Cycloaliphatic Epoxy Research Articles

Graphene reinforced UV-curable epoxy resins: Design, manufacture and material performance

Abstract Graphene and its derivatives (graphene oxide, reduced graphene, functionalised graphene oxide, and functionalised reduced graphene oxide) are found to improve the mechanical properties of the polymers in which they are dispersed. In the present work, the potential of graphene and its derivatives in terms of their anti-scratch performance is thus investigated. In particular, graphene oxides, as-is graphene nano-platelets and reduced graphene oxides that were functionalised with amino-propyl triethoxy silane (APTES) were blended as reinforcing phases in UV curable epoxy coatings on polycarbonates, and the resulting performances were comparatively evaluated. Additionally, UV curable epoxy coatings covalently bonded to amino-functionalised silica-nanoparticles were studied. The experimental analyses involved FT-IR spectroscopy to study the chemical interactions that occurred among the different compounds in the investigated mixtures, progressive and constant load scratch tests and SEM images of the residual scratch patterns to evaluate the micro-mechanical response and scratch visibility of the coatings. APTES-functionalised reduced-graphene oxide was found to be able to reduce the scratch visibility, thus revealing its suitability to promote the effective anti-scratch properties of UV-curable bis cyclo-aliphatic epoxy resins deposited on polycarbonate.

Strain rate sensitivity of toughened epoxy

The high strain rate behaviour of toughened epoxy is explored under compressive loadings. A cycloaliphatic epoxy was toughened using different types of preformed fillers: epoxy-coated elastomeric poly(dimethylsiloxane) (CSR) and thermoplastic polystyrene microspheres. The toughening ability of the fillers was quantified in terms of improvement in izod impact strength. Our studies revealed that the disadvantages associated with liquid rubber toughening, especially lowering of the glass transition temperature (T g) and storage modulus, could be overcome by using poly(dimethylsiloxane) (PDMS) microspheres. The izod impact strength increased by 33 % upon addition of 3 % w/w amino-polystyrene microspheres, and ~125 % upon introduction of CSR (5 % w/w). High strain rate studies performed using split Hopkinson pressure bar revealed that the compressive strength of epoxy and the toughened compositions were significantly enhanced at high strain rates (~103 s−1) compared with that at quasi-static loading conditions (~10−1 s−1). The effect of filler type on the strain rate sensitivity of the base polymer was established by comparing the property enhancement factor (PEF). Although introduction of elastomeric microspheres led to a lower compressive strength of epoxy, the PEF associated with the rubber-toughened composites was substantially higher than that with the thermoplastic-toughened analogous compositions, which was attributed to the viscous energy absorption in PDMS resulting from the dynamic rubber to glass transition at high strain rates.

Application of microencapsulated unsaturated polyester toward temperature-triggered healing in epoxy composites

In this article, we demonstrate the potential of encapsulated unsaturated polyester resin toward introduction of temperature-triggered healing functionality in a representative cycloaliphatic epoxy matrix. Unsaturated polyester resin was encapsulated in poly(urea–formaldehyde) shell by dispersion polymerization technique which resulted in the formation of free-flowing microcapsules (diameter ∼130 ± 49 µm) with a core content 58 ± 4%. Calorimetric studies confirmed the chemical activity of the encapsulated unsaturated polyester resin, which spontaneously polymerized in the presence of a free radical initiator, 2,2′-azobis(2-methylpropionitrile), at temperature as low as 80°C. Temperature-triggered healing of epoxy-microcapsule composites was performed at 110°C and the healing efficiency was quantified as the ratio of impact strength of healed and virgin specimens. The healing efficiency was found to increase with the increasing amount of microcapsule in the formulation and reached a maximum (100 ± 2%) at 20% (w/w) loading. Fractographic analysis of the surface revealed the flow pattern of chemically active resin from the ruptured microcapsules, which subsequently cured in the presence of 2,2′-azobis(2-methylpropionitrile) pre-dispersed in the matrix.

Influence of the rise rate of voltage and leakage distance on flashover gradient and partial discharges level for various polymeric materials under AC stress

This paper presents results of investigations on the influence of the rise rate of voltage and the leakage distance (Lf) on flashover gradient (FOG) and partial discharges (PD) activity on insulators issued of different polymers materials in dry conditions; the aim of this study being the development of new generation of high voltage piercing connectors. The investigated polymers are of three distinct classes among the mostly used in electrical industry: thermoplastics, thermosetting and elastomers. The considered thermoplastics are polyamide 6 (PA6/50), fireproofed polyamide 66 (PA66/50), polycarbonate (PC/40) and polyarylamide (PARA/50); the thermosetting are two cycloaliphatic epoxy resins (EP1 and EP2); and as concerns elastomers, two EPDM materials noted EPDM and EPDM V0 (fireproofed) have been tested. It is observed that generally the increase of the rise rate of voltage increases the flashover gradient while the increase of leakage distance leads to the decrease of flashover gradient. The magnitude and time duration of voltage, chemical structure of polymer and leakage distance influence the magnitude of PDs. Small degradations are observed in the vicinity of high voltage electrode for thermoplastics and EPDM elastomers after the occurrence of flashover (arc) especially for PC/40. The surface of cycloaliphatic epoxy resins (EP1 and EP2) appears to be the most resistant to flashover arcs and PD activity making them suitable to be used in high voltage connectors.

Incompatible hazard investigation of a cycloaliphatic epoxy resin using green analytical method

A green analytical method was applied to evaluate the incompatible hazard for 3,4-epoxycyclohexane methyl-3′4′-epoxycyclohexyl-carboxylate (EEC) mixed with its synthetic materials. During the manufacturing process, numerous accidents of human poisoning, explosion, or fire have been reported due to the chemical’s incompatible reaction. A calorimetric application and product’s analysis approach have been employed to obtain related information for the incompatible hazard investigations of chemicals. This study also used nonlinear regression analysis to establish a kinetic model. The results proved that H2SO4 can cause an abnormal curing reaction and release significant amounts of heat of the curing reaction for EEC, increasing the occurrence probability of accidents.

Non-reactive and reactive block copolymers for toughening of UV-cured epoxy coating

Abstract Reactive and non-reactive diblock copolymers based on polyethylene oxide (PEO) and a poly(glycidyl methacrylate) (PGMA, reactive) or polystyrene (non-reactive) block, respectively, are prepared via ATRP and those are incorporated into a cycloaliphatic epoxy matrix. Crosslinking of the matrix is then performed by cationic UV curing, producing modified thermosets. 1 H NMR and SEC measurements are carried out and used to analyze the composition, the molar mass and dispersity of the prepared block copolymers. The viscoelastic properties and morphology of the modified epoxy are determined using DMTA and FESEM, respectively. The addition of 4 and 8 wt% of the reactive PEO-b-PGMA block copolymer into epoxy resin has only minor effects on the glass transition temperature, T g . The reactive homopolymer PGMA significantly increases and the non-reactive block copolymer PEO-b-PS slightly decreases the glass transition temperature of the epoxy matrix. The non-reactive block copolymer PEO-b-PS causes a little decrease in T g values. The measurement of the critical stress factor, K IC , shows that the fracture toughness of the composite materials is enhanced by inclusion of the non-reactive block copolymer. In contrary, the reactive block copolymer has negative effect on the fracture toughness especially in case of short PEO block. FESEM micrographs studies on the fracture surfaces sustain the microphase separation and the increase in surface roughness in the toughened samples, indicating more energy was dissipated.

Cure Kinetics of Cycloaliphatic Epoxy/Silica System for Electrical Insulation Materials in Outdoor Applications

The cure kinetics of a neat epoxy system and epoxy/silica composite were investigated by DSC analysis. A cycloaliphatic type epoxy resin was diglycidyl 1,2-cyclohexanedicarboxylate and curing agent was anhydride type. To estimate kinetic parameters, the Kissinger equation was used. The activation energy of the neat epoxy system was 88.9 kJ/mol and pre-exponential factor was 2.64×1012 min−1, while the activation energy and pre-exponential factor for epoxy/silica composite were 97.4 kJ/mol and 9.21×1012 min−1, respectively. These values showed that the silica particles have effects on the cure kinetics of the neat epoxy matrix.

High performance composite coatings on plastics: UV-curable cycloaliphatic epoxy resins reinforced by graphene or graphene derivatives

In this work, the design and manufacture of functional composite coatings on plastic substrates were investigated. In particular, graphene nano-platelets and graphene derivatives, that is, graphene reduced oxide modified by amino organo-silane compounds, were used to reinforce a radiation curable cycloaliphatic epoxy resin. The resulting composite materials were deposited on polycarbonate. The chemical structure of the coatings was characterized by FT-IR. Physical properties of the coatings, especially thermal stability, were evaluated by differential scanning calorimetry. Chemical endurance of the coatings was tested by dipping in acidic, saline and basic environments. Special protocols were, then, developed to evaluate the friction of the coatings as well as their potential to prevent the adhesion of contaminants on their surface (i.e., anti-soiling properties). Mechanical performance of the coatings was evaluated by pencil test (pencil hardness) and progressive load scratch test (scratch hardness). Graphene-reinforced cycloaliphatic epoxy resins were found to ensure good combination of physical, chemical and mechanical properties. Therefore, they can be considered attractive functional materials to deposit on advanced plastic substrates.

Synthesis of a liquid zirconium hybrid resin and the ability of the resin to accelerate the curing of a transparent silicone-modified cycloaliphatic epoxy nanocomposite

A liquid zirconium hybrid resin (Zr–QR) was synthesized through sol-gel reactions of zirconium butoxide with silanol-terminated polydimethylsiloxane (DMS-S12) and γ-glycidoxypropyltrimethoxysilane (Z-6040). The sol-gel reactions were monitored using Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance spectroscopy. The Zr–QR morphology was investigated using field emission transmission electron microscopy. The Zr–QR had a well-ordered morphology and the dimensions were less than 5 nm. These properties were achieved because DMS-S12 was used to separate the zirconium clusters and Z-6040 was used to stabilize the Zr–QR. The acceleration of the curing reaction between silicone-modified cycloaliphatic epoxy (SEP) and methylhexahydrophthalic anhydride (MHHPA) caused by the Zr–QR was investigated. Differential scanning calorimetry and FTIR spectroscopy investigations showed that the Zr–QR first reacted with MHHPA, producing chelating ligands and carboxylic acid. Unlike in the conventional method (adding acetic acid to cause non-reactive chelating ligands to form), the carboxylic acid produced effectively accelerated the curing reaction between the SEP and MHHPA. The chelating ligand produced from the Zr–QR and MHHPA suppressed the gelation of the Zr–QR itself during the nanocomposite (SEP–Zr–QR) curing process. The cured SEP–Zr–QR nanocomposite exhibited excellent optical transmittance at visible wavelengths.© 2015 Society of Chemical Industry

Nanomorphology of Polymer Blends for a Light-Scattering Thermosetting Plate Based on Self-Assembly

An approach to optical plate production using the nanomorphology of polymer blends in light-scattering thermosetting plates based on self-assembly was investigated without using the conventional approach of blending nanoparticles such as silica sol, zirconia sol, phosphor, or chromophore into the polymer matrix. For this purpose, two specified polymers having carboxylic acid and epoxy groups were blended using a light-emitting diode for use in liquid crystal displays. The developed light-scattering thermosetting plate containing poly(acrylic acid) with the carboxylic acid at four different weight average molecular weights in a cycloaliphatic epoxy polymer was shown to achieve regular nanoparticles of 30–350 nm for light-scattering, light-scattering rates of over 10% at a wavelength of 300 nm, a thermal stability up to 230 °C, O2 gas barrier properties approximately 50 times smaller than that of polyethylene, and solvent resistance after polymerizing.

Degradation of various polymeric materials in clean and salt fog conditions: measurements of AC flashover voltage and assessment of surface damages

This paper is aimed at the assessment of the resistance to tracking of insulators made of several polymers, widely used in electrical industry (medium voltage cable accessories such as terminations and insulators and anchoring clamps and mechanical screw fuses), under polluted environments. This new method performed on one insulator model is based on the electro-geometrical characteristics (AC flashover voltage versus leakage distance). The tested materials cover thermoplastics, (namely polyamide 6 (PA6/50), fireproofed polyamide 66 (PA66/50), polycarbonate (PC/40) and polyarylamide (PARA/50)) thermosetting (namely two cycloaliphatic epoxy resins (EP1 and EP2)) and elastomers (namely two EPDM materials noted EPDM and EPDM V0 (fireproofed)). Polluted environments such as clean (light) and salt (heavy) fogs have been created to assess the resistance of polymers to partial discharges (erosion and tracking). Results regarding the flashover voltage (FOV) show a significant reduction in the presence of clean fog equal to 50% of the value measured in dry conditions for all polymers. This decrease is more pronounced in salt fog (-80% reduction of FOV). Surface degradations suggest that epoxy resins and EPDM elastomers are subjected to fewer damages in salt fog when being compared to thermoplastics. It is established that epoxy resins behave better than EPDM elastomers against discharges. In addition, polycarbonate (PC/40) exhibits the worst properties because of large tracking paths that form on its surface.

Synthesis and degradable properties of cycloaliphatic epoxy resin from renewable biomass-based furfural

Furfural-based diepoxide with acetal linkages is synthesized. The cured product can degrade in acidic solutions, showing applications in recovery of precious metal and carbon fiber from electronic waste and composite materials fabricated with it.

Novel phosphorus–nitrogen–silicon flame retardants and their application in cycloaliphatic epoxy systems

In this work, we prepared two novel reactive-type halogen-free and UV-curable phosphorus–nitrogen–silicon synergistic flame retardants.

Preparation of nanocomposites by swelling of a UV cured cycloaliphatic epoxy film in a silica precursor

In this work, nano composites were prepared from a UV cured cycloaliphatic epoxy resin by swelling the cured film in tetramethoxysilane (TMOS) followed by exposure to humid atmosphere at an elevated temperature. The flexibility of the resin was tuned by using different modifiers, namely hexanediol-diglycidylether (HDGE) and a diglycidoxy terminated polydimethylsiloxane (GTMQ). Glycidoxypropyl trimethoxysilane (GPTS) was also added to the UV-curable mixture in order to promote the swelling of the cured films in TMOS, thus obtaining the silica phases through a sol–gel approach. The swelling was performed at different temperatures (40 and 80 °C); the subsequent hydrolysis and condensation reactions were carried out in dry and humid atmospheres at 80 °C. The obtained films were investigated through DSC and TGA analyses; their submicro- nano- morphology was assessed by SEM. The UV-cured films showed silica rich surfaces, the morphology of which was related to the presence of GPTS and of the reactive comonomers and to the experimental conditions adopted for the sol–gel process. The TMOS absorption and hence the subsequent hydrolysis-condensation processes seem to occur at the surfaces of the films probably due to the selective migration of the silicone chains towards the air interface. The pencil scratch hardness values too were found to increase after the sol–gel treatment on the films.

Curing kinetics of self-healing epoxy thermosets

The curing kinetics of self-healing epoxy compositions was investigated by non-isothermal differential scanning calorimetric (DSC) studies. Cycloaliphatic epoxy resin was encapsulated in urea–formaldehyde (UF) using emulsion polymerisation technique to prepare epoxy-loaded UF microcapsules. Triethylene tetramine (TETA) hardener was immobilised on a mesoporous siliceous substrate (SBA 15) and both these additives were dispersed into an epoxy resin, which was subsequently cured using TETA. DSC studies revealed the autocatalytic nature of epoxy curing, which remained unaltered due to addition of the above-mentioned fillers, responsible for introducing self-healing functionality. The kinetic parameters of the curing process were determined using both Friedman and Kissinger–Akahira–Sunose (KAS) method. The activation energy at different degrees of conversion (E α ) was found to decrease with increasing degree of cure (α). Although UF resins possess secondary amine functionalities, which have the potential to react with the epoxy groups, no significant differences in the curing kinetics of the base resin were observed. Kinetic parameters were used to predict the curing behaviour of compositions at higher heating rates using KAS method. As expected, the onset curing temperature (T onset) and peak exotherm temperature (T p) of epoxy shifted towards higher temperatures with increased heating rate; however, introduction of fillers does not affect these characteristic temperatures significantly. Also, the overall order of reaction does not vary significantly which supports the autocatalytic nature of curing reaction. The results suggests that although 2° amino groups are available with the UF resin, these do not directly participate in the curing reaction, as the primary amino groups in TETA are more easily accessible.

Stabilisation of heavy metals in polymeric matrices: Studies on leaching behaviour

Heavy metal salts of Cr, Pb, Hg, Ni, Mn and Zn were stabilised in a cycloaliphatic epoxy resin as the immobilising material. The polymeric matrices were subjected to leaching studies as per ANSI/ANS-16.1-1986 leach test. The leachability index was found to be acceptable as per the test standard. The leach test data was used to develop an understanding of the leaching behaviour of the metal salts. The leaching rate was found to be dependent on the water penetration depth, the total leachable salt and leaching depth. Leaching depth was controlled by effective diffusivity and solubility of the salt. Salt leaching depth signifies the dissolution front, which progresses with time. A leach model based on diffusion controlled dissolution kinetics was developed to simulate the tests, which can be used to formulate standards for safe disposal. The leaching data was further correlated using the dimensionless time approach. The critical model parameters included effective unencapsulated salt concentration, salt leaching depth, porosity of matrix and effective diffusivity of salt.

Effect of functionalized kaolinite on the curing kinetics of cycloaliphatic epoxy/anhydride system

Silane grafted kaolinite (KGS) was prepared through grinding kaolinite and then grafting with 3-aminopropyltriethoxysilane. The influence of KGS on the curing kinetics of cycloaliphatic epoxy resin was studied by non-isothermal differential scanning calorimetry at different heating rates. The reaction activation energy (Ea) was determined based on the Flynn–Wall–Ozawa method. The results of dynamic differential scanning calorimetry (DSC) kinetic analysis show that the surface hydroxyl groups of clay decreases the Ea from 70.6kJmol−1 to 62.8kJmol−1 and accelerates the curing reaction of the epoxy resin. The silane grafting reactions consume the surface hydroxyl groups of kaolinite and lead to a decrease in the catalytic efficiency of KGS in the curing of epoxy resin.

Structures and properties of nanocomposites based on a cured cycloaliphatic epoxy resin

The effect of nanoparticles on glass-transition temperature Tg and the elastic modulus of a cycloaliphatic epoxy resin cured with methylhexahydrophthalic anhydride is theoretically analyzed. The analysis was performed with allowance for the following factors: the chemical structure of the polymer, the chemical structures of the nanoparticles and their surfaces if they are modified, the concentrations and shapes of nanoparticles (spherical, plate, cylindrical), the concentration of functional groups on the surfaces of nanoparticles, the energy of intermolecular interaction between a polymer and a nanoparticle, and the possibility of chemical interaction between a polymer and the surfaces of nanoparticles. The most pronounced effect on Tg is exerted by cylindical nanotubes, whose surfaces are modified with OH groups, which give rise to hydrogen bonding. The least effect is exerted by spherical nanoparticles. After the introduction of SiO2 nanoparticles, the elastic moduli of nanocomposites increase by a factor of 1.15 at an amount of nanoparticles up to 20%.

Morphologies and applied properties of free radical/cationic UV-cured CPUA/TMPTMA/CER composite films

A UV-cured composite film was prepared by free free-radical photopolymerization from a blend containing oligomer cycloaliphatic polyurethane acrylate (CPUA) and reactive diluent trimethylolpropane trimethaacrylate (TMPTMA) with the same weight (coded as UT) in the presence of free free-radical photoinitiator Irgacure 754. It was proved to be a homogeneous system featuring only one phase by means of scanning electron microscopy (SEM). Cycloaliphatic epoxy resin (CER) was introduced to enhance mechanical properties of the UV-cured UT composite film in the presence of cationic photoinitiator Irgacure 250, and a series of UV-cured CPUA/TMPTMA/CER composite films with different component ratios were prepared by free radical/cationic hybrid UV UV-curing technique. Results of conversion curves, SEM, and Fourier- transform infrared spectroscopy illustrated that UT was cured faster than CER, leading to dynamically asymmetric photopolymerization-induced phase -separation behaviors. The thermal and mechanical properties were evaluated via thermal degradation analysis, dynamic mechanical analysis, and stress–strain curves. Surface properties such as pencil hardness, pendulum hardness, shrinkage rate, contact angle, flexibility, and glossiness were also studied. All these measurements revealed that component ratios, intermolecular attractions, photopolymerization velocities, and viscosities had remarkably influenced on the morphologies and applied properties of UV-cured composite films, and interpenetrating polymer network films had better comprehensive performances than other UV-cured composite films with different microstructures. POLYM. COMPOS., 36:1177–1185, 2015. © 2014 Society of Plastics Engineers

Modification of epoxy binders using cycloaliphatic epoxy imides

The influence of epoxy imide cycloaliphatic epoxy resin EPOX-01 on the rheological properties of the epoxy amine system was investigated. The effect of the amount of amine hardener for solidification process of modified system is evaluated. It is shown that the use of epoxy imide cycloaliphatic resin allows one to obtain materials with improved technological characteristics of film technology (RFI).