phenomena when bonding wood materials, mutual arrangement of pores in the wood substrate, and depth of liquid adhesive penetration into wood. Electron microscopic methods such as atomic force and scanning tunneling microscopy are used along with optical methods. They allow evaluating the influence of factors describing the interaction between the liquid adhesive molecules and the porous wood surface. Phenol formaldehyde resin modified with pectol and urea formaldehyde resin modified with lignosulfonates were used for substantiation of the interaction mechanism between modified adhesives and wood. Electron microscopy was used to study the depth of adhesive penetration into veneer. The plywood was produced using modified urea and phenol formaldehyde adhesives. After conditioning, samples with a thickness of 0.025 mm were cut out and examined with a scanning electron microscope. The article shows that the interaction between liquid phenol formaldehyde adhesive modified with pectol and wood results in a sequential increase in the molecular weight of the substances and, consequently, in the penetration degree (depth). The studied wood species (birch, pine and larch) and modified thermosetting urea and phenol formaldehyde adhesives are polar materials (adhesive interacts with wood molecules with the formation of intermolecular bonds, including hydrogen bonds). The molecular weight growth and the freely joined nature of the main chain (liquid modified adhesive macromolecules), which contains a large number of polar functional groups (adhesive and wood), promote intermolecular association. The formation of an adhesive bond between urea formaldehyde adhesive modified with lignosulfonates and wood occurs due to chemical interaction between hydroxyl groups of cellulose macromolecules and methoxyl groups of urea resin with the formation of esters (hydrogen atoms of hydroxyl groups OH are substituted with hydrocarbon radicals R). The formation of a bond between the adhesive and the wood surface is the result of molecular interaction forces at the liquid adhesive – wood interface, when the distance between molecules of the same polarity (adhesive and wood) is less than 0.5 nm. Then, adsorption equilibrium sets in. For citation: Rusakov D.S., Varankina G.S., Chubinsky A.N. Theoretical and Experimental Substantiation of the Nature of Interaction between Modified Binders and Wood. Lesnoy Zhurnal = Russian Forestry Journal, 2022, no. 6, pp. 153–163. (In Russ.). https://doi.org/10.37482/0536-1036-2022-6-153-163

Effect of plasma treatment on the surface characteristics and adhesive penetration performance of heat-treated wood

Abstract The present study used an atmospheric dielectric barrier discharge (DBD) plasma treatment to modify the interfacial properties of heat-treated wood (HTW). The changes in the wood surface characteristics, such as the microstructure, chemical structure, and wettability, were investigated using scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), Fourier-transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). Further, the fluorescent tracer technique was used to analyze the effect of plasma treatment on the adhesive penetration inwood. Results showed that the wettability of water and phenol-formaldehyde adhesives on the surface of HTW significantly improved after plasma treatment due to the increase in the hydrophilic and oxygen-containing functional groups. The average penetration (AP) and effective penetration (EP) of the phenolic adhesive into HTW also increased significantly after plasma treatment; the AP value of the E-E (earlywood bound to earlywood) HTW samples increased from 909 to 1674 μm, and the EP value from 60 to 183 μm upon plasma treatment. These observations indicate that the DBD plasma treatment is a promising method to improve the bonding properties of the glued HTW products.

The properties of particleboard composites made from three sorghum (Sorghum bicolor) accessions using maleic acid adhesive

It is very important to develop green composite materials owing to increasing global environmental issues. One of the alternative raw materials for the production of green composites is biomass. Bagasse sorghum is a promising alternative raw material for the manufacturing of particleboard composites. The influence of sorghum accessions on the performance of particleboard composites was analyzed in this study. In addition, the particleboard quality was made using maleic acid (MA) adhesive and compared with citric acid (CA) and phenol-formaldehyde (PF) adhesives. Three accessions of sorghum, 4183A, super 1, and Pahat, were used as raw materials in particleboard manufacturing. The 20 wt% MA adhesive was applied in particleboard manufacturing. The board dimensions and density targets were 30 × 30 × 0.9 cm3 and 0.8 g/cm3, respectively. The particle mat was pressed 200 °C for 10 min with a maximum of 6.5 MPa. For reference, the JIS A 5908–2003 was used to evaluate physical and mechanical properties, SNI 7207–2014 was used for the resistance against termites, and JIS K 1571–2004 for evaluated the particleboard against decay. The results showed that the sorghum accession in this research did not affect the quality of the particleboard. The thickness swelling (TS), internal bond (IB), modulus of elasticity (MOE), and modulus of rupture (MOR) of particleboard satisfied JIS A 5908–2003 type 8. The particleboard using MA was comparable with those bonded with CA and had better durability against termites and decay than PF adhesives. The ester linkages were formed due to the reaction between MA (carboxyl groups) and the sorghum bagasse (hydroxyl groups) after being analyzed using Fourier transform infrared (FTIR). Therefore, particleboard in this study has good quality.

A Comparison among Lignin Modification Methods on the Properties of Lignin-Phenol-Formaldehyde Resin as Wood Adhesive.

The research aim of this work is to determine the influence of lignin modification methods on lignin–phenol–formaldehyde (LPF) adhesive properties. Thus, glyoxal (G), phenol (P), ionic liquid (IL), and maleic anhydride (MA) were used to modify lignin. The modified lignins were used for phenol substitution (50 wt%) in phenol–formaldehyde adhesives. The prepared resins were then used for the preparation of wood particleboard. These LPF resins were characterized physicochemically, namely by using standard methods to determine gel time, solids content, density, and viscosity, thus the physicochemical properties of the LPF resins synthesized. The panels dimensional stability, formaldehyde emission, bending modulus, bending strength, and internal bond (IB) strength were also measured. MA-modified lignin showed by differential scanning calorimetry (DSC) the lowest temperature of curing than the resins with non-modified lignin and modified with IL, phenolared lignin, and glyoxal. LPF resins with lignin treated with maleic anhydride presented a shorter gel time, higher viscosity, and solids content than the resins with other lignin modifications. Equally, the particleboard panels prepared with LPF resins with maleic anhydride or with ionic liquid had the lowest formaldehyde emission and the highest mechanical strength among all the synthesized resins. The dimensional stability of all panels bonded with modified lignin LPF resins presented no difference of any significance.

Investigating the characteristics of cactus seeds by-product and their use as a new filler in phenol formaldehyde wood adhesive

The current study investigates the properties of cactus waste seeds (CWS) unexplored by-product as partial replacement of phenol formaldehyde (PF) adhesives in comparison to previously used olive stones (OS) for the production of wood composites. The chemical composition, structure, and thermal properties of CWS were studied for the first time to evaluate their suitability for incorporation into PF resins. The bonding strength, wood failure, and rheological properties of the formulated adhesives were investigated as well as the mechanical properties of the plywoods panels. The results showed that CWS could be considered as a new lignocellulosic resource, showing a higher amount of cellulose content (27%) compared to OS (15%). The crystallinity and thermal stability were higher in CWS, which was expected to improve the performance of the formulated adhesives positively. Moreover, the resins containing 10% and 15% of CWS and OS, respectively, showed comparable bonding strength and wood failure to that of a control PF resin. While plywood bonded with 10% of CWS:PF resin showed better mechanical performance in dry, cold, and 8h boiling water conditions than other adhesives, formaldehyde emission levels of bonded panels with both formulations were lower than those of a control PF. • Cactus waste seeds (CWS) were used to partially substitute PF-resins. • The chemical compositions of CWS are rich in lignin (37%) and cellulose (27%). • Crystallinity and thermal stability of CWS were higher compared to olive stones (OS). • PF-resin filled with CWS and OS showed good mechanical and rheological properties. • The optimal adhesives were practical for plywood application.

Preparation of a starch-based adhesive cross-linked with furfural, furfuryl alcohol and epoxy resin

Furfural and furfuryl alcohol originating from agriculture were used as crosslinkers to develop a renewable starch-furanic adhesive with good water resistance. Electrospray ionization mass spectroscopy and 13 C nuclear magnetic resonance measurements indicated that furfural and furfuryl alcohol reacted with starch under acidic conditions and that the –CH 2 –O– groups were involved in the cross-linking of the starch-furfural-furfuryl alcohol adhesive (SFF). The gel time of SFF was longer than that of the starch-furfural adhesive (SF), while the dry shear strength of the SFF-bonded plywood suggested that the cured SFF adhesive acquired a performance better than that of starch (S) and SF adhesives. Moreover, the water resistance of the SFF adhesive cross-linked with 9% epoxy resin was further enhanced with respect to that of the S, SF, and commercial phenol formaldehyde adhesives.

Effect of Tannin Addition in Phenol-Formaldehyde Adhesive on Reducing the Curing Temperature

Effect of Tannin Addition in Phenol-Formaldehyde Adhesive on Reducing the Curing Temperature

Synthetic Process of Bio-Based Phenol Formaldehyde Adhesive Derived from Demethylated Wheat Straw Alkali Lignin and Its Curing Behavior

Lignin is a natural biopolymer with a complex three-dimensional network, commercially obtained from waste liquid of paper pulp and bioethanol production, and could be a candidate for preparation of environment-friendly bio-based polyphenol material. In the present work, the demethylated wheat straw alkali lignin (D-Lig), prepared by demethylation of wheat straw alkali lignin (Lig) using an <i>in-situ</i> generated Lewis acid, was used to synthesize bio-based phenol formaldehyde resin adhesive (D-LPF) applied in plywood. Effects of synthetic process’s factors, including lignin substitution for phenol, NaOH concentration and molar ratio of formaldehyde to phenol, on the bonding strength and free formaldehyde content of D-LPF were investigated in detail, and the optimum synthetic process of D-LPF was obtained as following: Lignin substitution for phenol 60%, NaOH concentration 5.0% and molar ratio of formaldehyde to phenol 2.0, and under the optimum reaction condition, the D-LPF presented lower free formaldehyde content (0.18%) and higher bonding strength (2.19 MPa), which was better than those of containing-lignin phenol formaldehyde resin adhesive(LPF). Additionally, the curing behavior of the adhesive was studied by differential scanning calorimetry (DSC) combined with gel time. It can be obtained that D-LPF resin adhesive had the shortest gel time, and fastest curing rate, compared with those of PF and L-PF resin adhesives. The curing kinetics data was fitted well by Kissinger model using non-isothermal DSC method, and the average activation energy value was 85.3 kJ/mol, slightly higher than that of commercial PF resin, while lower than that of LPF (90.2 kJ/mol). Finally, based on the analytical results of high temperature fourier transform infrared spectroscopy (FTIR), a possible curing mechanism of D-LPF was proposed.

The potential of using agricultural waste: Corn husk for particleboard raw material

The development of manufactured particleboard using non-wood raw materials has been significant due to the decrease of wood as the main raw material for the particleboard industry. In this study, corn husk, an agricultural waste, was used for experimental manufacturing of particleboard bonded with natural and synthetic adhesives. The influence of adhesive types and concentration on the physical and mechanical properties of particleboard were investigated. The synthetic adhesive types used were urea-formaldehyde (UF) and phenol-formaldehyde (PF) with 8,10 and 12 wt% adhesive concentration. The natural adhesive used was citric acid with 15, 20, and 25 wt% adhesive concentration. The target density of particleboard was set at 0.80 g/cm3. The boards were manufactured at a pressing temperature of 130°C for UF, 150°C for PF and 200°C for citric acid, pressing time of 10 minutes, and 2.5 MPa for hot-pressing pressure. Generally, this study confirms that types of adhesive and adhesive concentrations influence the properties of particleboard. Results show that particleboard with citric acid adhesive has better physical and mechanical properties than particleboard bonded with UF and PF adhesives.

Improving the Reactivity of Sugarcane Bagasse Kraft Lignin by a Combination of Fractionation and Phenolation for Phenol-Formaldehyde Adhesive Applications.

The low reactivity of lignin hinders its application as a phenol substitute in phenol–formaldehyde (PF) resin. Therefore, the combination of fractionation and phenolation was adopted to enhance the reactivity of lignin for preparing a phenol–formaldehyde resin adhesive. Sugarcane bagasse kraft lignin and its fractions were employed to replace 40 wt% of phenol to prepare a PF adhesive. The fractionation increased the reactivity of lignin, however the as-prepared lignin-based PF (LPF) hardly met its application requirements as an adhesive. Therefore, the phenolation of lignin under an acidic condition was adopted to further improve its reactivity. The phenolated lignin was characterized by FTIR, gel permeation chromatography, and NMR, indicating its active sites increased while its molecular weight decreased. The phenolated lignin was used to replace 40 wt% of phenol to prepare a PF adhesive (PLPF) which was further employed to prepare plywood. The results indicated that the combination of fractionation and phenolation effectively enhanced the reactivity of lignin, and eventually improved the properties of the PLPF and its corresponding plywood. The free formaldehyde content of PLPF decreased to 0.16%. The wet bonding strength of the as-prepared plywood increased to 1.36 MPa, while the emission of formaldehyde decreased to 0.31 mL/L.

Juvenile Wood from Pinus patula Schltdl &amp; Cham for Multilaminated Panel Production

ABSTRACT Wood scarcity, attacks by primates and insects, and fungal damage in forest plantations make the introduction of new species necessary. Given this, it is important to understand the potential uses of wood in the production chain. Pinus patula Schltdl & Cham presents good adaptation to Brazilian conditions and is a candidate for wood supply. Its juvenile wood density however, is lower than that of other pine species. This study aimed to evaluate the properties of veneer on panels produced with twelve-year old P. patula wood compared with panels produced with P. taeda wood of the same age, which is commonly used for panel production. Panels were bonded with urea-formaldehyde and phenol-formaldehyde adhesives using veneers applied on two types of plywood panel. The P. patula panels showed lower strength, stiffness and density when bonded with urea-formaldehyde, and higher strength, density and stiffness when bonded with phenol-formaldehyde in comparison with P. taeda. P. patula panels can be used for multilayer panel production.

The Effects of Some Synthetic Adhesives on the Formaldehyde Emission of the Particleboard

The formaldehyde emission is the one of the major problems of the particleboard industry that harms to human health and environment. The purpose of this study was to determine the effect of the adhesive type on the formaldehyde emission of three-layered particleboard. The urea formaldehyde (UF), phenol formaldehyde (PF) and melamine-urea formaldehyde (MUF) adhesives were used as adhesives. Black poplar (Populus nigra) was used as wood raw material. The panels produced with PF and MUF adhesives had the required level of formaldehyde emission value specified in EN 312-2 (1996) and these panels could be classified as E-1 grade particleboard. The particleboard samples produced with UF adhesive had more than the formaldehyde emission value required for E-1 class particleboards.

Physical and mechanical properties of urea formaldehyde and phenol formaldehyde-bonded particleboards made from corn stalk

Biomass from annual fibers and agricultural wastes as a raw material to produce particleboard or other composite panels has gained increased popularity. The purpose of this study was to investigate the suitability of corn stalk as a material for particleboard manufacturing. The effect of adhesive type and concentration on the physical and mechanical properties of particleboard manufactured from corn stalk was evaluated. Particleboards were produced using hot-pressing machine at temperature of 130 °C for urea formaldehyde (UF) and 150 °C for phenol formaldehyde (PF) adhesives until 10 min. The size of particleboards and target density were 25 mm x 25 mm x 0.9 mm and 0.8 g/cm3, respectively. The adhesive content was varied from 8, 10 and 12 wt%. The results showed that the physical and mechanical properties of particleboards had better values with increasing the adhesive concentration. The board bonded with PF adhesive showed better physical and mechanical properties than the board bonded with UF adhesive. The modulus of rupture, modulus of elasticity and internal bond of the board bonded with 12 wt% of PF fulfilled the requirement of the JIS A 5908 (2003) for type 13 particleboard.

Evaluation of synthetic bio-phenol resins derived from biomass gasification in bio-adhesive formulation

Bio-phenol formaldehyde adhesives formulated from sustainable biomass sources is an excellent alternative to phenolic petroleum-based adhesives with lower pollution level. This study aimed to formulate bio-adhesive from two types of biomass namely palm kernel shell (PKS) and Leucaena sp. Wood. The intention was to find the best process condition which results in maximum content of bio-phenol in the product. The bio-based phenolic resins (bio-oils) were produced from gasification process and their physical and chemical properties were determined. Both produced bio-oils were involved in formulation of bio-based phenol formaldehyde adhesives (resinification) at different operating conditions (temperature, time and catalyst loading). The chemical functional groups and individual compounds of the phenol resins and bio-adhesive samples were identified by GC-MS. The results indicated that temperature has persistent increasing effect on phenol percent of the bio-oil from Leucaena sp. wood however for the bio-oil from PKS the increase of phenol was until the temperature of 85 °C. Reaction time and catalyst loading were observed to have similar effects on resinification of both bio-oil samples. The bio-adhesive produced under best operating condition has the highest amount of bio-phenol and therefore is considered an environmental friendly adhesive with lower cost and pollution than the petroleum-based types.