This article covers the introduction to polymer composites, phenol formaldehyde resin, phenol formaldehyde composites, and foams along with their properties and applications. The previous research in ...the fields of phenol formaldehyde composites, nanocomposites, and PF foams is also covered in depth. Various combinations of nanomaterials and processes have been investigated in the field of structural composites to meet the requirements of industries such as automotive, aerospace, military, civil, and construction. Due to their different features and possibilities when compared to equivalents composed of other polymers, particularly thermosets, phenol‐formaldehyde reinforced composites are commonly used for large load bearing structural applications. Composite properties can be improved by using nanoparticles, which are materials that have been developed as a result of advances in nanotechnology. This research focuses on a literature review of nanofillers' use to improve the structural properties of phenol‐formaldehyde composites and foams published in the last two decades. The use of nanomaterials to modify composites is examined in depth.
The high-value recycling of discarded phenol-formaldehyde resins (PF) remains an unresolved challenge. Herein, we propose a novel approach leveraging γ-Al2O3 to convert PF into high-value ...hexamethylbenzene at a low temperature using a one-pot method. This study explores the degradation capability of PF, methylation reaction efficiency, and hydrodeoxygenation capacity among various cost-effective commercial catalysts: γ-Al2O3, ZrO2, and TiO2. It reveals the influence of different reaction times on PF pyrolysis and product distribution, and it was found that high value-added hexamethylbenzene exhibited the highest yield (73.33 wt%) with selectivity (75.83%) using γ-Al2O3 at 350 °C and 2 h of reaction. Experiments using PF models demonstrate the crucial synergy between γ-Al2O3 and C(aryl)-OH in the cleavage of C(aryl)-C(alkyl) bonds and methylation reactions. A pathway for PF C-C/C-O bonds cleavage-methylation tandem reaction is proposed, based on 13C methanol isotope experiments. PF undergoes C(aryl)-C(alkyl) bond cleavage to produce phenolic intermediates, which were then methylated; this is accompanied by the cleavage of C(aryl)-OH and C(aryl)-OCH3, culminating in C-alkylation to form hexamethylbenzene. This research provides new insights into the high-value recycling of PF.
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•One-pot method for converting phenol-formaldehyde resin into hexamethylbenzene.•The mechanism for catalysts facilitating CC bond cleavage is clarified.•A tandem reaction pathway for C-C/C-O bonds cleavage and methylation is proposed.
•Carbons were derived from modified phenol–formaldehyde resin via steam activation.•The surface area up to 1439m2g−1 was reached at an activation temperature of 950°C.•The N content of activated ...carbons decreased with increasing activation temperature.•A maximum CO2 adsorption capacity of 6.71molkg−1 was attained at 273K and 1atm.•The adsorption isotherms of CO2 could be described by the Redlich–Peterson equation.
Highly porous activated carbons were prepared from melamine-modified phenol–formaldehyde resins via steam activation at different activation temperatures (700–950°C) and then used for CO2 capture at atmospheric pressure. The porosity and surface properties of the activated carbons and their CO2 adsorption capabilities were studied and compared with those derived from common phenol–formaldehyde resin. An adsorption capacity for CO2 of 6.71molkg−1 (29.5wt.%) was attained at 0°C and 1atm and decreased significantly with increasing operating temperature. The prepared activated carbons could be well applied in temperature-swing adsorption processes. Of the three isotherm equations (Langmuir, Freundlich, and Redlich–Peterson), the adsorption of CO2 on activated carbons could only be satisfactorily described using the three-parameter Redlich–Peterson equation.
This paper considers the use of lignin during the preparation of phenol-formaldehyde resins. The effect of lignin on the properties of phenol-formaldehyde resins and materials based on them is ...studied. The obtained resins are characterized by differential scanning calorimetry (DSC). The results show that, in the case of increasing the concentration of lignin, the time of the polycondensation reaction, the energy of activation, and the curing time of lignin-containing resins increase. The main parameters of the lignin-containing resins correspond to GOST (State Standard) 20907–2016 except for the concentration of free formaldehyde. The obtained resins are used to obtain a foam composite material—phenolic foam. It is noted that phenolic foams based on resins containing 5–10% lignin in the composition have a higher compression strength in comparison with other samples. At a concentration of lignin in the resin of 20%, the compression strength of the ready-to-use thermal-insulation materials decreases relative to other samples, while it turns out to be impossible to obtain a foam material in the case of using a resin with 30% lignin. The results of the study make it possible to recommend the use of a small amount of lignin (5–10%) in the production of phenol-formaldehyde resins and further production of a thermal-insulation material with an increased compression strength.
Owing to the increasing interest in sustainability and bio-based materials, softwood kraft lignin (SKL) was acetone-fractionated to reduce its heterogeneity and then demethylated to substitute phenol ...in lignin-phenol-formaldehyde (LPF) resins to be used as bio-based wood adhesives. This study investigated the effect of the demethylation of acetone-soluble SKL (AS-SKL) on the adhesion of LPF resins, where phenol was partially replaced with acetone-soluble demethylated kraft lignin (AS-DKL). Characterization of SKL, AS-KL, and AS-DKL using gel permeation chromatography (GPC), FTIR, and
31
P NMR spectroscopy showed that the demethylation was successfully performed; the molecular weight (MW) and the number of methoxy groups decreased, and the number of -OH groups increased. The MW, chemical reactions, and curing behavior of LPF resins synthesized with different AS-DKL levels (10, 20, 30, and 50 wt%) were also characterized. With the increase in AS-DKL content, the viscosity and MW of the resin increased, whereas the gelation time decreased. LPF resins with 10% AS-DKL showed the highest tensile shear strength and lowest peak curing temperature. These results suggest that 10% is an optimal AS-DKL level in LPF resins for plywood bonding and that demethylation is an effective way of utilizing SKL.
•Lignin-phenol-formaldehyde (LPF) resin was a promising wood adhesive.•Organosolv lignins from bamboo were ideal materials for LPF resin synthesis.•The synthesis of LPF resin was disturbed by ...long-chain hydrocarbon derivatives.•The performance of a LPF resin was affected by various factors.
The synthesis and performance of a lignin-phenol-formaldehyde resin are significantly related to the properties of the lignin used. In an effort to provide a fundamental understanding of lignin structure-property relations for lignin-phenol-formaldehyde resin synthesis and application, two distinct technical lignins were examined as-obtained from an acidic (L1) and an alkaline (L2) organosolv pulping of bamboo. These samples were thoroughly characterized and the structural and compositional features of them were charted. The content of β-O-4′ linkages in L1 were 23.83 per 100Ar, followed by some β-β′ linkages (1.27 per 100Ar). However, almost all the side-chain linkages in L2 were cleaved. The purities of the two lignins both exceeded 81.0%, but significantly more extractives were found to be present in L2. Subsequently, two lignin-phenol-formaldehyde resins were successfully synthesized using L1 and purified L2 at a substitution rate of 50% to phenol. The high content of extractives contaminating L2, especially long-chain hydrocarbon derivatives, severely affected the synthesis of lignin-phenol-formaldehyde resin. The successful removal of this fraction was necessary before the material could be put to use.
TGA results for cured lignin–phenol–formaldehyde resins (in N
2 at 30
mL/min and 10
°C/min).
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.
The potential of addition of calcium lignosulfonate as an eco-friendly additive with a phenol-formaldehyde (PF) resin, at different ratios, to produce medium-density fibreboards (MDF) with acceptable ...properties, was investigated in this work. The fibreboards were fabricated in the laboratory with low PF resin percentage (3%, 4%, 5%), while the addition levels of calcium lignosulfonate varied from 5% to 15% (on the dry fibres). The physical and mechanical properties of the fibreboards were evaluated, and further statistically analysed in order to determine the optimal values of PF resin content and lignosulfonate addition for fulfilling the European standards. It was shown that at the low PF resin content (3%), addition of lignosulfonate should not exceed 10% to avoid deterioration in the mechanical properties. It was concluded that PF resin content of 3.5% can be recommended for the production of lignosulfonate-PF bonded MDF panels to comply with the EN standard requirements.
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