Low Molecular Weight Phenol Formaldehyde Research Articles

A Dual Resin Application System for Improved Bamboo-Wood Bonding

In this work, a dual resin application system using commercial phenol formaldehyde (PF) resins with different molecular weight (MW) was investigated to improve bonding performance of bamboo and wood composite laminates. Water droplet contact angle was deemed to be unreliable for assessing resin wettability on bamboo due to its unique tissue structure compared with wood. Microscopic observation of the resin penetration showed high MW PF largely remained in the glueline and only entered the lumens of cut or damaged bamboo cells near the bondline. Low MW PF appeared in cell corners of bamboo parenchyma but not lumens. Applying low MW PF to the bamboo and high MW PF to the wood surface separately significantly improved bond shear strength with reduced difference between dry and wet conditions. The dry and wet bond strengths using the new method were enhanced by 36.5% and 97.4%, respectively, compared to high MW PF alone. The results suggest that low MW PF can permeate bamboo cell walls and fortify them against swelling and stress on the bamboo-resin interface in wet conditions. Further modifications are required to produce a stronger adhesive than the bamboo tissue to improve wet shear fiber failure rates and develop a viable structural bond qualification test for bamboo and bamboo-wood composites.

EFFECT OF ANATOMICAL STRUCTURE ON DIMENSIONAL STABILITY OF LOW MOLECULAR WEIGHT PHENOL-FORMALDEHYDE IMPREGNATED WOOD

This research deals with low molecular weight-phenol formaldehyde (LMW–PF) impregnation on sepetir (Sindora spp), nyatoh (Palaquium spp.), and pisang putih (Mezzettia spp.) woods to determine the effect of different anatomical structure on weight percent gain and dimensional stability improvement. The wood samples were impregnated using LMW–PF solutions with 7, 8, 9, 10, and 11% of concentrations (w/w), vacuum-pressured (–98 kPa, 15 min, 350 kPa, 4 h), and re-immersed in 80°C for 3 h. According to the findings, LMW–PF impregnation reduced coefficient of swelling by 9.64–29.95%, and increased anti-swelling efficiency by 12.24–29.91%. Additionally, the water absorption and thickness swelling reduced by 2.43–38.75% and 15.94–34.21%, respectively, indicating the improvement of dimensional stability. Microscopy and NIR analysis revealed the presence and reaction of LMW–PF within porous wood matrix. The effect of diverse anatomical structures caused complexity on LMW–PF impregnation. Sepetir-treated wood with fewer anatomical barriers resulted in better dimensional stability improvement than others.

Review paper: properties of low molecular weight phenol formaldehyde – treated bamboo composite

Impregnation of bamboo in phenol formaldehyde (PF) solution is one of the promising solutions to overcome the drawback of the material. The use of low molecular weight PF resin (LMW PF) in the production of bamboo composite materials not only improves the dimensional stability but also increases the mechanical strength of the material. The bonding interface between bamboo elements and adhesives is presumed to be significantly influenced by the degree of adhesive penetration into the porous network of interconnected cells of bamboo surfaces. The permeation of PF resins in bamboo is closely related to their molecular weight. LMW PF resin will overpenetrate and lead to an undesirable starved bondline while high-MW PF resins only remain in the bondline and it is difficult to form mechanical interlocking. This paper discusses the research results on the bonding quality of bamboo strips when impregnated in LMW PF solution with different ratios and different pressing technology parameters; at the same time, physical and mechanical properties of bamboo composite materials treated with PF PTLT such as: water absorption resistance, dimensional stability, bonding strength, modulus of rupture (MOR), modulus of elasticity (MOE) are also significantly improved. This is a scientific basis that can serve as a premise for the research on technology to produce composite materials from bamboo and LMW PF in Vietnam.

Effects of Compression Ratio and Phenolic Resin Concentration on the Properties of Laminated Compreg Inner Oil Palm and Sesenduk Wood Composites

Due to its inferior properties, oil palm wood (OPW) extracted from the inner layer of the oil palm (Elaeis guineensis) trunk, referred as inner OPW in this study, is frequently regarded as a waste. Phenolic resin treatment and lamination of inner OPW with other hardwoods may be an excellent way to improve the properties of the inner OPW. In this study, inner OPW were treated with two different concentrations (15% and 20%) of low molecular weight phenol formaldehyde resin (LmwPF) and compressed at different compression ratios (10%, 20%, and 30%). The physical and mechanical properties of the modified inner OPW’s were evaluated according to British Standards (BS) 373: 1957. The results revealed that inner OPW treated with the highest compression ratio (30%) and resin concentration (20%) exhibited the highest weight percent gain, polymer retention and density. In the following phase of the research, the treated inner OPW was used as the core layer in the fabrication of a three-layer laminated compreg hybrid composites, with untreated and treated sesenduk (Endospermum diadenum) wood serving as the face and back layers. The compression ratios of 10% and 20% and resin concentrations of 10% and 20% were used in this phase of study as laminated boards made with 30% compression ratio failed. The findings showed that resin concentration had a significant impact on both the inner OPW and the laminated compreg hybrid panels. Markedly, higher resin concentrations (20%) resulted in improved physical properties, i.e., thickness swelling and water absorption, as well as enhanced mechanical properties (modulus of rupture and modulus of elasticity). Although compression ratios had no significant effect on the properties of the laminated products, those compressed at higher compression ratios (20%) performed slightly better than the panels compressed at lower compression ratios (10%).

SELECTED PROPERTIES OF COMPREGNATED WOOD USING LOW MOLECULAR WEIGHT PHENOL FORMALDEHYDE AND SUCCINIC ANHYDRIDE

The aim of this study was to investigate the effect of impregnating materials (low molecular weight phenol formaldehyde or LmwPF and succinic anhydride or SA), their concentrations (5and 10%), and compression ratios (20 and 40% from initial thickness)on improvement of specific gravity (SG) and dimensional stability on nyatoh, sepetir, and pisang putih wood; and then compared them to control and densified wood. The results showed that SG and dimensional stability of compregnated wood were affected by all parameters studied. Higher compression ratio and concentration will result in a greater improvement.In general, SG and dimensional stability of compregnated wood were better than the control.SG of LmwPF-and SA-compregnated wood increased by 10.69‒22.31% and 6.96‒23.09%, respectively. Utilization of LmwPF and SA has significantly reduced the spring-back, butthe latter is better. Thecompression-set recovery after compregnation was 18.34‒33.99%, while after densification was 47.86‒71.49%.

Synthesis of SBA 15 graphene oxide composite membrane using phenol–formaldehyde resin pore modifier for CO2 separation

AbstractPresent study highlights the development of carbon‐loaded SBA 15 membrane on clay‐alumina tubular support and its performance on the CO2 separation efficiencies from different mixture gases. To modify the large pores of SBA 15 by graphitic carbon, low molecular weight phenol–formaldehyde (PF) resin was incorporated into the mesoporous channel followed by calcination under inert atmosphere. The modified ordered pore structure of the membrane has been characterized by low‐angle XRD, TEM, and pore size distribution analysis. The chemical state of the deposited carbon phase into the SBA 15 pores was analyzed by X‐ray photoelectron and Raman spectroscopy. Carbon having graphitic nature mainly in graphene oxide has been deposited into the mesopore of SBA 15 resulting decrease in pore size from 8.9 to 1.0 nm. Finally, the developed SBA 15 carbon membranes were characterized by CO2 permeation and separation selectivity of CO2/CH4, CO2/CO. Highest CO2/CH4 separation factor was achieved as 16.9 with CO2 permeance 13.6 × 10–8 mol/m2/s/Pa at 200 kPa feed pressure by the 20% resin with 2 times coated membrane. In flue gas analysis, highest CO2/CO separation factor of 32.8 was achieved. This study offers an observation on CO2 separation from simulated BF gas for the first time and the results show the potential of the developed SBA 15/C composite membranes in commercial application.

Evaluation of water related properties of birch wood products modified with different molecular weight phenol-formaldehyde oligomers

Abstract This study investigated the effect of phenol-formaldehyde (PF) resin treatment on the dimensional stability of birch solid wood and plywood. Therefore, three different low molecular weight PF resins with average molecular weights (M w ) of 292, 528, and 884 g/mol were synthesized and used for silver birch (Betula pendula) solid wood (20 × 20 × 20 mm3) and veneer (100 × 100 × 1.4 and 300 × 300 × 1.4 mm3) impregnation to produce plywood. The weight percent gain (WPG) and bulking after curing of resin treated wood specimens were determined. The leaching was performed to evaluate the PF resin fixation stability. All tested resins at all concentrations were similarly fixed in wood blocks after the leaching (1.5–2.0% WPG loss). The dimensional stability of birch wood after treatment with all tested PF resins was significantly improved. The anti-swelling efficiency (ASE) of birch wood blocks treated with PF resins after seven water soaking-drying cycles was in the range of 39–53%, 46–65% and 49–65% using 10, 15 and 20% solution concentrations, respectively. Whereas, the ASE of plywood obtained from veneers treated with 10% of PF solution was improved by 6–20%. The equilibrium moisture content (EMC) and volumetric swelling (VS) of PF treated plywood at 98% of relative humidity (RH) decreased significantly. All PF resin treated plywood surfaces were more hydrophobic compared to untreated plywood.

Sorption isotherm and physico-mechanical properties of kedondong (Canarium spp.) wood treated with phenolic resin

Kedondong (Canarium spp.) wood was modified with low molecular weight phenol formaldehyde (LmwPF) resin in order to reduce its hygroscopicity. Kedondong wood were impregnated with LmwPF resin at different concentrations, namely 15, 20 and 30%, followed by curing at high temperature. The physico-mechanical properties, surface wettability, and sorption isotherm of the treated and untreated wood were investigated. Surface wettability of the modified wood reduced as a result of the treatment. Thickness swelling and water absorption of the modified kedondong wood reduced while positive anti-swelling efficiency increased along with increasing resin concentration. However, there was no significant difference observed for mechanical properties between modified and unmodified wood. The equilibrium moisture content (EMC) for unmodified kedondong was higher than impregnated samples. At 95% RH, unmodified kedondong showed an EMC of 19.10% whereas samples treated at 15%, 20% and 30% LmwPF concentration recorded EMC of 18.27%, 18.14% and 17.12%, respectively. Furthermore, the hysteresis loop of untreated sample results was slightly higher than treated sample. The highest hysteresis value was marked at 80% RH with value 3.74% for untreated sample and the value decreased slightly in treated woods. The results indicate that the treatment reduces the hygroscopicity of kedondong wood.

Effects of low and high molecular weight of phenol-formaldehyde (PF) on the properties of strand boards from kiri wood (Paulownia tomentosa)

ABSTRACT Kiri (Paulownia tomentosa) wood is a promising material for lightweight strand boards (SBs); however, kiri SBs have displayed a limited dimensional stability. The aim of this study was to evaluate the possibility of using low molecular weight (LMW) phenol-formaldehyde (PF) resin not only as an adhesive but also as a treatment (impregnating) agent to manufacture SBs. SBs from kiri wood were manufactured with densities of 400 kg m−3 and 500 kg m−3. PF resin with low and high molecular weight as well as its 50-50% mixture was studied at two adhesive formulation contents of 10% and 20% related to the strand mass. At 400 kg m−3 density, internal bond strength (IB), screw withdrawal resistance (SWR) and thickness swelling (TS) of SBs containing LMW PF were significantly higher than those of HMW PF at 10% adhesive content and the differences slightly decreased as the adhesive content increased to 20%. At 500 kg m−3 density, IB, TS and SWR of SBs were considerably enhanced by LMW PF at both adhesive contents. We concluded that using LMW PF may cause higher strength and dimensional stability, at least, when the strand material and the SBs exhibits very low density, which is highly compressed during SBs manufacturing.

Effects of the drying process on the shear strength and morphology of the bonding interface of laminated wood

To investigate the influence of the drying process on the bonding properties of laminated wood, a poplar veneer was impregnated with low molecular-weight phenol formaldehyde (PF) resin and laminated wood was created and studied. The effects of drying temperature, drying time and solid content of the PF resin on the moisture content (MC) of the impregnated veneer after drying and the shear strength of the laminated wood were analyzed with an orthogonal experiment. The microscopic mechanism of the bonding performance of the laminated woods was investigated by fluorescence microscopy. The experimental results showed that the higher the PF resin solid content was, the larger the weight gain percentage of the impregnated veneer was. In addition to drying temperature and drying time, the solid content of PF also had a significant influence on the MC of the impregnated veneer after drying. The shear strength of the laminated wood affected by the drying temperature, solid content of PF and drying time and the drying temperature had a more significant effect than the other two factors. The best drying process was a drying temperature of 50 °C, a drying time of 2 h, and a PF solid content of 30%. The fluorescence analysis showed that the shear strength of the laminated wood was affected by the intensity of the PF resin on the bonding interface, and the average and effective penetration depth of the PF resin in the veneer increased with the increase in the drying temperature.

Fatigue behavior of beech and pine wood modified with low molecular weight phenol-formaldehyde resin

Abstract Modification of wood improves certain properties of natural wood and presents competitive alternatives to synthetic materials that may have larger environmental impacts. One aspect of modified wood that is currently not fully understood is the dynamic performance and how it is affected by the modification process. In this study, low-molecular weight phenol formaldehyde (PF) resin was applied to Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) wood. The effect of this modification was evaluated using a three-point bending test undergoing cyclic loading. Compared to reference samples, modified wood showed higher static performance but revealed a reduction in cyclic fatigue strength (9% for pine and 14% for beech). Cyclic fatigue strength of unmodified wood was found to be 67% of the static modulus of rupture for both species. With PF resin modification, the fatigue strength dropped to 58% for pine and 53% for beech. While fatigue strength decreased, there was no reduction in cyclic modulus or change in the creep rate within the stationary creep phase. It is important to consider the reduction in fatigue strength when using PF modified wood for any construction purposes with expected cyclic loading conditions.

Bolt-Bearing Yield Strength of Three-Layered Cross-Laminated Timber Treated with Phenol Formaldehyde Resin

The effect of impregnation treatment of low molecular weight phenol formaldehyde (MWPF) resin on the bolt-bearing yield strength (BBYS) of a three-layered cross-laminated timber (CLT) composed of two face layers of southern pine (Pinus taeda) and one core layer of sweetgum (Liquidambar styraciflua) was investigated together with two additional factors of material type and loading direction. Experimental results indicated that the amount of low MWPF resins penetrating into sweetgum was more than the ones into southern pine. Sweetgum had more uniform distribution of low MWPF resins penetrating longitudinally than southern pine. Impregnation treatment using a low MWPF resin at a concentration of 20% can enhance the BBYS of three-layered CLTs with a 60% increase. The BBYS of a core layer material in three-layered CLTs can significantly alter the overall BBYS of the three-layered CLTs.

Influence of drying and curing parameters on phenol-formaldehyde impregnated wood veneers

ABSTRACTThe purpose of this experimental research study was to obtain new understanding on adhesion and mechanical characteristics of impregnated spruce veneer samples wherein a low molecular weight phenol formaldehyde (PF) resin simultaneously acts both as impregnant and as adhesive. Impregnated veneer specimens were pre-dried by varying drying temperature and duration in order to obtain samples with different intermediate states of condensation. After bond formation, tensile shear strength and corresponding wood failure amount were determined. In the second part of this study, press parameters (i.e., pressing temperature and pressing time) were varied to obtain knowledge about the curing behaviour of pre-dried PF-impregnated veneer specimens. Tensile shear strength of the adhesive bond, tensile strength, the corresponding modulus of elasticity and hardness of the substrate material were determined in addition.As a result, clear effects of the various investigated parameters could be observed. While drying temperatures mainly affected the tensile shear strength, excessive pressing temperatures and times showed an impact on both, the tensile shear strength and (negatively) on the mechanical properties of the wood substrate.

Resistance improvement of rubberwood treated with zinc oxide nanoparticles and phenolic resin against white-rot fungi, Pycnoporus sanguineus

Phenolic resin or phenol formaldehyde (PF) resin containing different percentage of zinc oxide (ZnO) nanoparticles was prepared and used to treat rubberwood. Three types of treatment solutions were prepared, namely (1) low molecular weight phenol formaldehyde resin (LMwPF), (2) 1.5 wt % nano ZnO dissolved in water (ZnO/H2O), and (3) combination of both LMwPF and 1.5 wt % nano ZnO (LMwPF/ZnO). The rubberwood samples were submerged into the treatment solutions for 60, 90, and 120 min, before vacuum impregnation. The untreated rubberwood samples served as the controlled samples. The thermal stability behaviour and resistance against white-rot fungi (Pycnoporus sanguineus) of the treated rubberwood samples were evaluated. The results reveal that the treated rubberwood had slightly better thermal stability compared to the untreated samples. In terms of decay resistance, the rubberwood treated with LMwPF and LMwPF/ZnO possess very high resistance against white-rot fungi. On the other hand, the rubberwood treated with ZnO/H2O did not attain similar effectiveness as the other two treatments, except for the samples that were submerged in ZnO/H2O for 120 min. The results indicate that 1.5 wt % nano ZnO could be sufficient in imparting superior durability to rubberwood provided that longer submersion time is adopted.

The potential of phenol–formaldehyde as plasticizing agent for moulding applications of wood veneer: two-dimensional and three-dimensional moulding

Two phenol–formaldehyde resols, namely a low and a medium molecular weight phenol–formaldehyde, were investigated for their applicability as plasticizers in moulding of European beech veneer (Fagus sylvatica L.). Therefore, beech veneers specimens were impregnated with both phenol–formaldehyde resol types in various concentrations. Subsequently, two-dimensional mouldability of the veneer was tested in a three-point-bending test along and perpendicular to the grain. Additionally, three-dimensional moulding of the phenol–formaldehyde impregnated veneer was tested throughout a modified Erichsen cupping test, where the veneer is pressed through a circular shaped coining die. The obtained results indicate a significantly improved mouldability of the treated beech veneers compared to untreated, water-saturated control specimens. Even at low phenol–formaldehyde concentrations plasticizing effects were detected in longitudinal direction and perpendicular to the grain. These findings are substantiated by results from three-dimensional moulding. Furthermore, the low molecular weight phenol–formaldehyde treated veneers displayed a higher mouldability than medium molecular weight phenol–formaldehyde specimens at similar phenol–formaldehyde concentration.

The physical properties of treated oil palm veneer used as face layer for laminated veneer lumber

The depletion of our tropical timber supply has encouraged the Malaysian wood-based industry to seek alternative resources such as fast-growing plantation trees and crops for wood-based products. Oil palm tree (Elaeis guinensis) has been identified as one of the potential alternative raw materials for the production of value-added products such as plywood, laminated veneer lumber (LVL) and even solid oil palm lumber. As we know, the properties of oil palm lumber or veneer is inferior to those of wood. Modification and treatment to the oil palm are needed to enhance the quality and dimensional stability. The main objective of this study is to determine the physical properties of LVLs made from oil palm veneers (OPVs) treated with low molecular weight phenol formaldehyde (LMWPF) resin with different resin solid content and different initial moisture content (MC) of veneer. OPVs were soaked into LMWPF and re-dried to semi gel condition before being hot-pressed. There was no additional resin was added to bond the veneers together into LVL. The physical properties such as density, moisture content, thickness swelling, water absorption and weight percent gain were determined in this study. The results showed that the LVLs made by treated OPVs exhibited better physical properties compared to LVLs made from untreated OPVs but still inferior with rubberwood LVL. It can be concluded that treating OPVs prior to their usage for LVL-making is essential and effective to produce LVLs with convincing physical properties.

Properties of phenol formaldehyde resin modified with silane coupling agent (KH550)

In the present work, the organic silane coupling agent KH550 (γ-aminopropyltriethoxysilane) was added in the preparation of phenol formaldehyde (PF) resin by direct copolymerization. Such an addition modified the thermosetting low molecular weight PF resin, blocking the phenolic hydroxyl and improving its electrical insulation performance in humid environments. The volume resistance and bonding strength of the resins were tested before and after soaking in hot water. The improvement of the properties was studied in terms of resin composition and curing behavior. A common PF resin and a commercial insulation PF resin were used for the comparison. The results showed that KH550 was grafted onto the PF resin, effectively blocking the polar phenolic hydroxyl group, reducing the water absorption and increasing the volume resistance of the cured PF resin. The preparation process was simple and the prepared resin was water-soluble. The low molecular weight PF resin modified with 5% in mass of KH550 (based on the mass of phenol) exhibited better curing properties and superior volume resistance and bonding strength in humid environments.

The Influence of Media Treatments on Color Changes, Dimensional Stability, and Cracking Behavior of Bamboo Scrimber

The purpose of this study is to evaluate the influence of media treatments on color changes, dimensional stability, and cracking behavior of bamboo scrimber, which has many applications in construction. The bamboo scrimber specimens comprised bamboo bundles with a low molecular weight phenol formaldehyde resin which were manufactured via a cold-in and cold-out hot-pressing process. Small clear specimens were sampled and treated under ten different conditions: water immersion at 25°C, 63°C, and 100°C; oil immersion at 100°C and 150°C; air drying at 63°C, 100°C, and 150°C; and infrared drying at 100°C and 150°C. Then, tests were conducted to determine the color changes, dimensional stability, and cracking behavior of the bamboo scrimbers. The results showed that the bamboo scrimber specimens became darker after all treatment conditions, especially the oil treatments and infrared drying. The color of the oil-treated bamboo scrimbers was found to be more homogenous than the others. The dimensional stability of the bamboo scrimbers was more or less influenced by the water treatments, air drying, and infrared drying, and the oil-treated bamboo scrimbers were relatively stable. Moreover, during the 4-hour treatments, cracks were found in the bamboo scrimbers after air drying at 150°C or infrared drying at 100°C or 150°C.

Scrimber board (SB) manufacturing by a new method and characterization of SB’s mechanical properties and dimensional stability

Abstract A novel process has been developed for manufacturing poplar wood scrimber boards (SBs), in the course of which thick veneers are produced first and then the oriented wood fiber mats (OWFMs) are fabricated in a pilot scale fluffing machine. A low molecular weight phenol-formaldehyde (PF) resin is applied for gluing and the cold-prepressing of the mats is followed by hot-curing between 120 and 130°C for 12 h. The mechanical properties and dimensional stability of the SBOWFMs were measured. The new process resulted in significantly better mechanical properties of SBOWFMs compared with those of raw wood and other poplar wood-based composites. All data including the dimensional stability of SBOWFMs increased with increasing density.

A comparison between the properties of low and medium molecular weight phenol formaldehyde resin-treated laminated compreg oil palm wood

In order to improve the inherently poor properties of oil palm wood (OPW), this study examines the effects of resin molecular weight, diffusion time and compression ratio on the properties of laminated compreg OPW. Treating solutions used were medium molecular weight phenol formaldehyde (MmwPF) and low molecular weight phenol formaldehyde (LmwPF). OPW strips were soaked in the treating solutions for 24 h before wrapping in a plastic bag and leaving them for diffusion for 2, 4 and 6 days, respectively. Then, three-layer laminated compreg OPW were fabricated and compressed in hot press at 150°C for 20 minutes to achieve compression ratios of 55%, 70% and 80%. Results indicated that dimensional stability and mechanical properties of the phenolic resin treated laminated compreg OPW were significantly better than the untreated laminates. MmwPF-treated laminates exhibited inferior properties in comparison to that of LmwPF-treated laminates. Nevertheless, MmwPF-treated laminated compreg OPW emitted significantly lesser formaldehyde.