Boron-modified Phenolic Resin Research Articles

Research Progress in Boron-Modified Phenolic Resin and Its Composites.

As one of the most successful modified phenolic resins, boron-modified phenolic resin (BPF) has excellent heat resistance and ablative resistance, good mechanical and wear resistance, and flame retardancy. BPF and its composites can be widely used in areas such as aerospace, weapons and equipment, automobile brakes, and fire retardants. In this review, the current state of development of BPF and its composites is presented and discussed. After introducing various methods to synthesize BPF, functionalization of BPF is briefly summarized. Particular emphasis is placed on general methods used to fabricate BPF-based composites and the heat resistance, ablative resistance, mechanical property, wear resistance, flame retardancy, and water resistance of BPF-based composites. Finally, the challenges of this research area are summarized and its future outlook is prospected.

Design and preparation of resin matrix composite coating with good ablation resistance performance under high-energy laser irradiation

High-energy lasers can cause severe damage to conventional materials in an extremely short time. Highly reflective coatings are effective against damage, but they cannot withstand high laser power densities. In this study, a composite coating with two characteristics, namely, reflection and energy consumption, was designed and prepared. TiO2 and BN powders, as light reflective media, were introduced into a boron-modified phenolic resin (BPF) to prepare an anti-laser composite coating. The results show that the initial reflectivity of the composite coating can reach 78.8% at a wavelength of 1064 nm. After damage-free protection for 0.4 s, ablation occurred in the irradiation region. Owing to the formation of residual char, which is the pyrolysis product of BPF, the coating maintained its protective performance. When the composite coating was irradiated at 1000 W/cm2 for 10 s, the back-surface temperature was 186 °C, which indicates decent anti-laser performance. We also studied the role of BN by setting a control experiment. The high conductivity and energy consumption caused by the evaporation of B2O3, which is the oxidation product of BN, helped in improving the anti-laser performance. The residual char with high porosity and degree of graphitization proved to be effective to isolate laser energy. This study provides a new design for protection of conventional materials against laser damage.

Design and Preparation of Localized Heat-Resistant Coating.

Localized heat sources, such as flame guns and high-energy lasers, can cause severe damage to conventional materials. In this study, a novel localized heat-resistant coating with a high in-plane thermal conductivity was designed and prepared. Reduced graphene oxide (rGO) effectively improved the in-plane thermal conductivity of the polyvinyl alcohol (PVA) film, while maintaining the thermal insulation of the resin matrix in the through-plane direction. This characteristic of the rGO/PVA film was combined with the thermal insulation of boron-modified phenolic resin (BPF), and the prepared composite coating with two layers of rGO/PVA films effectively lowered the back-surface temperature in the flame ablation test from 151 to 107 °C. In addition, the area of the ablation-affected region of coating was increased to 103.6 cm2 from 31.9 cm2, indicating an excellent heat transfer performance. The layer-by-layer structure could realize the compatibility of high in-plane thermal conductivity and good through-plane thermal insulation. The synergy of these two different characteristics is demonstrated to be the key to improving the localized heat-resistant performance of the composite coating. This study effectively expands the application range of high-conductive film, and the obtained coating could act as a shield against butane flame, high energy lasers, and other localized heat.

Broadband electromagnetic shielding performance of carbon nanotube-carbon fibre/silicon carbide cross-scale laminated composites

A carbon nanotube-carbon fibre/silicon carbide (CNT-CF/SiC) laminated composite, with a density of 1.61 g/cm3, thickness of 2.7–3.0 mm and conductivity of 6.10 S/cm, was prepared by densifying a single layer with boron-modified phenolic resin and then welding it with resin-derived carbon layer by layer. This laminated composite was alternately composed of a relatively dense CNT buckypaper/SiC composite layer and a relatively porous three-dimensional needled CF felt/SiC composite layer. The CF felt with a laminated constructure produced a laminated substructure nested within the layers. Expanded graphite with laminated structures produced laminated substructures nested within the interfaces. The average total shielding efficiency values of the composites with 5 layers (CNT-CF/SiC-5), 4 layers and a CNT buckypaper/SiC composite layer on the top surface, and 4 layers and a CF felt/SiC composite layer on the top surface were 45.14, 37.70 and 38.85 dB, respectively, throughout the X-band and were 52.31, 45.56 and 43.54 dB, respectively, throughout the Ku-band. The transmission coefficient of CNT-CF/SiC-5 was as low as 10−5−10−6 orders of magnitude over the entire frequency range of 8.2–18 GHz except for very few frequency points. The optimal number of layers for this multilevel and multiscale laminated composite is believed to be 5.

Morphology controlled carbon aerogel with enhanced thermal insulation and mechanical properties: a simple route for the regulated synthesis

A simple route was proposed to prepare size-controlled carbon aerogel with superior thermal insulation and mechanical properties. Boron-modified phenolic resin (BPR) and hexamethylene-tetramine (HMTA) were crosslinked to build three-dimensional network structure initially followed by CO2 supercritical drying and carbonization. In order to regulate the microstructure of BPR aerogels, the best proportion of HMTA to BPR was confirmed as H/P = 1/5 based on the micromorphology performance in SEM. The interaction between HMTA and BPR was also studied by FTIR spectra, and microstructure evolution of the target product- carbon aerogels were illustrated by SEM technique. SEM patterns indicated that the carbon aerogels maintain a stable porous structure at 1000 °C (carbonization temperature), and pore size distribution were between 321∼612nm based on N2 adsorption-desorption method. The synthesis method is convenient and flexible, permitting a tailor of porous structure, mechanical strength, density and thermal conductivity by adjusting carbonization temperature and time. Consequently, the obtained carbon aerogel with high compressive strength (1.0∼2.3 MPa), low density (0.16∼0.26 g‧cm−3) and low thermal conductivity (0.023∼0.036 W m−l K−1) deserve to be a competitive candidate for high-temperature heat insulation material.

Design and preparation of composite coatings with increased reflectivity under high-energy continuous wave laser ablation

High-energy continuous wave (CW) laser ablation can cause severe damage to structural materials in an extremely short time, which generates considerable concern in terms of material safety. For the purpose of reducing or even eliminating such laser-induced damage, a novel composite coating consisting of a boron-modified phenolic formaldehyde resin incorporating ZrC and SiC has been designed and prepared. The experimental results reveal that ZrC and SiC are rapidly oxidized to ZrO2 and SiO2 respectively, leading to the formation of a white ceramic layer consisting of ZrO2 particles and melted SiO2. After ablation at 1000 W/cm2 for 50 s, elemental analysis indicates that no Si can be found in the central ablation zone because of gasification. A relatively compact ZrO2 layer is formed through the sintering of adjacent ZrO2 particles, which effectively improves the reflectivity of the coating from 7.3% (before ablation) to 63.5% (after ablation). The high reflectivity greatly reduces the absorption of laser energy. In addition, no obvious ablation defects are observed in the composite coating. The excellent anti-laser ablation performance of the coating makes it a promising system for protecting a material against the effects of long-term CW laser ablation.

Ablation behavior of boron-modified phenolic resin irradiated by high-energy continuous-wave laser and its evolution of carbon structure

Despite many years of use of boron-modified phenolic resin (BPF) in the aerospace and auto industry, it is still unknown if such resin can be used in extreme environments, especially under exposure to high energy continuous-wave (CW) laser that can totally destroy many traditional materials in several seconds. Compression molded BPF plates are tested with high energy CW laser to study the laser ablation behavior. Results reveal that the laser parameters including irradiation time and laser power density have a great effect on the ablation morphology and mass ablation rate. BPF keeps decomposing into residual char due to the high temperature caused by laser. The graphite structure of residual char is gradually improved during laser irradiation, resulting in improved thermal stability of residual char. In addition, the micro-morphologies reveal that the residual char possess porous structure which leads to the thermal insulation property and minimizes the ablation damage propagating into the BPF bulk. Both the improved thermal stability and the thermal insulation property of the residual char can mitigate the ablation damage caused by the high energy CW laser.

Phenolic resin modified by boron-silicon with high char yield

In order to improve the thermal stability, oxidation resistance and storage stability of phenolic resin, and to avoid complicated synthetic methods, herein, a facile, environmental friendly, controllable and low-cost strategy was designed and a novel boron-and silicone-containing phenolic resin (BSiPF) was prepared, in which silicone was reacted with commercial boron-modified phenolic resin (BPF). The as-prepared BSiPF solution has a long shelf life (more than 8 months) at room temperature. Structure, molecular weight, gel properties, curing behavior and heat resistance of BSiPF were characterized. Compared with common PF resin, the maximum decomposition rate (Dmax) of BSiPF in N2 and air atmosphere decreased by 0.81%/min and 1.52%/min, respectively, while the char yield at 800 °C(R800) of BSiPF in N2 and air atmosphere increased by 12.0% and 22.5%, indicating that the introduction of silicon and boron obviously enhance the heat resistance and anti-oxidation property of phenolic resin. With superior thermal stability and low viscosity, BSiPF can be used as a novel high performance matrix resin for ablative materials.

Preparation, ablation behavior and mechanism of C/C-ZrC-SiC and C/C-SiC composites

ZrC precursor was synthesized by a solution approach using ZrOCl2·8H2O, acetylacetonate, glycerol and boron-modified phenolic resin. A ZrC yield of ~ 40.56wt% was obtained at 1500°C in the C/Zr molar ratio of 1:1. C/C-ZrC-SiC composites were fabricated by a combined processes of chemical vapor infiltration (CVI) and precursor infiltration and pyrolysis (PIP) using the synthesized ZrC precursor. For comparison, C/C-SiC composites were prepared by CVI. Thermogravimetric analysis showed that C/C-ZrC-SiC composites exhibited better oxidation resistance than C/C-SiC composites. After oxyacetylene torch ablation, the mass ablation rate of C/C-ZrC-SiC composites was 9.23% lower than that of C/C-SiC composites. The porous ZrO2 skeleton in the ablation center was prone to be peeled off by the flame flow, resulting in the higher linear ablation rate of C/C-ZrC-SiC composites. The oxide layers of ZrO2 and SiO2 were formed on the transition and brim region of C/C-ZrC-SiC composites and acted as effective heat and oxygen barriers. For C/C-SiC composites, the C-SiC matrix was severely depleted in the ablation center and the formed SiO2 layer in the brim region could protect the matrix against further ablation.

Curing kinetics and curing process of phenolic impregnated carbon ablator

ABSTRACTPhenolic impregnated carbon ablator (PICA), which is composed of the phenolic resin (PR) and carbon fiber, is of particular interest to researchers in the aerospace field. In this work, PICA was prepared by the double‐stage isothermal heating curing. Then, the curing kinetics of boron‐modified phenolic resin (BPR) was investigated by non‐isothermal differential scanning calorimetry method in order to optimize the curing temperature of BPR. Further, the effect of the heating rate during curing process on the compressive strength of PICA was discussed in detail. The experimental data show that the curing of BPR needs more energy so that the curing temperature of BPR under different condition is higher than that of virgin PR. Notably, with the increasing heating rate during the curing process, the micro‐cracks increase and the compressive strength of PICA decreases. Once the heating rate exceeds a critical value, the micro‐cracks no longer increase and the heating rate has insignificant effect on the compressive strength. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45434.

Novel cardanol-containing boron-modified phenolic resin composites

To improve the thermal stability of phenolic resin and develop functional sustainable adhesive, a thermal-resistant cardanol-containing boron–phenolic resin (CBPR) was prepared by copolymerizing salicyl alcohol, cardanol, and boric acid. The structure of CBPR was characterized by Fourier transform infrared spectroscopy. Thermal stability of the investigated composites was estimated using thermogravimetric analysis (TGA). The results of TGA indicated that the modified resin exhibited excellent thermal stability. Specifically, the B-0.2 thermoset had a char yield of 69% when the boron content was only 1.27 wt%. The curing kinetic behavior was well described by differential scanning calorimetry and model-free kinetic analysis. Further, CBPRs, nano-aluminum oxide powders, glass powders with low melting point, and vitreous silica fibers were used as resin matrix, filler, forming additive, and reinforced material, respectively, to produce a novel ceramizable phenolic molding composite. The ablative characteristics of the co-cured blends were explored in terms of linear/mass ablation rate and microscopic pattern of ablation via the oxyacetylene torch tests. After thermal treatment, the formation and growth of the ceramic phase enhanced the thermal stability and ablation performance of the composites at high-temperature region. The morphology and phase composition of the residual chars were studied by scanning electron microscopy and energy dispersive spectroscopy, respectively. The linear and mass ablation rates for the modified composites decreased obviously in comparison with those of the unmodified composites, indicating that the modified composites possessed enhanced thermal stability and ablation property.

Preparation and thermal stability of boron-containing phenolic resin/microcrystalline muscovite composites

In order to further improve thermal stability of the boron-modified phenolic resin, we combined boron-modified phenolic resin and microcrystalline muscovite over a range of microcrystalline muscovite loadings (5–20 wt-%) to prepare composites. Microcrystalline muscovite was modified by titanate coupling agent. Fourier transmission-infrared analysis showed that the titanate coupling agent chemically bonded with the microcrystalline muscovite powder. The modified microcrystalline muscovite was mixed with boron-modified phenolic resin matrix in the molten state, and the composites were cured by compression moulding. Thermogravimetric analysis showed the effect of microcrystalline muscovite content to enhance decomposition temperatures and residual weight at 1000°C of the composites. Flexural test showed that the flexural strength before heat-treated was reduced with incremental loadings of microcrystalline muscovite fillers. On the contrary, after heat-treated at 1000°C, the flexural strength is increased. Scanning electron microscopy illustrated the microstructure evolution of the composites at elevated temperatures.

The role of microcrystalline muscovite to enhance thermal stability of boron-modified phenolic resin, structural and elemental studies in boron-modified phenolic resin/microcrystalline muscovite composite

A polymer matrix composite was prepared by incorporating microcrystalline muscovite fillers into a boron-modified phenolic resin. Thermogravimetric analyses indicated that microcrystalline muscovite significantly enhanced the thermal stability of boron-modified phenolic resin under air atmosphere. Then the composite was heated in a furnace. After heated, the homogeneous structure of the composite was converted into a layered structure with a ceramic shell on the surface. The layered structure was investigated by electron probe micro-analysis and energy dispersive spectroscopy. The elemental content and chemical binding state of the layered structure were investigated by X-ray photoelectron spectroscopy. On the surface, the reaction between SiO2 and Al2O3 occurred, thus microcrystalline muscovite fillers were transformed into mullite shell. The mullite shell could protect char from further oxidation at elevated temperatures. Therefore, a amount of reserved char could react with SiO2 to generate Si–C bond in the inner of the composite.

Synthesis and properties of graphene oxide–boron-modified phenolic resin composites

Boron–modified phenolic resin (BPR) has a good thermal property, but it has deficiencies in mechanical performance. To obtain PR materials with good thermal property, graphene oxide (GO) was added along with BPR to form a GO–boron-modified PR (GO-BPR). In this study, BPR and GO-BPR were prepared and their thermal resistance and mechanical properties were investigated. In addition, the effects of GO content on the thermal resistance of GO-BPR were studied. Results demonstrate that the optimal GO content was 0.5%. The thermal properties of GO-BPR with 0.5% GO improved 1.06 times when compared with that of BPR, and the peak degradation temperature of GO-BPR increased by approximately 10°C. When compared with BPR composite, the bending, tensile, and impact strengths of the GO-BPR composite materials with 0.5% GO-BPR increased by 46, 38, and 53%, respectively.

Characterization of Boron Modified Phenolic Resin and its Curing Behavior

Boron modified phenolic (BPF) resins with different boron amounts were synthesized with a special synthesis technology. The structure of BPF resin was analyzed by Fourier transform infrared spectra (FTIR) and its curing behavior was analyzed by differential scanning calorimeter (DSC). The results showed that boric acid reacted with the hydroxyl groups in phenolic resin to form a new cross-linked bond such as B-O. At the same time, the heat resistance of BPF resin was improved about 18% with addition of boric acid of 0.8wt%. The obtained BPF had a high curing temperature of 254.6when the boric acid amount was 0.8wt%.

Joining of C/C–SiC using boron-modified phenolic resin with SiO2 and B4C additives

Joining of carbon fibre reinforced C– SiC dual matrix composite has been realized through a reaction joining process using boron-modified phenolic resin with B4C and SiO2 additives. The effect of the technological parameters on the strength of joints was investigated. The optimized technological parameters are the curing temperature of 200°C, the curing time of 2 hours and the curing pressure of 30 kPa, under which conditions, the obtained strength of the joint is equal to 82.6% of that of the substrate. The interlayer composed of Si, C, B and O is basically uniform and dense. There are no obvious cracks nor pores at the interfaces. The elements migrate across the interfaces, contributing to the enhancement of the joint strength. The results of heat treatment at 1500°C show good heat resistance of the joints. The B4C and SiO2 additives contribute to the densification of the interlayer and the adhesion at the interfaces.

Joining of C/C–SiC using boron-modified phenolic resin with SiO2and B4C additives

Joining of C/C–SiC using boron-modified phenolic resin with SiO₂and B₄C additives

The effect of high-temperature heat-treatment on the strength of C/C–SiC joints

Joining of carbon fiber reinforced C–SiC dual matrix composite (denoted by C/C–SiC) is critical for its aeronautical and astronautical applications. Joining of C/C–SiC has been realized through a reaction joining process using boron-modified phenolic resin with micro-size B4C and nano-size SiO2 powder additives. The effect of the heat-treatment temperature on the retained strength of the joints, calculated by dividing the strength of the heat-treated joints by the strength of the joints before heat-treatment, was studied. The maximum retained strength of the joints is as high as 96.0% after the heat-treatment at 1200 °C for 30 min in vacuum, indicating good heat resistance of the joints. The thickness of the interlayer of the joint after the heat-treatment is about 18 μm and it is uniform and densified. There are no obvious cracks or pores at the interfaces. During the heat-treatment, carbon, oxygen, silicon, and boron diffuse at the interfacial area. The interlayer is composed of B4C, SiO2, glassy carbon, amorphous B2O3, and borosilicate glass. SiC appears in the interlayer of the joint heat-treated at 1400 °C for 30 min in vacuum. The addition of B4C and SiO2 powders contributes to the densification of the interlayer, the bonding at the interfaces and the heat resistance of the joints.

The effect of high temperature heat-treatment on the strength of C/C to C/C–SiC joints

Joining of carbon fiber reinforced carbon matrix composite to a carbon fiber reinforced C–SiC dual matrix composite has been realized through a reaction joining process using boron-modified phenolic resin with micro-size B 4C and nano-size SiO 2 powder additives. The effect of the heat-treatment temperature on the retained strength of the joints, calculated by dividing the strength of the heat-treated joints by the strength of the joints before heat-treatment, was studied. The maximum retained strength of the joints is 91.9% after heat-treatment at 1200 °C for 30 min in vacuum, indicating good heat-resistance of the joints. The interlayer with a thickness of about 25 μm is uniform and densified. There are no obvious cracks or pores at the interfaces. The interlayer is composed of B 4C, SiO 2, glassy carbon, B 2O 3 and borosilicate glass. Si diffuses from the interlayer into the substrates and reacts with carbon to form SiC. Both B and O migrate from the interlayer into the substrates, contributing to the interfacial bonding. The B 4C and the SiO 2 powder additives contribute to the densification of the interlayer, the bonding at the interfaces and the heat-resistance of the joints.

Boron-modified phenolic resins for high performance applications

A boron-modified phenolic resin (BPR) that flows at usable processing temperatures was prepared from the solvent-less reaction of triphenyl borate (TPB) and paraformaldehyde (PF). The reaction of TPB and PF was performed at three different resinifying temperatures, 130, 120 and 90 °C. The BPR produced at 90 °C melted upon reheating, which indicated promising processing applications for this resin. 1H and 13C NMR spectra of resins from the three resinifying temperatures had the same pattern of absorptions. Substitution of methylol groups occurred at the ortho and para positions of the ester phenyl rings (4.86–4.75 ppm). Aromatic, methylene and ether linkage protons were assigned at about 7.45–6.74, 4.93–3.36 and 5.30–4.91 ppm, respectively. The synthesis of BPR from the reaction phenolic resins, produced under basic conditions (resoles) and boric acid was not feasible. The reactivity of the resoles species with each other is more favorable than that with boric acid.