Phenolic Matrix Research Articles

A novel numerical method to evaluate the thermal conductivity of the unidirectional fiber‐reinforced composites

AbstractIn this study, an effective microscale method based on the parametric modeling scheme of the finite volume method is improved to evaluate the effective thermal conductivity and localized thermal fields of the fiber‐reinforced composites. By comparing with the finite element method and experimental data, it is indicated that the proposed microscale method exhibits a high accuracy in solving their effective properties. On this basis, the mesh sensitivity and fiber volume fraction influence on the thermal conductivity are both investigated. The number of 36 × 36 sub‐cells is employed as the RVE model to balance the computational efficiency and simulating accuracy. In addition, affected by the thermal conductivity and microstructure of constituent materials, the heat flux distribution near the interface between phenolic resin matrix and glass fiber is relatively uniform. The study on the influencing factors of the volume fraction shows that the equivalent thermal conductivity increases slowly at the low volume fraction, while the growth rate of the equivalent thermal conductivity increases significantly at the high‐volume fraction.

Oxidation Behavior of Carbon Fibers in Ceramizable Phenolic Resin Matrix Composites at Elevated Temperatures.

Carbon fiber fabric-reinforced phenolic resin composites are widely used as thermal protection materials for thermal protection systems in hypersonic vehicles and capsules. In this work, carbon fiber fabric-reinforced boron phenolic resin composites modified with MoSi2 and B4C were prepared via a compression molding technique. The high-temperature performance of the composites as well as the oxidation behavior of the carbon fibers was studied. The results indicate that the incorporation of B4C improves the performance of composites at high temperatures. The residual weight rate of composites with 15 phr B4C (BP-15) sufficiently increased from 23.03% to 32.91% compared with the composites without B4C (BP-0). After being treated at 1400 °C for 15 min, the flexural strength of BP-15 increased by 17.79% compared with BP-0. Compared with BP-0, the line ablation rate and mass ablation rate of BP-15 were reduced by 53.96% and 1.56%, respectively. In addition, MoSi2 and B4C particles had a positive effect on the oxidation of carbon fibers in the composites. After treatment at 1400 °C, the diameter of the as-received carbon fiber was reduced by 31.68%, while the diameter of the carbon fiber in BP-0 and BP-15 decreased by 15.12% and 6.14%, respectively. At high temperatures, the liquid B2O3 from B4C and MoSi2-derived complex-phase ceramics (MoB, MoB2, Mo2C, Mo4.8Si3C0.6) acted as an oxygen barrier, effectively mitigating the oxidation degree of the carbon fibers.

Ablative properties, thermal stability, and compressive behaviour of hybrid silica phenolic ablative composites.

Silica phenolic composites are used as thermal protection systems for high temperatures applications like atmospheric re-entry modules, rocket nozzles etc. Lightweight silica phenolic composites (SPGB) were developed using chopped silica fibre, phenolic matrix, and hollow glass microspheres through a compression moulding technique to achieve a cost advantage in thermal protection systems. Ablative properties were evaluated using an Argon plasma jet at a stagnation heat flux of 500 W/cm2. The mass-loss and erosion rates under plasma exposure reduced up to 48% and 32%, respectively, with the addition of hollow glass microspheres. The heat of ablation of composites increased up to 33%. The thermal degradation behaviour of raw materials and SPGB composites was investigated through thermogravimetric analysis, and the scientific know-how was established. Compressive behaviour under uniaxial loading was evaluated, and the theoretical model for the developed three-component composite was established.

Silica sol nanoparticles hybridized allyl phenolic resins for improving mechanical and thermal performance

In order to improve the mechanical and thermal performance of traditional phenolic resins, nonpolar silica sol nanoparticles with different particle sizes were introduced into allyl phenolic resins with the presence of solvents. A series of allyl phenolic resins with various etherification degrees were designed and synthesized to investigate phase separation phenomenon between sol nanoparticles and allyl phenolic resins. Cured organic-inorganic hybrid samples for performance evaluation were then prepared under the pressure of 1 MPa and pressureless conditions at 250 °C, respectively. SEM observation results reveal that parameters of particle size, etherification degree, and pressure have remarkable influence on phase separation behaviors. Mechanical test and thermal stability evaluation using TGA, muffle furnace and butane torch burning tests prove that both mechanical performance and thermal stability of allyl phenolic resin could be extensively enhanced through the introduction of silica sol nanoparticles. This study provides fundamental understandings about functions and phase separation behaviors of silica sol nanoparticles in the phenolic resin matrix. Organic-inorganic hybrid materials were prepared from nonpolar silica sol nanoparticles with varied particle sizes and allyl phenolic resins with a series of etherification degrees. The hybrid materials exhibit enhanced mechanical strength and remarkable anti-ablative performance by forming a dense protective layer on the burned surface. • Nonpolar silica sol nanoparticles can be homogeneously distributed in the matrix of PRMs in the nanometer level. • Phase separations in hybrid samples can affect the thermal properties of PRMs. • The content and size of silica sol nanoparticles in the matrix evidently influence the mechanical performance of PRMs. • In the butane torch ablation tests, silica sol nanoparticles can remarkably enhance the anti-ablative performance.

Healable ablative composites from synergistically crosslinked phenolic resin

Due to the excellent processability and high char yield, phenolic resin plays a pivotal role in ablative thermal protection systems for the aerospace industry. However, internal defects in conventional phenolic resin matrix composites could potentially scrap the entire thermal protection system and cause devastating safety hazards to the spacecraft. Herein, hexamethylenetetramine (HMTA) and phenylboronic acid are applied as the co-curing agents of novolac resin. With the HMTA amount below 2.5 phr, a series of synergistically crosslinked phenolic resin (HPNR), which consist of both traditional methylene linkages and dynamic boronic ester linkages, are successfully synthesized. By tuning the ratio of the traditional/dynamic bonds, the HPNR demonstrates high char yield and controlled plasticity. Compared with its conventional counterparts, the carbon fabric reinforced HPNR matrix composites show healing capability and superior mechanical properties and ablation resistance, with an interlayer shear strength and mass ablation rate of 37.0 MPa and 0.055 g/s, respectively. The synergistic crosslinking strategy provides a promising pathway for designing and preparing healable ablative thermal protection system materials.

Recovery of polyimide waste film by mechanical method to improve the heat fade resistance of BPR matrix friction composites

With the increasing concern of vehicle safety, higher requirements are put forward for the stability of friction performance of brake linings and clutch surface materials. This work introduces a feasible method to prepare boron phenolic resin (BPR) matrix friction composites with improved heat fade resistance by using recycled polyimide (PI) powders as tribological modifier fillers. The friction and wear behavior of the BPR matrix composites during dry sliding with GCr15 at 100 °C, a heating process of 100–350 °C, and a temperature of 350 °C were investigated. Experimental results showed that recycled PI powders could improve the stability of friction coefficient at high temperatures and reduce the heat fade rate of composites since PI powders could effectively reduce the generation of friction debris under high temperatures peeling. SEM showed that the PI powders could be well embedded in the matrix, and they were tightly and continuously bonded. The wear rate of modified composites was reduced by 61.1% at 350 °C, mainly due to the formation of a lubricating film on the contact surfaces, which protected the polymer matrix from severe wear during sliding. When the PI powders content was 10 wt%, the heat fade rate was only about 4.69% for enlarging the applications in the brake linings.

High performance carbon–carbon composites obtained by a two-step process from phthalonitrile matrix composites

Carbon–carbon composites (C/C) were produced from carbon fiber reinforced phthalonitrile (CFRP) matrix composites in a two-step impregnation–carbonization procedure. After graphitization at 1800 °C, the obtained C/C composites demonstrated highly crystalline structure and properties characteristic of composites derived from phenolic matrix CFRP by the industrial procedure: d = 1.73 g cm−3, interlaminar shear strength was 14.1 MPa, compression strength was 139.8 MPa, and coefficient of friction was in the range 0.32–0.34.

Preparation of a Ceramifiable Phenolic Foam and Its Ceramization Behavior.

Ceramifiable phenolic foam (GC-PF) with a low ceramization temperature has been prepared by incorporation of low melting point glass frits (LMG) containing B2O3 and Na2O as main components into a phenolic resin matrix. Fourier transform infrared spectrometry, X-ray diffractometry, and scanning electron microscopy were used for assessment of the structure, phase composition, and morphology of GC-PF before and after combustion analysis, respectively. A glassy ceramic protective layer is formed when GC-PF is exposed to flame or a high temperature environment. The presence of LMG not only reduces the level of defects in the phenolic foam cell wall (gas escape pore), but also promotes the generation of a glassy ceramic protective layer that could inhibit heat feedback from the combustion zone and reduce the rate of formation of volatile fuel fragments. Thermogravimetric analysis and differential scanning calorimetry were used to establish that GC-PF exhibits excellent thermal stability. Limiting oxygen index (LOI) determination suggests that GC-PF displays good flame retardancy. The LOI of GC-PF was as high as 45.6%, and the char residue at 900 °C was six times greater than that for ordinary phenolic foam (O-PF). The area of the raw material matrix of GC-PF after combustion for 60 s was about 1.7 times larger than that for O-PF. A possible mode of formation of glassy ceramics has been proposed.

Facile fabrication of lightweight carbon fiber/phenolic ablator with improved flexibility via natural rubber modification

The rigidity and low strain-to-failure of the phenolic impregnated carbon ablator seriously restrict the application of this state-of-the-art thermal protection material. In this study, to improve the flexibility of carbon fiber/phenolic ablator (CFPA), natural rubber (NR) was deposited homogeneously onto the surface of the carbon fibers through impregnation. Thus, a “bridge” was built between the carbon fiber reinforcement and the phenolic resin aerogel matrix, allowing the interface better connection and better deformation ability. Experimental results indicate that, compared with the unmodified, modified CFPA has lower flexural modulus and higher fracture strain, 6.3 MPa and 39.6% at the optimal NR latex mass fraction respectively, while maintains low density, good thermal insulation properties, and excellent ablation properties. The facile fabrication via natural rubber modification of CFPA improved its flexibility and could broaden the application scenarios of lightweight carbon/phenolic composite.

Optimization and modelling of the fracture inhibition potential of heat treated doum palm nut fibres in phenolic resin matrix polymer composite: a Taguchi approach

The chemical treatment of natural fibres for its surface modification for the development of polymer composites is popular but it comes with an adverse effect of a chemical change of the fibres. In this study, the surface modification of natural fibres (doum palm nut (DPN) fibres) with low-temperature heat treatment (30 °C–75 °C) has been reported as an alternative method to the treatment of natural fibres for the development of polymer composites. Taguchi method of the design of experiment was employed to determine the effect of temperature and fibre content on the mechanical properties (hardness and fracture toughness) of DPN fibre-reinforced phenolic resin polymer composite. The process showed that the best combination of fibre content and fibre treatment temperature for optimum hardness and fracture toughness and results proved to be at 5% and 75 °C respectively. Statistical analysis established the significance of heat treatment in improving the fracture toughness of DPN fibre reinforced phenolic resin composites. Physical observation with scanning electron microscope and Fourier-transform infrared spectroscopy confirmed the improvement in interfacial bonding between the fibre and the matrix with the increase in fibre treatment temperature without a change in the chemical properties of the treated fibres. The study concludes that the treatment of fibres with temperature is an alternative and effective method to the chemical treatment.

Adopting bio-inspired interfacial modification and reinforcements simultaneously for optimizing the tribological performance of fabric composites

The tribological properties of fabric liners were seriously affected by the poor interfacial adhesion and high-temperature carrying capacity. Therefore, it was necessary to modify the fabric surface and enhance the thermal stability of fabric liners to meet the requirements of harsh conditions. Herein, dopamine (DA), polyethyleneimine (PEI), and SiO2 nanoparticles were co-deposited onto the surface of Basalt/PTFE fabric in an eco-friendly and mild method to enhance interfacial adhesion. The obtained organic-inorganic hybrid coating endowed the fabric surface with increased reactive groups and roughness, promoting the mechanical interlocking and chemical bonding between fabric and phenolic matrix, leading to an increase of 89% in interfacial adhesion. Moreover, the CaF2 and Si3N4 incorporated into the fabric composites coordinated with the interfacial modification to enhance the tribological performance of fabric composites. The thermal stability of fabric composites presented an effective improvement with the addition of CaF2 and Si3N4. It was surmised that the Fabric@SiO2/CaF2-Si3N4 composites showed the optimal tribological performance with wide temperature range resulting from the enhanced interfacial adhesion and thermal stability as well as the formed robust tribofilm.

A comparative assessment of chemical, mechanical, and thermal characteristics of treated oil palm/pineapple fiber/bio phenolic composites

AbstractIn this study, the alkali‐treated and untreated hybrid fibers incorporated with bio phenolic matrix to enhance the chemical interactions, mechanical and thermal properties have been investigated. The oil palm fiber (OPF) and pineapple fiber (PALF) were utilized as reinforcements into bio phenolic resin. The improvements in chemical interactions were monitored by the Fourier transform infrared spectrometer. The modifications of the surface for hybrid natural fibers (OPF/PALF) were enhanced in comparison to pure fiber composites. The composites' dynamic mechanical behavior such as storage modulus, loss modulus, and damping properties were also investigated by dynamic mechanical analysis. Thermogravimetric analysis analyzed the performance of untreated (OPF and PALF) and treated (OPF/OPF) composites at elevated temperature and observed adequate interfacial bonding as a result of the improvements in thermal stability. The results presented that alkali) NaOH(incorporation in hybrid composites (OPF/PALF) results in increased the tensile strength and modulus among all composites. Furthermore, the tensile strength and modulus improved to the maximum value for treated 50% PALF composite compared to other composites. The hybridisation of treated alkali (5% NaOH/50% PALF) fiber shows best performance on tensile strength and modulus with 33.3 and 7535.2 MPa, respectively compared to other composites. The alkali‐treated hybrid composites (NaOH/1OPF.1PALF) exhibited the greatest flexural strength (99.8 MPa) and modulus (8813.1 MPa). The enhancement of the interfacial adhesion between pure and hybrid fiber composites and bio phenolic matrix through the mercerisation of OPF and PALF fibers reinforced composite played an essential role in improving the mechanical properties of composites via alkali treatment with NaOH solution. Natural fiber reinforced composites are commercially attractive for high‐volume applications; while their properties can be improved by adding alkali solution as stabilizers. It can be recommended from the findings of this study that the alkali treatment (5% NaOH) can be used to enhance the efficiency of agriculture waste biomass. Additionally, the hybridization of bio‐fiber composites has potential to develop novel type of biodegradable and sustainable composites suitable for various industrial and engineering applications.

The implication of phenolic acid matrix effect on the volatility of ethyl acetate in alcohol-free wine model: Investigations with experimental and theoretical methods

Hydroxycinnamic acids and ethyl acetate were assessed in simulated alcohol-free wine solutions to explore the effect of phenolic acids on the aroma volatility of esters. The results showed that the phenolic acids could inhibit the volatilization of ethyl acetate, and the extent of inhibition was influenced by the concentration and structure of the phenolic compounds. The ultraviolet absorption spectra of the phenolic acids and ethyl acetate confirmed the interaction between the two compounds. The thermodynamic parameters of the interaction implied a spontaneous exothermic interaction, driven primarily by hydrophobic effects. Meanwhile, the results of the fluorescence-quenching analysis indicated electron transfer between the reactants. The quantum chemical investigations revealed negative and positive charge density distributions in the structures of ethyl acetate and the phenolic acids, respectively. These results will provide some data reference and theoretical support for further research on the effects of phenolic acid matrix on other structural esters.

Durable mechanical properties of unidirectional flax fiber/phenolic composites under hydrothermal aging

Natural fibers show great potential in polymer composites reinforcement, it remains challenging to tackle the mechanical stability of the composites under moist/water condition for long-term outdoor applications. Herein, unidirectional flax fiber reinforced phenolic (FFRP) composites were developed to systematically study the effects of water absorption on their mechanical properties. Water absorption tests were conducted by immersing composite specimens into distilled water at three different temperatures (23, 37.8, and 60 °C) for a period up to 3 years. Water absorption curves indicate FFRP achieved adsorption equilibrium within 64 days, exhibiting diffusion coefficients (D) of 7.3 mm2/s and maximum moisture contents (Mm) of 18.3%, which reveal the water absorption by FFRP composites in the initial stages followed Fickian behavior. After aging for 3 years, the mean values for tensile strength and Young's modulus were 57 MPa and 15 GPa, respectively, 77.7 and 47% lower, respectively, and the shear strength decreased by about 71.7% compared to the unaged specimens. The effects of hydrothermal aging on the tensile and interlaminar shear characteristics of the composites Long-term hydrothermal aging was found to weaken interlaminar shear characteristics of the composites, causing degradation/deformation of the flax fibers and degradation of the phenolic matrix. A hydrothermal aging mechanism defined as “swelling-debonding-matrix degradation-fiber degradation” at molecular scale is proposed for FFRP composites, promising to steer the future design and exploitation of natural fiber reinforced polymer composites to accommodate the prolonged adaptability at water conditions.

Organic-inorganic composites for novel optical transformation induced by high-energy laser ablation

High-energy continuous-wave (CW) laser has been considered as a significant technology in recent decades. Such laser can destroy conventional materials in an extremely short time, necessitating their protection. In this study, zirconium carbide (ZrC) and silicon carbide (SiC) particle-modified short silicon carbide fiber-reinforced phenolic resin matrix composites (SiC/BPF-ZS) with significant anti-laser performance were designed and prepared. Our results showed that the ceramic particles and SiC fibers rapidly oxidized, leading to the formation of a ceramic coating composed of ZrO2 and SiO2. Owing to the formation of the ceramic coating, the reflectivity of the composites improved significantly from 15.8% to 73.2% after ablation at 500 W/cm2 for 30 s. Additionally, the SiC fibers played an important role in the formation of a high-reflectivity coating during laser ablation. Contrast experiments indicated that SiC fibers lead to better performance than the carbon fibers. The high reflectivity and low mass ablation rate are demonstrated to be the key factors improving the anti-laser ablation performance of the SiC/BPF-ZS composites.

Impact of the Phenolic Matrix in Terms of Phenolic Polymerization on the Bioaccessibility and Bioavailability of the Low Molecular Phenolic Compounds, and the Antioxidant Activity, of Pressurized Liquid Grape Stem Extracts

Impact of the Phenolic Matrix in Terms of Phenolic Polymerization on the Bioaccessibility and Bioavailability of the Low Molecular Phenolic Compounds, and the Antioxidant Activity, of Pressurized Liquid Grape Stem Extracts

The influence of polyphenol supplementation on ester formation during red wine alcoholic fermentation

Pre-fermentative polyphenol supplementation in industrial scales (100-hL) and simulated fermentation (350 mL clarified juice) were conducted. Results showed that in practical winemaking, adding QCE (quercetin, caffeic acid and ellagic acid) increased acetate concentrations in wines and extra grape seed tannins (T) enhanced the effect of QCE supplementation. In simulated fermentation with clarified juice, the synergy effect of QCE and T was evidenced that ester formation was only promoted through mixed QCET supplementation. Besides, QCE supplementation benefited the formation of 4-vinylcatechol adducted malvidin-3-O-(acetyl/coumaroyl)-glucoside and decreased other anthocyanin derivatives derived from pyruvic acid and acetaldehyde, leading more pyruvic acid and acetaldehyde left in yeast to enhance the metabolic fluxes of esters. Findings manifested the connection between the formation of esters and anthocyanin derivatives during red wine alcoholic fermentation, which would be influenced by the phenolic matrix. This work could provide a perspective in winemaking industry for modulating aroma profile via polyphenol supplementation.

Cacao Pod Husk Extract Phenolic Nanopowder-Impregnated Cellulose Acetate Matrix for Biofouling Control in Membranes.

The ultrafiltration membrane process is widely used for fruit juice clarification, yet the occurring of fouling promotes a decline in process efficiency. To reduce the fouling potential in the membrane application in food processing, the use of natural phenolic compounds extracted from cocoa pod husk is investigated. The cocoa pod husk extract (CPHE) was prepared in phenolic nanoparticles form and added into the polymer solution at varying concentrations of 0.5 wt%, 0.75 wt%, and 1.0 wt%, respectively. The composite membrane was made of a cellulose acetate polymer using DMF (dimethylformamide) and DMAc (dimethylacetamide) solvents. The highest permeability of 2.34 L m−2 h−1 bar−1 was achieved by 1.0 wt% CPHE/CA prepared with the DMAc solvent. CPHE was found to reduce the amount of Escherichia coli attached to the membranes by 90.5% and 70.8% for membranes prepared with DMF and DMAc, respectively. It is concluded that CPHE can be used to control biofouling in the membrane for food applications.

Improving damping performance of fiberglass-reinforced resin matrix composites by designing viscoelastic sandwich layer

A new type of damping composite structure was fabricated by embedding polymer materials into the phenolic resin matrix fiberglass-reinforced laminates. The damping layer of novel damping composites shows the characteristics of anti-aging and strong adhesion compared with the traditional damping composites. The ingredients of the polymer material were studied according to the orthogonal test method. The curing mechanism of resin matrix and vulcanized characteristics of polymer damping material were combined in the design process. The damping composite structures were researched by single cantilever beam vibration and modal analysis techniques to determine its damping characteristics. The least square method was used to calculate the loss factor of the damping composites. It was observed that the damping performance of co-cured composites was significantly enhanced compared to traditional damping composites. When the thickness of damping layer is only 0.1 mm, the composite loss factor increases by as much as 49%. The embedding of damping layer has a positive effect on structural stiffness. The work indicates that the low-temperature co-cured phenolic resin matrix damping composite has broad application prospects in vibration reduction.

The Effect of Prestressing and Temperature on Tensile Strength of Basalt Fiber-Reinforced Plywood.

The reinforcement of plywood is demonstrated by laminating pretensioned basalt fibers between veneer sheets, to fabricate so-called prestressed plywood. Belt type basalt fibers bearing a specific adhesion promoting silane sizing were aligned between veneer sheets with 20 mm spacing and were pretensioned at 150 N. Three-layer plywood samples were prepared and tested for tensile strength at room temperature and at 150 °C. The room temperature tensile tests revealed a 35% increase in tensile strength for prestressed plywood compared to that of the conventional specimen. The reinforcement effect deteriorated at 150 °C but was restored upon cooling to room temperature. The deterioration is attributed to the weakening of bonding between the basalt fibers and phenolic resin matrix at elevated temperatures due to the softening of the resin.