Phenol Resorcinol Formaldehyde 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.

In-situ characteristic elastic properties of bond-lines in laminated engineered wood products using microscopic digital image correlation

Adhesively laminated engineered wood products (EWPs), such as glue-laminated timber (GLT) and cross-laminated timber (CLT), have gained global popularity due to the increasing development of tall wood buildings. The mechanical performance of a bond-lines is crucial for the structural behavior of EWPs. In this study, a novel method was developed for evaluating in-situ elastic properties of a bond-line in adhesively laminated solid wood products. This method deployed the microscopic digital image correlation (DIC) technique to capture the strain distribution along the bond-line under axial (0°) and off-axis (45°) tensile loading. Three types of adhesives, namely polyurethane (PUR), emulsion polymer isocyanate (EPI), and phenol–resorcinol–formaldehyde (PRF), were used to make specimens. The modulus of elasticity (E) and modulus of shear (G) of a bond-line were accordingly calculated based on the strain along a bond-line and load applied on a specimen. For verification purpose, finite element (FEA) models on CLT and GLT beams were, considering the elastic properties of bond-lines and disregarding the elastic properties, developed to evaluate the effects of the elastic properties of a bond-line on the stress distribution. It was found that the proposed method could be used to accurately determine the in-situ characteristic elastic properties of bond-lines in EWPs. The elastic properties of a bond-line exhibited a large variability, but did not appear to have a significant impact on the overall stress distribution in a specimen. The E and G of bond-lines might be neglected in the structural analysis of large-sized laminated wood products such as GLT and CLT.

Comparison of microscopy and quality control testing to examine the durability of adhesive bondline in cross-laminated timber

Adhesive bonding quality significantly contributes to the integrity and quality of cross-laminated timber (CLT). There are several factors affecting bonding quality in glued-layered wood products such as CLT that are generally categorized as the properties of wood, adhesive type and curing conditions. The adhesive bonding performance of five different types of CLTs made from yellow-poplar and southern pine lumber using phenol-resorcinol formaldehyde and polyurethane structural adhesives were studied using light microscopy and ANSI/APA PRG-320 mechanical evaluation tests. The results show that CLTs with a thin bondline and the highest effective penetration had the highest shear strength, and with least face delamination. The effect of wood anatomy on bonding quality was demonstrated in mixed species CLT with different penetrations into different species. The effect of adhesive curing was observed through the presence of generating gaps and microbubbles in adhesive lines.

Bonding performance and surface characterization of cold-bonded acetylated beech (Fagus sylvatica L.) laminated veneer lumber.

Acetylation of wood with acetic anhydride reduces the wood-moisture interaction, improves the dimensional stability and resistance against biodegradation. However, the adhesive bonding is affected by the modification, which is crucial to manufacture engineered wood products, such as laminated veneer lumber (LVL). In this study we report the bonding of 8-layered acetylated beech (Fagus sylvatica L.) LVL boards to 2-layered LVL beams. The beams were glued together at room temperature adding three common load-bearing construction adhesives: melamine-urea-formaldehyde (MUF), phenol-resorcinol-formaldehyde (PRF), and one-component polyurethane (PUR). The bonding performance was tested by assessing its dry and wet tensile shear strength(TSS) and wood failure percentage(WF). Also evaluated were the material's density and moisture content(MC). The surface was characterized prior to bonding by its pH, roughness, and contact angle(CA). The adhesive penetration was observed by fluorescence microscopy. Aside from MUF, applying PRF and PUR adhesives achieved good bonding performance on acetylated LVL and references. Acetylated LVL displayed a more hydrophobic behaviour, a higher pH, a somewhat smoother surface, and an increased density.

Experimental investigation of the mode I fracture toughness behaviour of timber adhesive joints: The synergistic effect of the adhesive type and the bondline thickness

Timber is a construction material widely used for structural applications. In the last decades, the improvements of both the bonding techniques and the quality of the adhesives enabled to overcome the intrinsic limitations of sawn timber, resulting in a wide spread of engineered wood products (EWPs). Understanding and assessing the bonding quality of structural EWPs has become nowadays a crucial point to assure their load-bearing capacity and even to increase their performance. One of the most revealing properties to assess the bonding quality and behavior is the fracture energy (or toughness), which could be estimated by performing suitable tests. In the present work, the results of an experimental campaign aimed to define the mode I fracture toughness of timber-to-timber adhesive bonding are presented and discussed. The fracture toughness behavior of three different categories of adhesives for structural applications was investigated, namely melamine-urea-formaldehyde (MUF), polyurethane (PU) and phenol-resorcinol-formaldehyde (PRF). In addition, the effect of the adhesive bondline and precrack thickness (0.15 and 0.30 mm) was also investigated. The results revealed different fracture toughness behaviour between the various adhesives and bond line thickness, in terms of both crack initiation and propagation. In fact, the mode-I fracture toughness appears to be highly dependent on the adhesive type, as also seen by the related analysis of variance. The fractured surfaces are also characterized by means of optical microscopy, giving insights about the local failure modes.

Predicted and Experimental Bending Behaviour of Glulam Bonded by RPF Adhesive.

In this study, alder, spruce, and beech woods were used for homogeneous symmetric, inhomogeneous symmetric (combined) and inhomogeneous non-symmetric glued laminated timber (glulam) beams glued with resorcinol phenol formaldehyde (RPF) adhesive. The aim of this paper is to determine and compare the modulus of elasticity of glulam beams using three methods, i.e., analytical calculation, numerical model (FEM) and experimental testing. As an additional characteristic, the bending strength (MOR) of the beams was determined during experimental testing. Analytical calculation was used to calculate the modulus of elasticity (MOE) of glued laminated timber based on the knowledge of the modulus of elasticity of solid wood and to estimate the location of the neutral axis during bending. According to calculations, for symmetrical combinations, the deviation from the real neutral axis does not exceed 5%. In the case of the modulus of elasticity, the deviation is an average of 4.1% from that of the actual measured beams. The numerical model includes finite element modelling, where the deflection of the modelled beams can be calculated with a deviation of up to 10%. The last method was experimental testing of glued beams using four-point bending, in which, among homogeneous beams, beech glulam beams achieved the highest MOE and MOR, while alder glulam beams achieved the lowest. The combination of wood species resulted in an increase in both MOE and MOR compared to homogeneous spruce and alder beams.

Burning Properties of Combined Glued Laminated Timber

This study delved into the combustion properties of combined glulam bonded using polyurethane (PUR) and resorcinol-phenol-formaldehyde (RPF) adhesives. The experiment involved three distinct wood species, namely, spruce, alder, and beech, which were combined in homogeneous, non-homogeneous symmetrical, and non-homogeneous asymmetrical arrangements. These species were selected to represent a spectrum, namely, softwood (spruce), low-density hardwood (alder), and high-density hardwood (beech). The varying combinations of wood species illustrate potential compositions within structural elements, aiming to optimize mechanical bending resistance. Various parameters were measured during combustion, namely, the heat release rate (HRR), peak heat release rate (pHRR), mass loss rate (MLR), average rate of heat emission (ARHE), peak average rate of heat emission (MARHE), time to ignition (TTI), and effective heat of combustion (EHC). The findings indicate that incorporating beech wood into the composite glulam resulted in an increase in heat release, significantly altering the burning characteristics, which was particularly evident at the second peak. Conversely, the use of spruce wood exhibited the lowest heat release rate. Alder wood, when subjected to heat flux at the glued joint, displayed the highest heat emission, aligning with the results for EHC and MARHE. This observation suggests that wood species prone to early thermal decomposition emit more heat within a shorter duration. The time to ignition (TTI) was consistent, occurring between the first and second minute across all tested wood species and combinations. Notably, when subjected to heat flux, the glulam samples bonded with PUR adhesive experienced complete delamination of the initial two glued joints, whereas those bonded with RPF adhesive exhibited only partial delamination.

Producing Hardwood Cross-Laminated Timber (HCLT) Mats from Low-Grade Red Oak Lumber

Abstract The use of cross-laminated timber (CLT) has significantly grown in North America, but hardwood species have not yet been deemed a viable raw material for manufacturing CLT panels. Therefore, softwood species continue to serve as the only approved material for CLT in structural applications according to ANSI/APA PRG-320. Nonstructural CLT products that utilize low-grade lumber from hardwood species, are a good option for introducing hardwoods into the CLT market. Of the hardwood species located within Appalachia, northern red oak (Quercus rubra) is readily available. The purpose of this research was to develop hardwood cross-laminated timber mats utilizing low-grade red oak lumber. In order to manufacture red oak CLT mats, the best adhesive and bonding parameters had to be identified. Overall, sample CLT panels were made using three adhesives with nine different setups for each adhesive. The sample panels were processed into smaller blocks and separated for cyclic delamination and shear-block tests following the ANSI/APA PRG-320 standards. This research determined that a phenol–resorcinol formaldehyde (PRF) adhesive produced the lowest percentage of delamination, satisfying the delamination requirements. The PRF adhesive also produced the largest percentage of wood failure in shear-block testing, however, the results fell short of meeting the requirements. A Taguchi statistical analysis was used to predict the optimal bonding parameters for each adhesive. The optimized bonding parameters for the polyurethane (PUR) adhesive produced favorable results, indicating the delamination results have the potential to nearly meet the standard requirements, while the predicted shear results would exceed the requirements.

The effect of long and short term elevated temperatures on the behaviour of lap glued joints of load-bearing spruce elements

The paper deals with the behaviour of glued joints of wooden sections exposed to long and short term elevated temperatures. If the adhesive is not sufficiently temperature resistant, the glued joint may lose adhesion, which could result in a change in behaviour of the glued element cross-section when exposed to fire. Moreover, detailed knowledge of the behaviour of bonded joints under such long and short term thermal exposures will enable us to make informed decisions about the need for major structural intervention in structures post exposure. Three types of adhesives: phenol-resorcinol-formaldehyde (PRF), polyurethane (PUR) and emulsion polyisocyanate (EPI), commonly used in load bearing wooden structures, were chosen for the experimental work. Thermal analysis showed that the PRF and PUR were not sufficiently cured, especially the PRF. Calorimetric analysis showed the point at which thermal degradation of all three adhesives began, at 135 °C for EPI and at about 160 °C for PRF and PUR. Spruce lap joints, with a cross section of 40 × 48 mm, bonded using these adhesives were exposed to temperatures of 140 and 170 °C. To properly distinguish the effect of thermal exposure duration on the lap joints, different thermal durations were used: 20, 40, 60 and 80 min, plus 3 h and 1 day. The thermal resistance at each of the elevated temperatures was investigated through measurement of the reduction in tensile shear strength. At an elevated temperature of 140 °C there was no significant strength reduction in all of the tested adhesives, it was only a longer duration (1 day) that produced a reduction in the tensile shear strength properties (31.0% for PRF, 16.2% for PUR and 34.1% for EPI). A temperature of 170 °C produced a greater decrease in strength, a significant drop (more than 15%) was found for PRF and EPI after an exposure of 40 min; for PUR after 60. Moreover, the longer duration exposures to a temperature of 170 °C resulted in a total loss in strength for PUR and a half loss of strength for EPI; for both these isocyanates adhesives this was confirmed by the total loss of wood failure criterium. On the contrary, a strength reduction of 50.0% and a sufficient wood failure criterium for a 1day temperature exposure at 170 °C was found for PRF.

Characteristics laminates composite bamboo

The main plants in Indonesian people's plantations are apus bamboo (Gigantochloa apus), wulung bamboo (Gigantochloa atroviolacea) and tutul bamboo (Bambusa maculat). Apart from being used as a craft material, bamboo is also suitable for boards in the form of laminated composites bamboo which are usually called laminated bamboo boards. One of the main criteria for laminated bamboo boards is their good adhesion, which is determined by their shear performance (shear strength). The shear strength of laminated bamboo boards is influenced by several factors such as the type of bamboo used, adhesive/matrix type and laminate configuration. This research used three variations of bamboo species: Gigantochloa apus (GA), Gigantochloa atroviolacea (GV) and Bambusa maculat (BM). The matrix/adhesive used is phenol resorcinol formaldehyde (PRF). The bamboo laminated composite arrangement or horizontal configuration is assembled into a three-layer structure using a hand lay up technique. Testing to determine the performance of bamboo laminated composites, with a shear test, using an Instron universal testing machine (UTM) (serial number CP105207), maximum load cell 100 kN with 8 Kg. The results show that the type of bamboo has an effect on the shear performance of bamboo laminate composites. The BM, GV, GA bamboo, respectively, have better performance, greater shear strength.

Investigations into the Influence of Temperature on the Tensile Shear Strength of Various Adhesives.

The temperature resistance of glued timber, which is crucial for glued wood construction, represents a significant assessment criterion. To gain insights into this aspect, this study utilized methods such as a shear strength test in accordance with EN 302-1:2013-06 under thermal loading (from 20 °C to 200 °C), and Differential Scanning Calorimetry (DSC) to determine the glass transition temperature (Tg). An increase in thermal load resulted in a decrease in shear strength and an increase in wood breakage. A hierarchy of adhesive groups was established based on strength performance and wood failure percentage (WFP) at 200 °C. Thermoset adhesives (MF: Melamine Formaldehyde, PRF: Phenol Resorcinol Formaldehyde) led the ranking, followed by elastomer adhesives (1C-PUR: One-Component Polyurethane, EPI: Emulsion Polymer Isocyanate), with thermoplastic adhesive (PVAc: Polyvinyl Acetate) last. Thermoset adhesives further cured under heat. PUR adhesives exhibited higher strength performance at 150 °C and lower temperatures.

Manufacturing Study on Different Glue Spread and Press Pressure for Glued Laminated Timber Made from Laran

Amidst challenges such as dwindling timber log supply from natural forests, concerns about timber quality, and rising timber costs, the timber industry has increasingly turned to engineered lumber solutions, including glued laminated timber (glulam) crafted from fast-growing species. However, the performance of glulam derived from plantation trees, notably swift-growing varieties like Laran, remains an area warranting exploration. This study addresses critical aspects of glulam production, encompassing adhesive selection, spread rate, and press pressure, which collectively influence material performance. The objectives of this research encompass an assessment of the bonding integrity of glulam originating from Laran plantation species and an evaluation of the optimal adhesive spread rate and press pressure for Laran-derived glulam. Various adhesive spread rates (200 g/m2, 250 g/m2, 350 g/m2 and 400 g/m2) and press pressures (0.7, 1.0 and 1.4 MPa), utilizing Phenol-Resorcinol Formaldehyde (PRF) adhesives, were systematically investigated in alignment with the guidelines stipulated in MS 758: 2020. Bonding integrity was evaluated via block shear and cyclic delamination tests. The study reveals that these parameters indeed exert a tangible influence on the bonding efficacy of PRF adhesive with Laran species. Remarkably, an optimal adhesive spread rate of 399.78 g/m2 and press pressure of 1.18 MPa emerged as pivotal thresholds for superior bonding outcomes. Notably, the significance of adeptly designed glulam beams within wooden structural frameworks is underscored, particularly in light of the multifaceted imperatives of sustainability, economics, and environmental conscientiousness.

Influence of particle granulometry and panel composition on the physico‐mechanical properties of ultra‐low‐density hemp hurd particleboard

AbstractThis study investigated Australian hemp hurd (Cannabis sativa L., “Frog One”) as a lignocellulosic raw material for ultra‐low‐density hemp particleboard (ULHPB) with densities ranging from 213 to 309 kg/m3. The hurd was first milled and fractionated into three particle size categories, that is, fine (F), medium (M), and coarse (C). Twelve unique ULHPB variants were then fabricated comprising varying particle loadings from four particle size mixes, that is, 100% C, 100% M, 50%/50% CM, 25%/50%/25% CMF, and adhesive contents of bio‐epoxy (EPX), phenol resorcinol formaldehyde (PRF), and emulsifiable methylene diphenyl diisocyanate (MDI), respectively. The panel assessments, conducted in accordance with the Australian reconstituted wood‐based panels standard AS/NZS 1859.1 (2017), revealed a significant effect of particle dimension on most physico‐mechanical properties. Furthermore, the resination method and pressing temperature controlled post‐cure panel expansion and additional panel characteristics. Notably, MDI‐ULHPB exhibited drastically different behavior and properties compared to EPX and PRF equivalents, demonstrating greater bending strength, stiffness, screw withdrawal strength, and dimensional stability. Importantly, all MDI variants conformed to the 15% thickness swelling limit for moisture resistant particleboard. Surface lamination of MDI‐bonded ULHPB with sheets of aluminum, Masonite, and Kraft liner significantly improved the inherently low flexural properties, suggesting the potential suitability of ULHPB as a core layer in lightweight sandwich composite panels. The integration of agricultural by‐products, such as hemp hurd, into engineered building materials presents a promising opportunity to mitigate the depletion of finite timber resources and aligns well with circular economy principles.Highlights Utilizing agricultural residue as sustainable raw material in building products. Hemp hurd enables ultra‐low‐density particleboard with thermosetting resins. Coarse particle size mix enhances mechanical performance in panels. Panel characteristics controlled by resination method and pressing temperature. Lamination enhances functionality of lightweight hemp hurd sandwich panel.

Evaluation of wet tensile shear strength and surface properties of finger-jointed acetylated beech (Fagus sylvatica L.) laminated veneer lumber

Experiments on finger-jointing acetylated beech (Fagus sylvatica L.) laminated veneer lumber (LVL) have been made. The specimens were examined on its wet tensile shear strength (TSS) using three adhesives, including phenol resorcinol formaldehyde (PRF), one-component polyurethane (PUR) (without primer), and melamine urea formaldehyde (MUF). Contact angles (CA) of uncured and drop-applied MUF, PRF, and PUR adhesives on freshly cut finger-joints were evaluated. Surface roughness was measured using a laser-scanning-microscope (LSM). Results showed that PRF bonded acetylated specimens had highest wet TSS, followed by specimens with PUR bonding. MUF performed poorly, which was most likely caused by its inadequate water resistance and changes in chemical reactions due to remaining acetic acid. Acetylated finger-joints had a topography similar to untreated joints. Moreover, CA were just barely lower for MUF and PRF on acetylated wood than on untreated references.

Adhesively bonded joints between spruce glulam and birch plywood for structural applications: experimental studies by using different adhesives and pressing methods

ABSTRACT Due to the increasing interest in reducing the usage of metals in the construction sector, birch plywood has shown good potential in structural engineering and timber connections as a substitute for the more conventional slotted-in metal plate solutions. However, a proper way of bonding birch plywood with other timber parts that results in adequate connection strength has not been fully investigated. In this paper, experimental studies were carried out to investigate the proper workflow when manufacturing bonded connections made of birch plywood and spruce glulam beams. Tensile shear mechanical tests were then conducted on produced bonded joints to evaluate the bond strength. Three adhesives, i.e. melamine-urea-formaldehyde (MUF), phenol–resorcinol–formaldehyde (PRF), and two-component polyurethane (2C PUR) were evaluated in dry and moist conditions. The influence of three pressing methods, i.e. (a) screw-gluing, (b) clamping by means of clamps, and (c) clamping by application of weight loads, on the bonding strength was investigated. The bonding strength was thereafter compared with the shear strength of spruce glulam and the wood failure percentage was also examined in this study.

Performance of Six-Layered Cross Laminated Timber of Fast-Growing Species Glued with Tannin Resorcinol Formaldehyde

The aim of this study were to evaluate tannin resorcinol formaldehyde (TRF) for the preparation of cross-laminated timbers (CLTs) made from fast-growing tree species and to analyze the physical and mechanical properties of CLTs. TRF copolymer resin was prepared by using the bark extracts of Swietenia mahagoni (L.) Jacq. It was observed that the TRF adhesive possessed less solid content (23.59%), high viscosity (11.35 poise), and high pH values (10.0) compared to the standard phenol resorcinol formaldehyde. The TRF adhesive was applied to produce CLTs with the addition of 15% tapioca and flour as an extender. The six-layered CLTs were produced from sengon (Falcataria moluccana Miq.), jabon [Anthocephalus cadamba (Roxb) Miq.], coconut (Cocos nucifera L.), and the combination of coconut-jabon and coconut-sengon wood. The analysis of variance revealed that the layer composition of CLT significantly affected the physical and mechanical properties of the beam. While the modulus of rupture met the standard, the moisture content and modulus of elasticity values did not fulfill JAS 1152-2007. All of the CLTs produced in this study demonstrated low formaldehyde emission, ranging from 0.001 mg/L to 0.003 mg/L, thereby satisfying the JAS 1152 for structural glue laminated timber.

Effects of Adhesive Types and Structural Configurations on Shear Performance of Laminated Board from Two Gigantochloa Bamboos

Semantan (Gigantochloa scortechinii) and beting (Gigantochloa levis) bamboo are the two Malaysian bamboo that are suitable to be converted into laminated bamboo boards. One of the main criteria for laminated board is its good bondability, which is determined by shear performance. The shear performance of laminated board is influenced by several factors such as the species used, adhesive types and lamination configurations. Therefore, in this study, laminated bamboo boards were produced using Semantan and Beting bamboo bonded with phenol–resorcinol–formaldehyde (PRF) and polyurethane (PUR) adhesives. Different configurations (lay-up patterns and strip arrangements) were used during the consolidation of the laminated boards. The bamboo strips were arranged in three different arrangements, namely vertical, horizontal and mixed, and then assembled into a three-layered structure with two lay-up patterns, which are perpendicular and parallel. Shear performances, such as shear strength, bamboo failure and delamination of the boards, were evaluated. The results revealed that the adhesive type and lay-up pattern were the most influential factors on the shear performance. PRF-bonded laminated bamboo boards outperformed PUR-bonded laminated bamboo boards in terms of shear strength and bamboo failure but PUR bonding had better bond durability as indicated by its low delamination. Boards laminated parallelly significantly outperformed those bonded perpendicularly. As for strip arrangement, PRF-bonded laminated boards were less influenced by it compared to PUR-bonded laminated boards. The results suggested that PRF is a better adhesive for bamboo lamination due to its higher shear performance and more consistent performance across structural configurations (lay-up patterns and strip arrangements).

Flow, curing and mechanical properties of thermoset resins – wood-fiber blends for potential additive-manufacturing applications

ABSTRACT This study examined the use of softwood mill residues (50–90%) with two thermosetting resins (i) urea-formaldehyde (UF) and (ii) phenol-resorcinol-formaldehyde (PRF) resin, for potential use in additive manufacturing (AM) of wood composite materials. The curing behavior of these blends was evaluated using differential scanning calorimetry and dynamic rheology. Curing kinetics was determined using the Kissinger and Cranes method. The presence of wood fibers reduced the curing peak temperatures for both resin blends at the same heating rates but curing peak temperatures increased with heating rates. The activation energy (Ea ) increased with the addition of wood for the wood-PRF blends but reduced for the wood-UF blends in comparison to the neat resins. Ea values were 51 and 271 kJ/mol for PRF and wood-PRF samples and 100 and 367 kJ/mol for UF and wood-UF samples. Frequency sweep flow curves of the green wood-resin blends showed shear thinning behaviors with viscosity values between 103–108 Pa.s at 30°C. Mechanical properties of the wood-resin composites generally showed a reduction in flexural modulus with an increase in wood content. Wet wood (50%)-PRF blend was successfully extruded and showed promise for use in AM; however, the wood-UF blend was not successful.

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.

Effects of Particle Dimension and Constituent Proportions on Internal Bond Strength of Ultra-Low-Density Hemp Hurd Particleboard

The recent legalisation of hemp seeds for human consumption has revitalised the cultivation of hemp in Australia. This provides opportunities for the valorisation of the stem’s residual xylemic core (hemp hurd). This study investigated the effect of particle dimension and constituent proportions on the internal bond strength (IB) of single-layer, ultra-low-density hemp hurd particleboard (ULHPB) with densities between 219 to 304 kg/m3. Particle size distributions (PSD) and granulometry assessments were conducted on three particle size classes (fine (F), medium (M), coarse (C)) based on digital image analysis using ImageJ. Subsequently, four particle size mixes (100% C, 100% M, 50/50% CM, 25/50/25% CMF) were considered for the ULHPB manufacture with bio-epoxy (EPX), phenol resorcinol formaldehyde (PRF) and emulsifiable methylene diphenyl diisocyanate (MDI) adhesives, respectively. The effect of particle loading and adhesive content varied significantly per adhesive type. Internal bond (IB) performance increased in most ULHPB comprising coarse particles and declined with the addition of smaller particle sizes. The granulometry assessment showed the smallest mean elongation amongst particles in the coarse PSD. The IB results confirmed a strong interdependence of particle size and constituent proportions and indicated that various MDI-ULHPB variants can surpass the minimum IB strength requirement of 0.30 MPa stipulated for standard particleboard (>12–22 mm) in AS/NZS 1859.1. Utilising residual hemp biomass as an alternative, renewable lignocellulosic feedstock in the manufacture of engineered lightweight panel products is a key principle of circular economy and an environmentally friendly strategy to address the increasing resource scarcity in the wood-based panel industry.