Resol-type Phenol Formaldehyde Research Articles

Phenolation to Improve Hardwood Kraft Lignin for Wood Adhesive Application.

Lignins, naturally occurring aromatic polymers with phenylpropane units, are promising bio-based alternatives for petroleum-based products. Resole-type phenol formaldehyde (PF) adhesive is commonly used in wood composites requiring durability and weather-proofness. However, PF adhesive is a petroleum-based product. The objective of this study is to transform the low-reactivity hardwood kraft lignin (KL) as the phenol substitute in the PF adhesive formulation by acidic phenolation. The variations in the molecular weights, chemical structures, and functional groups in lignins were investigated before and after the phenolation. The results indicate that the KL can be cleaved, and phenols are crosslinked onto KL to produce phenolated kraft lignin (PKL) under the suitable phenolation condition, heating 3/5 (w/w) of KL/phenol at 90 °C for 2 h with 5% H2SO4 as the catalyst. Resole-type PKL-PF adhesives can be directly synthesized after the phenolation in the same reactor. Plywood laminated with this adhesive obtains satisfactory strength and low formaldehyde emission. This not only reduces the usage of petroleum-based phenol but also increases the reactivity and applications for hardwood KL.

Production of pyrolytic lignin for the phenolic resin synthesis via fast pyrolysis

Recycling of waste wood into resol type phenol-formaldehyde (PF) resins via fast pyrolysis was demonstrated. Waste wood collected from the building demolition site in Finland was pyrolyzed with 20 kg/h circulating fluidized bed pyrolysis pilot unit. Pilot was operated with high organic liquid yield (60 wt% on average) and the produced fast pyrolysis bio-oil was fractionated by water addition into aqueous phase and water insoluble phase. The obtained fractions were characterized, and the water-insoluble viscous lignin fraction was used in the synthesis of PF-resins. Commercial phenol was successfully replaced by pyrolytic lignin fraction at 10 wt%, 20 wt%, 30 wt%, 40 wt% and 50 wt% producing resins of low in free formaldehyde content, but resins with high replacement ratio exhibited higher viscosities. The use of H2O/n-butanol mixture as solvent at a ratio 70:30 wt/wt% proved capable to prolong the storage time of the resin and helped to maintain the viscosity at acceptable values for at least 2 weeks before their use in the targeted application. Finally, the gluing performance of the resins was evaluated by measuring the tensile shear strength of lap joints formed by gluing 5 mm thick beech wood veneers. All the produced resins fulfilled a dry strength limit of ≥ 10 N/mm2. Wet strength limit ≥ 7 N/mm2 was fulfilled by the resins with the replacement ratio up 40 wt%, but resins with replacement ratio of 50 wt% had somewhat reduced wet strength. These results confirm a promising protentional application of pyrolysis derived lignin fraction in phenolic wood adhesives, at least in dry conditions.

Resole-Type Phenol–Formaldehyde Resin with Neutralized Liquid Products of Fast Pyrolysis of Birch Wood

A method of preparation of a phenol–formaldehyde resin by replacing phenol with liquid products of the fast pyrolysis of wood is described. Strength tests reveal that substituting a pyrolysis liquid for 60% of phenol in the phenol–formaldehyde resin allows strength to be increased by 6% relative to the control sample.

Screening allergic reactions to resol resin based on phenol and formaldehyde in a clinic of occupational dermatology.

Allergic reactions to resol-type phenol formaldehyde resin [phenol formaldehyde resin 2 (PFR2)] are relatively common. It has been suggested that PFR2 should be included in baseline series. However, a recent international study found clinical relevance in only 25% of patients. To report the results of screening with PFR2 over a 5-year period (2012-2016), and to study the clinical relevance of allergic reactions to PFR2 over a 15-year period (2002-2016). At the Finnish Institute of Occupational Health, PFR2 was added to the baseline series in 2012. We had previously tested PFR2 in the plastic and glue series. We searched the patch test files for patients with allergic reactions to PFR2, and analysed their patch test results, occupation, exposure, and diagnosis. During the screening period of 5 years, a total of 10 (1.6%) patients reacted positively to PFR2. Seven of these had occupational allergic contact dermatitis caused by phenol formaldehyde resin (PFR). In 3 patients, we found no exposure to PFR. Over the preceding 10 years, the clinical relevance of 10 additional allergic reactions to PFR2 was similarly high. In an occupational dermatology clinic, 70% of PFR2 reactions were clinically relevant. Further studies in general dermatology clinics are needed.

The Synthesis of Phenol–Formaldehyde Copolymers Based on Phthalide-Containing Monophenol

When o-benzoylbenzoic acid chloride interacts with phenol in dioxane solution in the presence of catalyst ZnCl2, the phthalide-containing monophenol 3-phenyl-3-(4′-hydroxyphenyl)phthalide (I) is formed. When a mixture of the synthesised monophenol and phenol in different weight ratios (from 5:95 to 40:60) interacts with formaldehyde in the presence of catalytic amounts of ammonia, resol-type phenol–formaldehyde cooligomers are obtained, and heat-resistant crosslinked polymers based on them.

Properties of molding plates made with albizia wood particles impregnated with alcohol-soluble PF resins prepared from phenol-liquefied lignins

Abstract Alkaline lignin and de-alkaline lignin were liquefied in phenol with H2SO4 or HCl as catalysts. Liquefied lignins were reacted with formalin under weakly alkaline condition, and in this manner, alcohol-soluble resol-type phenol-formaldehyde (PF) resins (PFlignin) were prepared. Small particles of albizia [Albizia falcataria (L.) Fosberg] passing 100-mesh sieve were impregnated with these resins, and the resulting molded test plates (MTPlignin) with the dimensions of 10×10×0.4 cm3 were analyzed. Differential scanning calorimeter revealed that the PFlignin resins need higher temperatures for curing than those of industrial PF resin (control). MTPlignin has higher internal bonding and bending strengths than those of the MTPcontrol. Thermogravimetric analysis of MTPs shows three distinct degradation rates, and the following heat resistance was found: MTPcontrol>MTPAL>MTPDAL. MTPs have, after carbonization at 800°C, a uniform internal structure as revealed by dimension shrinkage analysis.

Synthesis of hierarchical porous carbon particles by hollow polymer microsphere template

Carbon particles with hierarchical pore structure are prepared from resol-type phenol–formaldehyde resin using hollow polymer microspheres as template. The template microspheres have a polystyrene shell with transverse hydrophilic channels connecting to the interior cavity. They are stable and permeable, so a crosslinking catalyst can be previously loaded into the cavity reservoir. Following the incorporation of resol phenol–formaldehyde resin, the aggregates of resin and hollow microspheres have been achieved. Porous carbon particles are derived from carbonization of the composite particles. The structures of carbon materials can be tuned from open wall to closed wall by varying the resol/template weight ratio. The carbon particles are comprised of a series of pores with broad size distribution: from micropore, mesopore to macropore. The porosity development in the carbon materials has been investigated by electron micrograph and N 2 adsorption.

Synthesis and Properties of Resol-Type Phenol-Formaldehyde Copolymers Containing Phthalide and Phthalimidine Groups

Synthesis and Properties of Resol-Type Phenol-Formaldehyde Copolymers Containing Phthalide and Phthalimidine Groups

Preparation of nanoporous composite carbon membrane for separation of rhodamine B dye

In this work, a clay-supported carbon membrane has been synthesized by carbonizing a blend of polyethylene glycol and resole-type phenol formaldehyde resin at 500 °C. The membrane thus prepared was characterized with respect to its pore structure and surface morphology. The hydraulic permeability was found to be considerably higher than that reported in literature. The thickness of the carbon membrane was determined to be 30 μm and the molecular weight cutoff experiments gave the average pore size of 1.8 nm. Experiments show that the real rejection of the dye is in the range of 90–100% and depends on the pressure and concentration of the dye. In the pH range of 6–8, the dye tends to dimerize and forms greater aggregations due to attractive electrostatic interaction, suggesting separation of the dye from its solution due to sieving by the membrane. In addition, since the membrane has charge opposite to that of the dye, it is likely that the latter may have adsorbed on the pore mouth as well as pore wall, this way offering much lower pore diameter than 1.8 nm to the flow of dye solution.

Air Oxidation of Carbon Spheres. I. Master Curves of Pore Parameters

Carbon spheres prepared from a resol-type phenol–formaldehyde resin at 1000°C were activated in a flow of dry air in order to understand the process of pore development through the use of master curves for each pore parameter. Pore development in the carbon spheres by such oxidation was characterized through analyses of nitrogen adsorption isotherms by different methods.The adsorptivity of the activated carbon spheres towards phenol was measured as a function of oxidation temperature and time, its dependence on the micropore volume being discussed.The development of pores by air oxidation was interpreted in terms of master curves measured at the reference temperature (400°C) for each pore parameter, viz. surface areas and pore volumes due to different pores. The pore parameters were determined via the BET, αS-plot, BJH and DFT methods.The results presented suggest that the effect of oxidation temperature and time on pore development could be converted with each other as well as oxidation yield. The temper...

Comparative study of carbon dioxide and nitrogen atmospheric effects on the chemical structure changes during pyrolysis of phenol–formaldehyde spheres

The effect of CO 2 atmosphere on the chemical structure changes of resol-type phenol–formaldehyde spheres during pyrolysis was investigated, in comparison with that of N 2 atmosphere, using FT-IR, TGA, and elemental analysis techniques. It was found that, in contrast to the expectation that CO 2 may act as an oxidizing agent at high temperature, it behaves very similar to N 2 during pyrolysis of PF spheres up to 700 °C, but results in a somewhat different extent of some specific reactions. That is, although the reactions occurring up to 700 °C were dominated by crosslinking and/or polyaromatization under both CO 2 and N 2 atmospheres, fewer alkyl–phenolic ether bonds were formed under CO 2 than under N 2. As a consequence, the samples carbonized under CO 2 at 700 °C were found to have more pendant groups on the edge carbon atoms of carbon in the carbonized samples than those prepared under N 2 atmosphere.

Influence of carbon-fiber felts on the development of carbon–carbon composites

Abstract Oxidized PAN-fiber felt was carbonized to 600, 1000, and 1800 °C, respectively. Different carbon/carbon composites (C/C composites) were prepared from oxidized PAN-fiber felt, the carbonized felts, and resol-type phenol–formaldehyde resin. These composites were then carbonized and graphized at temperatures of between 600 and 2400 °C. The C/C composite made with oxidized PAN-fiber felt showed a strong fiber/matrix bonding, and those developed from the carbonized felt (heat-treatment of 1800 °C) showed a poor fiber/matrix bonding. The graphitized composites reinforced with the oxidized PAN-fiber felt resulted in having a high flexural strength (325 MPa), and the graphitized composites reinforced with the carbonized felt (carbonized at 1800 °C) had a low flexural strength (9 MPa). It was found that the stress-orientation promoted the formation of the anisotropic texture around the fibers as well as between the fibers. This felt may very well be able to provide a low-cost route for producing multidimensional C/C composites.

Effect of carbon fiber surface functional groups on the mechanical properties of carbon–carbon composites with HTT

The present investigation describes the quantitative measurement of surface functional groups present on commercially available different PAN based carbon fibers, their effect on the development of interface with resol-type phenol formaldehyde resin matrix and its effect on the physico–mechanical properties of carbon–carbon composites at various stages of heat treatment. An ESCA study of the carbon fibers has revealed that high strength (ST-3) carbon fibers possess almost 10% reactive functional groups as compared to 5.5 and 4.5% in case of intermediate modulus (IM-500) and high modulus (HM-45) carbon fibers, respectively. As a result, ST-3 carbon fibers are in a position to make strong interactions with phenolic resin matrix and HM-45 carbon fibers make weak interactions, while IM-500 carbon fibers make intermediate interactions. This observation is also confirmed from the pyrolysis data (volume shrinkage) of the composites. Bulk density and kerosene density more or less increase in all the composites with heat treatment up to 2600 °C. It is further observed that bulk density is minimum and kerosene density is maximum upon heat treatment at 2600 °C in case of ST-3 based composites compared to HM-45 and IM-500 composites. It has been found for the first time that the deflection temperature (temperature at which the properties of the material start to decrease or increase) of flexural strength as well as interlaminar shear strength is different for the three composites (A, B and C) and is determined by the severity of interactions established at the polymer stage. Above this temperature, flexural strength and interlaminar shear strength increase in all the composites up to 2600 °C. The maximum value of flexural strength at 2600 °C is obtained for HM-45 composites and that of ILSS for ST-3 composites.

The effect of formaldehyde to phenol ratio on the curing and carbonisation behaviour of resole resins

Two resole-type phenol formaldehyde resins were synthesised with a formaldehyde to phenol (FP) molar ratio of 1.2 and 1.8 and their structure on curing examined by 13C CP-MAS solid state NMR. The FP=1.8 material was considerably more complex than the FP=1.2 material. This has been interpreted as due to the formation and subsequent cleaving of ethers in the FP=1.8 system. The structural changes in each resole after heating were observed by 13C CP-MAS NMR up to 500°C, and their surface areas after carbonisation at 1000°C were measured using N 2 and CO 2 gas adsorption. The FP=1.2 material was found to possess narrower micropores than the FP=1.8 material. These results are significant for those industries where the high-temperature behaviour of phenol formaldehyde materials is important.

Application of a cone/plate rheometer for the characterization of resol-type phenol formaldehyde resins

Application of a cone/plate rheometer for the characterization of resol-type phenol formaldehyde resins

Coconut-fiber-reinforced thermosetting plastics

Thermosetting plastic composites have been prepared with phenol–formaldehyde resins as well as unsaturated polyesters as binders and coconut hair as fibrous reinforcement. Using resole-type phenol–formaldehyde resins, the effect of coconut fiber pretreatment by NaOH, the precondensation time of the impregnated fibrous press material, the resin–fiber ratio, and pressing parameters have been studied. Especially advantageous press-material has been obtained using 60–65 wt % linear novolac type phenol-formaldehyde resin as binder and 35–40 wt % of coconut hair. Applying unsaturated polyester (UP) as binder, BMC (bulk molding compound)-type press material can be prepared using coconut fiber reinforcement instead of glass fibers. To achieve better coupling between coconut fiber and UP matrix, coconut fiber was pretreated by NaOH and/or gamma-preirradiation. It has been found that in glass-fiber-reinforced UP press materials a significant part of glass fiber could be changed for short-cut coconut fiber.