Resol-type Phenolic Resin Research Articles

Studies on the effect of concentration of formaldehyde on the synthesis of resole-type epoxidized phenolic resin from renewable resource material

Epoxidized cardanol/formaldehyde resins (ERCF) were synthesized by reacting resole type cardanol/formaldehyde resin and epichlorohydrin in basic medium at 120 °C. Resole-type phenolic resins were synthesized by reacting cardanol and formaldehyde (molar ratios 1:1.3, 1:1.5, 1:1.7, 1:1.9,and 1:2.1) in the presence of sodium hydroxide, as catalyst, at five different temperatures ranging between 60 and 80 °C with an interval of 5°C for a maximum period of 6 h. A set of samples were characterized by Fourier transform infrared and nuclear magnetic resonance spectroscopic analysis. The molecular size distribution of resole phenolics was studied by high-resolution gel permeation chromatography. Differential scanning calorimetry technique was used to investigate the curing behavior of the synthesized epoxy resins. Single-step mass loss in dynamic thermo gravimetric traces for the ERCF was observed.

Electrospun preparation of microporous carbon ultrafine fibers with tuned diameter, pore structure and hydrophobicity from phenolic resin

Microporous carbon ultrafine fibers with different diameter were prepared by electrospinning from resole-type phenolic resin, followed by heat curing and one-step carbonization, and their adsorption performance for benzene and water was evaluated. Average diameter of as-spun fibers changed from 1.1 to 0.33μm with increasing dimethylformamide content in the spinning solution, caused by more fiber divisions. The carbon ultrafine fibers with smaller diameter exhibited enhanced benzene adsorption and diminished water adsorption due to improved specific surface area, micropore volume and hydrophobicity. In addition, the relatively developed hydrophobicity of the prepared carbon ultrafine fibers resulted in much higher adsorption tendency for benzene over water, in comparison to common polyacrylonitrile-based electrospun activated carbon nanofibers.

PLA/wood biocomposites: Improving composite strength by chemical treatment of the fibers

A resol type phenolic resin was prepared for the impregnation of wood particles used for the reinforcement of PLA. A preliminary study showed that the resin penetrates wood with rates depending on the concentration of the solution and on temperature. Treatment with a solution of 1wt% resin resulted in a considerable increase of composite strength and decrease of water absorption. Composite strength improved as a result of increased inherent strength of the wood, but interfacial adhesion might be modified as well. When wood was treated with resin solutions of larger concentrations, the strength of the composites decreased, first slightly, then drastically to a very small value. A larger amount of resin results in a thick coating on wood with inferior mechanical properties. At large resin contents the mechanism of deformation changes; the thick coating breaks very easily leading to the catastrophic failure of the composites at very small loads.

Processing and characterization of nanographene platelets modified phenolic resin as a precursor to carbon/carbon composites (part II)

Nanocomposites were formed by curing the dispersion of carbon nanofillers—nanographene platelets and vapor grown carbon nanofibers—in resole type phenolic resin. X-ray diffraction, fourier transform infrared spectroscopy, scanning electron microscopy, thermal expansion, and thermogravimetric and flexure testing were carried out to study the morphology and thermal and mechanical properties of the manufactured nanocomposites. The coefficient of thermal expansion decreased by 15.36% (73.83 µm/m℃) and 14.23% (74.81 µm/m℃) with 1.5 wt% nanographene platelets and 1.5 wt% vapor grown carbon nanofibers, respectively, compared with neat phenolic (87.23 µm/m℃) in the temperature range 60–80°. The flexure strength of neat phenolic resin increased by 31.62% (48.57 MPa) and flexure modulus by 42.23% (2.9 GPa) at 0.5 wt% nanographene platelets. Comparatively, vapor grown carbon nanofibers at 1.5 wt% increased the flexure strength by 14.3% and flexure modulus by 23.5%. Nanographene platelets and vapor grown carbon nanofibers increased the char content of neat phenolic resin. The char content increased by 200% at 800℃ in 5 wt% nanographene platelet nanocomposites, compared with 75% increase in 3 wt% vapor grown carbon nanofibers nanocomposite. Nanographene platelets were more effective than vapor grown carbon nanofibers in lowering the coefficient of thermal expansion of neat phenolic, in improving its flexure strength and modulus and in increasing the char yield. The results indicate that nanographene platelets can be effectively used as carbon nanofiller in the manufacture of carbon/carbon composites.

Processing and characterization of nanographene platelets modified phenolic resin as a precursor to carbon/carbon composites—part I

Nanographene platelets have been explored as nanofillers for resole type phenolic resin (GP 486G34) with catalyst (GP 4826C) supplied by Georgia Pacific Resins. Previous studies have shown that carbon nanofillers including single-walled carbon nanotubes, vapor-grown carbon nanofibers and graphite powder are shown to increase dimensional stability, carbon content and thermomechanical properties. In the present study, 0.5%, 1.5%, 3% and 5% by weight dispersions of nanographene platelets in phenolic resin were compared with corresponding dispersions of vapor-grown carbon nanofibers in phenolic resin to investigate the effect on curing reaction and rheological and wetting behaviors. 0.5 wt% nanographene platelets increased the heat of curing of neat phenolic resin by 33% compared with 26% increase in 0.5 wt% vapor-grown carbon nanofibers. Due to the mechanism of inter-platelet sliding of nanographene platelets, 0.5 wt% nanographene platelets reduced the steady shear viscosity of phenolic resin by 48% compared with that of neat resin after 1.5 h at 1% strain rate. The lower viscosity of 0.5 wt% nanographene platelets dispersion led to lower (20°) contact angle compared with neat phenolic (29.57°) with 8-harness satin weave carbon fabric after 10 s of contact with the fabric. Due to lower viscosity of nanographene platelets/phenolic dispersions and higher heat of curing, nanographene platelets could be potential carbon nanofiller for densifying carbon/carbon composites during manufacture.

Mechanical properties and network structure of phenol resin crosslinked hydrogenated acrylonitrile‐butadiene rubber

AbstractThe tough and stretchable crosslinked hydrogenated acrylonitrile–butadiene rubber (HNBR) could be prepared by resol type phenol resin as a crosslinker. The mechanical properties and the network structure of the phenol resin crosslinked HNBR were investigated by comparing with those of the peroxide crosslinked HNBR having the higher crosslink density and the heterogeneous network structure. The elastic modulus and the strain at break of the phenol resin crosslinked HNBR were much higher than those of the peroxide one. The residual strain was below 20 % after stretching up to 650 % and then releasing from the cramps. Since the crosslink density is low, the high elastic modulus and the good recovery deformation are attributed to the stiffness and rigidity of the crosslink junctions obtained by phenol resin. Small‐angle X‐ray scattering measurements revealed that the network structure is spatially homogeneous and the results of the wide angle X‐ray diffraction indicate that the strain‐induced crystallization is suppressed, which enable the longer elongation. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Synthesis of reduced graphene oxide/phenolic resin-based carbon composite ultrafine fibers and their adsorption performance for volatile organic compounds and water

Reduced graphene oxide (RGO)/carbon composite ultrafine fibers were prepared from resole-type phenolic resin and graphene oxide (GO) by electrospinning and subsequent carbonization, and their adsorption performance for water and volatile organic compounds (VOCs) was evaluated. SEM images showed that RGO/carbon composite fibers exhibited consecutive fibrous structure. Nitrogen adsorption measurements showed that the specific surface area and pore volume of RGO/carbon composite fibers were slightly lower than the case of pristine carbon fibers owing to the constraint of RGO. Water contact angles and adsorption isotherms suggested that improved hydrophobicity was observed with RGO/carbon composite fibers due to embedded RGO with more sp2 carbon atoms. Consequently, VOC and water adsorption isotherms suggested that RGO/carbon composite fibers had a higher adsorption tendency for VOCs over water.

Synthesis of Carbon Nanofibers Based on Resol Type Phenol Resin and Fe(III) Catalysts

The carbon nanofibers (CNFs) used in this study were synthesized with an iron catalyst and ethylene as a carbon source. A concentration of 30 wt % iron(III) acetylacetonate was dissolved in resol type phenol resin and polyurethane foam was put into the solution. The sample was calendered after being cured at <TEX>$80^{\circ}C$</TEX> in air for 24 h. Stabilization and carbonization of the resol type phenol resin and reduction of the <TEX>$Fe^{3+}$</TEX> were completed in a high-temperature furnace by the following steps: 1) heating to <TEX>$600^{\circ}C$</TEX> at a rate of <TEX>$10^{\circ}C/min$</TEX> with a mixture of <TEX>$H_2/N_2$</TEX> for 4 h to reduce the <TEX>$Fe^{3+}$</TEX> to Fe; 2) heating to <TEX>$1000^{\circ}C$</TEX> in <TEX>$N_2$</TEX> at a rate <TEX>$10^{\circ}C/min$</TEX> for 30 minutes for pyrolysis; 3) synthesizing CNFs in a mixture of 20.1% ethylene and <TEX>$H_2/N_2$</TEX> at <TEX>$700^{\circ}C$</TEX> for 2 h using a CVD process. Finally, the structural characterization of the CNFs was performed by scanning electron microscopy and a synthesis analysis was carried out using energy dispersive spectroscopy and X-ray photoelectron spectroscopy. Specific surface area analysis of the CNFs was also performed by <TEX>$N_2$</TEX>-sorption.

Composites from a forest biorefinery byproduct and agrofibers: Lignosulfonate-phenolic type matrices reinforced with sisal fibers

The replacement of phenol with sodium lignosulfonate and formaldehyde with glutaraldehyde in the preparation of resins resulted in a new resol-type phenolic resin, sodium lignosulfonate-glutaraldehyde resin, in addition to sodium lignosulfonate-formaldehyde and phenol-formaldehyde resins. These resins were then used to prepare thermosets and composites reinforced with sisal fibers. Different techniques were used to characterize raw materials and/or thermosets and composites, including inverse gas chromatography, thermogravimetric analysis, and mechanical impact and flexural tests. The substitution of phenol by sodium lignosulfonate in the formulation of the composite matrices increased the impact strength of the respective composites from approximately 400 Jm-1 to 800 J m-1 and 1000 J m-1, showing a considerable enhancement from the replacement of phenol with sodium lignosulfonate. The wettability of the sisal fibers increased when the resins were prepared from sodium lignosulfonate, generating composites in which the adhesion at the fiber-matrix interface was stronger and favored the transference of load from the matrix to the fiber during impact. Results suggested that the composites experienced a different mechanism of load transfer from the matrix to the fiber when a bending load was applied, compared to that experienced during impact. The thermogravimetric analysis results demonstrated that the thermal stability of the composites was not affected by the use of sodium lignosulfonate as a phenolic-type reagent during the preparation of the matrices.

Preparation and one-step activation of microporous carbon nanofibers for use as supercapacitor electrodes

Microporous carbon nanofibers were prepared by electrospinning from resole-type phenolic resin, followed by one-step activation. KOH was utilized to tune the fiber diameter and improve porous texture. By adjusting KOH content in the spinning solution, the fiber diameter could be controlled in the range of 252–666nm and the microporous volume and specific surface area could be greatly improved. The electrochemical measurements in 6M KOH aqueous solution showed that the microporous carbon nanofibers possessed high specific capacitance, considerable rate performance, and superior specific surface capacitance to conventional microporous carbons. The maximal specific capacitance of 256Fg−1 and high specific surface capacitance of 0.51Fm−2 were achieved at 0.2Ag−1. Furthermore, the specific capacitance could still remain 170Fg−1 at 20Ag−1 with the retention of 67%. Analysis showed that the high specific surface capacitance of the resultant carbons was mainly attributed to optimized pore size (0.7–1.2nm) and the excellent rate performance should be principally due to the reduced ion transportation distance derived from the nanometer-scaled fibers.

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.

Preparation of Hollow Carbon Spheres with Large Size and High Specific Surface Area from Phenolic Resin

Millimeter size Hollow carbon spheres (HCSs) with high specific surface area were successfully prepared from resole-type phenolic resin by suspension polymerization method at ordinary pressure. During the polymerization process, large sums of small molecule gathered at the center and formed the hollow part, bigger spheres with a broad size distribution were then formed under stirring force and surface tension, the maximum external diameter of the obtained HCSs was 1.2mm and the hollow diameter was about 0.35mm. After activating at 800°C under a stream of steam, the specific surface area and total pore volume of the HCSs were reached as 1117m2/g and 0.61cm3/g.

Thermomechanical properties and morphology of polyethylene oxide and phenolic resole blends

AbstractBlends of poly(ethylene oxide) (PEO) and resole type phenolic resin were prepared by a solution cast method using water as a solvent. The cured blends were made by heat curing without using any catalyst. The blends were characterized by dynamic mechanical analysis (DMA), which indicated that PEO forms compatible blend with the resole. The glass transition values, read from the DMA traces, showed a positive shift as compared to the theoretical values calculated by the Fox equation. This suggests a strong H‐bonding interaction between the phenolic resole and PEO as established by Fourier transformed infrared spectroscopy. Flexural test indicated an enhanced flexibility of the blends when compared to the neat phenolic resin. The fracture surface analysis by using a scanning electron microscope (SEM) revealed an increase in plastic deformation with increasing PEO concentration in the blend. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

무인항공기용 경량화 직접메탄올연료전지 스택 개발을 위한 복합소재 분리판 제작 및 성능 평가 (I)

A bipolar plate is a major component of a fuel cell stack, which occupies 50~60% of the total weight and over 50% of the total cost of a typical fuel cell stack. In this study, a composite bipolar plate is designed and fabricated to develop a compact and light-weight direct methanol fuel cell (DMFC) stack for a small-scale Unmanned Aerial Vehicle (UAV) application. The composite bipolar plates for DMFCs are prepared by a compression molding method using resole type phenol resin as a binder and natural graphite and carbon black as a conductor filler and tested in terms of electrical conductivity, mechanical strength and hydrogen permeability. The flexural strength of 63 MPa and the in-plane electrical conductivities of 191 S <TEX>$cm^{-1}$</TEX> are achieved under the optimum bipolar plate composition of phenol : 18%; natural graphite : 82%; carbon black : 3%, indicating that the composite bipolar plates exhibit sufficient mechanical strength, electrical conductivity and hydrogen permeability to be applied in a DMFC stack. A DMFC with the composite bipolar plate is tested and shows a similar cell performance with a conventional DMFC with graphite-based bipolar plate.

REDUCTIVE DEGRADATION OF LIGNIN IN SUPERCRITICAL SOLVENT AND APPLICATION IN PHENOLIC RESIN SYNTHESIS

The lignin was readily decomposed into phenol compounds via reductive liquefaction in supercritical ethanol media(formic acid decomposed into hydrogen at reaction temperatures),opening a promising opportunity to lignin-derived value-added aromatic compounds for highly possible application in phenol-formaldehyde resin production.The supercritical ethanol was the ideal reaction medium for lignin degradation,and the in situ generated hydrogen exactly promoted the decomposition reactions to smaller molecules via encapping the lignin radicals to terminate the further coupling and condensation.The liquefaction mechanism was radical thermal degradation.Some transition metal salts could catalyze the above lignin thermal decomposition,including nickel nitrate,cobalt nitrate and chloroplatinum acid.The yield of the lignin-degraded liquid increased with the increase of formic acid used in the ethanol solvent,while slightly deceased when the reaction temperature increased.The molecular weight of the lignin-derived liquid highly decreased with increase of the reaction temperature,e.g.at 350℃ the number average molecular weight was 143 while for the original lignin feedstock it was 588.The optimum reaction conditions are found to be ethanol-formic acid weight ratio at 1∶1;lignin load at 10 wt%;reaction temperature at 350℃for 4 h.The lignin-derived phenols were characterized by GC-MS technique,and the liquefied product was mainly phenol derivatives with simple structures.Compared with the lignin,the bio-phenols possessed highly improved solubility and reactivity in phenol-formaldehyde synthesis.As the ideal replacement of industrial phenol,lignin-degraded bio-phenol was utilized readily in resol type phenolic resin production with a replacement higher than 50 wt%.The thermal stability was slightly decreased with the increased amount of lignin-derived biophenol in the phenolic resin formula.The results showed the effective reductive degradation of lignin in supercritical ethanol would have a promising outlook in value-added phenol compounds and biomass-based renewable phenol-formaldehyde resins.

Preparation and Processing Characterization of Glass/Phenolic Prepregs

Glass/phenolic prepreg is one of the most applicable prepregs used for making composites for structural parts. To investigate the effective parameters on the processing and properties of these prepregs, thirty samples of glass/phenolic prepregs containing about 50 wt.% resins were prepared by using a resole type phenolic resin and satin glass fibre fabric. They were B-staged or pre-cured at 110 °C and 120 °C for different times from 15 to 50 min, to control the flow behaviour and tack properties. Tack and resin flow were characterized, in order to determine the conditions in which flow and tack properties are optimum. Results show that the levels of pre-cure or conversion were between 2% and 55%. The maximum tack was achieved at 5.3% conversion. Cure behaviour and rheological properties of these prepregs were studied by using differential scanning calorimetry and rheometry. An appropriate cure cycle is presented with the aid of these results. After curing the prepregs on the basis of this cure cycle, a flexural strength of 172.6 MPa and flexural modulus of 17 GPa were obtained.

Santosh K. Gupta: Professor extraordinaire and inspiration to several generations

Santosh K. Gupta: Professor extraordinaire and inspiration to several generations

Effects of graphite filler loading and heat treatment temperature on the properties of phenolic resin based carbon-carbon composites

Carbon/carbon composites (C/Cs) were prepared through polymer pyrolysis using PAN based carbon fabric (Panex(R) 35) and resol type phenolic resin having 0, 10, 20, 30, and 40 wt% of graphite fillers. These precursor composites were heat treated at 600, 900, and 1200°C. The effects of filler loading on the precursor composites and their C/Cs were investigated through density, microstructure, and mechanical properties. Since, the precursor composites were prepared under similar processing conditions and technique, at any particular filler loading when the heat treatment temperature increases, the bulk density of the samples decreases. The filler addition accelerates the formation of the carbon basal planes in the matrix supported by X-ray diffraction studies. The properties such as tensile strength and strain decrease continuously mainly due to change in the matrix structure and decrease of density, whereas, the interlaminar shear strength (ILSS) and interlaminar fracture toughness (ILFT) increase mainly because of improvement in the modulus of matrix. At any particular heat treatment temperature, depending on the filler content and matrix type, the density, tensile properties, ILSS, and ILFT of the samples show different trends. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Recent advancement on polybenzoxazine—A newly developed high performance thermoset

AbstractPolybenzoxazine is a newly developed addition polymerized phenolic system, having a wide range of interesting features and the capability to overcome several shortcomings of conventional novolac and resole type phenolic resins. They exhibit (i) near zero volumetric change upon curing, (ii) low water absorption, (iii) for some polybenzoxazines Tg much higher than cure temperature, (iv) high char yield, (v) no strong acid catalysts required for curing, (vi) release of no byproduct during curing and also possess thermal and flame retarding properties of phenolics along with the mechanical performance. Though benzoxazine based materials possess several advantages, they have not yet became very attractive to the industries. To improve the mechanical properties and processibility several strategies have been reported including (i) synthesis of benzoxazine monomers with additional functionality, (ii) incorporation of benzoxazine in polymer chain, and (iii) benzoxazine based composites or alloys. In this article, we have discussed about the recent development of benzoxazine chemistry. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5565–5576, 2009

Effect of dynamic cross-linking on mixing torque behavior and tensile yield behavior of isotactic polypropylene (iPP) / ethylene-propylene diene rubber (EPDM) /nitrile rubber (NBR) elastomeric blends

The mixing torque behavior of ter blends of isotactic-polypropylene (iPP) with ethylene-propylene diene rubber (EPDM)/Nitrile rubber (NBR) was studied with the help of Rheometer using resole type phenolic resin as a cross-linking agents. Systematic changes with varying blend composition were observed in stress-strain behavior in the yield region viz., width of yield peak, work of yield, yield stress and yield strain. Analysis of yield stress data was made on the basis of various mathematical expressions of first power and two-thirds power laws of blend composition dependence and the porosity model. It led to consistent result from the expressions about the variation of stress concentration effect in both uncross-linked and cross-linked blend systems. With the aid of scanning electron microscopy (SEM) shapes and sizes of dispersed elastomer phase (EPDM / NBR) domains at varying blend compositions were studied.