Phenol Resorcinol Formaldehyde Resin Research Articles

Controlling the stability and adhesion performance of cold-setting phenol–resorcinol–formaldehyde resin adhesives through methanol addition

Phenol–resorcinol–formaldehyde (PRF) resin adhesives are commonly used in the manufacture of laminated timber products, and they are cold-set at room temperature rather than hot-pressed to generate a three-dimensional polymer structure in the products. However, their excellent reactivity often leads to poor storage stability and a short pot life. This study examines the influence of methanol addition on the stability and adhesion performance of PRF resins. These resins were synthesized by various levels of methanol addition (5 %, 10 %, and 15 %), and their structures were investigated using Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies. Furthermore, differential scanning calorimetry (DSC) was used to analyze their thermal behavior, and their cure kinetics were analyzed with two isoconversional analyses: Kissinger–Akahira–Sunose (KAS) and Vyazovkin (VYZ) method. The adhesion performances of PRF resins were evaluated for glue-laminated timber (GLT). The results demonstrated that the viscosity and solids content of PRF resins decreased while their gelation time increased as the methanol addition level increased. Methanol addition has also improved the resin stability over time. The chemical structure of PRF resins did not change considerably with an increase in the methanol level. However, methanol interaction with formalin in a hardener presumably hindered the reactivity of PRF resins. This was supported with an increase in the apparent activation energy of the curing process of PRF resins as the methanol level increased. In addition, decreasing the methanol levels from 15 % to 5 % enhanced the adhesion performance of GLT bonded with PRF resins. The results indicated that adding methanol to PRF resins improved its stability while simultaneously weakened its performance. However, 5 % methanol level is recommended for PRF resins.

Flexural Modulus of Larch Boards Laminated by Adhesives with Reinforcing Material

Economical use of larix (larch) boards (grade 3) in industries is lower than that of imported hardwood; thus, studies have been conducted toward performance improvement of larix boards. Herein, flexural modulus of larix board samples laminated with wood adhesives polyurethane resins, poly (vinyl acetate) resins, phenol–resorcinol–formaldehyde resins, melamine–formaldehyde resins, and urea–formaldehyde resins was compared with that of the samples bonded with adhesives reinforced with mesh-type basalt fibers. Moreover, the flexural moduli of the laminated samples bonded by mesh-type basalt fibers were compared with those of reinforced samples. The results showed that boards laminated with polyurethane and urea-formaldehyde resin adhesives had higher flexural modulus than those without the lamination. In particular, the increase in the flexural modulus was relatively significant for the 2- and 3-ply board structures laminated with polyurethane adhesives compared to those with reinforcement. The 3-ply board structure without reinforcement had the highest flexural modulus when the urea–formaldehyde resin adhesive was used.

Solar-Driven Generation of Hydrogen Peroxide on Phenol-Resorcinol-Formaldehyde Resin Photocatalysts.

Photocatalytic generation of H2O2 from water and O2 under sunlight is a promising artificial photosynthesis reaction to generate renewable fuel. We previously found that resorcinol-formaldehyde resin powders prepared with a high-temperature hydrothermal method become semiconductors comprising π-conjugated/π-stacked benzenoid-quinoid donor-acceptor resorcinol units and are active for photocatalytic H2O2 generation. Here, we have prepared phenol-resorcinol-formaldehyde resins with small amounts of phenol (∼5 mol % relative to resorcinol), which show enhanced photocatalytic activity. Incorporating phenol bearing a single -OH group in the resin matrices relaxes the restriction on the arrangement of the aromatic rings originating from the H-bonding interactions between the resorcinol -OH groups. This creates stronger donor-acceptor π-stacking and increases the electron conductivity of the resins. We have demonstrated that simulated sunlight illumination of the resins in water under an atmospheric pressure of O2 stably generated H2O2 with more than 0.9% solar-to-chemical conversion efficiency.

Effect of ACQ treatment on surface quality and bonding performance of four Malaysian hardwoods and cross laminated timber (CLT)

The objective of this study is to determine the effects of alkaline copper quaternary (ACQ) treatment on the surface quality and bonding performance of four Malaysian hardwood species, namely batai, sesenduk, rubberwood and kedondong. The samples were impregnated with 2% ACQ preservatives and bonded with phenol-resorcinol–formaldehyde resin for cross laminated timber (CLT) fabrication. The changes in density and the retention of both ACQ and copper after the treatment were recorded. Surface roughness and wettability of both treated and untreated samples were measured. Block shear and delamination tests were performed to evaluate the bond-line strength of CLT. The study revealed that the average surface roughness (Ra) of each species increased significantly. Wettability of batai, sesenduk, rubberwood and kedondong was significantly higher than that of the untreated samples suggesting an improvement in surface wettability. For single-species CLT, treated rubberwood has the highest shear strength followed by kedondong, sesenduk and batai with values of 9.53 N/mm2, 6.00 N/mm2, 5.68 N/mm2 and 4.19 N/mm2, respectively. While for mixed-species CLT, the combination of ACQ-treated rubberwood-sesenduk-rubberwood has the highest block shear strength with a value of 8.05 N/mm2. No delamination was observed from all samples. ACQ treatment was found to not affect the block shear strength significantly. Therefore, ACQ preservatives can be used to produce CLT with good bonding performance.

Properties of Glued Laminated Timber Made from Fast-growing Species with Mangium Tannin and Phenol Resorcinol Formaldehyde Adhesives

This study characterized the chemical compounds in tannin from mangium (Acacia mangium) bark extract and determined the physical–mechanical properties of glued laminated timber (glulam) made from sengon (Falcataria moluccana), jabon (Anthocephalus cadamba), and mangium wood. The adhesives used to prepare the glulam were based on mangium tannin and phenol resorcinol formaldehyde resin. Five-layer glulam beams measuring 5 cm × 6 cm × 120 cm in thickness, width, and length, respectively, were made with a glue spread of 280 g/m2 for each glue line, cold pressing at 10.5 kgf/cm2 for 4 h and clamping for 20 h. Condensed mangium tannin consisted of 49.08% phenolic compounds with an average molecular weight of 4745. The degree of crystallinity was 14.8%. The Stiasny number was 47.22%. The density and the moisture content of the glulams differed from those of the corresponding solid woods with mangium having the lowest moisture content (9.58%) and the highest density (0.66 g/cm3). The modulus of rupture for all glulam beams met the JAS 234-2003 standard but the modulus of elasticity and the shear strength values did not. Glulam beams made with tannin had high delamination under dry and wet conditions, but glulam made from sengon and jabon wood met the standard’s requirements. All glulam beams had low formaldehyde emissions and were classified as F**** for formaldehyde emissions according to the JAS 234 (2003) standard.

Characterizing Star-sawn Pattern–Produced and Orthogonally Glued Specimens of Southern Pine

Abstract In this study, triangular specimens of southern pine (Pinus spp.; SP) generated by a star-sawn process were characterized according to knots and deformation. SP specimens were used to understand the differences among glue-line combinations of radial-to-radial, radial-to-tangential, and tangential-to-tangential faces bonded with phenol resorcinol formaldehyde resin. The specimens were tested for shear strength, dimensional stability, wood failure, and delamination rate in accordance with ASTM D1037 and D2559 standards. Among the star-sawn triangular samples studied, bows in tangential-face sections occurred the most. The radial-face sections of SP triangular specimens had more knots but a much lesser degree of deformation than the tangential-face sections. The tangential-to-tangential face glue-line samples showed a lower shear strength, more wood failure, and a greater tendency of delamination and dimensional change, especially when subjected to wet conditions. Confocal microscopic pictures revealed that the tangential-to-tangential glue line showed a greater tendency of deformation in the earlywood part and helped to explain the reason for poor glue-line durability and low shear strength. This article revealed that the star-sawn–process generated wood radial-face samples were more stable than others tested and are perhaps a good alternative for massive panel manufacturing.

Curing behavior and bonding strength of two-component fast-setting adhesives prepared with phenol-liquefied Cryptomeria japonica wood

Honeymoon adhesive is a special adhesive system that contains two components which are applied onto two substrates separately for glulam manufacturing to provide a fast-setting capability. It has been confirmed that phenol-liquefied wood can be used as a raw material for preparing phenolic resins. In this study, liquefied wood (LW) was obtained by liquefying Cryptomeria japonica wood in phenol with sulfuric acid as a catalyst. Resorcinol–formaldehyde resin (RF), phenol-resorcinol–formaldehyde resins (PRF), LW–PF and LW–PRF (synthesized using LW as a raw material), and RF/LW and RF/LW–PF (blended RF with LW and LW–PF) were prepared. The properties such as non-volatile content, pH, viscosity gelation time and DSC curing behavior of these resins were measured. The results show all resins can be cured at room temperature when paraformaldehyde is added as a hardener, except for the LW–PF. The honeymoon adhesive was prepared by using RF and PRF that contains 10% paraformaldehyde as the A-component and LW–PRF, RF/LW and RF/LW–PF without paraformaldehyde as the B-component. After mixing the A-component and B-component, the gelation time of RF and PRF can be shortened. The glued lumber was prepared by separately applying the A-component and B-component on the surface of two wood strips and combining them. The result shows using RF/LW–PF as the B-component has faster bonding strength development than others. When PRF and RF are used as the A-component, they have a bonding strength of over 5.4 MPa, the requirement of CNS 11031 standard for the glued lumber of C. japonica, at pressing times of 2 and 4 h, respectively.

Quality assessment of glued ash wood for construction engineering

Delamination resistance and tensile shear strength (TSS) are essential for load-bearing timber structures. Thus these two factors were investigated on industrially bonded ash wood (Fraxinus excelsior L.) to check for the suitability of adhesively bonded ash wood as a building material. Two melamine urea formaldehyde (MUF) resins, two polyurethanes (PUR), one emulsion polymer isocyanate and one phenol resorcinol formaldehyde resin were taken for bonding. Face milled and planed surface series were made to highlight potential differences. For PUR, an additional series with dimethylformamide primed surfaces was also made. The influence of the mixing ratio and the closed assembly time were analysed for one MUF system. The samples for the TSS were tested in dry and wet conditions. 80 % of the tested series met the standard requirements (EN 15425; EN 301) in dry condition, whereas only 30% passed in wet condition. None of the adhesives tested were able to pass the delamination test. No distinct influence of the different parameters studied is notable for most of the adhesive systems, only extended CATs and lower MRs seem to improve the bond quality of MUF. In addition, chemical analyses were performed to find evidence for the poor bonding performance. It was found that acidic extractives, fatty acid content and pH of ash fell within the range of beech and spruce wood, with only formic acid being an exception with an amount four times higher than the other two wood species.

Bonding Performance of Adhesives with Lamina in Structural Glulam Manufactured by High Frequency Heating System

The bonding performance of two types of wood adhesives, namely phenol-resorcinol-formaldehyde (PRF) resin and melamine-urea-formaldehyde (MUF) resin for glued laminated timber manufactured by high frequency (HF) heating was evaluated. The HF heating system consists of HF oscillator with dielectric heating system for curing adhesives, and hydraulic press system for clamping glued laminated timber. The designed frequency and output power of the HF system was as 5 MHz and 60 kW, respectively. To verify dielectric heating mechanism under HF oscillation, the heat loss factors of laminae and adhesives were measured. The results show that it is possible to selectively heat adhesives for their curing due to the remarkably higher loss factor of the adhesives than those of wood laminae. The temperature of adhesive in the bonding line reached up to the set temperature within a few seconds by high frequency oscillating, which advanced the curing of adhesive afterwards. The bonding performance, such as shear strength of bonding line, water soaking delamination, and boiling water soaking delamination of PRF resin met the requirement of Korean Standard (KS), however the MUF resin did not meet the KS requirement of boiling water soaking delamination. These results indicate that the HF heating system is successful to manufacture glued laminated timbers with PRF resins to meet the bonding requirements.

Specific fracture energy at glue joints in European beech wood

The specific fracture energy G at glue joints in hardwood was investigated by using a novel approach of testing and data evaluation. European beech wood was bonded with a specific one-component polyurethane (PUR) adhesive and a specific phenol resorcinol formaldehyde resin (PRF) to produce double cantilever beam (DCB) specimens. These specimens were stored at different relative humidities (50%, 65% and 95%) prior to testing. Additionally, DCB specimens manufactured out of differently aged glulam elements were also evaluated. Special care was given to a constant crack propagation rate during examination, and only the middle part of the specimens was evaluated to avoid influences of the discontinuities at crack initiation and final rupture. The PUR series were tested at three different crack propagation rates to check for a potential influence on G. The PRF specimens failed mostly in the wood, with an average wood failure of 90%. Thus no difference was notable between the PRF and solid wood samples. Their G was around 0.85N/mm for the regular and dry climates and 1.35N/mm for the wet climate. All aged series had a 10–15% reduced G, but with lack of significance. The PUR specimens failed in adhesion, independent from climate, ageing or testing speed, and had an average G of 0.24N/mm. The novel approach, i.e. with constant crack propagation rate and evaluating the data only partially, worked well and can be recommended for further research.

구조용 집성재 제조용 접착제(Phenol-Resorcinol-Formaldehyde Resin) 유전 가열을 위한 고주파 전기장 세기 추산

ABSTRACT For enhancing productivity of glulam, high frequency (HF) curing technique was researched in this study. Heat en-ergy is generated by electromagnetic energy dissipation when HF wave is applied to a dielectric material. Because bothlamina and adhesives have dielectric property, internal heat generation would be occurred when HF wave is applied toglulam. Most room temperature setting adhesives such as phenol-resorcinol-formaldehyde (PRF) resin, which is popu-larly used for manufacturing glulam, can be cured more quickly as temperature of adhesives increases. In this study,dielectric properties of larch wood and PRF adhesives were experimentally evaluated, and the mechanism of HF heat-ing, which induced the fast curing of glue layer in glulam, was theoretically analyzed.Result of our experiments showed relative loss factor of PRF resin, which leads temperature increase, was higher than that of larch wood. Also, it showed density and specific heat of PRF, which are resistance factors of temperature increase, were higher than those of wood. It was expected that the heat generation in PRF resin by HF heating would occur greater than in larch wood, because the ratio of relative loss factor to density and specific heat of PRF resin wasgreater than that of larch wood. Through theoretical approach with the experimental results, the relative strengths of ISM band HF electric fields to achieve a target heating rate were estimated.

Comparative adhesion analysis at glue joints in European beech and Norway spruce wood by means of nanoindentation

To gain a better insight into the delamination behaviour of glue joints in hardwood, the adhesion at the cell wall level was investigated. By the use of nanoindentation techniques, the adhesion, hardness and Young's modulus of adhesively bonded European beech wood (Fagus silvatica L.) was analysed. To highlight differences between soft- and hardwood adherends, Norway spruce wood (Picea abies KARST.) was also investigated. One-component polyurethane (PUR) and phenol resorcinol formaldehyde resin (PRF) were used for bonding. Untreated and aged samples (artificially and naturally weathered) were analysed and compared to silylated samples as reference, assuming the silylation reduces the adhesion to a minimum. From the gathered results it can be concluded that artificial ageing has the same effect as natural weathering on, both, adhesion and the properties of the single components of a bond. In beech wood, weathering increases the adhesion of PUR significantly. For PUR in spruce wood, the adhesion is not affected by any treatment. Tensile shear tests signified a reduced adhesion in all silylated samples. Additionally, the stiffness and hardness of both adhesives were found to be reduced by approximately 10%. As a consequence, the applied silylation is not considered as adequate treatment for reference samples.

Preparation of macroporous carbon foams using a polyurethane foam template replica method without curing step

Macroporous carbon foams were synthesized without a curing step using polyurethane (PU) foam as the sacrificial template and resorcinol-formaldehyde (RF), phenol-formaldehyde (PF), and phenol-resorcinol-formaldehyde (PRF) resins as the carbon precursors. PU foam was impregnated with these three aqueous resin solutions and carbonized directly at 830 °C in an inert atmosphere for 3 h without a pre-curing step. During heating to carbonization temperature, the impregnated resins were cured and subsequently carbonized. The curing, degradation of PU foam and carbonization mechanism were examined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The pore structure, electrical conductivity, and compressive strength of the prepared carbon foams using the RF, PF, and PRF resin carbon precursors were measured. Among them, the carbon foam fabricated from PF resin had a surface area, electric conductivity and compressive strength of 63 m2/g, 3.409 S/m and 0.25 MPa, respectively.

Influence of moisture on stress–strain behaviour of adhesives used for structural bonding of wood

Tensile strength, Young's modulus and stress–strain behaviour of adhesive films were investigated by means of tensile tests at 23°C under various ambient moisture conditions (5–95% RH, water exposure and redrying). The adhesive films were produced from two one-component moisture-curing polyurethane adhesives (1C PUR), one phenol–resorcinol–formaldehyde resin (PRF) and one melamine–urea–formaldehyde resin (MUF). These four adhesive films are commonly used for structural bonding of wood. In addition, films were made from three non-commercial 1C PUR prepolymers, all of which had their ethylene oxide (EO) proportions specifically modified. For all the tested adhesives other than PRF, the findings of the tensile tests revealed a linear dependency of tensile strength and Young's modulus on the relative humidity (RH). Both parameters decreased significantly with increasing RH. The redried samples illustrate the reversibility of this effect. These observations are mainly attributed to physical bonds like hydrogen bonds, which are disrupted by water molecules entering the polymer film and re-established whilst re-drying. No evidence was found for an influence of the EO content of the prepolymers on their tensile strength or Young's modulus at high RH. Regarding the 1C PURs at high RH the findings revealed an influence of hydrophilic catalyst on tensile strength, but not on Young's modulus. Under all tested ambient conditions, the fracture strain of PRF and MUF specimens remained below 5%, whereas that of the 1C PURs and the prepolymers reached at least 20%. This illustrates the ductility of the tested 1C PUR polymers on all tested climate stages in contrast to the brittleness of MUF and PRF polymers.

“Blue glue”: A new precursor of carbon aerogels

New carbon aerogels have been prepared from urea-branched phenol–resorcinol–formaldehyde resin. Such material, called “blue glue” and used as cold-set adhesive for wood, has been modified in order to obtain highly porous organic gels. The latter were prepared at different pH (5, 7 and 9), dried with supercritical methanol, and carbonised at two different heating rates (2.5 and 5°Cmin−1). FTIR analysis confirmed the expected chemical structure of the gel, and GC–MS analysis of the solvent condensed after supercritical drying suggested a slight chemical degradation of the gels during the drying process. However, low-density (0.15–0.31gcm−3), monolithic, carbon gels could be successfully derived from these materials, having high BET surface areas (900–1300m2g−1) and high mesopore fractions (60–80%). These ranges of values originate from the conditions tested for preparing the materials. Such carbon aerogels are two times cheaper than their traditional resorcinol–formaldehyde-based counterparts and present similar, if not more developed, porous structures.

Characterization of mixed-mode I/II fracture properties of adhesively bonded yellow-poplar by a dual actuator test frame instrument

Abstract Experimental results for the fracture behavior under mixed-mode in-plane loading conditions of adhesively bonded wood specimens are reported. The material systems considered involved yellow-poplar (Liriodendron tulipifera), a hardwood of the Magnoliaceae family, as adherends bonded with two different adhesives, a moisture-cure polyurethane (PU) and a phenol/resorcinol/formaldehyde (PRF) resin. A dual actuator test frame permitted fine scanning of fracture behavior over a full range of mixed-mode I/II levels for double cantilever beam (DCB) geometry specimens. These tests showed that, in the considered material systems, the critical strain energy release rate, c, tends to increase as the mode-mixity of the loading increases. In particular, the increase is steeper in proximity to pure mode II loading for the PRF bonded specimens. The experimental values of c obtained were fairly scattered, as is common when testing wood systems. This variability is due in part to the natural variability of wood but also to other factors such as the orientation of the grain in the bonded beams and variations of bondline thickness. In particular, measurements of adhesive layer thickness were performed. This analysis was implemented with microscopic examination of samples cut from untested DCB specimens, where the bondline had not been disrupted by the test. Although the wood parts were power planed prior to bonding, rather large variations of the adhesive layer thickness were observed: on the order of 1–100 μm for specimens bonded with the PU resin and 10–50 μm for specimens bonded with the PRF resin, which showed somewhat more consistent fracture behavior.

Chemical emissions from adhesive-bonded wood products at elevated temperatures

Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was employed to examine the chemical emissions from the glued wood samples at elevated temperatures (150, 200, 250, 300, 350, 400, 450, and 500°C). Two wood species, Douglas-fir (Pseudotsuga menziesii) and southern pine (Pinus palustris), one structural adhesive, phenol–resorcinol–formaldehyde (PRF), PRF-bonded Douglas-fir, and PRF-bonded southern pine were evaluated. The volatile compounds with a mass range of 35–300 m/z emitted from the pyrolysis samples were separated by gas chromatography (GC) and identified by mass spectrometry (MS). The results indicated that compared to neat wood and resin film samples, several additional pyrolysis products were observed for the PRF-bonded wood samples including (1) acetaldehyde and butanedial for PRF-bonded Douglas-fir and (2) acetaldehyde, furfural, 2-furanmethanol, butanedial, 2,3-butanedione, cyclopropyl carbinol, 1,2-benzenediol, and 1-(acetyloxy)-2-propanone for PRF-bonded southern pine. These additional compounds were possibly associated with the interaction between wood and PRF resin. The results also indicated that bonded wood products would be less thermally stable than those of neat wood and PRF resin samples.

Acetaldehyde emission from glued–laminated timber using phenol–resorcinol–formaldehyde resin adhesives with addition of ethanol

Acetaldehyde emission from glued–laminated timber using phenol–resorcinol–formaldehyde resin adhesives with addition of ethanol

DIFFERENTIAL SCANNING CALORIMETRY AND DINAMIC MECHANICAL ANALYSIS OF PHENOL-RESORCINOL-FORMALDEHYDE RESINS

Differential scanning calorimetry ( DSC ) and dinamic mechanical analysis ( DMA ) were use to study the curing reactions of two phenol - resorcinol- formaldehyde ( PRF ) adhesives with 15 and 25 % resorcinol content, synthesized in laboratory. The PRF resin with lower resorcinol content ( PRF1 ) shows a double exothermic peak ( 99.9 and 158.2 °C ) while PRF2 ,with greater resorcinol content ( 25 %) shows only one peak at 93.9 °C. The DMA storage modulus E' confirm the differences in the curing behavior of PRF adhesives. In the delamination resistance test during accelerated exposure only PRF2 with a greater content of resorcinol, fulfilled the ASTM D 2559 requirements for beams treated with two CCA retention levels. The cross-linking reactions was produced in the curing process at lower temperature in PRF2 , enhanced the adhesion durability to glulams treated with CCA preservatives

Direct measurement of strain distribution along a wood bond line. Part 2: Effects of adhesive penetration on strain distribution

Abstract The effect of adhesive penetration into wood on the distribution of strain along a mechanically strained bond line was evaluated. With this goal, spruce wood specimens were bonded with phenol-resorcinol-formaldehyde (PRF) and one-component polyurethane resin (PUR). Penetration of the adhesives into cell cavities was observed in a zone extending over several 100 μm from the bond line. Electronic speckle pattern interferometry was used to record the elastic deformations caused by mechanical tests in transverse compression. By differentiating 2D displacement maps, the strain distribution was calculated. Both adhesives provided an increase in the stiffness of the adhesive-wood interface due to penetration into cell cavities. Compression strain was much lower in the bond line area than in the wood. Shear strain was also low in the bond line and increased gradually with increasing distance. No change was observed in wood unaffected by the adhesive. The effects were more pro-nounced for PRF resin than for PUR.