Low Molecular Weight Phenol Formaldehyde Resin Research Articles

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.

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.

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.

Tensile and Impact Bending Properties of Chemically Modified Scots Pine

This study deals with the influence of chemical modification on elasto-mechanical properties of Scots pine (Pinus sylvestris L.). The elasto-mechanical properties examined were impact bending strength, determined by impact bending test; tensile strength; and work to maximum load in traction, determined by tensile tests. The modification agents used were one melamine-formaldehyde resin (MF), one low molecular weight phenol-formaldehyde resin, one higher molecular weight phenol-formaldehyde resin, and a dimethylol dihydroxyethyleneurea (DMDHEU). Special attention was paid to the influence of the solution concentration (0.5%, 5%, and 20%). With an increase in the concentration of each modification agent, the elasto-mechanical properties decreased as compared to the control specimens. Especially impact bending strength decreased greatly by modifications with the 0.5% solutions of each agent (by 37% to 47%). Modification with DMDHEU resulted in the highest overall reduction of the elasto-mechanical properties examined (up to 81% in work to maximum load in traction at 20% solution concentration). The results indicate that embrittlement is not primarily related to the degree of modification depended on used solution concentration. It is therefore assumed that molecular size and the resulting ability to penetrate into the cell wall could be crucial. The results show that, in the application of chemically modified wood, impact and tensile loads should be avoided even after treatment with low concentrations.

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.

Possibility of enhancing the dimensional stability of jelutong (Dyera costulata) wood using glyoxalated alkali lignin-phenolic resin as bulking agent

The utilization of low molecular weight phenol formaldehyde (LmwPF) resin as bulking agent to enhance the dimensional stability of wood brought some disadvantages, such as phenol is derived from non-renewable petrochemicals while formaldehyde is a known carcinogen. Hence, the possibility of using bulking agent made of glyoxalated alkali lignin (GL) incorporated in LmwPF resin to enhance the dimensional stability of wood was investigated. FT-IR spectroscopy showed that polymerization of GL and LmwPF resin was accomplished via the formation of methyl ether (CH2OCH2) bridge. Small amount of crosslinked polymer network was accomplished via the formation of methylene (CH2) bridge. Oven dried jelutong wood was evacuated under vacuum followed by soaking in 15, 20 and 25% concentrations of glyoxalated alkali lignin-low molecular weight phenol formaldehyde (GL-LmwPF) (67% solid of GL: 33% solid of LmwPF based on the total solute content) and LmwPF resins, respectively at ambient temperature for 24 h. The impregnated wood was then cured at 190 °C for 30 min. The weight percent gain (WPG) and dimensional stability in terms of antiswelling efficiency (ASE), moisture excluding efficiency (MEE) and water absorption (WA) as well as leachability of bulking agents were determined and compared with untreated wood and wood treated solely with LmwPF resin. The WPG of GL-LmwPF treated wood was lower than LmwPF treated wood. GL-LmwPF treated wood exhibited positive ASE, but the values were lower compared to LmwPF treated wood. The MEE and WA of GL-LmwPF treated wood were also inferior to LmwPF treated wood and untreated wood. GL-LmwPF resin was leached out from the treated wood whereas no leaching was found for LmwPF treated wood after three leaching cycles in distilled water. The formaldehyde release of GL-LmwPF resin treated wood was 25.76% less than of wood treated with LmwPF resin. Wood treated with 25% GL-LmwPF resin yielded highest ASE value compared to 15 and 20% GL-LmwPF treated wood. Hence, wood treated with 25% GL-LmwPF resin together with external coatings could be used in several end applications such as parquet flooring, paneling and furniture component.

Characterisation of phenolic resin and nanoclay admixture and its effect on impreg wood

Bulking treatment with low molecular weight phenol formaldehyde (LmwPF) resin has been found to successfully enhance the properties of low-density wood but emit higher formaldehyde. Incorporation of nanoparticle to the phenolic matrix could possibly reduce the use of high concentration LmwPF and thus lower the formaldehyde emission (FE) without adversely affecting the other properties. The aim of the study was to examine the characteristics of LmwPF resin and nanoclay admixture and determine its effects on the performance of impreg wood. Montmorillonite nanoclay nanomer (0.5–1.5 % w/w based on solid PF) was dispersed in LmwPF resin (10–20 % w/v) using ultrasonication technique. The dispersion of nanoclay in LmwPF was examined using X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM). XRD and TEM analyses confirmed that the nanoclay dispersion in the resin was in exfoliated form. Air-dried sesenduk (Endospermum diadenum) wood was impregnated with these admixtures using vacuum pressure process followed by curing at 150 °C for 30 min. The FE, dimensional stability and strength properties were evaluated and compared with impreg wood treated solely with LmwPF. The results showed that the polymer retention and density of the LmwPF/nanoclay-impregnated samples were higher than the LmwPF-impregnated samples. This admixture had successfully bulked the cell wall of the wood and imparted higher dimensional stability to the treated wood. The modulus of rupture and modulus of elasticity, compressive stress and hardness of the LmwPF/nanoclay impreg were more superior compared to the LmwPF impreg. The admixture was also found to be able to reduce the FE compared to LmwPF resin.

Decay Resistance of Medium Density Fibreboard (MDF) Made from Pineapple Leaf Fiber

Medium density fiberboard (MDF) production is increasing due to the development of manufacturing technologies. MDF products are utilized for traditional wood applications that require fungal resistance. This study investigated some of the important biodegradation properties of MDF composite board made from renewable biomass from pineapple leaf fiber ( Ananas comosus ). The variable factors were type of board and type of resin. Two different types of board with a target density of 0.8 g/cm3 were manufactured. The boards were prepared in three layers of about 1:1:1 weight ratio in crossoriented and unidirectional pattern, using low molecular weight (LM) phenol formaldehyde (PF) resin type PL-3725 and high molecular weight (HM) PF resin type PL-2818 for impregnation and adhesive purposes. Decay resistance (white and brown rot fungi) of the MDF was evaluated to assess its biological performance. In this study, fiber orientation had no effect on the decay resistance to white and brown rot fungi of the specimens. However, a slight increase was found for the mass loss of the low molecular weight PF resin board specimens compared with the mixed low and high molecular PF resin board specimens. The total resin content of 20% of the type I boards prohibits degradation by decay.

The Effect of Microwave Pretreatment on the Impregnation of Poplar Wood

Microwave pretreatment can increase the transverse permeability of wood. The effects of impregnation on microwave-pretreated wood with low-molecular weight phenol formaldehyde resin was investigated. The results showed that the improved transverse permeability of poplar wood that had received microwave pretreatment resulted in a positive influence on the effect of the impregnation. The maximum impregnation weight gain rate was 51.08%, with the average being approximately 40%. The average density of the specimens impregnated for 1.50 h at 0.8 MPa was 584.8 kg•m-3. During the course of the study, the resin present in the wood became distributed evenly in the vessel elements, wood fiber lumens, and intercellular spaces. Finally, the chromogenic reaction area accounted for 78.11% of the total area in the fluorescent staining diagram of the cross section.

Investigation of Low-molecular Weight Phenol Formaldehyde Distribution in Tracheid Cell Walls of Chinese Fir Wood

Treatment with water-soluble low-molecular weight phenol-formaldehyde resin is an effective method to improve wood properties. In this paper, plantation wood of Chinese fir was modified with low-molecular weight phenol-formaldehyde resin. The absorbance by tracheid cell walls of phenol-formaldehyde resin in treated and untreated reference samples were measured with an ultraviolet micro-spectrophotometer. The UV absorbance values of earlywood tracheids and middle lamella in treated wood were significantly increased, with an average increase of 49% and 23%, respectively. Moreover, after treatment with low-molecular weight phenol-formaldehyde resin, the UV absorbance of the earlywood tracheid cell walls of Chinese fir increased to more than 47%, regardless of whether or not the cell lumens were filled with resin. After treatment with low-molecular weight phenol-formaldehyde resin, the UV absorbance of earlywood tracheid cell walls at different locations did not vary greatly. This study provides direct support for the improvement of the physical and mechanical properties of resin-modified Chinese fir in terms of penetration of the resin into the cell walls.

Durability of phenolic-resin-treated oil palm wood against subterranean termites a white-rot fungus

Oil palm wood (OPW) is seen as a strategic alternative wood material, especially in a country with huge oil-palm-planted areas such as Malaysia. The material is low in quality and various techniques have been used to improve its quality. This study was carried out to evaluate the resistance of low-molecular-weight phenol formaldehyde (Lmw-PF) resin treated OPW against subterranean termites and a white-rot fungus. Four sample groups including untreated OPW and treated OPW samples with three different compression levels (0%, 25%, and 50%) were prepared. Five specimens for each sample group were tested for resistance against subterranean termites (Coptotermes curvignathus) and the white-rot fungus Pycnoporous sanguineus, based on ASTM D 3345-74 and ASTM D 1413-99, respectively. Results showed that both treatment and compression level had significant effects on the percentage weight loss and mean decayed surface of the samples. Treated OPW with 50% compression yielded the best performance with the lowest weight loss on both termite and decay tests. Overall, Lmw-PF resin treated OPW with 25–50% compression can be used as an effective method to improve the durability of OPW.

Photostabilization of wood using low molecular weight phenol formaldehyde resin and hindered amine light stabilizer

Phenol formaldehyde (PF) resin containing low molecular weight hydroxymethyl phenol species and a water soluble hindered amine light stabilizer (HALS) was synthesized and used to treat wood veneers. Treated veneers were exposed to natural weathering for 25, 35 and 50 days and the effectiveness of the modified PF resins as photoprotective treatments for wood was assessed. We hypothesized that the photostability of veneers would be positively correlated with concentration of PF resin (10, 20 and 30% w/v) and HALS (1 or 2% w/w) in solutions used to treat veneers. There was an inverse relationship between resin concentration in treatment solutions and tensile strength losses of treated veneers exposed to natural weathering. Mass losses of veneers treated with solutions containing 20 or 30% PF resin were lower than those of veneers treated with 10% PF resin. The addition of 2% HALS to solutions containing 30% PF resin had a significant (p < 0.05) effect at restricting mass and tensile strength losses of treated veneers exposed to the weather for 50 days. A PF resin treatment containing 30% resin and 2% HALS was as effective as chromic acid (a noted photostabilizer for wood) at restricting mass and tensile strength losses of veneers during natural weathering. Treated veneer in a plywood-type composite became darker and redder when exposed outdoors, but the addition of HALS to the resin restricted color changes of veneer treated with 10% PF resin. A 30% PF resin treatment on its own or containing 2% HALS protected wood's cellular structure from destruction during accelerated weathering and restricted, but did not prevent, delignification of wood. We conclude that the effectiveness of low molecular weight PF resin as a photoprotective treatment for wood can be improved by increasing the concentration of PF resin and by combining it with a water soluble HALS.

Effects of treatment with low molecular weight phenol formaldehyde resin on the surface characteristics of oil palm (Elaeis quineensis) stem veneer

Even though oil palm (Elaeis quineensis) stem (OPS) is highly potential as an alternative raw material in wood industry, it possesses some inferior characteristics. One of the critical weaknesses is a high degree of veneer surface roughness that resulted in high resin consumption during plywood manufacture. The objective of this study was to investigate effects of treatment with low molecular weight phenol formaldehyde (LMWPF) resin on the wettability and surface roughness of OPS veneer. OPS veneers were segregated into two categories namely outer and inner layer veneer, prior to soaking in LMWPF resin solution to obtain weight percent gain of 16–20%. The wettability of OPS veneers was assessed with contact angle measurement according to the sessile drop method. The veneer surface roughness was evaluated by determining the average roughness (Ra), mean peak-to-valley height (Rz), and maximum roughness (Rmax) using a stylus profilometer in accordance with DIN standard 4768. The results show that the effect of LMWPF resin treatment on the surface roughness of the veneers is statistically significant. The technique used in the study was able to enhance the surface properties as well as improved the physical and mechanical properties of OPS plywood.

Acacia mangium Tannin as Formaldehyde Scavenger for Low Molecular Weight Phenol-Formaldehyde Resin in Bonding Tropical Plywood

One of the limitations in using low molecular weight phenol-formaldehyde (LmwPF) resin as a binder for wood-based panels is the amount of the free formaldehyde being emitted during soaking, pressing and sometimes during the earlier stage of application. Tannin from bark extracts is rich in phenolic compounds, and thus may be able to absorb this free formaldehyde and at the same time provide strength to the joint. In this study, tannin–phenol-formaldehyde adhesives were prepared by blending Acacia mangium bark extracts (40% solids) with low molecular weight phenol-formaldehyde (40% solids at 1:1 ratio). The tannin–LmwPF adhesive produced cured within 4 min at 130°C, reduced the free formaldehyde to level E1 of European norm EN-120. The 3-ply plywood had acceptable shear strength (>1.0 MPa) exceeding the minimum requirements of European norms EN-314-1 and EN-314-2:1993 for interior and exterior applications, respectively. The study has shown that Acacia mangium tannin can be used as formaldehyde scavenger in LmwPF resin without compromising the strength of the joints.

Properties Enhancement of Oil Palm Plywood through Veneer Pretreatment with Low Molecular Weight Phenol-Formaldehyde Resin

One of the problems dealing with oil palm stem (OPS) plywood is the high veneer surface roughness that results in high resin consumption during the plywood manufacturing. In this study, evaluation was done on the effects of pretreatment of OPS veneers with phenol-formaldehyde resin on the bond integrity and bending strength of OPS plywood. OPS veneers were soaked in low molecular weight phenol-formaldehyde resin (LMW PF) for 20 seconds to obtain certain percentage of resin weight gain. OPS plywoods were produced using two types of lay-ups (100% outer veneer type and 100% inner veneer type) and two urea-formaldehyde (UF) adhesive spread amounts (200 g/m2 and 250 g/m2). The results show that pretreating the veneer with LMW PF could reduce the penetration of the adhesive into the fibres during gluing step. UF adhesive spread amount of 200 g/m2 is sufficient to produce good quality OPS plywood. The technique used in this study was able to enhance the mechanical properties of OPS plywood as well as reduce the amount of resin consumption.

Effect of curing time on physical and mechanical properties of phenolic-treated bamboo strips

Effect of pressing time on physical and mechanical properties of phenolic-impregnated bamboo strips was evaluated. Bamboo strips ( Gigantochloa scortechinii) were impregnated with low molecular weight phenol formaldehyde (LMwPF) resin. Samples were submerged in LMwPF resin using a vacuum chamber of 750 mmHg for 1 h before it was released within 1.5 h. Treated strips were dried in an oven with a temperature of 60 °C within 6–9 h. It was hot pressed at 14 kg m −2 and a temperature of 140 °C for 5, 8, 11, 14 and 17 min. The physical and mechanical properties of the test indicated that the properties of phenolic-treated strips have significantly increased as compared to control samples. Dimensional stability (water absorption, thickness swelling and linear expansion) of the phenolic-treated properties were significantly lower than control after 5-min pressing time. The antishrink efficiency (ASE) of phenolic-treated strips increased when pressing time were extended from 5 to 17 min. The mean value of modulus of rupture (MOR) for the control samples (177 N mm −2) showed a significant difference with phenolic-treated strips after 17-min pressing time (224 N mm −2). However, there is no significant difference in compression parallel to grain. The MOE of phenolic-treated strips was 21,777 N mm −2 and for control was 18,249 N mm −2, whereas the compression parallel to grain values for phenolic-treated and control samples were 94 and at 77 N mm −2, respectively.

Strength, decay and termite resistance of oriented kenaf fiberboards

The development of oriented fiberboards made from kenaf (Hibiscus cannabinus L.) and their suitability as a construction material has been investigated. Three different types of boards consisting of five layers with individual orientations were prepared using a combination of low molecular weight and high molecular weight phenol-formaldehyde (PF) resin for impregnation and adhesion purposes. Additional boards with the same structure were prepared using high molecular weight PF resin only. The mechanical properties of the boards have been examined as well as their resistance against fungal decay and termite attack. All kenaf fiberboards showed elevated mechanical properties compared with medium-density fiberboard made from wood fibers, and showed increased decay and termite resistance. Differences in the decay and termite resistance between the board types were caused by the presence of the low molecular weight PF resin for the impregnation of the fibers. No significant difference was found for the mechanical properties. The effect of the PF resin for impregnation was much clearer in fungal decay resistance than for termite resistance; however, fiber orientation had no effect on both decay and termite resistance of the specimens.

Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin V: effects of steam pretreatment

This study evaluated the potential of steam pre-treatment for making highly compressed phenol-formaldehyde (PF) resin-impregnated wood at a low pressing pressure. Sawn veneers of Japanese cedar (Cryptomeria japonica) were first subjected to saturated steam at different steaming temperatures (140°-200°C), followed by impregnation with a 20% low molecular weight PF resin aqueous solution resulting in a weight gain of around 50%-55%. Four oven-dried treated veneers were laminated and compressed up to a pressing pressure of 1 MPa at a pressing temperature of 150°C and pressing speed of 5 mm/min, and the pressure was held for 30 min. Steam treatment, causing partial hydrolysis of hemicellulose, accelerated the compressibility of Japanese cedar in the PF resin-swollen condition. As a consequence, a discernible increment in density was achieved at a pressing pressure of 1 MPa due to steam pretreatment between 140° and 200°C for 10 min. It was also found that even a short steaming time such as 2 min at 160°C is sufficient for obtaining appreciable compression of PF resin-impregnated wood. The density, Young’s modulus, and bending strength of steam-treated (200°C for 10 min) PF resin-impregnated wood composite reached 1.09 g/cm3, 20 GPa, and 207MPa, respectively. In contrast, the values of untreated PF resin-impregnated wood composite were 0.87 g/cm3, 13 GPa, and 170MPa, respectively.

A morphological study of the wood/phenol-formaldehyde adhesive interphase

This paper evaluates the morphology of the wood/phenol-formaldehyde adhesive interphase by dynamic mechanical analysis and 13C CP/MAS NMR. It is shown that a low molecular weight phenol-formaldehyde (PF) resin (M n = 270 g/mol, M w /M n = 1.2) interacts with the wood cell wall polymers on the nanometer scale, as demonstrated by enhanced intermolecular coupling near the main glass transition of wood lignin. With CP/MAS NMR, T H 1ρ measurements indicated that the low molecular weight PF significantly increased the relaxation time of wood polymers. Nanoscale miscibility is proposed to occur for the low molecular weight PF resin and amorphous wood polymers. On the other hand, a high molecular weight PF resin with a broad distribution of molecular weights (M n = 2840 g/mol, M w/M n = 5.0) did not enhance the intermolecular cooperativity around the glass transition but rather enhanced molecular motions, as indicated by a lower glass transition temperature of the composite. The high molecular weight resin did not affect the T H 1ρ of wood polymers, suggesting an overall phase separated system. The enhanced molecular motions in the PF-High composites were attributed to a low molecular weight fraction that effectively penetrated the wood structure while remaining uncrosslinked and thus acting as an internal plasticizer.

Compressive deformation of wood impregnated with low molecular weight phenol formaldehyde (PF) resin III: effects of sodium chlorite treatment

To obtain high-strength phenol–formaldehyde (PF) resin-impregnated compressed wood at low pressing pressure, we investigated the effects of sodium chlorite (NaClO2) treatment on wood prior to low molecular weight PF resin impregnation. Sawn veneers of Japanese cedar (Cryptomeria japonica) were treated with 2% aqueous NaClO2 solution at 45°C for 12 h to remove lignin, and the process was repeated up to four times, resulting in weight loss of 21%. NaClO2 treatment has shown considerable potential for high compression of PF resin-impregnated wood at low pressing pressure, especially after adding moisture to a content of 10%–11%. This deformation is further enhanced during pressure holding by creep deformation. The density, Young’s modulus, and bending strength of PF resin-impregnated veneer laminated composites that were treated with NaClO2 four times and compressed at 1 MPa, reached 1.15 g/cm3, 27 GPa, and 280 MPa, respectively. The values in untreated PF resin-impregnated wood reached 0.8 g/cm3, 16 GPa, and 165 MPa, respectively.