Resol-type Phenolic Resin Research Articles

High temperature ablation and thermo-physical properties improvement of carbon fiber reinforced composite using graphene oxide nanopowder

Ablative nanocomposites were prepared by incorporating graphene oxide (GO) nanosheets into resole type phenolic resin and then impregnating them into rayon-based carbon fabric. GO were dispersed into phenolic resin at 0.25, 0.75, and 1.25wt.% loadings using high shear mixing to insure uniform GO dispersion. The morphology and structure of graphene oxide nanosheets (synthesized by a Hummers method) and the structural, thermal and ablative properties of the samples were characterized using Fourier Transform Infrared spectroscopy(FTIR), X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), oxyacetylene flame test, and Thermo-Gravimetric Analysis (TGA) methods. It was found that the thermal stability and ablative properties of the GO/phenolic resin/carbon fiber composites were greatly enhanced due to the well dispersion of GO sheets in polymer matrix and the strong interfacial interaction between the GO sheets and phenolic matrix as well as layered carbon structure after pyrolysis. The specimen with 1.25wt.% GO showed the best results in the rate of ablation, thermal diffusivity and thermal stability compared to other samples. This laminate had constant thermal diffusivity at different temperatures, and improved char yield and ablation rate to about 10% and 51%, respectively.

Studies on the structural changes during curing of epoxy and its blend with CTBN

Cashew nut shell liquid (CNSL), an agricultural renewable resource material, produces natural phenolic distillates such as cardanol. Cardanol condenses with formaldehyde at the ortho- and para-position of the phenolic ring under acidic or alkaline condition to yield a series of polymers of novolac- or resol-type phenolic resins. These phenolic resins may further be modified by epoxidation with epichlorohydrin to duplicate the performance of such phenolic-type novolacs (CFN). The structural changes during curing of blend samples of epoxy and carboxyl terminated poly (butadiene-co-acrylonitrile) (CTBN) were studies by Fourier-transform infrared (FTIR) spectrophotometer. The epoxy samples were synthesized by biomass material, cardanol. Blend sample was prepared by physical mixing of CTBN ranging between 0 and 20weightpercent CTBN liquid rubber into cardanol-based epoxidized novolac (CEN) resin. The FTIR spectrum of uncured blend sample clearly indicated that there appeared a band in the region of 3200–3500cm−1 which might be due to the presence of phenolic hydroxyl group and OH group of the opened epoxide. Pure epoxy resin showed peaks near 856cm−1 which might be due to oxirane functionality of the epoxidized novolac resin. Both epoxy and its blend sample was cured with polyamine. The cure temperature of CEN resin was found to be decreased by the incorporation of CTBN. The decomposition behavior was also studied by thermogravimetric analyzer (TGA). Two-step decomposition behavior was observed in both epoxy and its blend samples.

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.

Thermal Study of Gels Obtained From Resol Type Phenolic Resins Modified With Lignin

SummaryGels were obtained from resol type phenolic resins, with resorcinol, formaldehyde and lignin as precursors. Thermal response was evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and curing kinetics were determined from the SDTA curves using Flynn–Wall–Ozawa and Friedman iso‐conversional models. Additionally, it was used Fourier transform infrared spectroscopy (FTIR) to evaluate the progress of the curing reaction. These analyzes were performed for two gels, one of them prepared with lignin (lignin resin), and a reference (resorcinol resin). Lignin resins tend to be more thermally stable than resorcinol resins. Average values found for activation energy of the curing processes are 55.07 kJ mol−1 and 60.60 kJ mol−1 for resorcinol resin and lignin resins respectively using Flynn–Wall–Ozawa method; values of 51.94 kJ mol−1 and 53.14 kJ mol−1 were obtained using Friedman method. It was possible to conclude that the lignin affects positively the thermal stability of the resin; the curing reaction takes place in the first six hours and the Flynn–Wall–Ozawa model fits better.

Synthesis of microporous carbon nanofibers with high specific surface using tetraethyl orthosilicate template for supercapacitors

Microporous carbon nanofibers (CNFs) with a high specific surface area were prepared by sol–gel, electrospun, carbonization and pickling processes. Resol type phenolic resin (PF) acted as carbon source, tetraethyl orthosilicate (TEOS) worked as template and polyvinyl-pyrrolidone worked as spinning additives. The specific surface area and total pore volume of the CNFs were increased obviously with the increased amount of TEOS. A high specific area of 2164 m2 g−1, high microporosity and relatively narrow pore size distribution were achieved. The electrochemical performance was evaluated in 6 M KOH aqueous solution. The microporous CNFs exhibited outstanding electrochemical performance as binder-free electrode of supercapacitors, including a high specific capacitance (316 F g−1 at 0.2 A g−1), considerable rate performance (210 F g−1 at 20 A g−1) and good cycle stability (95% after cycling 1000 times). The microporous CNFs were promising electrode materials for high-performanced supercapacitors.

Aromatic dialdehyde precursors from lignin derivatives for the synthesis of formaldehyde-free and high char yield phenolic resins

Commercial resol-type phenolic resins are mainly synthesized from the highly toxic and highly volatile formaldehyde. Aromatic aldehydes such as 4-hydroxybenzaldehyde, vanillin and syringaldehyde are not toxic and are obtained by depolymerization of the cheap and abundant lignins. They can be green and environmentally benign surrogate of formaldehyde in resol-type phenolic resins. For this purpose, reactivity of aromatic aldehydes has been studied in function of the nature and positions of aromatic substituents prior to the aldehyde function. Results prove that those bio-based compounds are not reactive in resol synthesis reactions but their reactivity can be triggered by masking their free-hydroxy groups. A functionalization method from 4-fluorobenzaldehyde has been designed and new difunctional and bio-based aromatic aldehyde precursors were synthesized in excellent yields. Those starting materials proved to be excellent alternatives to formaldehyde leading to bio-based resol-type phenolic resins free of formaldehyde with higher thermal stability and char yield properties.

Synthesis and Characterization of Composite Material Based on Modified Phenolic Resin

Acid and base catalyzed polycondensationreaction of phenol and bisphenol A with crotonaldehyde and cardanol results in novolac and resol type phenolic resins. Phenolic oligomers are characterized by their viscosity, average molecular weight and FT-IR spectral studies. Glass reinforced composites of all phenolic oligomers were prepared. Composites are characterized by their synergetic thermal stability by Thermo gravimetric analysis (TGA), Differential scanning calorimery (DSC), Scanning electron microscopy (SEM), and mechanical properties such as flexural strength, impact strength and hardness, chemical resistance, fibre content over a broad range of compositions. The thermal and curing behavior of the resins are found to vary markedly with the mole ratio and the purity of crotonaldehyde or cardanol. Composites prepared from these resin having very good mechanical properties.

Thermal Properties and Mechanical Performance of Unsaturated Polyester/Phenolic Blends Reinforced by Kenaf Fiber

In this study, unsaturated polyester resin (UP) is blended with resole type phenolic resin (PF) to develop a material with good flame retardancy. The UP/PF resin blends are expected to show good compatibility when compounded with natural fibers which in this research is kenaf fiber. The thermal properties were investigated by thermogravimetric analysis (TGA). The char yields of the UP/PF blends reinforced kenaf composite increased with PF content. The degradation temperature of the composite at 50% weight loss rose to 410.13°C as the PF content was increased to 40%. The result shows with additional of PF to UP resin enhance the thermal stability of the composite. Meanwhile the mechanical performance of UP/PF kenaf composite were evaluated and compared with neat UP and PF reinforced with kenaf fiber using tensile and impact testing. The mechanical properties of all resin blends at different mixing proportions slightly decrease by increasing the phenolic content but shown an improvement as compared to the PF kenaf fiber composite. The fracture surface morphology of the tensile testing samples of the composites was performed by scanning electron microscopy (SEM).

New method for the synthesis of formaldehyde-free phenolic resins from lignin-based aldehyde precursors

Phenolic resins are mainly obtained from phenol and the highly toxic and volatile formaldehyde. In order to synthesize new formaldehyde substituents for the synthesis of resol-type phenolic resins, we designed a method to functionalize phenolic compounds with aliphatic aldehydes by a two-steps reaction: the functionalization of an acetal group on aromatic hydroxyl functions and the subsequent deprotection of theses acetal groups into aliphatic aldehyde groups. This method was used on the lignin-based aromatic aldehyde precursors i.e. 4-hydroxybenzaldehyde and vanillin to turn them into reactive and difunctional biobased aromatic aldehyde precursors. Those precursors proved to lead to formaldehyde-free and biobased phenolic resins with competitive thermal properties compared to the usual formaldehyde resins.

SYNTHESIS AND CHARACTERIZATION OF NATURAL FIBRE REINFORCED POLYURETHANE COMPOSITES BASED ON CARDANOL

In recent studies importance has been given to the use of natural products from renewable resources due to the decrease in the supply and price escalations of petroleum raw materials. Cardanol based resole type phenolic resin has been synthesized by condensing cardanol with furfural in a particular mole ratio using dicarboxylic acid catalyst such as phthalic acid. Polyurethane sheets were prepared by treating cardanol furfural resin with 4,41 – methylene bis(cyclohexyl isocyanate) and the catalyst dibutyltin dilaurate. Natural fibres are prospective reinforcing materials and their use until now has been more traditional than technical. Among the various fibres sisal is of particular interest in that its composites have high impact strength besides having moderate tensile and flexural properties compared to other fibres. Fibre reinforced polyurethane composites have been prepared by treating sisal fibre (10%) into polyurethane. The physico chemical, spectral and thermal properties of polyurethane and fibre reinforced polyurethane composites have been studied.

Studies on the Thermal, Mechanical and Chemical Resistance Properties of Natural Resource Derived Polymers

Cardanol-based epoxidized resole resins (ERCF) were synthesized by reacting resole type phenolic resin (RCF) and epichlorohydrin in basic medium, at 120 °C. Resole type phenolic resins were synthesized by reacting cardanol (C) and formaldehyde (F) in the presence of sodium hydroxide, as catalyst, at five different temperatures ranging between 60-80 °C with an interval of 5 °C for a maximum period of 6h. These prepared samples were cured using 15% polyamide as curing agent at 120 ± 2 °C for 1h. Mechanical and chemical resistance characteristics of prepared samples were evaluated to assess the possibility of using such thermosetting resins as a new eco-friendly material for engineering applications. Upon evaluation, it was found that the prepared resins systems exhibit better properties compared to commercial epoxy resin in term of increase in tensile strength, elongation-at-break and impact strength, of castings and gloss, scratch hardness, adhesion and flexibility of the films. The anticorrosive properties from chemical resistance of the prepared resin systems are found to be superior than unmodified epoxy resins. The TG/DTG thermograms showed two step decomposition behaviors in all the prepared samples.

Activated carbon production by co-carbonization of feathers using water-soluble phenolic resin under controlled graphitization

We attempted to use feathers for the production of activated carbon (AC). A water-soluble resol-type phenolic resin was hybridized to prevent the liquefaction of the feathers and to control the graphitization degree of charcoal. The hybridization could effectively increase the yield of charcoal over 30% and maintained the graphitization degree at approximately 0.1, suitable for the production of AC. The Brunauer–Emmett–Teller (BET) surface area and the iodine-adsorption capacity of hybrid charcoal-based AC were 706m2/g and 550mg/g, respectively, which were 1.7-1.8 times greater than those of the feather-based AC at a similar activation level.

Electrospun phenolic resin-based carbon ultrafine fibers with abundant ultra-small micropores for CO2 adsorption

Recently, phenolic resin has been a promising precursor to synthesize electrospun carbon ultrafine fibers with well-controlled pore structure favorable for CO2 capture. We report the facile and large-scale preparation of freestanding microporous carbon ultrafine fibers from resole-type phenolic resin by electrospinning and following one-step carbonization, and investigate for the first time their CO2 adsorption performance at ambient temperature. The obtained samples were characterized by scanning electron microscopy, Raman spectra, X-ray photoelectron spectroscopy and N2 adsorption. Small average diameter of 820nm, high specific surface area (650m2g−1) and narrow micropore size distribution are associated with the prepared fibers. Remarkably, the ultrafine fibers possess much more ultra-small micropores (0.50–0.63nm) than common polyacrylonitrile-based activated carbon nanofibers and commercial porous carbon samples. With such well-designed structure, the resultant fibers show outstanding CO2 equilibrium adsorption capacities and good reversibility. At 25°C, the stable capture capacity of the fiber is 2.92mmolg−1 at 1bar and 0.44mmolg−1 at 40mbar, which offers great potentials for CO2 capture and storage.

Effect of the Fiber Orientation Relatively to the Plasma Flow Direction in the Ablation Process of a Carbon-Phenolic Composite

Composite materials are vastly employed in rocket nozzle extensions and as thermal protection shields in aerospace industry. In both cases, ablative and thermal properties play an important role for material choice and equipment sizing. These properties are strongly dependent on the way the pieces are manufactured. For the case of nozzle extensions, wrapping is the most common technique employed, which can be done by diverse ways. In this work, samples of the carbon reinforced carbon fiber (CRCF) were extracted from pre-forms obtained by biased and parallel tape wrapping processes with a resol-type phenolic resin used as polymer matrix, in order to study the influence of the fiber angle in the ablative behavior and thermal conductivity. Experimental results for both manufacturing techniques were obtained through ablation tests carried out in a plasma torch, were compared and had the different behaviors discussed. A computational simulation based in a two-front ablation model was also performed, in order to explain the influence of thermal conductivity on the different behaviors presented for biased fiber samples. Results show that the angle of the fibers relative to the heat flux direction is an important parameter to determine the ablative properties and the thermal performance of composite wrapped structures.

Preparation and characterization of nanoscale ZrB2/carbon–resol composite for protection against high-temperature corrosion

An advanced method combines using ZrB2 ceramic nanoparticles as filler within the carbon fiber–resol type-phenolic resin (C/Ph) composite for the superior ablation properties of thermal protection systems. The oxy-acetylene torch test suggested that ZrB2 nanoparticles could effectively protect C/Ph composite from ablation at 2,000 °C for 160 s. The ablation rate decreased when C/Ph composite was filled with 7 mass% of ZrB2 ceramic nanoparticles (Zr/C/Ph) over unfilled composite. In comparison to neat C/Ph composite, the introduction of nanosized ZrB2 particles embedded in the matrix significantly improved the ablative properties in terms of mass loss and erosion rate. During oxidation and ablation, the interface between carbon matrix and fiber is effectively protected by ZrO2 due to the reaction of ZrB2 with the oxygen, and the resultant zirconium oxide may form a film to resist the oxygen at high temperature.

Synthesis of Triazole-functionalized Phenolic Resin and its Inherent Flame Retardant Property

A novel triazole-functionalized phenolic resin was developed, and its thermal and flame-retardant properties were investigated. The triazole group was incorporated as a pendant unit on the phenolic resin via copper- mediated click chemistry between propargylated phenolic resin and benzyl azide. The newly-developed triazole-functionalized phenolic resin showed higher thermal stability and char yield, together with a reduced total heat release (THR), than the non-functionalized bare phenolic resin, indicating enhanced flame retardancy for the triazole-functionalized phenolic resin. and superior mechanical and ablative properties. 1,2 Phenolic resins are generally prepared by reactions bet- ween formaldehyde and phenol in the presence of acid or base. When prepared by acid catalysis, they are normally called novolac-type resins. In these resins, the molar ratio of formaldehyde to phenol is less than 1, and substitution occurs mostly at the ortho position of the phenol. In contrast, base-catalyzed pathways produce more cross-linked struc- tures, and are called resole-type phenolic resins, with sub- stitutions at both ortho- and para-positions. Phenolic resins with improved thermal and pyrolysis characteristics are desirable for producing composites for thermo-structural applications. 3,4 Although conventional phenolic resins are already considered to be temperature- resistant polymers and are currently in use for the above- mentioned applications, some of the properties of phenolic resins need further improvement for meeting the ever- increasing performance requirements. With sufficient heat and oxygen, most organic polymers will burn. Fundamentally, four processes are involved in the polymer combustion cycle: heating, decomposition, ignition, and combustion. In order to increase its flame resistance, the polymer system should function to interrupt this cycle. 5 A

Physico-mechanical properties of resol phenolic adhesives derived from liquefaction of oil palm empty fruit bunch fibres

Utilization of oil palm empty fruit bunch (EFB) fibres in the production of phenolic (PF) resin is an alternative way to reduce the dependency of petroleum-based phenol. In this study, resol-type phenolic resin was synthesized from oil palm EFB fibres via liquefaction process using phenol and sulfuric acid, followed by resinification reaction with formaldehyde in alkaline condition. The increase of the ratio of formaldehyde/liquefied EFB (F/LEFB) results in the increase in the viscosity and molecular weight of the produced PF resin. The obtained FTIR spectra confirmed that the chemical functionalities of the produced PF resin are almost similar to that of commercial PF resin. The NMR analyses indicated that the phenol para position was favoured for the reaction over the ortho position in both commercial resin and resin synthesized due to the existence of steric hindrance effect from the hydroxyl phenol and phenol derivatives of liquefied EFB. The shear strength of the produced PF resins is fulfilling the requirement as specified in JIS K-6852.

Microwave-assisted synthesis and characterization of resole-type phenolic resins

Resoles were prepared under microwave irradiation with different phenols, such as phenol, o-, p-, and m-cresols, separately with formaldehyde having formaldehyde/phenol ratio of 2:1 in basic medium. Analogical synthesis was performed using conventional heating for comparing the methods. The methylolation of phenol was confirmed by Fourier transform infrared spectroscopic analysis and a reaction mechanism was proposed. The number-average molecular weight was found by gel permeation chromatography technique. On the basis of the calculated value of kinetic chain length, the structure of the resole-type phenolic resin was proposed. Differential scanning calorimetry technique was used to investigate the curing behavior. As assessed by dynamic thermogravimetry, traces of resole sample prepared from p-cresol were found to possess better thermal stability, both in conventional as well as microwave-irradiated systems, among all other resole samples. The tensile strength, elongation at break, and impact strength showed an increasing trend. The main advantage of the process is about sixfold reduction of reaction time of the process carried at microwave reactors in comparison with the conventional heating.

레졸형 구형 페놀입자의 합성에서 반응물의 조성이 입자 형성에 미치는 영향

페놀-포름알데히드를 이용하여 레졸형 구형 페놀수지 입자를 합성함에 있어 반응물의 조성이 입도분포, 수율 및 밀도에 미치는 영향을 확인하였다. 분산매의 양을 감소시킴에 따라 현탁액의 점도가 증가하며 이로 인해 입도분포의 변화 및 응집 현상의 원인이 됨을 확인하였고, 안정제의 양을 증가시킴에 따라 현탁입자의 표면적을 증가시키기 위해 평균입도가 감소하는 것을 확인하였다. 적정량 이상의 경화제의 사용은 입도분포 및 수율에는 영향을 미치지 않으나 형성된 입자 내부의 격렬한 경화반응으로 인해 발생하는 물분자의 탈출이 원활하지 않게 되어 밀도가 감소하는 것을 SEM 사진을 통해 확인하였다. The effects of reactant composition on the particle size distribution, synthetic yield, and density of Phenol-formaldehyde bead were examined in the synthesis of resol-type phenolic resin. Decrease of the content of DI water as dispersion media can increase the viscosity of suspension, which may cause the difference of particle size distribution and aggregation. The average particle size of synthesized beads was also decreased with the increasing content of stabilizer which can affect the interfacial area. The amount of crosslinking agent showed no effect on the size distribution and synthetic yield, but it made a decrease in the density of synthesized bead due to the macropore in the bead.

Growth of Carbon Nanofibers Using Resol-Type Phenolic Resin and Cobalt(II) Catalyst

This study investigated carbon nanofibers (CNFs) grown on reticulated vitreous carbon (RVC) foam through catalytic deposition of ethylene. Before growing the CNFs, Co(II) on the RVC foam was expected to act as a catalyst by deposition. The preparation of the CNFs was a two-step process. The first step was preparing the RVC from polyurethane (PU) foam. Changes in weight over time were evaluated using two kinds of resol. The change in the mass and state of the sample with the change in temperature was studied during the carbonization process. The second step was to prepare the CNFs. An OH group was attached by the oxidation of the RVC foam. A change in the shape and mass of the sample was observed due to a change in nitric acid concentration and oxidation time. Then, cobalt was deposited to grow CNFs on the RVC foam. Hydrolysis helped to deposit the Co(ll) on the RVC foam. The appropriate time and temperature were investigated for the reduction process. In the last step, CNFs were prepared by the introducing ethylene gas. The resulting samples were analyzed using scanning electron microscopy, energy dispersive spectroscopy, N2-sorption, and X-ray photoelectron spectroscopy.