Phenolic Systems Research Articles

Five-Axis Additive Manufacturing of a Thermoset Composite Formulation for Thermal Protection Systems

Thermal protection systems (TPS) are employed on space vehicles to protect against the heat fluxes faced upon re-entry to the Earth’s atmosphere. This work reports a method of 3D printing composite materials for TPS to reduce the time and cost associated with hand layup production methods. A phenolic resin system was tested to determine char yield, viscosity, cure behavior and cure evolutions. A commercial 3D printer was modified to move along two additional axes to accommodate the complex curves of typical heat shields on space vehicles. This technique can be scaled to produce full-sized TPS for industrial applications.

Elucidating the Role of Lignin Type and Functionality in the Development of High-Performance Biobased Phenolic Thermoset Resins.

In this work, a series of biobased phenolic resins were developed starting from kraft and soda lignin, suitably functionalized through esterification by means of succinic anhydride. As a result of an extensive optimization study of the functionalization and curing reactions, clear correlations between lignin type and chemical-physical characteristics and the properties of the resulting phenolic resin systems were described. In particular, the esterification reaction through succinic anhydride was found to play a key role in enhancing the chemical reactivity and in facilitating the successful incorporation of lignin into the resin formulations. The obtained high-lignin-content thermoset materials were shown to exhibit tunable chemical (functionality, gel content, and cross-linking density), thermal (glass transition temperature and thermo-oxidative stability), and mechanical (surface hardness, indentation modulus, and creep behavior) characteristics, which could outperform those of fully oil-based reference phenolic resins by judicious control of lignin concentration and chemical characteristics. In particular, succinylated kraft lignin was found to enable more efficient incorporation into the cured systems. This work provides the first demonstration of the incorporation of succinic-anhydride-modified-lignin in the formulation of high-performance phenolic resins, ultimately contributing to the definition of structure-property-performance correlations for rational biobased material design in the context of advanced and sustainable manufacturing.

Response surface optimization of pitch phase change densification using composite phenolic resin co-carbonization to prepare high performance carbon refractories

The response surface method was used to successfully predict the optimal addition amounts of phenolic resin and bitumen binding system for cold isostatic pressing carbon blocks as 14 wt% and 2 wt%, respectively, and ultra-high performance carbon blocks with a compressive strength of 104.25 MPa and pore sizes below 1 µm accounted for 90.8 % were predicted and prepared. We proposed the phase change densification theory for pitch successfully explaining the secondary densification of carbon blocks by pitch powder during shaping and curing. Besides, In the carbonization stage with the carbon block firing schedule, we determined that the carbon structure of pitch after carbonization with the participation of the phenolic resin matrix and organic small molecules of phenolic resin volatilization and pyrolysis consisted of lamellar carbon with a greater number of defects, and proposed that the interface between the non-graphitizable carbon after the carbonization of the phenolic resin and graphitizable carbon after the carbonization of pitch is the carbon binding mode and mechanism of the nucleation and growth of domain structures at the defects of lamellar carbon. Therefore, We determined that the mosaic and fine mosaic binding between the high strength and high brittleness non-graphitizable carbon carbonization of phenolic resin and the low strength and high ductility graphitizable carbon carbonization of pitch as well as the aforementioned carbon binding mechanism based on domain structure also were the important reasons for the performance enhancement of pitch composite phenolic resin bonded carbon blocks.

EFFECT OF VULCANIZATION SYSTEMS AND CROSSLINK DENSITY ON TENSILE PROPERTIES AND NETWORK STRUCTURES OF NATURAL RUBBER

The mechanical properties of natural rubber (NR) vulcanizate depend strongly on several factors, i.e., vulcanization systems and crosslink density. These two parameters are originally from the formulation design of the vulcanizate. To focus more on such details, influences of three different vulcanization systems (sulfur, peroxide, and phenolic resin) with variations in their crosslink densities were studied by focusing on the change of curing properties, crosslink densities, mechanical properties and network structures of the NR vulcanizates. The crosslink density of various vulcanization systems increased with increasing curing promotors, as revealed by temperature scanning stress relaxation measurement. The tensile modulus at 100% strain increased with increasing crosslink density in all systems but the tensile strength varied with the vulcanization systems and degree of crosslink density. At the same crosslink level, the greatest tensile strength was obtained when the sulfur was used as a crosslinker, which was 100% greater than those obtained from peroxide and 200% over phenolic systems. In comparison to the phenolic resin system, sulfur and peroxide crosslink systems had a more uniform distribution of the crosslink network structure. The size of the network structure was found to be independent of the tensile strength. The peroxide system had the most uniform distribution of the crosslink network structure.

Synthesis and property study of novel maleimide‐cardanol based modifiers for epoxy resins

AbstractThe biomass‐based chemicals from renewable resources are countermeasures to ease the problem of fossil fuel shortage. This work is to develop a biobased functional reactive modifier for thermosetting epoxy resins appropriate for excellent overall performance. The novel maleimide‐cardanol modifiers (CA‐HPM) is synthesized from natural extract cardanol (CA) and N‐(4‐hydroxyphenyl) maleimide (HPM), which is then mixed with phenolic epoxy resin and linear phenolic novolac resin systems. CA‐HPM plays a versatile role in tuning the comprehensive properties of epoxy such as thermal property, adhesive property, and thermo‐mechanical property. Systems with CA‐HPM show slightly lower curing activity and distinct decreased single glass transition temperature (Tg). Besides, the crosslinking density of the cured resin increases, meanwhile the thermal stability keeps at high level, which is due to the rigid five‐membered ring structure of maleimide. Metal lap shear test results manifest that the adhesion between epoxy resin and metal interface augments. With 10% CA‐1HPM, the cured resin exhibits lower equilibrium water sorption (1.88%) and diffusion coefficient (2.94 × 10−8 s−1 cm2). This biobased functional reactive modifier has provided balanced overall performance and would pave the way to a wide range of possible “eco‐friendly” applications.

Study on the curing behavior of polythiol/phenolic/epoxy resin and the mechanical and thermal properties of the composites

Phenolic/epoxy resin (EP-PF) composites were prepared, in which phenolic resin and epoxy resin was used as matrix, polythiol and triethanolamine as curing accelerators. The uniform experimental design method was used to obtain the scheme, in which the resin system had minimum curing temperature. The curing kinetics and the apparent activation energy of the resin system were studied and calculated by the differential scanning calorimetry., and the mechanical and thermal properties of the composite was analyzed. The results show that when the content of polythiol was 12% and the content of triethanolamine was 11%, the peak curing temperature of the resin system was 118°C, which was lower than the phenolic resin or phenolic/epoxy resin. Tg dropped from 212 °C of PF to 157 °C of EPF and then to 147 °C of EPF-B. The thermal decomposition temperature and residual carbon rate also showed a slight downward trend, but the mechanical properties were greatly improved. The strength and flexural modulus of EPF-B have increased from 291.4 MPa and 11.2 GPa of EPF to 440 MPa and 12.3 GPa, an increase of 49% and 27%. This research provides a theoretical basis for broadening the application range of phenolic resin and epoxy resin blending system.

Synergistic Effects of Aluminum Diethylphosphinate and Melamine on Improving the Flame Retardancy of Phenolic Resin

A series of novel flame retardants (aluminum diethylphosphinate and melamine) were used to improve the fire performance of phenolic resin. Fourier transform infrared spectroscopy (FTIR) was used to characterize the modification results. Thermo-gravimetric analysis (TGA) was used to study the thermal decomposition of phenolic resin system, and the flame retardancy of phenolic resin system was tested by vertical combustion test (UL-94) and limiting oxygen index (LOI). The combustion properties of modified phenolic resin were further tested with a cone calorimeter(CCT). Finally, the structure of carbon residue layer was measured by scanning electron microscopy (SEM). The results show that with the introduction of 10 wt % aluminum diethylphosphinate in phenolic resin, the LOI reaches 33.1%, residual carbon content increase to 55%. The heat release rate (HRR) decreased to 245.6 kW/m2, and the total heat release (THR) decreased to 58.6 MJ/m2. By adding 10 wt % aluminum diethylphosphinate and 3 wt % melamine, the flame retardancy of the modified resin can pass UL-94 V-0 flame retardant grade, LOI reaches 34.6%, residual carbon content increase to 59.5%. The HRR decreases to 196.2 kW/m2 at 196 s, relatively pure phenolic resin decreased by 35.5%, and THR decreased to 51 MJ/m2. Compared with pure phenolic resin, the heat release rate and total heat release of modified phenolic resin decreased significantly. This suggests that aluminum diethylphosphinate and melamine play a nitrogen-phosphorus synergistic effect in the phenolic resin, which improves the thermal stability and flame retardancy of the phenolic resin.

Assessing the technical and environmental performance of wood-based fiber laminates with lignin based phenolic resin systems

Over the past five years, the mobilization of fiber wood assortments for promoting material use, and the integration of supply and conversion chains between biorefineries and the wood panel industry have been intensively investigated. In this regard, the production of fibers and by-products from industrial wood and the substitution of phenolic resin systems with natural polymers such as lignin offer a promising alternative for increasing the bio-based content in composite materials. A direct use of the natural lignin without intermediate downstream processing could support the implementation of energy efficient and short processing routes. But it also could open new challenges such as to identify the extent to which substitution of phenolic resins are technically feasible without compromising the required mechanic performances of the obtained products. For this reason it is needed to identify the material compositions in laminate production, which exhibit good mechanic performance values and in the same time contribute to the reduction of environmental impacts. Considering these constraints in material design, practical results from material testing of different composite materials were used to conduct a comparative Life Cycle Assessment (LCA). The environmentally most preferable compositions of beech fiber laminates are identified for the selected product compositions. Furthermore a LCA scenario analysis is applied to compare the environmental preferability of the use of industrial wood assortments in fiber provisioning against the use of industrial wood residues within coupled production schemes of the wood-based bioeconomy. The results show that in nine out of eleven impact categories reduction potentials of up to 39% are achieveable and that the use of residue streams shows a rather limited benefit in realizing further reduction potentials.

Bionic boron/silicon‐modified phenolic resin system with multifunctional groups: synthesis, thermal properties and ablation mechanism

A kind of silicon-and-boron-modified phenolic–formaldehyde resin (SBPF) with excellent thermal stability was fabricated via a simple two-step method and used for the matrix of ablation materials. The structure and thermal stability of the modified phenolic–formaldehyde resins (PFs) were characterised. The results showed that boron and silicon elements have been incorporated into SBPF in the form of a chemical bond. Meanwhile, the cured products showed an increase in graphite structure and a decrease in disordered structure due to the incorporation of boron and silicon. Compared with the ordinary phenolic resin, the initial thermal degradation temperature and charring yield at 800°C of SBPF increased by 73°C and 15 wt%, respectively. Further, the modified PFs, nano-Al2O3 powders, glass powders and vitreous silica fibres were used to obtain a novel ceramizable phenolic moulding composite. The morphology, chemical composition and ablative characteristics of the composites were explored. The results showed that a compact and homogeneous SiO2–Al2O3 layer formed on the ablated surface and protected the carbonised matrix and fibres from further oxidation. Compared with the ordinary PF composites, the SBPF composites showed a highly decreased linear/mass ablation rates, indicating the synergistic effect of boron and silicon modification on the enhanced ablation property.

A high-temperature plugging system for offshore heavy oil thermal recovery.

There are many heavy oil reservoirs in offshore oilfields in China. Steam and multiple thermal fluid stimulation technologies are of increasing interest and have been applied to an increasing number of projects. During the stimulation or displacement of heavy oil reservoirs during thermal recovery, several factors, such as reservoir heterogeneity, are prone to cause channeling phenomena and affect the thermal recovery effect of steam stimulation. According to the unique requirements for the stimulation of multiple thermal fluids for offshore heavy oil, this study used transmission, blocking and relieving, heat resistance and a comprehensive evaluation of parallel sand tube experiments to conduct a screening evaluation of plugging systems for the stimulation of multiple thermal fluids, screen out a commonly used plugging agent in the current stage and propose corresponding guidance for the selection basis. The results show that foam, gel, foam gel and temperature-sensitive gel systems have a good transmission performance, whereas the oil sludge exhibits a poorer performance. The phenolic resin system exhibits great plugging properties, followed by oily sludge, temperature-sensitive gel, gel, foam gel and foam. Considering about washing resistance properties, phenolic resin system shows the best quality, followed by oily sludge and temperature-sensitive gel. The oily sludge system brings the best performance in plugging a high-permeability channel than phenolic resin gel and temperature-sensitive gel.

The Study on Double Cross-linking Gel Plugging System

In this paper, double cross-linked gel system was first screened. Organic chromium cross-linking agent was selected as primary cross-linking gel system, hyperbranched polyacrylamide as primary cross-linking system main polymer, phenolic resin system as a cross-linking agent for secondary cross-linked gel system, cationic polyacrylamide as a cross-linking agent for secondary cross-linked gel systems. Through the experiment, the formula of the double cross-linked gel system was that the amount of fixed hyperbranched polyacrylamide was 2000mg/L, the amount of internal network cross-linking agent was 300mg/L, the amount of stabilizer was 800mg/L, the amount of cationic polyacrylamide was 2000mg/L, the amount of enhancer was 150mg/L and the system performance was evaluated.

Preparation and thermal stability of heat-resistant phenolic resin system constructed by multiple heat-resistant compositions containing boron and silicon

This work reports a boron- and silicon-containing phenolic-formaldehyde (PF) resin exhibiting an extremely high thermal decomposition temperature and char yield and formed by copolymerizing phenol, formaldehyde, boric acid (BA), and phenyltriethoxysilane (PTES). The structure of BA and PTES-modified PF (BSPF) resin was characterized by Fourier transform infrared spectroscopy. Thermal stability of the investigated composites was estimated by means of thermogravimetric analysis (TGA). The results of TGA indicated that the modified resin exhibited excellent thermal stability. Specifically, the thermoset had a char yield of 77.0% when the boron and silicon contents were only 1.27 wt% and 1.7 wt%, respectively. Compared with the unmodified resin (PF), the temperature at the maximum decomposing rate of the BSPF increased by 84°C and its charring yield was enhanced by 15.0%. The cured products of PF and BSPF were further investigated by X-ray diffraction and Raman spectroscopy, respectively. The incorporation of boron and silicon into the carbon lattice results in a decrease of interlayer spacing, and Raman ID/ IG values for PF and BSPF (2.63 and 1.32) show that the rearrangement of crystalline structure leads to an increase in graphite structure and a decrease in disordered structure upon the modification processes.

Honeycomb carbon foams with tunable pore structures prepared from liquefied larch sawdust by self-foaming

Honeycomb carbon foams with tunable pore structures were prepared from larch sawdust. The pore structure was controlled, on the nanometer scale, by addition of polyethylene glycol (PEG). The PEG molecules were dispersed and stretched in the aqueous phenolic resin system, occupying space. Some of the PEG molecules self-assembled to form an ordered net and banded structure, and then interacted with the resin to form stable polymers. Well-connected honeycomb cells and excellent pre-pore structures were formed simultaneously in the carbon foams through self-foaming. Many micropores and mesopores were present in the ligaments, nodes, and cell walls after carbonization. “Graphitic-like” regions were present in samples carbonized at 800°C, and the surface areas and pore volumes of the carbon foam were up to 1580.97m2/g and 0.885cm3/g, respectively. The number of mesopores and the extent of ordering of the carbon foam increased with PEG content; these changes also led to higher adsorption of vitamin B12.

Influence of cross-linked system on morphology and properties of thermoplastic vulcanizates based on isotactic polypropylene and ethylene propylene diene monomer

Thermoplastic vulcanizates (TPVs) based on isotactic polypropylene (iPP) and oil-free/oil-extended ethylene propylene diene monomer (EPDM) rubber were prepared by dynamic vulcanization. Their rheological and tensile properties as well as morphological peculiarities were examined and compared with those of uncured blends. Vulcanization was performed using two types of cross-linking agents: phenolic resin and sulfur-accelerating systems. Dynamic vulcanization was shown to change the melt viscosity of oil-free and oil-extended iPP/EPDM blends. These changes were found to depend on both rubber content and type of vulcanizing agent. For identical composition, the melt viscosity of TPVs cured by sulfur system was higher than that of blends cured by phenolic resin system (PRS). Dynamic vulcanization by PRS decreased tensile properties of TPVs in comparison with sulfur vulcanization. Morphology of iPP/EPDM blends studied by atomic force microscope was found to be dependent on the ratio of components, type of elastomer, and nature of vulcanizing system.

Rheological Behavior of Thermoplastic Vulcanizates

AbstractSummary: Dynamic and steady shear rheological properties of dynamically vulcanized iPP/EPDM blends were investigated. Two different curing systems based on sulfur or phenolic resin were applied on iPP/EPDM blends. The use of phenolic resin system allows producing materials with lower viscosity at higher rubber content in comparison with sulfur‐cured compositions. Melt rheological properties of iPP/EPDM blends with different loading levels of paraffinic oil were studied. Significant improvement in the flowability is observed for TPVs extended with 50 wt% oil. A partial replacement of EPDM on rubber powder decreases the viscosity of materials.

Effects of curing systems and polysulfonamide pulp on the curing characteristics, mechanical properties, and swelling behavior of ethylene–propylene–diene elastomer composites

AbstractThe effects of three curing systems and polysulfonamide (PSA) pulp on the curing characteristics, mechanical properties, and swelling behavior of ethylene–propylene–diene elastomer (EPDM) composites were investigated. The maximum torque value and the optimum curing time were highest for EPDM composites cured with a peroxide system, and they were closely followed by those cured with a sulfur system. In comparison with those cured with peroxide and phenolic resin systems, EPDM composites cured with the sulfur system showed higher mechanical properties and dimensional stability. With increasing PSA pulp content, the maximum torque value of the EPDM composites increased, whereas the optimum curing time of the composites decreased. The orientation percentage of the PSA pulp in the EPDM composites was maximum at 30 phr pulp, as determined from green strength measurements. In the longitudinal direction along which the pulp was oriented, the EPDM composites showed higher tensile strength as well as lower elongation and swelling ratios. Also, with increasing PSA pulp content, the tensile strength of the EPDM composites decreased up to 10 phr pulp and subsequently increased, whereas the elongation and swelling ratio of the EPDM composites decreased linearly. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Study of comparative tracking index on brominated epoxy and its application in copper clad laminates

AbstractThe study mainly investigates the improvement of the comparative tracking index (CTI) on brominated epoxy resins in a copper clad laminate. We compare the effects of the differences in structures of various epoxy resins on the CTI. In addition, on the basis of the proportion of inorganic fillers and type, we use Pauling's electronegativity theory to find inorganic materials that affect CTI. Experimental results show that the laminate surface CTI increases as the brominated epoxy resin content decreases. When looked at structurally, epoxys modified by phenolic resin systems had lower CTI values than those modified by bisphenol A type epoxy resin systems. Analyzing the effects of inorganic filler types, we found that the ideal bromide epoxy resin proportion and the CTI value of Al(OH)3 could exceed 600 V. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101:2814–2818, 2006

Processing and Properties of a Phenolic Composite System

Phenolic resin systems generate water as a reaction by-product via condensation reactions during curing at elevated temperatures. In the fabrication of fiber-reinforced phenolic resin matrix composites, volatile management is crucial in producing void-free quality laminates. A commercial vacuum-bag moldable phenolic prepreg system is selected for this study. The traditional single-vacuum-bag (SVB) process is unable to manage the volatiles effectively, resulting in inferior voidy laminates. However, a double-vacuum-bag (DVB) process is shown to afford superior volatile management and consistently yield void-free quality parts. The DVB process cure cycle (temperature/pressure profiles) for the selected composite system is designed, with the vacuum pressure application point carefully selected, to avoid excessive resin squeeze-outs and achieve the net shape and target resin content in the final consolidated laminate parts. Laminate consolidation quality is characterized by optical photomicrography for the cross sections and measurements of mechanical properties. A 40% increase in short beam shear strength, 30% greater flexural strength, 10% higher tensile and 18% higher compression strengths are obtained in composite laminates fabricated by the DVB process.

Effect of wood on the curing behavior of commercial phenolic resin systems

AbstractDifferential scanning calorimetry (DSC) was used to study the effect of wood on the curing behavior of two types of commercial oriented‐strand‐board phenolic resins. DSC analysis showed that the curing behavior of the core resin differed significantly from that of the face resin in terms of the peak shape, peak temperature, and activation energy. The addition of wood to the resins moved the two separated peaks in the DSC curves of the core resin adjacent to each other. It also accelerated the addition reactions in the curing processes of both the core and face resins. The two peaks in the DSC curves were the result of the high pH values of the resins. These two peaks became either jointed together or overlapped when the pH value of the resin was reduced. Wood also reduced the activation energies for both the core and face resins by decreasing the pH values of the curing systems. Moreover, the effects of wood on the curing behavior of the resins among the five species studied were similar. The lowest activation energy for a phenolic resin probably appeared at pH 10–11 under alkaline conditions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 185–192, 2005

Chemorheology of cyanate ester—organically layered silicate nanocomposites

The effect of nanoparticle addition on the flow and curing behavior of a phenolic triazine cyanate ester resin system has been studied using chemorheological, thermal and spectroscopic techniques. While the neat system exhibited Newtonian flow, the nanodispersed prepolymer exhibited pseudoplastic flow behavior, typical of polymeric fluids such as gels and pastes. Evolution of the morphology during curing has been found to be dependent on the rate of intergallery diffusion of the prepolymer and subsequent gelation and vitrification, as well as the intra and extragallery cure kinetics. Curing reactions of the cyanate ester nanocomposite system consisting of a di-functional phenol, a halogen cyanate and organically layered silicates were studied. Gel times were measured as a function of temperature by time sweeps on a controlled stress rheometer. Gelation and vitrification times and activation energies for the nanocomposite systems were lower than that of the neat resins, indicating a catalytic effect of the clays on the curing reaction. Curing kinetics experiments performed on DSC and FTIR confirmed this phenomenon. Based on above experiments, time–temperature-transformation diagrams for the different systems were constructed.