O-cresol Novolac Research Articles

Influence of thermal diffusion on the solvent absorption kinetics of highly cross-linked epoxy resins

The influence of heat transfer on the solvent absorption kinetics of an epoxy o-cresol novolac resin composite which is applied for the encapsulation of heat emitting devices is investigated theoretically. The fundament of the model is the PC-SAFT equation of state which is extended by a network term for including the arising elastic forces in the epoxy resin network. PC-SAFT supplies an expression for the chemical potential which is the driving force in a non-equilibrium thermodynamic approach to account for the coupled heat and mass transfer. With this model, it is investigated how the influences of the solvent absorption kinetics due to thermal diffusion depend on factors such as the temperature gradient, the polarity and state of the solvent. It was found that in heat induced polymer matrices, the coupling of mass and heat transfer cannot be neglected. For the first time, it could be shown by the application of PC-SAFT in a non-equilibrium thermodynamic framework, that there is a large influence of the solvent polarity on the thermodiffusion.

Rosin-modified o-cresol novolac based vinyl ester thermosets containing methacrylated lignin model compounds: synthesis, curing and thermo-mechanical analysis

In the present research article, a detailed study on the synthesis, characterization, and structure–property correlation study of the vinyl ester resin (AVEOCN) based on the rosin modified o-cresol-formaldehyde epoxy novolac resin has been done. The rosin was condensed with o-cresol formaldehyde novolac resin to obtain the product (AOCN). The AOCN resin was epoxidized and subsequently esterified with methacrylic acid using triphenylphosphine as a catalyst and inhibitor hydroquinone to get vinyl ester resin (AVEOCN) having acid value ~ 7 mg of KOH per gram of solid. The chemical structures were confirmed using FT-IR, 1H-NMR, 13C-NMR, and DEPT-135° spectroscopic techniques, and their number average molecular weights were evaluated using 1H-NMR spectroscopy as well as Gel Permeation Chromatographic technique (GPC). The curing dynamics of synthesized VER with lignin modeled compounds, methacrylated eugenol (ME) and methacrylated guaiacol (MG), and petroleum-based styrene as reactive diluents was studied using Differential Scanning Calorimetry (DSC). The thermal stability analysis and mechanical performance of the VER samples were done using Thermogravimetric analysis (TGA) and Universal Testing Machine (UTM), respectively. Chemical resistance tests of the above VER samples were also assessed via exposing the sample coated panels to the different chemical environments for 90 days and their % weight loss was determined. The surface morphology of exposed samples was also studied using Scanning Electron Microscopy (SEM). The results obtained were compared to VER systems based on petroleum products and epoxy resins systems and the superior performance of rosin-modified VER systems indicate that they are suited for pressing demands for coating applications.

Modeling liquid absorption of highly cross-linked epoxy resins in aqueous electrolyte solutions

The solvent absorption of an epoxy o-cresol novolac resin composite has been measured in different aqueous electrolyte solutions (NaCl, CaCl2 and MgCl2) at different salt concentrations from 0.1 to 0.3 mg/l. Next to the total solvent uptake, which was measured by a gravimetric measurement, the absorption of ions was determined by ion chromatography and by atomic absorption spectroscopy. The measured solvent absorption in equilibrium was calculated by combining the ePC-SAFT equation of state with a network term, which takes into account elastic forces in the polymer network counteracting a further solvent absorption. In order to model the solvent absorption kinetics, the equation of state was combined with a Maxwell-Stefan diffusion approach and the viscoelastic Kelvin-Voigt model for chain relaxation. The model parameters were only fitted to the absorption in pure water, what was only possible because the epoxy resin absorbed a neglectable amount of ions. The fully predictively calculated values for the absorption in electrolyte solutions are in qualitative agreement to the measured data.

Modeling Highly Cross-Linked Epoxy Resins in Solvents of Different Polarities with PC-SAFT

The solvent uptake in equilibrium of a highly cross-linked epoxy o-cresol novolac resin in water, isopropanol, and heptane was experimentally measured and modeled with the perturbed-chain statistical association fluid theory (PC-SAFT) equation of state. As suggested in the literature, PC-SAFT was combined with a network term, which takes additional elastic forces into account. The model parameters of the epoxy resin were generated by fitting them to the measured solvent uptake in pure substances and to the density of the epoxy resin, which provided a very good agreement with the experimental data. Furthermore, the solvent uptake in the mixtures isopropanol/water and isopropanol/heptane was predicted in very good agreement to the experimental data. For the first time, a thermodynamic model was developed to calculate the solvent uptake in an epoxy resin.

Investigation of the composites of epoxy and micro-scale BaTi4O9 ceramic powder as the substrate of microwave communication circuit

BaTi4O9 (BT4) ceramic was sintered at 1270 °C and ground into fine ceramic powder with average particle size of about 3 μm. After that, the micro-scale BT4 ceramic powder with different concentrations (from 5 to 70 wt%) was mixed with O-Cresol Novolac (OCN) epoxy resin to form flexible epoxy-BT4 composites. The dielectric constant of epoxy-BT4 composites was first measured from 100 kHz to 100 MHz at room temperature by using the “plate method”. The measured dielectric constants of epoxy-BT4 composites were compared with the values predicted by Lichtenecker equation. We would show that the measured results were well fitted with the predicted values. In order to investigate the composites of epoxy and micro-scale BT4 ceramic powder for the application of microwave communication, the dielectric constants of epoxy-BT4 composites were also measured from 1 to 10 GHz at room temperature by using a “square cavity resonator” method. As the measured frequencies were at the range of GHz, the dielectric constants of epoxy-BT4 composites were almost unchanged with the increase of frequency. It conjectured that epoxy-BT4 composites could be used as the flexible substrates to fabricate the microwave filters and antennas.

Thermal and combustion behavior of phosphorus–nitrogen and phosphorus–silicon retarded epoxy

A novel trizine ring-based phosphorus–nitrogen flame retardant, 1,3,5-tris(3-(diphenylphosphoryl)propyl)-1,3,5-triazinane-2,4,6-trione (PN), was synthesized by the reaction of diphenylphosphine oxide and triallyl isocyanurate with triethylborane as catalyst. Chemical structure of the target compound was confirmed by Flourier transform infrared spectrum, nuclear magnetic resonances, matrix-assisted laser desorption/ionization time-of-flight mass spectrum measurements. The newly developed PN was used in the flame retardancy of o-cresol novolac epoxy/phenolic novolac hardener system. For comparison, another analogous phosphorus–silicon flame retardant, [(1,1,3,3-tetramethyl-1,3-disiloxanediyl)-di-2,1-ethanediyl]-bis(diphenylphosphine oxide) (PSi), was also applied in the same system. Experimental results revealed that PN showed superior flame retardant efficiency to that of PSi. In addition, the incorporation of flame retardants was in favor of the char formation during the thermal degradation process of epoxy thermosets. With the same flame retardant content, the char residue of epoxy thermosets with PSi was higher than that of epoxy thermosets with PN at 750 °C. Cone calorimeter results indicated that PN contributed to gas phase flame retardancy while PSi was more likely to take part in flame retardancy in the condense phase. X-ray photoelectron spectroscopy data revealed that the binding energies of phosphorus changed in different ways in PN and PSi after combustion. This implied that phosphorus exhibited different combustion behaviors when combined with nitrogen or silicon.

Measuring the frequency-dependent dielectric properties of microwave composites using simple measurement methods

BaTi4O9 (BT4) ceramic was sintered at 1270°C and ground into fine ceramic powder with an average particle size of 3μm, then the BT4 powder was mixed with O-Cresol Novolac (OCN) epoxy resin to form epoxy-BT4 microwave composites. Using the plate method, the dielectric constants of the epoxy-BT4 microwave composites were measured from 100kHz to 100MHz at room temperature, then from 20°C to 140°C at 1MHz. The measured dielectric constants were fitted to the values predicted by the Lichtenecker equation. The dielectric constants of the epoxy-BT4 microwave composites were also measured from 1GHz to 10GHz at room temperature using the “square cavity resonator” method. In the GHz range, the dielectric constants of the composites were almost unchanged. It is conjectured that in both measurement frequency ranges, dielectric relaxation was nonexistent in both the BT4 ceramic powder and the epoxy-BT4 composites.

Effect of CTBN Concentration on Thermal and Morphological Properties of Binary Copolymers of o-Cresol Novolac Epoxy Resin and Bismaleimide

Reactive rubber is the most used material to improve toughness of epoxy resins. Allylated o-cresol novolac resin with certain allylation degree was prepared and characterized, then was used to cure o-cresol novolac epoxy resin and 4,4′-Bismaleimide to prepare a heat-resistant epoxy resin. So, CTBN was introduced to improve its toughness. The effect of CTBN on thermal stability and morphology were studied. With the increase of CTBN, the storage modulus of BACC resins was increased basically indicating that CTBN was homogeneously dispersed in the matrix, and there were two glass transition temperatures of BACC resins indicating that the poor compatible between BACC and CTBN than between epoxy resin and CTBN. From the morphology of BACC resins, the effect of CTBN was similar to the other terminally reactive rubber. When the content was small, there was homogenous distribution of smaller CTBN particles in cured BACC matrix, and then the phase inversion occurred with the increase of CTBN. So, in order to improve toughness of cured BACC resin, a homogenous distribution of smaller CTBN particles is necessary. These conclusions revealed that the properties of BACC resins can be tailored and it must be useful to direct design of materials.

Influence of some vegetable oils on the photocrosslinking of coatings based on an o-cresol novolac epoxy resin and a bis-cycloaliphatic diepoxide

The influence of cashew nut shell oil (CNO), epoxidized soybean oil (ESO), castor oil (CO), and dioctyl phtalate (DOP) on the photocrosslinking kinetics of UV curable mixtures containing an o-cresol novolac epoxy resin (CNE), a bis-cycloaliphatic diepoxide monomer (BCDE), and a triarylsulfonium salt (TAS) as a cationic photoinitiator has been studied. The formulation with a weight ratio CNE/BCDE/TAS of 60/40/5 was found to have the highest cure rate and the greatest final conversion of epoxy groups upon UV exposure. The presence of an unsaturated oil or of DOP in the UV curable formulation, at a content ranging from 0.07 to 0.79 mol/kg, was shown to increase the initial polymerization rate of the epoxy groups from 12 up to 31 mol/kg s, and the epoxy conversion after 18 s UV exposure from 80 up to 95%. It was found that the UV cured coatings containing CNO or DOP at concentrations between 0.3 and 0.6 mol/kg and ESO at concentrations between 0.12 and 0.19 mol/kg exhibit the best performance. These results were explained by a number of competitive factors, mainly the effects of the chemical structure and content of the oils and of DOP on the polarity, viscosity, compatibility, and internal filter effect of the UV curable resins, as well as by the characteristics of the tridimensional polymer networks formed upon UV exposure. The materials produced under the optimal conditions determined in this study can be used as high performance decorative and protective coatings and also as adhesives in different sectors of applications.

Dielectric Behavior of Epoxy/(Ba0.9Sr0.1)(Ti0.9Zr0.1)O3 Composites

The (Ba0.9Sr0.1)(Ti0.9Zr0.1)O3 (BSTZ) dielectric ceramic powder is mixed with O-Cresol Novolac (OCN) epoxy resin to form epoxy/BSTZ composites. As the content of BSTZ ceramic powder increases from 0 to 70 wt%, the dielectric constants of epoxy/BSTZ composites increase from 5.72 to 25.23 and the loss tangents are almost unchanged as measured frequency increases. The dielectric constants of epoxy/BSTZ composites first increase as measured temperature increases and are unchanged as measured temperature is higher than the Cure temperature of BSTZ ceramic. This research proves that we can develop the epoxy/BSTZ composites with stable temperature- and frequency-dependent characteristics.

The development of prediction method for the permittivity of epoxy/(Ba0.9Sr0.1)(Ti0.9Zr0.1)O3 composites

The relative permittivity of O-cresol Novolac epoxy resin/(Ba0.9Sr0.1)(Ti0.9Zr0.1)O3 (epoxy/BSTZ) composites with various contents of BSTZ ceramic powder was measured at 10 kHz to 1 MHz. As the content of BSTZ ceramic powder increases from 0 to 70 wt%, the permittivity increases from 5.72 to 25.23. Four different mixing rules are used to predict the variation of permittivity of epoxy/BSTZ composites, and the Lichtenecker equation fits the measured results. The permittivity of epoxy/BSTZ composites slightly increases as the measured temperature increases, and is unchanged when the measured temperatures are higher than the Curie temperature of BSTZ ceramic. This research proves that we can develop the epoxy/BSTZ composites with characteristics of stable temperature and frequency dependence.

Preparation and properties of halogen-free flame retardant epoxy resins with phosphorus-containing siloxanes

Novel epoxy resin modifiers, DOPO–TMDS and DOPO–DMDP were synthesized by addition reaction of divinylsiloxane with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Halogen-free flame retardant epoxy resins were obtained through modification of o-cresol novolac epoxy resin cured by phenol novolac resin using DOPO–TMDS and DOPO–DMDP which were characterized by 1H NMR, 13C NMR, 31P NMR and FT-IR measurements. Effects of the phosphorus-containing siloxanes on thermal stabilities, mechanical properties and flame retardant properties of the epoxy resins were investigated. The cured epoxy resins exhibited better mechanical properties and greatly improved flame retardant properties due to the presence of phosphorus-containing siloxanes. The cured epoxy resins with phosphorus loading of 2.0 wt% showed LOI values of 32–33 and achieved UL94V-0 ratings.

Investigation of cure kinetics and storage stability of the o-cresol novolac epoxy nanocomposites with pre-intercalated phenolic hardeners

The cure kinetics of the epoxy-layered, silicate nanocomposites were studied by differential scanning calorimetry under isothermal and dynamic conditions. The materials used in this study were o-cresol novolac epoxy resin and phenol novolac hardener, with organically modified layered silicates. Various kinetic parameters, including the reaction order, activation energy, and kinetic rate constants, were investigated, and the storage stability of the epoxy-layered silicate nanocomposites was measured. To synthesize the epoxy-layered silicate nanocomposites, the phenolic hardener underwent pre-intercalation by layered silicate. From the cure kinetics analyses, the organically modified layered silicate decreased the activation energy during cure reaction in the epoxy/phenolic hardener system. In addition, the storage stability of the nanocomposite with the pre-intercalated phenolic hardener was significantly increased compared to that of the nanocomposite with direct mixing of epoxy, phenolic hardener, and layered silicate. This was due to the protective effect of the reaction between onium ions and epoxide groups.

New type of low-dielectric composites based on o-cresol novolac epoxy resin and mesoporous silicas: fabrication and performances

A series of o-cresol novolac epoxy (o-CNER)-based composites containing various amount of SBA-15, SBA-16, and MSU-X type mesoporous silicas were prepared, and their performances were evaluated. Morphological investigation by SEM reveals that the mesoporous silicas achieve a good dispersion in the o-CNER matrix due to an effective surface modification. The dielectric constants of all the composites were measured in the frequency range of 50–1,000 kHz. The investigation suggested that the dielectric constant could be reduced from 4.0 of the pure thermosetting o-CNER to 3.71, 3.73, and 3.73 by incorporating 5 wt.% SBA-15, SBA-16, and MSU-X, respectively. The reduction is attributed to incorporation of air voids stored within the mesoporous silicas, the air volume existing in the gaps on interfaces between the mesoporous silica and the matrix, and the free volume created by introducing large-sized domains. The composites present stable dielectric constants across the wide frequency range. An improvement of thermal stability of the o-CNER is achieved by incorporation of the mesoporous silica materials, while the enhanced interfacial interaction between the surface-modified mesoporous silica and the o-CNER matrix has also led to an improvement of toughness.

Water Diffusion Behavior in Epoxy Resins with Various Fluorine Contents

In this work, novolac resin with perfluorinated side chains was synthesized and cured with o-Cresol novolac epoxy resin to obtain epoxy resins with various fluorine contents. Attenuated total reflection Fourier transform infrared spectroscopy (ATR/FT-IR) was used to monitor the in situ water diffusion process in these systems. The diffusion coefficient of water first increased and then slightly decreased with increasing fluorine content, which could be attributed to two opposite effects induced by perfluorinated side chains: enhanced hydrophobicity and increased free volume. In addition, generalized two-dimensional (2D) correlation analysis was employed to investigate both the sorption and the desorption process of water diffusion, and two kinds of water molecules, named bound and free water, were found. It was interesting to find that in the sorption process, the change in the population of bound water molecules occurs earlier than the change in the population of free water molecules, while in the desorption process, the sequence was reversed.

Synthesis and effect of hyperbranched (3-hydroxyphenyl) phosphate as a curing agent on the thermal and combustion behaviours of novolac epoxy resin

A novel type of hyperbranched (3-hydroxyphenyl) phosphate (HHPP) with high functionality as a curing agent of epoxy resins was synthesized and characterized by FTIR, 1H NMR and vapor phase osmometry (VPO). The cured epoxy resin with HHPP possessed improved glass transition temperature. The thermostability and flame retardancy of O-cresol novolac epoxy resin cured with different contents of HHPP were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI) and cone calorimetry. The obtained results show that the samples containing a higher percentage of HHPP exhibit relatively lower thermostability at lower temperature while higher thermostability at elevated temperature and more char was formed compared with those containing a lower percentage of HHPP. The LOI value increased from 22.0 to 30.0 when HHPP, instead of 1,3-dihydroxybenzene, was used as a curing agent. The 25 wt% addition of HHPP in the curing agent complex effectively decreased the heat release rate and improved the char yield to the content nearly similar as those of the epoxy resin cured with pure HHPP.

Study on diffusion behavior of water in epoxy resins cured by active ester

Phenol novolac resin and a series of esterified phenol novolac resins with side groups of acetate, butyrate and phenylacetate are used as curing agents for O-Cresol novolac epoxy resin. The cured resins are named as EP, EPA, EPB and EPP respectively. The water diffusion behavior of epoxy networks is studied by ATR-FTIR spectroscopy and gravimetric method. The obtained results show that the diffusion type of EPA and EPP are quite approximate to Fickian diffusion, while EPB displays a typical Case II characteristic and EP follows anomalous diffusion. The diffusion coefficient of EP is much lower than EPA and EPP. In 2D-IR spectra the splitting of water OH vibration band in the range of 2800–3700cm−1 and 1500–1800cm−1 shows the existence of two different states of water as free and bound water. Water molecules first bind with specific hydrophilic groups as bound water and then diffuse into free volume (microvoids) or molecularly disperse with less hydrogen bonding (bulk dissolve) as free water. Evidence is also found for the strength order of hydrogen bonding interactions between water molecules and epoxy networks as EP > EPA > EPB > EPP.

Contributions of the network structure to the cure kinetics of epoxy resin systems according to the change of hardeners

The cure kinetics of epoxy resin systems was investigated according to the change of curing agents, and analyzed in respect of the network structure. An autocatalytic cure reaction can be shown in the epoxy resin systems with phenol novolac hardener regardless of the kinds of epoxy resin and the epoxy resin systems using Xylok and dicyclopentadiene type phenol resin curing agents follow nth-order kinetic mechanism. The conversion rates of novolac epoxy resins with phenyl and DCPD (dicyclopentadiene) moiety are higher than biphenyl epoxy resin (YX-4000H) and o-cresol novolac epoxy resin (EOCN-1020) systems. All kinetic parameters of each epoxy resin systems were reported in terms of generalized kinetic equation that considered diffusion term, and the network structure of each epoxy resin systems with different curing agents were analyzed using DiBenedetto equation. These kinetic data were interpreted in terms of network structure model in which a curing agent can act as a spacer and control the distances between epoxy resin units.

Effect of polymeric structure on the corrosion protection of epoxy coatings

Two epoxy resins, EP and EPA, with similar backbone structure but different water affinity, was obtained by curing o-cresol novolac epoxy resin with phenol novolac resin and phenol novolac acetate resin, respectively. By using these two resins, the effect of the polymeric structure on the corrosion protection of the coatings was studied. The free volume in EPA is larger than that in EP as demonstrated by room-temperature density measurement and positron annihilation, while water sorption of EPA is only half of that of EP. Therefore, water affinity of the resin is more important in determining water sorption of the resin than free volume. The cross-sectional area of water passage at coating/metal interface ( A w) was estimated using the electrochemical impedance spectroscopy and compared with that in the resin matrix ( A cs). It was found that, for EPA, A w is much less than A cs, which suggests a significant narrowing of water passage at the coating/metal interface. This narrowing of water passage at coating/metal interface due to the formation of a hydrophobic layer can greatly improve the corrosion protection of the coating.

Flame-retardant epoxy resins from novel phosphorus-containing novolac

A novel phosphorus-containing novolac (DOPO-PN) from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and 4-hydroxyl benzoaldehyde was obtained via simple addition reactions. The chemical structure of the obtained DOPO-PN was characterized with FT-IR, 1H and 31P NMR and elemental analysis. The DOPO-PN novolac, with multi-phenol groups in the molecular chain, was used as a poly-functional curing agent for epoxies. The activity and activation energies of the DOPO-PN curing reactions with epoxies were investigated with differential scanning calorimetry (DSC). The thermal properties and thermal degradation behaviors of the DOPO-PN-cured epoxy resins were also studied with DSC and thermogravimetric analysis. High glass transition temperatures (above 160°C) and extremely high thermal stability (above 300°C) were observed for the DOPO-PN/CNE200 ( o-cresol novolac epoxy)-based resins. High char yields and high limited oxygen index (LOI) values were also found to demonstrate the good flame retardancy of the DOPO-PN-cured epoxy resins. The LOI values of the epoxy resins were proportional to the phosphorus contents of the epoxy resins. A least phosphorus content of 2 wt% is detected for the DOPO-PN-cured epoxy resins to exhibit a LOI value of 26 and to pass the UL 94V-0 test.