Novolac Epoxy Research Articles

Fabrication and evaluation of structural film adhesive using oxazolidinone modified novolac epoxy resin

ABSTRACTEpoxy film adhesives are of prime importance for the fabrication of lightweight honeycomb structures for aerospace industries. This work involves the synthesis of oxazolidinone modified epoxy novolac resin (EPN‐OXA) via the reaction of EPN and toluene diisocyanate. EPN‐OXA was characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, gel permeation chromatography, and epoxy equivalent weight. EPN‐OXA was blended with solid epoxy resin, polyethersulfone (PES) toughened liquid epoxy resin, dicyandiamide, and aluminum powder to fabricate a film adhesive curing at 170–180 °C. Effect of additives and curative on the adhesive property was studied to optimize the composition. Effect of PES on the optimized composition was studied in detail. The best composition exhibited lap shear strength of 370 ± 10 kgf cm−2 at 25 °C and the strength was retained to 75% at −196 °C and 52% at 120 °C. PES significantly enhanced the interfacial strength at different temperatures (~1.6‐fold at −196 and 25 °C and ~1.8‐fold at 120 °C). It also improved tensile strength and fracture toughness by 1.4‐ and 2‐fold, respectively. The toughening effect of PES was further confirmed by scanning electron microscopy images. PES marginally reduced the glass‐transition temperature and it exhibited no effect on thermal stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47520.

A fabrication process of flexible IDE capacitive chemical sensors using a two step lift-off method based on PVA patterning

A versatile, two-step, lift-off method, for the fabrication of flexible capacitive chemical sensors based on interdigitated electrodes (IDEs) is presented. A Polyimide (PI) foil whose one side is coated with a thin Aluminum (Al) film is used as the sensor substrate. The IDEs are then formed on the Al film using conventional semiconductor processes. Precise patterning of the sensor sensing layer, on the surface of the Al IDEs, is achieved using a two-step lift-off process which involves a first lift-off during which a Polyvinyl alcohol (PVA) film is spin-coated and patterned, followed by the deposition or spin coating of the sensing layer and a second lift-off to pattern it on the IDEs area and form the final sensor. The process allows for upscaling when a single sensing layer is deposited and patterned in batch over the whole wafer or for the easy fabrication of chemical sensor arrays when depositing and precisely patterning different sensing layers on an array of IDEs. Showcasing the first approach, PHITA copolymer (a methacrylate tertrapolymer) is deposited and patterned over sensors with varying electrode gaps in order to fabricate simple humidity sensors, while in a following experiment, Poly(2-hydroxyethyl methacrylate) (PHEMA), Epoxy novolac resin (EPN), Poly(methyl methacrylate) (PMMA) and Poly(hydroxy styrene) PHS are patterned on the IDEs in order to form a sensor array. The different sensor configurations realized are evaluated when exposed to water, methanol and ethanol vapors with PHS sensor exhibiting a capacitance change of 44 fF (sensitivity: 1.87 fF / %RH), 7.4 fF and 4.6 fF at 10,000 ppm respectively.

Synthesis and Properties of Organosilicon-Grafted Cardanol Novolac Epoxy Resin as a Novel Biobased Reactive Diluent and Toughening Agent.

The aim of this work is to develop a biobased functional reactive diluent for thermosetting epoxy resins suitable for high-performance applications. An advanced organosilicon-grafted cardanol novolac epoxy resin (SCNER) was synthesized from cardanol novolac epoxy resin and heptamethyltrisiloxane. After the chemical structure of SCNER was identified by Fourier transform infrared, 1H NMR, and 13C NMR, it was used to modify the diglycidyl ether of the bisphenol A (DGEBA)/methylhexahydrophthalic anhydride system. The SCNER showed unique advantages, reducing the viscosity of DGEBA and improving the properties of the cured resin. With 10 wt % SCNER, the cured resin exhibited a higher tensile strength (78.84 MPa) and impact strength (32.36 kJ·m–2). The single glass transition temperature (Tg) step proved the homogeneous phase structure of the cured resin. Inevitably, the Tg of the cured resin decreased for the addition of SCNER. The dynamic mechanical analysis results indicated that the storage modulus of the cured resin decreased with the increasing content of SCNER. The morphology showing the ductile fracture of the cured resin was testified by scanning electron microscopy. The dilution and toughening properties of SCNER paves the way to a wide range of possible “eco-friendly” applications, especially in the fields of coatings, paintings, and adhesives.

Curing Kinetics and Properties of Epoxy Resin with 1, 4-bis (2, 4-diaminophenoxy)benzene

A multifunctional amine, 1,4-bis(2,4-diaminophenoxy)benzene (14BDAPOB), was prepared and used as a novel hardener for novolac epoxy resin (ER). The structure of 14BDAPOB was characterized with Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). The curing kinetics of the novolac epoxy resin/1,4-bis(2,4-diaminophenoxy)benzene (ER/14BDAPOB) system was studied by means of non-isothermal DSC experiments at five heating rates and determined by the Kissinger, Ozawa and Crane methods. The results showed that the activation energy Ea of the ER/14BDAPOB (74.56 kJ/mol) system was higher than that of the epoxy resin/LCA-30 (ER/LCA-30, 68.85 kJ/mol), where LCA-30 is a commercial modified diamine. The reaction order, frequency factor and the reaction rate constant at peak temperature of the two systems were calculated. The initial decomposition temperatures (Tonset) were 398.8 °C (ER/14BDAPOB) and 334.3 °C(ER/LCA-30). The tensile shear strengths were 21.63 MPa (ER/14BDAPOB) and 21.28 MPa (ER/LCA-30). The results showed that the two cured systems exhibited good thermal and mechanical properties.

Preparation and thermal properties of encapsulated ceramsite-supported phase change materials used in asphalt pavements

Two kinds of phase change materials (PCMs), poly(ethylene glycol) (PEG) and ethylene glycol distearate (EGD), were incorporated with ceramsite (CS) to obtain the composite PCMs (CPCMs) by vacuum impregnation method. The morphology of the samples was observed using scanning electron microscope (SEM) and the chemical compatibility was characterized by X-ray diffraction (XRD) and Fourier transformation infrared (FTIR). The PEG and EGD could be retained by 42.1 wt% and 34.0 wt% into pores of the CS, which was calculated according to the curves of the thermogravimetric (TG) analysis. The thermal properties and thermal reliability of the CPCMs were investigated via differential scanning calorimetry (DSC). The phase change temperature (Tm) and heat of fusion (ΔHm) of prepared CPCMs are in the range of 54–60 °C and 29–50 J/g, respectively. The ΔHm of the CPCMs decreased obviously after 100 melting/freezing cycling, which was improved by encapsulating the prepared CPCMs with novolac epoxy resins (NER) to produce the encapsulated CPCMs (E-CPCMs). The results of the leakage experiment and storage/release test also show that the E-CPCMs have good thermal exudation stability and thermal storage/release properties. Based on all the results of the experiment, the encapsulated PEG/CS composite (E-PEG/CS) was added into the asphalt mixture to substitute the corresponding aggregate for simulating the actual temperature-adjusting effects. The results indicate that the maximum temperature reduction of the upper surface reaches about 9.1 °C at 210 min. Therefore, the E-CPCMs have the potential to decrease the high temperatures and temperature fluctuations in the asphalt pavements.

Novel organophosphorus flame retardants and their synergistic application in novolac epoxy resin

The novel oligomeric organophosphorus compounds oligo[DOPAc-2-TAEI] (oDOPI), oligo[DOPAc-1-DMPAc-1-TAEI] (oDOMPI) and oligo[DMPAc-2-TAEI) (oDMPI) were prepared in a one-pot process. At first, a Phospha-Michael-addition of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and/or dimethylphosphite (DMP) to tris(acryloyloxy)ethyl isocyanurate (TAEI) was carried out using a ratio that approximately one third of the acrylate groups remained, which were subsequently polymerized. The novel FR's as well as two commercially available flame retardants (FR's), a phosphazene (PZ) and a phosphorus-containing oligomeric compound with aromatic OH-groups, were incorporated into the epoxy novolac resin system DEN438/DICY/Fenuron, with and without the synergists melamine polyphosphate (MPP) and boehmite (AlO(OH)). The influence on glass transition temperature (Tg) was determined by differential scanning calorimetry (DSC) and the minimum phosphorus contents needed to pass the vertical burning test UL-94 with a V-0 classification was identified. The synergistic approach, especially the addition of MPP, led to a highly increased performance with the amount of needed organophosphorus FR being reduced significantly without any drop of Tg. Most promising systems were investigated by TGA and cone calorimetry and the residue after the cone measurements was observed by scanning electron microscopy (SEM). These investigations indicate that the superior flame-retardant properties are evoked by formation of dense char combined with gas-phase action of the organophosphorus compounds.

Diffusion cell investigations into the acidic degradation of organic coatings

Protective organic coatings work by preventing contact between an aggressive environment and a vulnerable substrate. However, the long required lifetime of a barrier coating provides a challenge when attempting to evaluate coating performance. Diffusion cells can be used as a tool to estimate coating barrier properties and lifetime. In this work, a diffusion cell array was designed, constructed, and compared to previous designs, with simplicity being the most important design parameter. Sulfuric acid diffusion through five different coatings was monitored using a battery of cells, and a mathematical model was developed to simulate the experimental data and to study diffusion mechanisms. The diffusion cells allowed an objective and fast analysis of coating barrier properties. It was found that sulfuric acid deteriorated these properties as it diffused through the films. This was also expressed in the modeling results, where a three-step time dependency of the diffusion coefficient was required to simulate both acid breakthrough time and the subsequent steady-state flux. A vinyl ester-based coating proved to be the most effective barrier to sulfuric acid diffusion, followed by a polyurethane coating. Amine-cured novolac epoxies provided the least effective protection.

Phosphinated Poly(aryl ether)s with Acetic/Phenyl Methacrylic/Vinylbenzyl Ether Moieties for High-T g and Low-Dielectric Thermosets.

To achieve insulating materials with a low-dielectric characteristic for high-frequency communication applications, three phosphinated poly(aryl ether)s: P1-act (with acetic moiety), P1-mma (with phenyl methacrylic moiety), and P1-vbe (with vinylbenzyl ether moiety) were modified from a phenol-functionalized phosphinated poly(aryl ether) (P1). P1-act and P1-mma, both with active ester linkages (Ph–O–(C=O)−), were reacted with three commercial epoxy resins (diglycidyl ether of bisphenol A, HP7200, and cresol novolac epoxy) to obtain secondary hydroxyl-free epoxy thermosets. Because of the secondary hydroxyl-free structure, epoxy thermosets cured by P1-act and P1-mma show an 11–15% reduction in dielectric constant than those cured by P1. P1-vbe, with reactive vinylbenzyl ether moieties, was self-cured to a high-performance thermoset with a Tg value as high as 302 °C and a dielectric constant as low as 2.64U. High-Tg and low-dielectric thermosets have been developed in this work.

Molecular Dynamics Simulation: the Effect of Graphene on the Mechanical Properties of Epoxy Based Photoresist: SU8

SU8 is an epoxy-Novolac resin, which is used as photo initiator in micro- and nano- fabrication techniques. From literature, graphene has been proved that results in significant improvement in the properties of the composites. However, due to nanometer size of the graphene layers there is no any experimental tool to obtain insight of the fillers inside the resin especially when the materials are under mechanical deformations where simulation techniques work well. Therefore, SU8 and SU8-graphene nanocomposites as the model compounds were taken to be investigated from atomistic molecular dynamic approach to demonstrate the effect of graphene layers. This leads to mechanical property enhancement such as Young’s, bulk and shear modules being affected by the aspect ratio of the graphene layers high aspect ratio graphene in SU8 leads to an 81% improvement in Young’s, 100% in bulk and 83% in shear moduli in addition to higher density and less graphene wrinkling.

Determining the Glass Transition Temperature of an Epoxy Siloxane Composite by Thermal Analysis Methods

Thermomechanical analysis, dynamic mechanical analysis, differential scanning calorimetry, and dielectric thermal analysis were used to determine the glass transition temperature of hot-curing epoxy siloxane composites. The effect of polymethylphenylsiloxane resin on the parameters of the three-dimensional structure and on the deformation and strength properties of epoxy novolac resin during curing by 4,4′-diaminodiphenylmethane was established.

Synthesis and characterization of epoxy resins from fast pyrolysis bio-oil

Fast pyrolysis bio-oil was used to replace phenol up to 50 wt% to synthesize bionovolac resin. A glycidylation reaction was employed for epoxidizing novolac, bionovolac, fast pyrolysis bio-oil and α-resorcylic acid. Gas chromatography–mass spectroscopy was used to observe available compounds in the bio-oil, whereas Fourier transform infrared and phosphorus-31 (31P) nuclear magnetic resonance techniques were used for the characterization of the resulting resins. Epoxy resins were cross-linked by polyaddition reaction with the polyetheramine hardener Jeffamine T-403 at elevated temperatures. The thermal and thermomechanical properties of cured thermosets were measured by differential scanning calorimetry and dynamic mechanical analysis, respectively. The glass transition temperatures and moduli of novolac-based cross-linked systems were found to be superior to those of epoxy resins without novolacs. Additionally, Soxhlet extraction and scanning electron microscopy were performed to characterize solvent resistance and morphology, respectively. The incorporation of α-resorcylic acid-based epoxy enhanced the properties of cured polymers. The preparation of bio-based epoxy–novolac thermoset networks resulted in reduced consumption of petroleum-based chemicals.

Preparation and curing chemistry of ultra-low CTE epoxy composite based on the newly-designed triethoxysilyl-functionalized ortho-cresol novolac epoxy

For the design of the semiconductor packaging material, one of the most important challenges is to overcome the higher thermal expansion property of ‘organic’ epoxy composite than that of the ‘inorganic’ IC chip. Therefore, in order to prepare the epoxy composite with the ultra-low coefficient of thermal expansion (CTE), the new material class of epoxy, i.e., alkoxysilyl-functionalized novolac epoxy (Si(OEt)3-EOCN) was synthesized using the ortho-cresol novolac epoxy (EOCN) as a starting material. The new epoxy composite with the 85wt% of silica showed the CTE1 (at T < Tg) of 8 ppm/°C and CTE2 (at T > Tg) of 11 ppm/°C. Note that before alkoxysilyl-modification, the CTE1 and CTE 2 of the EOCN composite were 13 ppm/°C and 44 ppm/°C, respectively. In addition, the alkoxysilyl-functionalized epoxy was observed to show the unique curing chemistry due to the participation of alkoxysilyl group in epoxy curing reaction. In order to understand the chemistry of alkoxysilyl-functionalized epoxy, the reaction mechanism was studied using the model compounds.

Evaluation of active solvent modulation to enhance two-dimensional liquid chromatography for target analysis in polymeric matrices

A new methodology is presented for two-dimensional liquid chromatography (2D-LC) separations of polymers. Active solvent modulation (ASM) was evaluated in its effectiveness to enhance solvent compatibility for both separation dimensions. As an example the determination of target compounds in epoxy resins was used. Ultra-high pressure size-exclusion chromatography was applied in the first dimension using THF as the solvent. The second dimension separation was operated in reversed-phase mode using an acetonitrile/water gradient. ASM prevents sample breakthrough in the second dimension and produces chromatograms that are of great peak shape and high resolution. It enables very sensitive determination of target components down to the low ppm level. The resulting high-speed 2D-LC method (10 min analysis time) showed good linearity (R2 > 0.9995) and reproducibility (as low as 0.3–0.7% peak area RSD). ASM was also applied in comprehensive 2D-LC (SECxLC) mode for characterization of molecular weight and chemical composition distribution of a polymer blend consisting of epoxy novolac and phenol novolac. The SECxLC separation was executed at short run times (20 min). ASM technology can markedly enhance productivity in 2D-LC analysis for many complex sample matrices.

A study of the effects of filler particles on the degradation mechanisms of powder epoxy novolac coating systems under corrosion and erosion

Electrochemical impedance spectroscopy (EIS) tests were conducted on powder epoxy novolac (PEN) coating systems with different loadings and types of filler particles. The performance of the coatings was examined in an aqueous corrosive environment with a chloride concentration of 2000 ppm, pH of 3.5, temperature of 60 °C, and saturated with carbon dioxide (CO2). The coating’s performance under the influence of grit blast erosion was also studied. Equivalent circuit models were proposed to study the degradation mechanisms of the coating systems under the synergic effect of corrosion and erosion. Coating systems with a low amount of filler particles provided the best protection against corrosion in the testing environment, while systems with an increased amount filler particles provided the best erosion resistance. Platy shaped filler particles were found to be the best in reinforcing coating’s resistance against both corrosion and erosion.

Simultaneous acid exposure and erosive particle wear of thermoset coatings

Handling acidic chemicals is a challenge in the chemical industry, requiring a careful choice of contact material. Certain thermoset organic coatings are applicable in low pH environments, but when particulate erosion is also present the performance demand is increased. This is the case in, e.g., stirred tanks for agitated leaching of copper ore, where sulfuric acid is mixed with an erosive slurry. A pilot-scale agitated leaching tank was designed and constructed to explore the performance of selected thermoset coatings in such an environment. For reference, simple immersion experiments were conducted. Coating durability was estimated by observing the film thickness change during exposure. It was found to be a function of film swelling and film contraction, due to chemical exposure, as well as the “polishing” caused by erosive wear. Film reduction rates varied with radial position in the tank bottom-placed coating samples. Maximum rates were found about halfway between the reactor center and wall. Polishing rates also varied significantly with acid concentration, most likely due to chemical reactions taking place between the acid and the coatings, damaging surface mechanical properties, similar to the erosion/corrosion-type phenomena found in metals. A vinyl ester-based coating was the most resistant to the simultaneous erosive/acidic exposure, with a maximum polishing rate of $$3.24\,\pm \,0.61$$ $$\upmu$$ m/week, while novolac epoxy and polyurethane coatings showed high polishing rates of $$11.7 \pm 1.50$$ and $$13.4 \pm 0.57\,\upmu \hbox {m}$$ /week, respectively.

Novel epoxy prepreg resins for aircraft interiors based on combinations of halogen-free flame retardants

Heat release and smoke emission are crucial characteristics regarding the burning behaviour of materials used inside the cabin of a commercial aircraft. In this work, an approach to enhance these properties of epoxy novolac-based resin formulations is presented. The phosphorus-based flame retardant DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) is used in combination with inorganic flame retardants to merge different flame-retarding mechanisms. The effects of the single flame-retarding components on the fire behaviour of the neat epoxy resin are investigated at first by cone calorimeter measurements. Following, the interactions of combining (1) DOPO and ATH and (2) DOPO and boehmite are studied systematically. It is shown that the sole DOPO modification effectively reduces the heat release by gas phase mechanisms, but at the same time increases the smoke production tremendously due to the flame inhibition and the resulting incomplete combustion. By adding inorganic flame retardants, this increase in smoke release can be compensated for. Furthermore, the aforementioned combination of DOPO and ATH leads to a synergistic effect on time to ignition. Fire testing on sandwich structures, consisting of prepreg face sheets based on the resin systems described before, reveals that the relevant characteristics to meet fire safety requirements for aircraft interiors can be fulfilled. Additionally, the influence of the modifiers on the thermal and mechanical properties of the cured resins are presented and discussed. The inorganic flame retardants significantly increase the fracture toughness of the originally rather brittle epoxy novolac resins from around 0.5 MPa m1/2 up to approximately 0.8 MPa m1/2 for the boehmite type used and up to 1.0 MPa m1/2 for ATH at a filler loading of 33.3 wt% in both cases.

Heat Transfer in Vacuum Pyrolysis of Decomposing Hazardous Plastic Wastes

Vacuum pyrolysis has been widely used to decompose plastic wastes for obtaining purity chemicals or remove hazardous organic pollutants. The pyrolysis temperature determined the variety of pyrolysis products. The final (highest) temperature was the most investigated factor. However, temperatures used in vacuum pyrolysis were not equally distributed. The lowest temperature also determined the variety of the products. Regrettably, this vital factor has not been researched and reported. In this paper, the heat transfer process of vacuum pyrolysis was fully analyzed. The models for computing the lowest temperature were constructed. The models were certified by the vacuum pyrolysis of novolac epoxy particles collected from crushed waste printed circuit boards. According to the models, we found the heat transfer coefficient of the crucible and the inner diameters of the crucible and alundum tube were the key factors for controlling the lowest temperature. The models can help us to modify and adjust the lowest a...

Novel self-healing network and toughening epoxy-novolac resin

Novel self-healing network and toughening epoxy-novolac resin

Preparation and Characterization of DGEBA/EPN Epoxy Blends with Improved Fracture Toughness

The physical and mechanical properties of blends composed of two kinds of epoxy resins of different numbers of functional groups and chemical structure were studied. One of the resins was a bifunctional epoxy resin based on diglycidyl ether of bisphenol A and the other resin was a multifunctional epoxy novolac resin. Attempt was made to establish a correlation between the structure and the final properties of cured epoxy samples. The blend samples containing high fraction of multifunctional epoxy resin showed higher solvent resistance and lower flexural modulus compared with the blends containing high fraction of bifunctional epoxy resin. The epoxy blends showed significantly higher ductility under bending test than the neat epoxy samples. The compressive modulus and strength increased with increasing of multifunctional epoxy in the samples, probably due to enhanced cross-link density and molecular weight. Morphological analysis revealed the presence of inhomogeneous sub-micrometer structures in all samples. The epoxy blends exhibited significantly higher fracture toughness (by 23% at most) compared with the neat samples. The improvement of the fracture toughness was attributed to the stick-slip mechanism for crack growth and activation of shear yielding and plastic deformation around the crack growth trajectories for samples with higher content of bifunctional epoxy resin as evidenced by fractography study.

UV-light-induced curing of branched epoxy novolac resin for coatings

UV-light-induced curing of branched epoxy novolac resin for coatings