Formaldehyde Resol Resins Research Articles

Rheological Study of Phenol Formaldehyde Resole Resin Synthesized for Laminate Application.

Heat explosions are sometimes observed during the synthesis of phenol formaldehyde (PF) resin. This scenario can be attributed to the high latent heat that was released and not dissipated leading to the occurrence of a runaway reaction. The synthesis temperature and time played important roles in controlling the heat release, hence preventing the resin from hardening during the synthesis process. This study aims to assess the rheological and viscoelasticity behaviors of the PF resin prepared using paraformaldehyde. The prepared PF resin was designed for laminate applications. The rheological behavior of the PF resin was assessed based on the different molar ratios of phenol to paraformaldehyde (P:F) mixed in the formulation. The molar ratios were set at 1.00:1.25, 1.00:1.50 and 1.00:1.75 of P to F, respectively. The rheological study was focused at specific synthesis temperatures, namely 40, 60, 80 and 100 °C. The synthesis time was observed for 240 min; changes in physical structure and viscosity of the PF resins were noted. It was observed that the viscosity values of the PF resins prepared were directly proportional to the synthesis temperature and the formaldehyde content. The PF resin also exhibited shear thickening behavior for all samples synthesized at 60 °C and above. For all PF resin samples synthesized at 60 °C and above, their viscoelasticity results indicated that the storage modulus (G′), loss modulus(G″) and tan δ are proportionally dependent on both the synthesis temperature and the formaldehyde content. Heat explosions were observed during the synthesis of PF resin at the synthesis temperature of 100 °C. This scenario can lead to possible runaway reaction which can also compromise the safety of the operators.

Structural Characterization of Cure Bio-based Phenol Formaldehyde Wood Adhesive

Bio-phenol formaldehyde (BPF) resole resins were characterized by liquid-state 13C Nuclear Magnetic Resonance (NMR) spectroscopy. The liquid 13C NMR analysis indicated that the condensation reactions between the bark phenolic compounds and the formaldehyde occurred during the synthesis of the resins. Methylene ether bridges in the resins were more pronounced in the BPF resin when compared to the PF resin system. The liquid-state 13C NMR study revealed significant differences in the resins structures induced by the inclusion of bark-phenolic components. The bark-phenolic components favored the formation of para-ortho methylene linkages in the BPF resins and also enhanced the cure rate of the BPF resin system.

Thermal Kinetics and Post Curing Thermal Stability of Bio-Based Phenol Formaldehyde Resins for Its Potential in Particleboard Production

The thermal degradation kinetics and post curing behavior of phenol-formaldehyde and Bio-phenol formaldehyde (BPF) resole resins were investigated with thermogravimetry analysis at four different heating rates (5, 10, 15 and 20°C/min) from 25 to 700°C. The curing reaction for all the resole resins proved to be approximately 1st order, and the activation energies of the BPF resins at 25 wt% and 50 wt% bio-phenol replacement were 132.2 kJ/mol and 131.6 kJ/mol. These were comparable to that of the laboratory synthesized pure PF resin 131.0 kJ/mol but also remarkably lower than the commercial PF resin (138.1 kJ/mol) respectively. The result of the thermal degradation kinetics showed that the post-curing thermal stability of the 25 and 50 wt% BPF resins were similar to that of the commercial and laboratory synthesized pure PF resin but, that of 75 wt% differed from the commercial or laboratory synthesized PF resin.

Studies on Synthesis, Characterization of Modified Phenol Formaldehyde Resin and Metal Adsorption of Modified Resin Derived From Lignin Biomass

This study was related to development of economically viable method of extraction of lignin from saw dust in order to produce lignin modified phenolic resin and ecofriendly adhesives (bio-based resin). This study cover to improve the mechanical properties by modification of phenol formaldehyde resole resin using some additives such as boric acid, sulfuric acid and lignin biomass. The synthesis and metal adsorption capacity of resin derived from lignin biomass were explored. Lignin sample was extracted from sawdust of Acacia sp. collected from Batticaloa region by alkali extraction method called delignification process. Qualitative tests were carried out on the extracted alkali lignin and it was used to prepare modified resin. Resin synthesized by using lignin substitution phenol and allowed to condensation reaction in the presence of sodium hydroxide. Boron-modified phenol formaldehyde resin was prepared by using boric acid with formalim method. The above reaction was performed for four hours by refluxing with toluene. Which was produced a high viscous massive resin with 90% yield. The absorbtion peak of B-O bond at 1362cm-1 was observed at IR spectra. Rise in solid mass content leads to produce smooth resin surface without causing cracks and bubbling. Phenol formaldehyde resin was modified into their sulfonated forms to increase their ion exchange capacity, since the ion exchange capacity of virgin resin was found to be zero. Conductivity property shown by sulfonated resin(121mS/cm). The synthesized Lignin based PF resin was used to study the metal adsorption capacity of Cd2+ in aqueous solution. The adsorption capacity of heavy metal Cd2+ ion shown by lignin modified resin (55%) and lignin (86%). In this study sawdust lignin could be best substitution for phenol in synthesis of Phenol-Formaldehyde resin. It’s better due to their sustainability, environmental control, low production cost and their ability to adsorb heavy metals. Phenolic resin was modified with boric acid to improve thermal resistance property and to get smooth resin surface.

Effect of charcoal on formaldehyde emission, mechanical, thermal and dynamic properties of resol resin

The effect of charcoal (CH), on reducing the emission of free formaldehyde from phenol–formaldehyde resol resins and the properties of the modified resins were investigated. The reduction of free formaldehyde content (FFC) of the resol resin was monitored by Waker’s titration method. The charcoal was found to be very effective in reducing the FFC of the resin due to its high porosity and large surface area. With the incorporation of charcoal the free formaldehyde content of resol resin was almost reduced to zero. The mechanical properties of the PF resin were improved by modification with charcoal. SEM micrographs of tensile fractured surfaces were in agreement with improved mechanical properties. Modified samples exhibited improvements in elastic modulus, loss modulus and tan delta as indicated by dynamic mechanical analysis. The activation energy for the relaxation process in the glass transition region increased with the increase in the amount of charcoal. The thermogravimetric analysis showed that the charcoal had only marginal influence on the thermal stability of the resin.

Characterization of Modified Phenol Formaldehyde Resole Resins Synthesized in Situ with Various Boron Compounds

In this study, three different boron compounds were used together with alkaline catalyst to synthesize phenol formaldehyde (PF) resole resins in situ. The resin curing behavior, molecular structure, bonding performance, and properties of resin-impregnated wood were investigated. Results showed that boron compound-modified PF resins had a lower degree of polymerization than the control PF resin made in the laboratory. The curing kinetics, molecular structure, and functional groups of the modified resins varied depending on the type of boron compounds used. The thermal stability of cured modified PF resins was slightly lower than that of laboratory-made control PF resin. Boron compound-modified PF resins exhibited dry and wet bonding strengths comparable to the those of the laboratory-made control PF resin. Wood impregnated using modified PF resins had comparable dimensional stability, mechanical properties and improved fire resistance than the wood impregnated using lab made control PF resin regardless the type of boron compounds used.

Cure Kinetics, Bonding Performance, Thermal Degradation, and Biocidal Studies of Phenol-Formaldehyde Resins Modified with Crude Bio-oil Prepared from Ziziphus mauritiana Endocarps

Crude bio-oil, extracted from endocarp bio-waste of Ziziphus mauritiana by direct liquefaction (ethanol-water 1:1 w/w; 300 °C), was used to replace petro-phenol (30% to 75% w/w) in the development of bio-oil-phenol formaldehyde (BPF) resol resins. Cure kinetics of the BPF resins were studied by the DSC method, while the thermal degradation was studied by the TGA method. Bonding performance of the BPF resins was measured by single lap-shear method, while biocidal properties were investigated by antifungal index (%) and termite mortality (%) test. The DSC studies revealed that beyond 45% bio-oil incorporation (BOI), the curing process of the BPF resins got deferred. The TGA studies showed that BOI decreased the thermal stability of the BPF resins by lowering the decomposition temperatures and the char residue. The measured values of antifungal index (%) and termite mortality (%) revealed that incorporation of bio-oil enhanced the fungal and termite resistance of the resins. From data of thermal cure, bonding strength, thermal stability, and biocidal properties of the BPF resins it appears that petro-phenol could be substituted by up to 45% w/w of crude bio-oil safely in the development of bio-oil-phenol formaldehyde resol resins.

Recent Development in Forest Biomass Derived Phenol Formaldehyde (PF) Resol Resin for Wood Adhesives Application

Recent Development in Forest Biomass Derived Phenol Formaldehyde (PF) Resol Resin for Wood Adhesives Application

Characterization of Phenol-Formaldehyde Resins Modified with Crude Bio-oil Prepared from Ziziphus mauritiana Endocarps

This study was conducted to evaluate the effects of bio-oil incorporation on properties of bio-oil-phenol formaldehyde (BPF) resol resins along with the optimization of petro-phenol substitution level. Crude bio-oil prepared from endocarp shells of Ziziphus mauritiana by direct solvolytic liquefaction (ethanol-water 1:1 wt./wt. at 300 °C) was used to partially substitute the petro-phenol (30% to 75% wt./wt.) in the resin synthesis. The modified resins were subjected to measurement of various properties, including molecular weight, pH, viscosity, density, gel/cure time, non-volatile solid content, and limiting oxygen index. Bonding performance of the BPF resins was evaluated by measuring the mechanical and hygroscopic properties of the particle boards developed using such resins. With the incorporation of bio-oil, the viscosity and molecular weight of the BPF resins increased, while the values of pH, density, non-volatile solid content, and limiting oxygen index decreased. The gel, cure, and bonding tests revealed that with the addition of more than 45% bio-oil, the gel/cure times of the BPF resins increased, while the bonding performance decreased. Petro-phenol could therefore be substituted by crude bio-oil up to 45% wt./wt. safely.

Synthesis and characterization of valonea tannin resin and its interaction with palladium (II), rhodium (III) chloro complexes

Valonea tannin (TA) and formaldehyde condensation reaction was carried out under alkaline condition to prepare the valonea tannin–formaldehyde resol resin (TAR). Obtained resin was used as adsorbent for recovery of palladium (II) and rhodium (III) ions from chloride-containing solutions. This kind of recovery was very simple and useful for generating little secondary wastes. Interaction of adsorption also was investigated: Chloropalladium (II) species were reduced to Pd(0), while hydroxyl groups of TAR were oxidized during the adsorption. Proposed adsorption of the aquachlororhodium (III) species mostly takes place via ligand exchange mechanism. TAR, Rh-adsorbed TAR, and Pd-adsorbed TAR were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction spectroscopy, and Fourier transform infrared–attenuated total reflection spectroscopy.

Synthesis and Characterization of Pyrogallol-Formaldehyde Nano Resin and Its Usage as an Adsorbent

A pyrogallol (PG) and formaldehyde condensation reaction was carried out under alkaline conditions to prepare the pyrogallol–formaldehyde resol resin (PGNR). Polymerization was performed to establish the nano resin formation. Obtained nano resin was used as an adsorbent for recovery of rhodium(III) ions from chloride-containing solutions. This kind of recovery was very simple and useful for generating little secondary wastes. The interaction of adsorption also was investigated: The proposed adsorption of the aquachlororhodium(III) species mostly takes place via a ligand exchange mechanism. PGNR and Rh-adsorbed PGNR were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction spectroscopy, and Fourier transform infrared–attenuated total reflection spectroscopy. By utilizing such characteristics of polyphenol resin, PGNR can be applied to recover Rh(III) efficiently and simply with low cost.

Synthesis of biobased phenolic resins/adhesives with methylolated wood‐derived bio‐oil

AbstractBio‐oil from the hydrothermal liquefaction of Eastern White Pine (Pinus strobus L.) sawdust was methylolated with formaldehyde in the presence of sodium hydroxide. The obtained methylolated bio‐oil (MB) was used to synthesize methylolated bio‐oil–phenol formaldehyde (MBPF) resol resins with a phenol substitution ratio of up to 75 wt %. All of the resins were used as wood adhesives for the production of a three‐layered plywood. The MBPF resol resins were comprehensively characterized for their physical, chemical, thermal, and mechanical properties (e.g., viscosity, nonvolatile content, shelf life, free formaldehyde level, molecular weight and distribution, curing temperature, bonding strength) when used as plywood adhesives. All of the MBPF resins contained similar nonvolatile contents as the reference pure phenol formaldehyde (PF) resin but had higher viscosities and shorter shelf lives, depending on the amount of MB in the MBPF. All of the MBPF resins displayed a lower curing temperature than the reference PF resin, with the main curing peak around 140°C, which was similar to that of the pure PF resin. According to thermogravimetric analysis, the methylolation treatment of bio‐oil improved the thermal stability of the MBPF resins compared to the bio‐oil–PF resol resins, which used untreated bio‐oil. The dry/wet bonding strengths of the plywood specimens glued with the MBPF resol resins with up to 60 wt % phenol substitution exceeded or were comparable to those of the conventional PF resol resin. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Synthesis and Characterization of Gallic Acid Resin and Its Interaction with Palladium(II), Rhodium(III) Chloro Complexes

Gallic acid (GA) and formaldehyde condensation reaction was carried out under alkaline condition to prepare the gallic acid–formaldehyde resol resin (GAR). Obtained resin was used as adsorbent for recovery of palladium(II) and rhodium(III) ions from chloride-containing solutions. This kind of recovery was very simple and useful for generating little secondary wastes. Interaction of adsorption also was investigated: Chloropalladium(II) species were reduced to Pd(0), while hydroxyl groups of GAR were oxidized during the adsorption. Proposed adsorption of the aquachlororhodium(III) species mostly takes place via ligand exchange mechanism. GAR, Rh-adsorbed GAR, and Pd-adsorbed GAR were characterized by scanning electron microscopy, energy-dispersive spectrometry, X-ray diffraction spectroscopy, and Fourier transform infrared–attenuated total reflection spectroscopy.

Use of biocrude derived from woody biomass to substitute phenol at a high‐substitution level for the production of biobased phenolic resol resins

AbstractPhenolic bio‐oil produced by the direct liquefaction of Eastern white pine (Pinus Strobus L.) sawdust in a hot‐compressed ethanol‐water (1:1 w/w) medium at 300 °C was used to partially substitute for phenol in the synthesis of bio‐oil‐phenol‐formaldehyde (BPF) resol resins. Bio‐based resol resins with high levels of phenol substitution (up to 75 wt%) could be used as plywood adhesives because of the low molecular weights found for the phenolic bio‐oil (weight‐average molecular weight = 1072 g/mol, number‐average molecular weight = 342 g/mol). The properties of the BPF resol resins were analyzed by differential scanning calorimetry, Fourier transform infrared spectroscopy, gel permeation chromatography, and thermogravimetric analysis. All of the experimental BPF resins possessed broad molecular weight distributions but had similar chemical/thermal properties compared to a conventional phenol–formaldehyde (PF) resol resin reference (or 0 wt % BPF resin). The BPFs exhibited the typical properties of a thermosetting PF resin, for example, an exothermic curing temperature of 140–150°C and an acceptable residual carbon yield of 48–72 wt % nonvolatile content at 700°C. The experimental BPFs were applied as adhesives in the assembly of plywood, and then, the dry/wet tensile strengths were evaluated. The tensile strengths of the dry plywood samples bonded with the BPF resins up to a high ratio value of 75 wt % bio‐oil exceeded or were comparable to that of the conventional pure PF resin adhesive. All of the BPF‐resin‐bonded plywood samples gave wet tensile strengths comparable to those of the conventional PF adhesive. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Thermal degradation of lignin–phenol–formaldehyde and phenol–formaldehyde resol resins

Resol resins are used in many industrial applications as adhesives and coatings, but few studies have examined their thermal degradation. In this work, the thermal stability and thermal degradation kinetics of phenol–formaldehyde (PF) and lignin–phenol–formaldehyde (LPF) resol resins were studied using thermogravimetric analysis (TG) in air and nitrogen atmospheres in order to understand the steps of degradation and to improve their stabilities in industrial applications. The thermal stability of samples was estimated by measuring the degradation temperature (T d), which was calculated according to the maximum reaction rate criterion. In addition, the ash content was determined at 800 °C in order to compare the thermal stability of the resol resin samples. The results indicate that 30 wt% ammonium lignin sulfonate (lignin derivative) as filler in the formulation of LPF resin improves the thermal stability in comparison with PF commercial resin. The activation energies of degradation of two resol resins show a difference in dependence on mass loss, which allows these resins to be distinguished. In addition, the structural changes of both resins during thermal degradation were studied by Fourier transform infrared spectroscopy (FTIR), with the results indicating that PF resin collapses at 300 °C whereas the LPF resin collapses at 500 °C.

Synthesis of phenol–formaldehyde resol resins using organosolv pine lignins

Lignin was extracted from white pine sawdust by organosolv-extraction using hot-compressed ethanol–water co-solvent. The optimum conditions for extracting lignin from the pine sawdust were found to be at 180 °C with ethanol–water solvent (1:1 wt/wt), where the lignin yield attained ca. 26% with a purity of ca. 83%. The lignin under such conditions was oligomers with a broad molecular weights distribution: M n of 537, M w of 1150 and polydispersity of 2.14. Bio-based phenol–formaldehyde resol resins were synthesized using the resultant lignin as the replacement of petroleum-based phenol at varying ratios from 25 to 75 wt.% by condensation polymerization catalyzed by sodium hydroxide. Upon heating the lignin–phenol–formaldehyde resols could solidify with a main exothermic peak at around 150–175 °C, typical of the conventional phenolic resol resins, and a secondary peak at 135–145 °C, likely due to the exothermic reactions between the free formaldehyde with phenol or lignin to form methylophenols. The replacement of phenol with lignin at a large ratio deferred the curing process, and the introduction of lignin in the resin formula decreased the thermal stability of the resin, leading to a lowered decomposition temperature and a reduced amount of carbon residue at elevated temperatures. For practical applications, it is suggested that the replacement ratio of phenol with lignin be less than 50 wt.%. The thermal stability can however be improved by purifying the lignin feedstock before the resin synthesis.

Online monitoring of synthesis and curing of phenol–formaldehyde resol resins by Raman spectroscopy

The synthesis and curing of phenol–formaldehyde resol resins were monitored online by Raman spectroscopy. The synthesis of the resins (F/P 2.0, alkalinity 4.5wt%) was studied at rising temperature (40–90°C) for 90min and at constant temperatures (80°C, 90°C, 100°C, and 110°C) for 120min. The progress of the curing was investigated isothermally (80°C, 90°C, 100°C, and 110°C) for 120min for three resins with different degrees of condensation. The synthesis and curing of the resins were started in the reactor and the advancement of the methylolation and condensation reactions was followed through the window of the reactor in the wave number region of 2000–400cm−1 with use of a fiber optic probe for the data collection. The Raman spectra of six model compounds (formaldehyde, phenol, 2-hydroxybenzyl alcohol, 4-hydroxybenzyl alcohol, 2-benzylphenol, and 4-benzylphenol) were analyzed to facilitate the interpretation of the spectra of the resins. The consumptions of free phenol and free formaldehyde, as well as the progress of the methylolation and condensation reactions were easily monitored by following the changes in intensity of the characteristic Raman bands. The results for the cured resins obtained by Raman spectroscopy were in good agreement with the structures and residual reactivities studied by CP/MAS 13C NMR spectroscopy and differential scanning calorimetry (DSC), respectively. The results of the study show Raman spectroscopy to be a promising tool for the online monitoring and control of phenol–formaldehyde resol resin synthesis and curing; in addition, Raman spectroscopy offers an effective and fast method for structural study of the solid state resins.

Structural and Physical Changes in Phenol−Formaldehyde Resol Resin, as a Function of the Degree of Condensation of the Resol Solution

The structural and physical differences of phenol−formaldehyde resol resins collected during a resin synthesis were studied, as a function of the degree of condensation of the resin. The structural and physical properties of the resins were analyzed using nuclear magnetic resonance (NMR) spectroscopy, viscosity and refractive index measurements, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), solids content analyses, and contact angle determinations on wood veneer. As a result of the condensation reactions, the amount of methylol groups and free reactive sites of phenolic species decreased, while the amount of methylene bridges increased, as a function of the degree of condensation. The changes in the resin structure resulted in an increase in the viscosity, refractive index, and average molar masses, and a decrease in reactivity, with increasing degrees of condensation. The wetting of the surface of the wood veneer was reduced as the viscosity and average molar masses of the resin solution each increased.

Effects of silane and the lowering of pH on the properties of phenol–formaldehyde resol resins and resin coatings

AbstractPhenol–formaldehyde resol resins were modified by the addition of silane (3‐aminopropyltriethoxysilane) and the lowering of pH (formic acid). The effects of the modifications on the properties of the resins during storage were studied through comparison with the parent resins and by viscosity measurements, NMR spectroscopy, ultraviolet–visible spectroscopy, and differential scanning calorimetry. Resin coatings on paper were prepared to determine the influence of discoloration of the resin solution on the color of the cured resin. A decrease in the pH of the NaOH‐catalyzed resin solutions lightened the color of the solutions and corresponding coatings, whereas silane additions made the coatings slightly more yellow. The lowering of pH increased the viscosities and decreased the reactivities of the resin solutions compared with the unmodified reference resins during storage. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1933–1941, 2007

Cure rate of Phenol–Formaldehyde (PF) resol resins catalyzed with MgO

One of the main drawbacks that has prevented a wider use of phenol–formaldehyde (PF) resins in the manufacture of impregnated paper and wood composite panels is their relatively slow cure rate. In this study, the curing characteristic of PF resol resins catalyzed with MgO was studied with various formaldehyde (F)/MgO/phenol (P) ratios at various pH values. The results indicated that the pH value, nature of pH regulator and synthesis parameters, including the F/P ratio and MgO content, all influence the rate of cure. The pH value played an important role in affecting both the cure rate and cure time. The cure rate was fast when pH was below 7.5. The cure time decreased as the pH value decreased at all F/MgO/P ratios. The MgO/P ratio had a definite influence on the cure rate, the cure time decreased with the increase of MgO/P molar ratio, and the F/P ratio had no significant influence on the cure rate. Differential scanning calorimetry (DSC) results showed that MgO catalyzed PF resin can cure at a low temperature.