DGEBA Epoxy Research Articles

Highly Effective Flame Retardancy of a Novel DPPA-Based Curing Agent for DGEBA Epoxy Resin

The flame retardancy, thermal, and mechanical properties of the cured epoxy resins are difficult to be simultaneously improved. In the present work, a novel DPPA-based curing agent, 10-[(4-hydroxyphenyl)(4-hydroxyphenylimino)methyl]-5,10-dihydrophenophosphazine 10-oxide (H-DPPA), is successfully synthesized to serve as a co-curing agent of 4, 4′-diaminodiphenylmethane (DDM) for bisphenol A diglycidyl ether (DGEBA) epoxy resin. With the aid of 3.0 wt % of H-DPPA, the cured epoxy resin, in which the phosphorus content is as low as 0.22%, passes V-0 rating of UL-94 test with limiting oxygen index (LOI) of 31.8%. The high flame retardancy of epoxy resin modified by H-DPPA originated mainly from the formation of intumescent char layer during combustion. This new type of flame retardant containing both phosphine oxide structure and nitrogen moieties provides epoxy resins with excellent integrated performances.

High performance fire-retarded epoxy imparted by a novel phenophosphazine-containing antiflaming compound at ultra-low loading

A novel phenophosphazine-containing compound, HD-DPPA, was successfully synthesized via the addition reaction between 5,10-dihydro-phenophosphazinine-10-oxide and Schiff base obtained in advance by condensation of 4,4′-dimninodiphenylmethane (DDM) and 4-hydroxybenzaldhehyde, and used as a co-curing agent of DDM and a flame retardant for DGEBA epoxy resin. The cured epoxy resin passed UL-94 V-0 rating with limiting oxygen index (LOI) of 31.3% at only 2.5wt% HD-DPPA, where phosphorus content was as low as 0.19wt%. The formation of intumescent char layer and blowing-out effect during combustion are responsible for high flame retardancy of epoxy resin. The flame-retarded epoxy resin exhibited the improved tensile and impact strength compared with the pristine epoxy resin.

Evaluation of four curing agents of epoxy resin and their effects above their thermal and dinamomechanical properties

ABSTRACTWere synthesized four new hybrid hardener agents type amino tertiary functionalized with allyl groups from : l, 6-Hexanediamine, Diethylenetriamine, Trietilentriamine and Tris (2-aminoethyl) amine, using the basic nucleophilic substitution mechanism, replacing bromide by amino tertiary group in the presence of tetrabutylammonium bromide as phase transfer agent, producing allyl amine corresponding: ALA-4, ALA-5, ALA-6 and TRIS respectively, which were evaluated as a hardening of epoxy resin DGEBA through photopolymerization process by UV ligth curing, adding a 10, 20 and 40% molar percentage of hybrid materials and the thiol corresponding to carry out the thiol-ene reaction (TMP TMP, PTKMP) with DMPA as initiator. The resinic materials obtained, were evaluated by the technique of dynamic mechanical analysis (DMA) at a heating rate of 5° C/min in a range from - 50° C to 150° C in nitrogen atmosphere. The formulations with hybrid hardening agent ALA 4- 20% -PTKMP and TRIS 10% -PTKMP were the materials with modulus 2289, 2971 Mpa and tgs of 102,103°C, respectively.

Influence of Degassing and Nanoclay Loading on Physical and Flexural Properties of Epoxy

The mechanical and physical properties of epoxy-clay nanocomposites are known to be significantly affected by the dispersion and distribution of the clay particles in the epoxy matrix. The degree of dispersion of the clay particles in the epoxy matrix depends mainly on the processing parameters used to synthesize the nanocomposite.In this paper, the optimized high shear mixing parameters determined in an earlier work were used to disperse five different loadings of Nanomer I.30E nanoclay (1, 1.5, 2, 3 and 5 wt%) into DGEBA epoxy matrix. A systematic approach was adopted to optimize the degassing process of the mixture. X-Ray Diffraction (XRD) analyses showed that the optimum nanoclay dispersion was achieved for a degassing temperature of 120 °C. The flexural strength of the developed nanoclay/epoxy composite is found to increase by 15% for 1.5 wt% and due to the high stiffness of the clay, as compared with epoxy resin, the flexural modulus improved continuously with clay loading. The observed reduction in strength and fracture strain at high clay loadings is mainly attributable to the presence of clay agglomerations and voids formation. The diffusion of water molecules and maximum moisture uptake of epoxy are reduced considerably by the presence of nanoclay.

Dynamics and thermal properties of epoxy resin cured by new diamino disiloxanes

ABSTRACTTwo disiloxane compounds, 3,3′‐(1,3‐dimethyl‐1,3‐diphenyl‐1,3‐disiloxanediyl)bis(benzenamine) (C1) and 4,4′‐(1,3‐dimethyl‐1,3‐diphenyl‐1,3‐disiloxanediyl)bis(benzenamine) (C2) were synthesized and used as new curing agents of DGEBA epoxy resin with an epoxy value of 0.51 (E‐51). The curing kinetics of E‐51/C1 and E‐51/C2 systems was investigated by non‐isothermal differential scanning calorimetry (DSC) analyses. The activation energy (ΔE) and the characteristic cure temperatures of the two systems were determined. The two systems have the similar activation energy. The reactivity of E‐51/C1 is higher than that of E‐51/C2. The reaction orders of E‐51/C1 and E‐51/C2 are 0.88 and 0.87, respectively, illustrating that curing reaction between the epoxy resin and curing agent (C1 or C2) is complicated. The DSC result shows that E51 cured by C2 has higher Tg; whereas thermogravimetric analysis results indicate that E51 cured by C1 has higher thermal stability. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42385.

Development of technology to industrialise the production of 80000 MTPY epoxy resins

Purpose – The purpose of this paper is to establish a technology that is suitable for the production of the 80,000 MTPY series of epoxy resins on an industrial scale. Design/methodology/approach – This paper introduces the synthesis and processing of epoxy resins, including liquid epoxy resins (DGEBA) (E-51 and E-44), brominated bisphenol A-based epoxy resins (EX-23-80A), semisolid epoxy resins based on DGEBA (E-39D) and solid epoxy resins based on DGEBA (E-21). The study analyses the theoretical raw materials of epoxy resins per tonne, and lists an example of a distributed control system (DCS) to explain that the production process of 80,000 MTPY epoxy resins can be automated. Findings – A two-step method was used to produce either E-51 or E-44 sequentially in the pre-reactor, the reactor, the recycling kettle, refining kettle (1), the refining kettle (2) and the desensitizing kettle or the falling-film evaporator. An advancement process was adopted to manufacture EX-23-80A, E-39D and E-21 using E-51 as a raw material in the predominating kettle and the mixing kettle, the adding kettle (1) and the adding kettle (2), separately. All the processes were controlled automatically by DCS to yield the products. Originality/value – The results support the assertion that the technology developed by the authors ' company to produce 80,000 MTPY epoxy resins results in fewer side reactions and higher yield production.

Effect of core–shell rubber (CSR) nano-particles on mechanical properties and fracture toughness of an epoxy polymer

A DGEBA epoxy resin cured using dicyandiamide hardener, was modified by using two types of CSR nano-particles over a range of volume fractions from 0 vol.% to 38 vol.%. The size and microstructure of CSR particles were studied and the measured diameters are 203 nm (with a 16.9 nm shell thickness) and 74.1 nm respectively. Addition of CSR nano particles increased the glass transition temperature due to the interaction between matrix and particles. Addition of CSR particles increased the ductility and Poisson's ratio of epoxy, but reduced the Young's modulus and tensile strength. Young's modulus, Poisson's ratio and tensile strength were well predicted by theoretical models using an effective volume fraction of rubber. An optimum CSR content was found to exist, when the fracture energy increased from 343 J/m2 for matrix to 2671 J/m2 for epoxy modified by 30 vol.% of CSR particles, and then started to decline. The main toughening mechanisms were proved to be debonding of CSR particles from matrix, followed by plastic voids growth, which was accompanied by shear bands yielding. Large-scale plastic void growth was discovered at the subcritical tip of double notch four points bending test (DN-4PB), and the values of fracture energy were found to be proportional to the size of plastic damage zone measured from subcritical crack tip of DN-4PB. This proved the plastic void growth is the major toughening mechanism, which correlated well with the results of fracture energy modelling. A theoretical model was used to predict the fracture toughness increment due to the shear band yielding and plastic void growth. The analytical values showed good agreement with the experimental data, and further demonstrated the proposed toughening mechanism.

Water resistance and curing kinetics of epoxy resins with a novel curing agent of biphenyl-containing amine synthesized by one-pot method

In order to increase thermal stability and decrease water uptake of conventional epoxy resins, the biphenyl structure was introduced through the curing agent. A novel biphenyl-containing amine (BPDP) was synthesized by one-pot method and used as the curing agent for bisphenol-A epoxy resin DGEBA. Thermal property, water uptake and curing kinetics of the co-cured epoxy with diaminodiphenyl methane (DDM) were studied. The introduction of BPDP obviously improved the thermal stability, char yield, and water-uptake of the cured epoxy resins. The glass transition temperature Tg and weight-loss temperature increased with increasing BPDP content in the co-curing agent of BPDP and DDM. BPDP showed lower reactivity toward epoxy DGEBA than DDM with higher apparent activation energy Ea. Curing reaction of the epoxy resins co-cured with BPDP and DDM was investigated by non-isothermal DSC and the curing kinetics was described by a truncated two-parameter autocatalytic equation of the Šesták–Berggren model with experimentally determined parameters, which fitted the observed non-isothermal curing reaction rate quantitatively.

Modulation of surface electrical properties of epoxy resin insulator by changing fluorination temperature and time

In order to systematically investigate the modulating role of fluorination temperature and time on surface electrical properties of the epoxy resin insulator, epoxy resin sheets were surface fluorinated in a laboratory vessel using a F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 mixture with 12.5% F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> 2 by volume at 0.1 MPa and different temperatures of 25–95 °C for different times of 5–120 min. Conductivity measurements have shown that the intrinsic surface conductivity of the epoxy resin insulator could be modulated from an even lower value to a nearly four orders of magnitude higher value than the value prior to fluorination by changing the fluorination temperature and time. Surface conductivity increased with increasing fluorination temperature at the same fluorination time, while decreased to some extent with increasing fluorination time at a given fluorination temperature. Surface potential decay measurements showed consistent results with the surface conductivity measurements. ATR-IR analyses revealed substantial changes in surface chemical composition and structure, depending on the fluorination temperature and time. SEM images clearly showed an increase of the fluorinated layer thickness with increasing fluorination temperature and time. Surface cracks appeared only at elevated fluorination temperatures and increased with fluorination temperature, while the surface became compact with the duration of the fluorination. These results, compared with the previous results on an epoxy resin insulator made of DGEBA epoxy resin with a lower epoxy value, also indicated a significant influence of the epoxy resin insulator itself or the epoxy resin raw material on surface electrical properties and surface physicochemical characteristics after fluorination.

Synthesis and Characterization of DGEBA Epoxy and Novolac Epoxy Blends and Studies on their Curing and Mechanical Behavior

Synthesis and Characterization of DGEBA Epoxy and Novolac Epoxy Blends and Studies on their Curing and Mechanical Behavior

Decomposition mechanisms and kinetics of amine/anhydride-cured DGEBA epoxy resin in near-critical water

A reaction mechanism based on the homolysis of the bonds of epoxy resins system in near-critical water was discussed. Based on the observed information, a probable macroscopic mechanism was proposed.

Intumescent flame retardancy of a DGEBA epoxy resin based on 5,10-dihydro-phenophosphazine-10-oxide

Only 2.5 wt% DPPA makes the epoxy resin achieve a V-0 rating in the UL-94 test due to the combination of intumescent charring and the blowing-out effect.

Synthesis and performance of a novel nitrogen‐containing cyclic phosphate for intumescent flame retardant and its application in epoxy resin

ABSTRACTA novel nitrogen‐containing cyclic phosphate (NDP) was synthesized and well characterized by 1H, 13C, 31P NMR, mass spectra and elemental analysis. NDP was used as an additive intumescent flame retardant (AIFR) to impart flame retardancy and dripping resistance for diglycidyl ether of bisphenol‐A epoxy resin (DGEBA) curied by 4,4′‐diaminodiphenylsulfone (DDS) with different phosphorus content. The flammability, thermal stability, and mechanical properties of NDP modified DGEBA/DDS thermosets were investigated by UL‐94 vertical burning test, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Izod impact strength and flexural property tests. The results showed that NDP modified DGEBA/DDS thermosets exhibited excellent flame retardancy, moderate changes in glass transition temperature and thermal stability. When the phosphorus content reached only 1.5 wt %, the NDP modified DGEBA/DDS thermoset could result in satisfied flame retardancy (UL‐94, V‐0). The TGA curves under nitrogen and air atmosphere suggested that NDP had good ability of char formation, and there existed a distinct synergistic effect between phosphorus and nitrogen. The flame retardant mechanism was further realized by studying the structure and morphology of char residues using FT‐IR and scanning electron microscopy (SEM). It indicated that NDP as phosphorus‐nitrogen containing flame retardant worked by both of the condensed phase action and the vapor phase action. Additionally, the addition of NDP decreased slightly the flexural strength of the flame retarded DGEBA epoxy resins, and increased the Izod impact strength of these thermosets. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41859.

Photoelastic stress analysis assisted evaluation of fracture toughness in hydrothermally aged epoxies

The present work has investigated the fracture toughness of a model DGEBA epoxy system subject to Hidro-Thermal aging. A Photoelastic Stress Analysis technique has been implemented, showing the evolution of stresses arising throughout the water uptake process due to the non-uniform swelling of the material. Gravimetric and Dynamic Mechanical Thermal Analyses have further complemented the characterization, showing the onset of plasticization effects with aging. The correlation of all previous characterizations has allowed to conclude that an increase of KIC fracture toughness is obtained at the fully saturated condition. In particular Photoelasticity has also revealed the onset of relevant swelling induced stresses during the first stages of water absorption, leading to an increase of fracture toughness due to compressive stresses settling near the crack tip. A stress free condition is instead reestablished at the later stages of absorption, suggesting that the increased toughness of the saturated material is an effect of the modifications induced by aging on the polymer structure.

Effect of hydrothermal ageing on the thermal and delamination fracture behaviour of CFRP composites

This work investigates the hydrothermal ageing behaviour of a carbon fibre reinforced laminate and its epoxy matrix in bulk conditions. A model DGEBA epoxy is employed, and water uptake and dynamic mechanical thermal (DMTA) analyses have been performed on both the composites and bulk resin. Fracture toughness of the bulk resin has been measured, evidencing a substantially unmodified critical stress intensity factor KIC, although the evidence of plasticisation effects given by DMTA. Interlaminar Mode I fracture toughness of the composite showed a variable trend towards slight decreases or slight increases, according to the prevailing toughening or embrittling mechanisms activated by the aging conditions.

The synthesis and characterization of a novel phosphorus–nitrogen containing flame retardant and its application in epoxy resins

ABSTRACTA novel, halogen‐free, phosphorus–nitrogen containing flame retardant 2[4‐(2,4,6‐Tris{4‐[(5,5‐dimethyl‐2‐oxo‐2λ5‐[1,3,2]dioxaphosphinan‐2‐yl)hydroxymethyl]phenoxy}‐(1,3,5)‐triazine (TNTP) was successfully synthesized in a three‐step process, and characterized by FTIR, NMR spectroscopy, mass spectra, and elemental analysis. A series of modified DGEBA epoxy resin with different loadings of TNTP were prepared and cured by 4,4‐diaminodiphenylsulfone (DDS). Thermal gravimetric analysis and vertical burning test (UL‐94) were used to evaluate the flame retardancy of TNTP on DGEBA epoxy resin. The results showed that TNTP had a great impact on flame retardancy. All modified thermosets by using TNTP exhibited higher Tg than pure DGEBA/DDS. The loading of TNTP at only 5.0 wt % could result in satisfied flame retardancy (UL‐94, V‐0) together with high char residue (27.3%) at 700°C. The addition of TNTP could dramatically enhance the flame retardancy of DGEBA epoxy resins, which was further confirmed by the analysis of the char residues by scanning electron microscopy and FTIR. Furthermore, no obviously negative effect was found on the Izod impact strength and flexural property of DGEBA epoxy resins when TNTP loading limited in 5.0 wt %. DGEBA/DDS containing 2.5 wt % TNTP could enhance Izod impact strength from 10.47 to 10.94 kJ m−2, and showed no appreciable effect on the flexural property (85.20 MPa) comparing with pure DGEBA/DDS (87.03 MPa). Results indicated that TNTP as a phosphorus–nitrogen synergistic intumescent flame retardant could be used for DGEBA epoxy resin. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41079.

Effect of Methyltrimethoxy Silane Modification on Yellowing of Epoxy Coating on UV (B) Exposure

The exterior durability of epoxies is severely affected due to its poor weathering resistance. Epoxies exhibit chalking and discoloration under UV exposure caused as a result of photodegradation. The present work aims at studying the extent to which the color change and yellowing caused due to weathering under accelerated weathering conditions, of DGEBA epoxy, could be lowered by in situ modification of the epoxy polymer backbone with a silane, namely, MTMS. The epoxy resin and silane-modified epoxy resin were formulated into a TiO2-based white coating, applied on mild steel panels, and exposed in a UV (B) weatherometer. The color change (dE) and yellowness index (YI) values of weathered panels were evaluated using a spectrophotometer. The weathered samples were also characterized using FTIR-imaging technique to study the effect of weathering on the structural backbone of the formulated coatings. The silane-modified epoxy coatings showed lowered yellowing by 45% on UV exposure and the enhanced resistance to yellowing of the modified coatings was indicated by lowered dE and YI values. The enhanced resistance to yellowing by the silane-modified epoxy was attributed to the strengthening of the epoxy backbone by introduction of Si–O–C linkage onto the epoxy polymeric chain.

Influence of rubber on the curing kinetics of DGEBA epoxy and the effect on the morphology and hardness of the composites

The influence of the end groups of two liquid rubbers on curing kinetics, morphology, and hardness behavior of diglycidyl ether of bisphenol-A based epoxy resin (DGEBA) has been studied. The rubbers are silyl-dihydroxy terminated (PDMS-co-DPS-OH) and silyl-diglycidyl ether terminated (PDMS-DGE). Crosslinking reactions, investigated by shear rheometry, ranged 90–110 °C, using a constant concentration (5 phr) of liquid rubbers and 1,2-Diamino cyclohexane (1,2-DCH) as hardener agent. The gel time, tgel, of the neat epoxy significantly decreased when adding the elastomers, more so for the silyl-dihydroxy terminated elastomer; at 110 °C the reaction was nearly complete before rheological test started. The results suggest that the elastomers induced a catalytic effect on the curing reaction. Scanning electron microscopy revealed phase separation of the elastomer during the curing reaction with rubber domains about 5 μm size. However, the DGEBA/dihydroxy terminated elastomer composite cured at 110 °C exhibited a homogenous morphology, that is, the rapid reaction time would not allow for phase separation. Water contact angle tests evidenced either more hydrophilic (silyl-diglycidyl ether terminated rubber) or more hydrophobic (silyl-dihydroxy terminated rubber) behavior than the neat epoxy. The latter effect is attributed to the presence of aromatic rings in the backbone structure of PDMS-co-DPS-OH. Microindentation measurements show that the elastomers significantly reduced the hardness of the epoxy resin, the DGEBA/ether terminated composite exhibiting the lowest hardness values. Moreover, hardness increased as reaction temperature did, correlating with a reduction of microdomains size thus enabling the tuning of mechanical properties with reaction temperature.

Enhanced tensile performance of epoxy and E-glass/epoxy composites by randomly-oriented amino-functionalized MWCNTs at low contents

Effect of amino-functionalized multi-walled carbon nanotubes (NH2-MWCNTs) on the tensile performance of epoxy and E-glass/epoxy composites was investigated. Low weight percentages (0.3 and 0.4 wt%) of NH2-MWCNTs were dispersed into a DGEBA epoxy resin using combination of sonication and three-roll milling methods. Composites with plain weave E-glass fabrics were fabricated by compression molding process. Tensile test results showed a significant enhancement in strength, modulus and toughness of epoxy and E-glass/epoxy composites at 0.3 wt% loading of NH2-MWCNTs. Micrographs of NH2-MWCNTs-incorporated epoxy and E-glass/epoxy composites revealed better dispersion of nanotubes in epoxy, better bonding between nanotubes and polymer and improved interfacial adhesion between fiber/matrix at 0.3 wt% loading. Micromechanical models were used to predict the tensile properties and compared with the experimental results. An improved dispersion and hence an enhanced crosslink interaction between NH2-MWCNTs and epoxy lead to the improvements in the tensile properties of the epoxy nanocomposites close to predicted values at 0.3 wt% loading. A similar rationale applies for the increase in properties of E-glass/epoxy nanocomposites.

Material property prediction of thermoset polymers by molecular dynamics simulations

Molecular dynamics simulations are conducted to predict thermal and mechanical properties of a family of thermoset polymers. We focus on the effect of cross-linkers on density, glass transition temperature, elastic constants, and strength. The polymers are composed of the epoxy resin DGEBA (EPON825) and a series of cross-linkers with different number of active sites and rigidity 33DDS, 44DDS, APB133, TREN, and TAPA. Our simulations quantify effects of cross-linkers on thermal and mechanical properties.