Resol-type Phenolic Resin 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.

Supersonic hot jet ablative testing and analysis of boron nitride nanotube hybrid composites

Boron nitride nanotubes (BNNTs) are high-strength, high-modulus nanotubes with high thermal and oxidative stabilities. Two hybrid composites were prepared with satin weave carbon fiber (CF) and resole-type phenolic resin: one with surface layers of BNNTs and one with alternating interlayers of BNNTs. The samples were subjected to hot jet tests that simulate realistic high-pressure-temperature conditions to understand the behavior of BNNTs under high-pressure erosion. Adding BNNTs to CF/phenolic laminates enhanced the ablation resistance by reinforcing the char material and mitigated localized thermal damage. Hybrid laminates exhibited up to 14 % lower weight loss, 55 % increase in flexural modulus, higher thermal diffusivity, and improved char yield and microstructure compared to CF/phenolic samples. The surface layer hybrid had many surviving nanotubes reinforcing the char and crystalline oxide structures that could mitigate further oxygen diffusion. Various characterization methods were used to deduce possible mechanisms and their products, indicating that BNNTs could serve as growth templates for direct crystalline boron oxide formation. Overall, hybrid BNNT/CF/phenolic laminates displayed better ablation resistance and favorable microstructure evolution under high-pressure conditions.

Carbons derived from resole-type phenolic resins for use in lithium–sulfur batteries: templating the resins with sulfur leads to enhanced cell performance

Pyrolysed resole-type phenol-formaldehyde resins were used as carbonaceous sulfur-hosts in the cathodes of lithium–sulfur batteries.

Sustainable Chitosan/Polybenzoxazine Films: Synergistically Improved Thermal, Mechanical, and Antimicrobial Properties.

Polybenzoxazines (Pbzs) are considered as an advanced class of thermosetting phenolic resins as they overcome the shortcomings associated with novolac and resole type phenolic resins. Several advantages of these materials include curing without the use of catalysts, release of non-toxic by-products during curing, molecular design flexibility, near-zero shrinkage of the cured materials, low water absorption and so on. In spite of all these advantages, the brittleness of Pbz is a knotty problem that could be solved by blending with other polymers. Chitosan (Ch), has been extensively investigated in this context, but its thermal and mechanical properties rule out its practical applications. The purpose of this work is to fabricate an entirely bio-based Pbz films by blending chitosan with benzoxazine (Bzo), which is synthesized from curcumin and furfuryl amine (curcumin-furfurylamine-based Bzo, C-fu), by making use of a benign Schiff base chemistry. FT-IR and 1H-NMR spectroscopy were used to confirm the structure of C-fu. The impact of chitosan on benzoxazine polymerization was examined using FT-IR and DSC analyses. Further evidence for synergistic interactions was provided by DSC, SEM, TGA, and tensile testing. By incorporating C-fu into Ch, Ch-grafted-poly(C-fu) films were obtained with enhanced chemical resistance and tensile strength. The bio-based polymer films produced inhibited the growth of Staphylococcus aureus and Escherichia coli, by reversible labile linkages, expanding Ch galleries, and releasing phenolic species, which was 125 times stronger than bare Ch. In addition, synthesized polybenzoxazine films [Ch/Poly(C-fu)] showed significant dose-dependent antibiofilm activity against S. aureus and E. coli as determined by confirmed by confocal laser scanning microscopy (CLSM). This study suggests that bio-based Ch-graft-polymer material provide improved anti-bacterial property and characteristics that may be considered as a possibility in the near future for wound healing and implant applications.

Preparation of NaF Microcapsules for High-Temperature Thermal Storage.

A novel NaF phase change microcapsule with a carbon shell (NaF@C microcapsule) was prepared by a simple approach. The carbon shell was synthesized by carbonization of a resole-type phenolic resin shell, which was encapsulated onto the surface of NaF particles by a simple phase separation process induced by tetraethoxysilane. Scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, differential scanning calorimetry (DSC), and thermogravimetric analysis were used to characterize the morphology, composition, crystal phase, and thermal properties of the microcapsules. The size of the NaF@C microcapsule was 3–5 μm with a core–shell structure. DSC results showed that the melting point of the prepared NaF@C microcapsule was 988 °C, and the enthalpy value was 192 J/g. The prepared NaF@C microcapsules retained the powder morphology after 30 times of heat treatment at 1100 °C, with no NaF leakage detected, and the micromorphology remained stable, presenting good thermal stability. The NaF@C microcapsules can be used in the fields of thermal protection and thermal management in extreme high-temperature environments such as aerospace and solar energy.

Study on the feasibility of alternatives for phenolic resins used in sand casting

ABSTRACT Phenolic resins are in-organic polymers with properties that make them high-strength binders with great potential for modification. The base-catalyzed phenol-formaldehyde resins provide the desired hardness to the core avoiding sand slipping on the surface. A modified resol type phenolic resin is developed for this study with minimum ingredients to compare it with existing recipes in the literature. A batch of cores was prepared with the standard 1-inch cross-section briquettes (dog-bone) with modified resol and cured through hot-curing process. Hardness and ultimate tensile strength values of these cores were compared with previous data present in literature. The average hardness as well the tensile strength from modified resol was higher than the cores from previous hot coating resol recipes and the gas-set cores present in the literature. Furthermore, the surface roughness of the cores was examined through Atomic Force Microscopy (AFM), and the ten-point height (Rz) value was lower than existing recipes.

Terephthalaldehyde-Phenolic Resins as a Solid-Phase Extraction System for the Recovery of Rare-Earth Elements.

Rare-earth elements (REEs) are involved in most high technology devices and have become critical for many countries. The progress of processes for the extraction and recovery of REEs is therefore essential. Liquid–solid extraction methods are an attractive alternative to the conventional solvent extraction process used for the separation and/or purification of REEs. For this purpose, a solid-phase extraction system was investigated for the extraction and valorization of REEs. Ion-exchange resins were synthesized involving the condensation of terephthalaldehyde with resorcinol under alkaline conditions. The terephthalaldehyde, which is a non-hazardous aromatic dialdehyde, was used as an alternative to formaldehyde that is toxic and traditionally involved to prepare phenolic ion-exchange resins. The resulting formaldehyde-free resole-type phenolic resins were characterized and their ion-exchange capacity was investigated in regard to the extraction of rare-earth elements. We herein present a promising formaldehyde and phenol-free as a potential candidate for solid–liquid extraction REE with a capacity higher than 50 mg/g and the possibility to back-extract the REEs by a striping step using a 2 M HNO3 solution.

Modified resol type phenolic resin nanocomposites as surface metal coatings

AbstractNanocomposites based on resol resin as a matrix and prepared organoclay, from Egyptian bentonite clay, as reinforcement material were synthesized. The effect of organoclay content (i.e., 0.5, 1.0, 1.5, 2.0, and 2.5 phr) on the properties of the prepared samples with respect to the prepared composites and resol resin with no clay was investigated. The prepared samples with higher organoclay content (i.e., 2.0 phr) were modified with epoxy or/and urethane resin and characterized using transmission electron microscope (TEM), X‐ray diffraction (XRD), and Fourier transform infrared measurements (FTIR). TEM showed uniform dispersion of the clay while XRD showed exfoliated structures. FTIR measurements confirmed the bond formation between epoxy or/and diisocynate with phenolic hydroxyl groups of resol resin. Mechanical properties, chemical resistance, thermal properties, and electrical volume resistivity were studied. Results showed that epoxy modified resol resin film samples with 2.0 phr organoclay exhibited higher adhesion and scratch hardness values, higher chemical resistance, thermal stability, and lower electrical conductivity compared with mixed epoxy/urethane and urethane samples as well as unmodified resol resin nanocomposite film samples. The samples could be useful as surface metal coatings.

Condensed tannin resins extracted from Pinus radiata bark as a support matrix in carbon nanofiber-reinforced polymers

Condensed tannins extracted from the Pinus radiata bark (PRTs) were used as a replacement for phenol in the synthesis of resol-type phenolic resins (FRs) and tested as polymer matrix in carbon nanofiber (CNF)-reinforced composite materials. The PRTs used herein contained a phenol and lignin content of 31 (Eq/L) and 35 (%w/w), respectively. The molecular weights of these polyphenols indicated the presence of 16 flavonoid units. Tannin resins were synthesized, and their characteristics were compared with those of the synthesized FRs using a formaldehyde/phenol ratio of (1.6/1.0), which has the highest total solids content. The results showed that the gel time and useful life of the resins decreased with the addition of the tannins, while there was no significant variation in the degradation temperature with varying FR contents. The mechanical properties of the CNF-reinforced composite materials were determined by DMA, and the results showed an increase of 1000 MPa, due to the better distribution of the fibers in the matrix. The modulus (E') in the reinforced composite materials with tannin resins was 2322 MPa and 1803 MPa without tannins, while modulus E¨ for composite materials doubled for resins with tannins. Tannins improved the dispersion of CNTs and the matrix-filled interface.

High-Molecular-Weight PLA-b-PEO-b-PLA Triblock Copolymer Templated Large Mesoporous Carbons for Supercapacitors and CO2 Capture

High-molecular-weight PLA440-b-PEO454-b-PLA440 (LEL) triblock copolymer was synthesized through simple ring-opening polymerization (ROP) by using the commercial homopolymer HO-PEO454-OH as the macro-initiator. The material acted as a single template to prepare the large mesoporous carbons by using resol-type phenolic resin as a carbon source. Self-assembled structures of phenolic/LEL blends mediated by hydrogen bonding interaction were determined by FTIR and SAXS analyses. Through thermal curing and carbonization procedures, large mesoporous carbons (>50 nm) with a cylindrical structure and high surface area (>600 m2/g) were obtained because the OH units of phenolics prefer to interact with PEO block rather than PLA block, as determined by FTIR spectroscopy. Furthermore, higher CO2 capture and good energy storage performance were observed for this large mesoporous carbon, confirming that the proposed approach provides an easy method for the preparation of large mesoporous materials.

Competing hydrogen bonding produces mesoporous/macroporous carbons templated by a high-molecular-weight poly(caprolactone–b–ethylene oxide–b–caprolactone) triblock copolymer

In this study we developed a simple strategy to synthesize macro- and mesoporous carbons by using a high-molecular-weight triblock copolymer, PCL440-b-PEO454-b-PCL440 (CEC), as a single template, itself prepared through simple ring-opening polymerization from a commercial homopolymer (HO-PEO454-OH) as the bifunctional macroinitiator and a resol-type phenolic resin as the carbon source. We employed differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, and small-angle X-ray scattering to investigate the thermal behavior, hydrogen bonding, and self-assembled nanostructures of the phenolic/CEC blends. We obtained macro- and mesoporous carbons possessing cylinder or spherical micelle structures with large pores (> 50 nm) and high surface areas (>400 m2 g−1), the result of most of the phenolic OH units preferring to interact (based on FTIR spectral analyses) with the PEO segment rather than the PCL segment. These macro/mesoporous carbons displayed reasonable CO2 uptake and energy storage behavior.

Preparation and properties of nanocomposites composed of a water-soluble nylon and chitin nanofibers

Nanocomposites composed of a water-soluble nylon (P-70, polyalkyleneoxide-modified poly(ɛ-caprolactum), and chitin nanofibers (ChNFs) were prepared by a casting method of the aqueous resin/fiber dispersion. P-70 was crosslinked with a resol-type phenolic resin (PR) and its ChNF nanocomposites were prepared to provide water resistance. The P-70/PR and P-70/PR/ChNF exhibited excellent water-resistance. The FT-IR analysis revealed that the crosslinked structure was formed by the reaction of amide groups of P-70 and methylol groups of PR. The glass transition temperature (Tg) of P-70/PR increased with increasing PR content, whereas the dispersion of ChNFs was deteriorated. Although the addition of ChNF to P-70 hardly affected the Tg, the addition of ChNF to P-70/PR caused a lowering of Tg. The tensile strength and modulus for P-70/ChNF nanocomposites increased with increasing ChNF content. The tensile strength of P-70/PR was lower than that of P-70, which increased by the addition of ChNF.

Study of the ablative properties of phenolic/carbon composites modified with mesoporous silica particles

Mesoporous silica particles and carbon black were selected as fillers for a resol-type phenolic resin, to be used as a matrix for ablative materials. Composites were processed with the modified polymer and carbon fibers were used as continuous reinforcement. The ablative properties of the materials obtained were studied by the oxyacetylene torch test and the ablated samples were observed by scanning electron microscopy. Composites with 30 wt. % of carbon black achieved the lowest linear erosion rate and the highest insulation index, denoting the ability of the char produced to protect the virgin material. Considering that such composite has 44% by volume of carbon fibers, it could be inferred that its properties could be improved by increasing the fiber content and maintaining the amount of carbon black. The composite with 20 wt. % of mesoporous silica particles exhibited the lowest mass erosion rate, indicating a better stabilization of the char. Regarding dynamic-mechanical properties, the addition of particles induced a decrease in the modulus and glass transition temperature of all the systems studied.

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.

Studies on thermal decomposition of phenol binder using TG/DTG/DTA and FTIR-DRIFTS techniques in temperature range 20–500 °C

This paper presents results of thermoanalytical and structural research on phenolic binder used in foundry for the preparation of moulding sand. The binder has been prepared based on resole type phenolic resin with the addition of ester hardener. The aim of the study was to determine the structural changes taking place in the phenolic binder under the influence of temperature. Results show that in the investigated range of temperatures, phenolic binder exhibits three exothermic thermal effects accompanying the decomposition process. The test results using the Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) technique show that the addition of a hardener stabilizes the binder structure within methylene bridges. The reduction in the reaction rate observed in the DTA curve at about 330 °C can be associated with the formation of gaseous products by decomposition of the binder or, as suggested by the literature data, the formation of triple bonds and CN-HCN groups.

Studies on solvent based phenolic pre-pregs with various reinforcements

The Glass, rayon based carbon, PAN based carbon and high silica fabric reinforcements were impregnated with standard resole type phenolic resin in a vertical impregnating plant. The heating zones of prepreg plant converts resin impregnated fabric into partially polymerized state is called B-stage. The required volatile content and chang’s index are achieved by adjusting plant parameter based on online testing of prepreg, and it was noticed resin content varying depend on reinforcement used. The rayon carbon/phenolic prepregs had high wet resin content and glass/phenolic prepregs had low wet resin content

Bio-oil as Substitute of Phenol for Synthesis of Resol-type Phenolic Resin as Wood Adhesive

Abstract The bio-oil from fast pyrolysis of cornstalks was used as substitute of phenol to synthesize resol resin as an ideal wood adhesive. The effects of formaldehyde/phenol (F/P) molar ratios and oil/phenol (O/P) weight ratios on rehology, thermal cure, thermal resistance and adhension of plywoods were investigated. With the increase of bio-oil used in bio-resol, the gel time of the prepared bio-oil modified resol resin (bio-resol resin) increased gradually, and the exothermic peak temperature of thermal cure shifted slightly higher. It was found that the bio-resin with bio-oil/phenol = 0.5 (weight ratio) and F/P = 1.5 (molar ratio) had the best comprehensive properties. The plywoods made with the bio-resol resins fulfilled the standards of E0 and type I plywood, implying the bio-resol resins was a new environment-friendly adhesive.

Tailored Design of Bicontinuous Gyroid Mesoporous Carbon and Nitrogen-Doped Carbon from Poly(ethylene oxide-b-caprolactone) Diblock Copolymers.

Highly ordered mesoporous resol-type phenolic resin and the corresponding mesoporous carbon materials were synthesized by using poly(ethylene oxide-b-caprolactone) (PEO-b-PCL) diblock copolymer as a soft template. The self-assembled mesoporous phenolic resin was found to form only in a specific resol concentration range of 40-70 wt % due to an intriguing balance of hydrogen-bonding interactions in the resol/PEO-b-PCL mixtures. Furthermore, morphological transitions of the mesostructures from disordered to gyroid to cylindrical and finally to disordered micelle structure were observed with increasing resol concentration. By calcination under nitrogen atmosphere at 800 °C, the bicontinuous mesostructured gyroid phenolic resin could be converted to mesoporous carbon with large pore size without collapse of the original mesostructure. Furthermore, post-treatment of the mesoporous gyroid phenolic resin with melamine gave rise to N-doped mesoporous carbon with unique electronic properties for realizing high CO2 adsorption capacity (6.72 mmol g-1 at 0 °C).

Investigation into Mechanical, Thermal, Flame-Retardant Properties of Wood Fiber Reinforced Ultra-High-Density Fiberboards

The demand has grown in many fields for materials that are eco-friendly and sustainably developed. In this study, several formulations of novel wood fiber reinforced ultra-high-density fiberboards (UHDFs) using resol-type phenolic resin (RTPR) as binders were manufactured for application in decorative building facades. The influences of the various formulations on water resistance and the mechanical, thermal, and fire-resistant properties were systematically examined. All formulations of the UHDFs exhibited better water resistance, internal bonding, and fire resistance as the RTPR content and density increased. To better evaluate mechanical properties, the microstructure of the UHDFs was observed using scanning electron microscopy. After optimization of hot-pressing conditions, UHDFs with excellent mechanical properties of approximately 7.2 GPa, 85.9 MPa, and 5.4 MPa for bending modulus, bending strength, and internal bonding, respectively, were achieved. Good water and flame resistance were also achieved, which makes these materials competitive with other commercial products.

Innovative ablative fire resistant composites based on phenolic resins modified with mesoporous silica particles

Mesoporous silica particles were used as reinforcement of a phenolic resin to develop new ablative materials. A resol type phenolic resin was filled with mesoporous silica particles synthesized from tetraethyl orthosilicate (TEOS). Samples of neat phenolic resin, phenolic resin reinforced with carbon black and with mesoporous silica particles (5 and 20 wt %), were obtained. The ablative properties of the materials were studied by the oxyacetylene torch test and the ablated samples were observed by scanning electron microscopy (SEM). The composites were also characterized by dynamic mechanical analysis and transmission electron microscopy (TEM). Results showed a stronger chemical interaction between silica particles and the phenolic resin, than carbon black, thus increasing the glass transition temperature and mechanical properties of the silica/resin composites. In addition, the samples with mesoporous silica particles achieved lower erosion rates and back-face temperatures than the others, becoming promising thermal protection materials for the aerospace industry.