Novolac Epoxy Research Articles

Thymol-Derived Trifunctional Epoxy Novolac from Controllable Synthesis to Performance-Advantaged Thermosets

Thymol-Derived Trifunctional Epoxy Novolac from Controllable Synthesis to Performance-Advantaged Thermosets

Waterborne novolac epoxy‐based thermal resistant and fire‐retardant thermal insulation coatings

AbstractWaterborne novolac epoxy based thermal resistant and fire‐retardant thermal insulation coatings were developed in this work. Novolac (phenolic) epoxy emulsion (PEE) was prepared by the phase inversion method based on formulation optimization by orthogonal array testing. The prepared emulsions have similar particle size, viscosity, and stability to commercial bisphenol a glycidyl ether epoxy emulsion (PZ). DSC results showed that the varnish film based on PEE had a higher glass transition temperature and initial thermal decomposition temperature compared with PZ cured by the same curing agent. Waterborne thermal insulation coating with PEE and PZ as binders and hollow glass microspheres (HGMs) as thermal insulation fillers were studied. The results indicated that the thermal conductivity of the coating decreased with an increase in HGMs content. Specifically, the thermal conductivity of the PEE coating containing 20 wt% HGMs is as low as 0.093 W/(m·K). It reduces the exterior temperature of the hot tank from approximately 200 °C to approximately 106 °C. Furthermore, the HGMs/PEE waterborne thermal insulation coating exhibits good thermal stability and flame retardance.

Flammability of Novolac epoxy cured with aromatic diamines

The modification of Novolac epoxy with the organophosphorus compound 9,10-dihydro-9-oxa-10-phosphaphenanthren-10-oxide (DOPO) to reduce flammability and its influence on curing reactions has been investigated. Three aromatic diamine curing agents were used, namely 4,4′-diaminodiphenylmethane (DDM), 4,4′-diaminodiphenylsulphone (DDS), and diethyltoluenediamine (DETDA). The thermal stability and dynamic-mechanical behaviour of the cured resin depend on interactions of the curing agent with DOPO. The onset degradation temperature decreased with increasing phosphorus content, indicating the influence of DOPO on thermal stability. The DDM 3 %P sample exhibited the highest glass transition (Tg) of 136 °C, while DDS-crosslinked simples displayed the highest Tg of 147 °C among all samples. An improvement in the reaction of Novolac epoxy to fire was achieved by incorporating DOPO compound, as indicated by cone calorimetry results, showing up to a 67 % reduction in the peak heat release rate (pHRR) and 53 % reduction in total heat release (THR) for DDM 3 %P. The modified samples containing DOPO presented a self-extinguishing performance, displaying a UL-94 V-0 rating and a limiting oxygen index (LOI) values reached a maximum of 37.1 % for DDM 3 %P, with less flame propagation than for neat Novolac epoxy.

Functionalization and morphology control of graphene oxide for intelligent barrier coatings against corrosion

Designing intelligent fillers for high-performance corrosion protection coatings, especially for the strong corrosion harsh environment of desulfurized flue gas, remains a huge challenge. In this paper, a novel graphene-based intelligent nanofiller with tunable morphology was successfully synthesized via a self-assembly strategy. Using polydopamine (PDA) as gatekeeper, the mesoporous silica nanocontainer (MSNs) was loaded with the corrosion inhibitor benzotriazole (BTA), preparing the pH response MSNs-BTA/PDA (PBM) nanocontainers. Graphene oxide (GO) was modified by PBM through non-covalent interactions including hydrogen bond and π-π stacking. A self-unfolding GO/PBM (GO@PBM-5) was obtained through adjusting the ratio of GO to PBM. The active/passive corrosion protection properties of the novolac epoxy coating (EPN) are endowed by the GO@PBM-5 intelligent nanofiller with a self-unfolding structure, which can be ascribed to the corrosion inhibition and labyrinth effect. As a result, the value of |Z|0.01Hz of coating reinforced with GO@PBM-5(GO@PBM-5/EPN) remained above 1010 Ω cm2 after immersion in 10 wt% H2SO4 solution at 55 °C for 60 days. The thermal conductivity of GO@PBM-5/EPN is 0.312 W m−1 K−1. In addition, no cracking occurred after 400 cycles of −60–140 °C cold-thermal shock. Moreover, the GO@PBM-5/EPN is intact and no rust spots, bubbles, or peeling occur after the salt spray test for 14 days. Showing extremely strong barrier performance as well as thermal conductivity, cold-thermal shock resistance and high self-healing properties. This study opens a new avenue for improving the service life of organic coating in the strong corrosion environment of desulfurized flue gas.

Structural effects on heat capacity, moisture absorption and thermal expansion of epoxy-novolac polymers

Today epoxy novolac resins are of great interest for the aerospace industry. Thermal properties of the polymer matrix, as well as the effect of moisture on the characteristics of polymer composite materials (PCM) under thermomechanical impacts, are critical tasks in creating dimensionally stable structures operating in a wide temperature range. Particularly, thermal and moisture expansion as well as heat capacity are important parameters for evaluating of polymer matrices and modeling their properties. In this work, polymers based on a number of epoxy novolac resins with aromatic amine hardener were studied. The values of the crosslink density were experimentally determined, and a comparative analysis of thermal expansion and heat capacity for epoxy polymers with different crosslink density was carried out. The dependence of thermophysical properties on polymer crosslinking density is shown, both in glass and highly elastic states. Additionally, this study analyzes the process of water sorption by polymers and the coefficient of moisture expansion. The most significant dependence of the diffusion coefficient was observed with coefficient of moisture expansion.

Preparation and properties of novolac epoxy resins containing polycyclic aromatic hydrocarbons

AbstractTo meet the demands of high‐density and miniaturized integrated circuits, electronic packaging materials need to have excellent properties. One approach to enhance the performance is to design novel structures. In this study, two novolac oligomers containing naphthalene Naphthalene novolac oligomer (NPF) and biphenyl Biphenyl novolac oligomer (LPF) were synthesized and then reacted with epichlorohydrin to synthesize novel novolac epoxy resins containing polycyclic aromatic hydrocarbons (NPF‐EP and LPF‐EP). Their chemical structures were characterized by Fourier transform infrared and 1H nuclear magnetic resonance spectra. Tetrahydromethyl‐1,3‐isobenzofurandione (MeTHPA) was used as curing agent to prepare cured NPF‐EP/MeTHPA and LPF‐EP/MeTHPA thermosets. Both NPF‐EP/MeTHPA and LPF‐EP/MeTHPA exhibited better thermal and mechanical properties compared with novolac epoxy resin (PF‐EP/MeTHPA). In particular, NPF‐EP/MeTHPA presented the highest glass transition temperature of 193°C and LPF‐EP/MeTHPA had excellent mechanical properties, with tensile and flexural strengths of 94 and 151 MPa, respectively. Additionally, the cured NPF‐EP/MeTHPA and LPF‐EP/MeTHPA also exhibit a lower dielectric constant and dielectric loss, and low coefficient of thermal expansion compared with cured PF‐EP/MeTHPA. This investigation provides valuable insights for the manufacturing of high‐performance novolac epoxy resins for application in electronic packaging materials.

Tailoring peel strength in UV-responsive, nonconductive adhesives via photocleavable epoxy for micro-LED bonding and repair

To develop a UV-responsive epoxy-based nonconductive adhesive (NCA) with adjustable peel strength, a bifunctional epoxy (NBE) was synthesized. This compound included an ortho-nitrobenzyl ester that decomposes upon UV absorption, exhibiting absorption in the 240350 nm wavelength range and a thermal decomposition temperature at 1% weight loss of 214 ℃. When coupled with an imidazole catalyst, the curing of NBE began at 100 ℃ and reached a maximum exothermic peak at 136 ℃. The NCA was formulated using NBE together with bisphenol F epoxy, cresol novolac epoxy, and nadic methyl anhydride as a curing agent. Despite the increasing NBE content in the NCA, the curing behaviour remained almost the same. However, the decomposition temperature of the NCA decreased in proportion to the NBE content. NCA tapes bonded to quartz glass substrates exhibited a 90° peel strength of 7.1910.39 N/in, depending on the NBE content. When exposed to excimer laser irradiation at 100 mJ/cm2, the 90° peel strength decreased significantly to nearly 0 N/in.

Epoxidized technical Kraft lignin as a particulate resin component for high-performance anticorrosive coatings

Deterioration of steel infrastructures is often caused by corrosive substances. In harsh conditions, the protection against corrosion is provided by high-performance coatings. The major challenge in this field is to find replacements for the fossil-based resins constituting anticorrosive coatings, due to increasing needs to synthesize new environmentally friendly materials. In this study, softwood Kraft lignin was epoxidized with the aim of obtaining a renewable resin for anticorrosive coatings. The reaction resulted in the formation of heterogeneous, solid, coarse agglomerates. Therefore, the synthetized lignin particles were mechanically ground and sieved to break up the agglomerates and obtain a fine powder. To reduce the use of fossil fuel-based epoxy novolac resins in commercial anticorrosive coatings, a series of formulations were prepared and cured on steel panels varying the content of epoxidized lignin resin. Epoxidized lignin-based coatings used in conjunction with conventional epoxy novolac resin demonstrated improved performance in terms of corrosion protection and adhesion properties, as measured by salt spray exposure and pull-off adhesion test, respectively. In addition, the importance of size fractionation for the homogeneity of the final coating formulations was highlighted. The findings from this study suggest a promising route to develop high-performing lignin-based anticorrosive coatings.

Anticorrosive barrier coatings modified by core-shell rubber particles: effects on the property transients and premature crack initiation susceptibility of particle type and concentration

AbstractProtective epoxy coatings, as a result of their inherent brittleness, show insufficient resistance towards initiation and propagation of cracks, which can occur as early as during the curing process. To improve premature crack initiation resistance, it is essential to understand the underlying mechanisms. In this work, a solvent-based novolac epoxy, cured with a cycloaliphatic amine, was reinforced with either an epoxypropoxypropyl-terminated polydimethylsiloxane (PDMS), nanoparticles of strontium titanate (SrTiO3), or core-shell rubber (CSR) nanoparticles. The effects on coating property transients, curing-induced internal stress, and premature crack initiation susceptibility of the modifier types and CSR (MX 217 and MX 267) concentrations were investigated. In addition, using a digital microscope, the defect and crack morphology in coatings applied to rigid, flat substrates and inner 90-degree angles were characterized. Finally, to evaluate the anticorrosive barrier performance of the reinforced coatings, an electrochemical impedance spectroscopy analysis was employed. Despite a slightly reduced crack initiation susceptibility, the flexible PDMS chains, due to phase separation, resulted in a deteriorated barrier performance. The inclusion of SrTiO3 nanoparticles also led to a reduced anticorrosion performance, relative to a neat epoxy coating, with a slightly lower crack initiation susceptibility and a minor increase (around 0.2 MPa) in the average internal stress. For 5 wt% MX 217 and MX 267 CSR toughened coatings, the maximum internal stress and crack initiation susceptibility in the series, as well as an associated reduced corrosion resistance, were seen. In spite of a reduction in the elastic modulus, an improved barrier performance and a reduced internal stress and crack initiation susceptibility were observed for 25 wt% MX 217 and 37 wt% MX 267 CSR toughened coatings. To improve barrier properties and avoid premature crack initiation of epoxy coatings, guidelines on modifier selection are provided.

Designing multifunctional basalt-CeO2@C3N4/epoxy novolac composite coating with outstanding corrosion resistance and CO2 gas barrier properties

The greenhouse effect caused by CO2 emissions is becoming more and more serious, and the carbon capture, utilization and storage (CCUS) is a feasible strategy to reduce emissions. However, the corrosion problem brought by CCUS is unprecedentedly serious. In this paper, we present a composite epoxy novolac (EN) system for resisting corrosion of metals in CCUS environments. In this system, nanorod CeO2 and nanosheet C3N4 are simultaneously grown on the surface of the micron sheet basalt (Bt), which are used as effective additives to improve the corrosion resistance and CO2 gas barrier properties of EN. Only with 3 % of nanoparticles addition, a significant reduction of the gas diffusion of composite film to dry CO2 has been observed, up to 5.88 × 10−12 m2/s. This is associated with the synergistic enhancement of the physical shielding effect by the nano and micron sheets. Additionally, we found that adsorption of oxygen vacancy of CeO2 material with CO2 enhances the stability of corrosion resistance. Therefore, the |Z|0.01 Hz of the Bt-CeO2@C3N4/EN coating is above 106 Ω cm2 higher than that of the EN coating after 25 days of immersion in a 3.0 MPa CO2 aqueous solution at 70 °C. Overall, the anti-corrosion coating system combines long-lasting water resistance and low CO2 gas transmission in harsh corrosive environments, and thus has a high potential for CCUS applications.

Robustly Curing Epoxy Novolacs by Linear and Cyclic Siloxane-Functionalized Eugenol: Impact of Topologies of Cross-Linkers on Properties of Thermosets

Robustly Curing Epoxy Novolacs by Linear and Cyclic Siloxane-Functionalized Eugenol: Impact of Topologies of Cross-Linkers on Properties of Thermosets

Improvement of adhesive properties of modified epoxy-novolac resin by acrylonitrile-butadiene rubber grafted poly(chromium methacrylate).

The purpose of this work was to improve the adhesive properties of modified epoxy-novolac resin by acrylonitrile-butadiene rubber (NBR) grafted poly(chromium methacrylate). Chromium methacrylate was prepared by reaction of basic chromium sulfate with sodium methacrylate. Acrylonitrile-butadiene rubber grafted poly(chromium methacrylate) (GNBR) was successfully prepared by solution graft copolymerization to improve the adhesive properties of epoxy-novolac resin. In this copolymerization, the highest graft efficiency was obtained when 50 wt% of chromium methacrylate and 50 wt% of NBR are used for 4 h at 75 °C. The modified epoxy-novolac adhesive (GNBR-epoxy-novolac resin) was prepared by incorporation of GNBR into epoxy-novolac resin. Their chemical structures were characterized by Fourier transform infrared spectroscopy (FTIR) and the thermal properties were analyzed by thermogravimetry (TGA). The mechanical properties of GNBR-epoxy-novolac resins at both room temperature and 233 K were tested. The tensile strength, Young's modulus and failure strain of GNBR-epoxy-novolac resins were estimated from the tensile stress-strain curves and the lap shear strength (LSS) were evaluated using aluminum adherents, and the results showed that they were significantly improved. This is significant because it is one way to improve the disadvantage of high brittleness of epoxy-novolac adhesive.

Investigation of residual stress in epoxy-based coatings using X-ray and FEM-ANN techniques

Residual stresses play a significant role in the properties and performance of epoxy-based coatings, with their origins rooted in various factors encountered during production and application. This study focuses on quantifying residual stresses in three distinct epoxy-based coatings, commonly used as linings for crude oil storage tanks, namely, pure epoxy, Novolac epoxy, and glass-flake-reinforced epoxy. We employ X-ray diffraction to measure these residual stresses and compare them against predicted values obtained through finite element and artificial neural network methods. Our findings reveal notable differences in residual stresses among the three types of epoxy coatings. Specifically, pure epoxy coatings exhibit higher residual stresses, Novolac epoxy coatings display the lowest, and those reinforced with glass flakes fall in between. Utilising the FEM-ANN model for simulations yields results that closely align with experimental measurements obtained via the X-ray method. Test results demonstrate that the coatings cured at high temperatures have high residual stresses compared to those cured at lower temperatures. Increasing the curing temperature from 10 to 50oC will increase residual stresses by 40.81, 11.085, and 56.98% for coatings reinforced with glass-flake, Novolac, and pure epoxy-based coating, respectively.

Improving ablation-resistant properties of novolac epoxy coatings via boric acid or POSS-modified expandable graphite with a PDA bridge

Improving ablation-resistant properties of novolac epoxy coatings via boric acid or POSS-modified expandable graphite with a PDA bridge

Chemically-resistant epoxy novolac coatings: Effects of size-fractionated technical Kraft lignin particles as a structure-reinforcing component

To provide protection against corrosion in harsh environments, high performance anticorrosive coatings are applied on steel structures at all scales. However, to also limit the use of fossil-based ingredients, there is a growing demand to incorporate renewable raw materials in the coating formulations.In this study, to replace pigments and fillers of an epoxy novolac coating, technical Kraft lignin particles were ground and size fractionated (i.e., sieved), and used for formulation work. The effects of sieved and unsieved Kraft lignin, as structure-reinforcing components, on the anticorrosive and mechanical performance of epoxy coatings were subsequently investigated using the following methods: size exclusion chromatography (SEC), phosphorous nuclear magnetic resonance spectroscopy (31P NMR), scanning electron microscopy (SEM), differential scanning calorimeter (DSC), salt spray exposure, pull-off, König pendulum hardness, and chemical resistance tests.Compared to the unsieved-lignin reference (U-L EN), the coating based on lignin fines (S-L EN) showed about 31 % lower rust creep after 70 days of salt spray exposure. However, no surface defects or chemical degradation were observed for any of the coatings.For the S-L EN coating, excellent adhesion strength (23 MPa) and impact resistance (0.49 N), relative to reference values of 17 and 13 MPa and 0.41 and 0.07 N for commercial and lignin-based diglycidyl ether bisphenol F (L-DGEBF) coatings, respectively, were measured.The addition of lignin particles did not influence the chemical resistance, the hardness, and the glass transition temperature of the epoxy novolac coatings.In summary, chemically unmodified Kraft lignin particles, after grinding and sieving, can be incorporated in epoxy novolac coatings (up to 25 vol%), thereby providing a bio-based alternative to pigments and fillers in heavy duty coatings (primers in particular).

Recent progress in reinforcement of nanofillers in epoxy-based nanocomposites

Now a days, nanocomposites have brought the attentions due to their small dimensions, ultimate large surface area, along with large applications in industrial fields. This review gives detailed information about the epoxy composites and nanofillers to improve their crystallinity, nanostructures and mechanical strengths. Due to the presence of aromatic rings in the structure, epoxy polymer has heat and chemical resistance of high limit. Epoxy and their composites have large applications in coatings and aircrafts. Since their commercial inception in 1947 by the Devve-Raynolds Company, epoxy has become the most extensively studied, researched thermoset polymer. Bisphenol A and Epoxy Novolac Resins are most commonly used epoxy resins. Their multi functionality is about 2.5 to 6.0 which differs epoxy resins from standard Diglycidyl ether of Bisphenol A (DGEBA)based epoxy resins. Epoxy is preferred over other polymer matrix due to its high durability, chemical resistance and high adhesive properties. Currently modified epoxy resins are used in making of natural fibre reinforced composites and different instrumental parts in industries and aircrafts. This review also aims to give emphasis on the recent advancements in fabrication of epoxy polymer composites and their various strengths with respect to different concentration of nanofillers. As we know that formation of composite is an exothermic process, thus this review also carries the promise to enhance the thermal and electrical conductivity of the epoxy polymer by encapsulating suitable nanofillers with appropriate molecular wt%.

Collaborative printing and in-situ frontal curing of highly-viscous thermosetting composites

Rapid manufacturing of thermosets via frontal polymerization is very attractive for thermosetting composites due to the expected decarbonization and manufacturing flexibility with limited energy consumption; however, it is challenging for 3D printing and frontal curing of highly-viscous thermoset composites (e.g., >100,000 mPa.s at room temperature) because of the rheology requirement of the 3D printing process and limited pot life of frontal curable resin inks under elevated temperature, which is usually used to reduce the viscosity of inks. We report an in-situ combining materials-based 3D printing process for printing and in-situ frontal curing of highly viscous thermosets. Specifically, an ultrasonic atomizer sprays the curing agent solution during the printing process to achieve an in-situ mixing with the resin oligomers at a microscale level. Multiphysics simulation indicated the curing degree distribution through the thickness direction and a printing window is provided depending on the extrusion deposition rate, the deposition layer thickness, and the ultrasonic sprayer amplitude. Further experiments were carried out, and it was found that the frontal velocity increased, and the frontal temperature remained almost unchanged with the rise of the ultrasonic amplitude. The curing degree and curing uniformity were improved with the increase of the ultrasonic amplitude but decreased with the increase of the printing layer thickness. Samples with different ultrasonic amplitudes and extrusion layer thicknesses were printed, and their mechanical properties were tested. The tensile strength and Young's modulus of novolac epoxy resin reached 47.56 MPa and 2.19 GPa, respectively. The feasibility of this method for composite printing was demonstrated. At a 5 wt% loading of short fibers, the tensile strength and Young's modulus of as-printed composites reached 66.71 MPa and 3.65 GPa. This method provides a fast and energy-efficient way to manufacture highly viscous thermosets and their composites.

Facile synthesis of intrinsically flame‐retardant epoxy thermosets with high mechanical properties from lignin derivatives

AbstractPreparing bio‐based epoxy resins with high performance is crucial to sustainable development. However, seeking renewable and flame‐retardant epoxy resins with high mechanical properties are still challenging. Here, we reported a facile way to transform lignin derivatives to intrinsic flame‐retardant epoxy resins with satisfactory mechanical properties. Two guaiacol‐based novolac epoxy resins (i.e., GTEP/DDM and GPEP/DDM) were prepared as alternatives for petroleum‐based DGEBA/DDM. The cured GTEP/DDM product showed a high Tg of 209.5°C, a high tensile modulus of 3.13 GPa, and a high LOI of 28.6% with UL‐94 V‐1 rating, which outperformed DGEBA/DDM system. Specially, GPEP/DDM resin possessed more superior mechanical properties (e.g., tensile strength of 73.9 MPa, and tensile modulus of 5.85 GPa) owing to additional interactions (i.e., π–π interactions and hydrogen bonds), and outstanding anti‐flammability (e.g., LOI of 31.2% with UL‐94 V‐0 rating) due to the endow of phosphorus‐containing groups. The mechanical reinforcement and flame‐retardant mechanisms were clarified based on structural evolution and performance variation. This work provides an efficient synthesis route to achieve a high‐performance thermoset, which is a promising alternative for substituting conventional bisphenol‐A epoxy resin for use as fireproof materials.

Functionalized carbon nanotube and carbon nanodot modified multiblock poly(arylene ether ketone sulfone) copolymer as proton exchange composite membranes for fuel cell applications

AbstractThe present study describes the successful synthesis of –COOH functionalized carbon nanodots (f‐CNDs) via pyrolysis of citric acid and 4,4′‐bis(4‐hydroxyphenyl)valeric acid (DPA‐OH, Sigma Aldrich, St. Louis, Missouri, United States) based hydrophilic oligomer at 250 °C. The multiblock copolymers were prepared by a coupling reaction between phenoxide terminated valeric acid based poly(arylene ether ketone) (DPA‐OH) hydrophilic oligomer and decafluorobiphenyl (DFBP, Alfa Aesar, Haverhill, Massachusetts, United States) end‐capped poly(arylene ether sulfone) (BP‐X‐F) hydrophobic oligomers (where X is 6, 9 and 12). Multiblock poly(arylene ether ketone sulfone) copolymer crosslinked membranes were prepared using 6F‐bisphenol‐A based novolac epoxy resin (EFN) and –COOH functionalized multiwalled carbon nanotubes/functionalized carbon nanodots (f‐MWCNTs/f‐CNDs, Nanoshell company, Utah, U. S) were used for the preparation of acid doped composite membranes for fuel cell applications. From high resolution TEM images, the average size of the prepared f‐CNDs found to be ca 10–12 nm. The N1 multiblock copolymer membrane with loading of 0.9 wt% ratio of CNTs showed better proton exchange membrane related properties such as proton conductivity (0.136 S cm−1), ion exchange capacity (1.18 meq g−1) and selectivity ratio (0.17) compared to the prepared pristine, crosslinked and CND based composite membranes. The overall results revealed that the composite membranes with loading of 0.9 wt% of CNTs and CNDs exhibited a superior combination of fuel cell related properties such as higher proton conductivity, high dimensional and oxidative stability and low methanol permeability and also showed better fuel cell performance compared to the respective pristine and EFN crosslinked membranes. © 2022 Society of Industrial Chemistry.

Microstructure and mechanical properties of epoxy resin-reinforced geopolymer exposed to high temperatures

This study investigated the performance of fly ash/slag-based geopolymer composites at ambient and extremely high temperatures. Two types of commercially available epoxy resins, bisphenol F epoxy resin and phenol novolac epoxy resin with incorporating amounts of 1 and 2.5 mass%, were used to produce geopolymer composites. The heat resistance test was carried out at 500 °C, 750 °C, and 950 °C. The microstructure and mechanical strength of geopolymers unexposed and exposed to heat were examined. The results show that incorporating a small amount of epoxy resin could improve strength and reduce crack formation. Although the epoxy resin is sensitive to high temperatures, incorporating it into the geopolymer system did not significantly affect the high-temperature resistance of the geopolymer. This finding indicates that geopolymer reinforced with epoxy resin has the potential to be used in the application where exposure to high temperature is required.