Properties Of Epoxy Thermosets Research Articles

Simultaneously cured diglycidyl ethers of bisphenol A and polyethylene glycol: DSC, TGA, and DMA measurements

AbstractIn this study, to improve the physico‐mechanical properties of epoxy thermosets, simultaneous curing of two resins with a stoichiometric amount of an aromatic amine hardener was investigated. The two resins used included the well‐known diglycidyl ether of bisphenol A (DGEBPA) with relatively rigid molecular structure and a diglycidyl ether derived from a popular polymer, polyethylene glycol (PEG), with loose molecular structure (DGEPEG). DGEPEG was used in amounts of 10 and 25 mol% in the resin mixture. A single‐resin curing process, including only DGEBA, was also examined. Before isothermal curing, differential scanning calorimetry (DSC) was used to determine the position of the curing exotherm. To ensure the completion of the curing processes, infra‐red (IR) and DSC techniques were performed on both simultaneously‐cured thermosets and the control thermoset. The thermogravimetric analysis (TGA) of the prepared thermosets showed that the addition of DGEPEG resin in the curing process of DGEBA resin has no significant effect on reducing the thermal resistance of the thermoset. In addition, the storage moduli (E′) and the damping coefficients (tan δ) were measured by dynamic mechanical analysis (DMA). As the mole percentage of DGEPEG resin increased, the rapid drop in the E′ value and the α‐relaxation, which is a measure of the glass transition (Tg), occurred at lower temperatures.

Thermal Stability and Flame Retardancy of Epoxy Resin with DOPO‐Based Compound Containing Triazole and Hydroxyl Groups

AbstractA reactive flame retardant (DTP) is successfully synthesized and characterized, and then incorporated into epoxy resin (EP) as a co‐curing agent. The thermal stabilities and flame‐retardant properties of epoxy thermosets are evaluated. Compared to neat EP, the thermogravimetric analysis (TG) results show that the thermal decomposition rate of EP/DTP is reduced by 45% and the char yield at 750 °C is increased by 67%, when the addition amount of DTP is 12 wt%. In the cone calorimetry test (CCT), the values of the peak of heat release rate (pk‐HRR), total heat release (THR), total smoke produce (TSP), and average of effective heat combustion (av‐EHC) of EP‐DTP‐12 are exhibited a reduction of 36.6%, 26.4%, 40.5%, and 23.6% relative to neat EP, respectively. Meanwhile, the value of the limiting oxygen index (LOI) of EP/DTP‐12 can reach 34.83%, and 6 wt% or more loading of DTP make EP/DTP pass the V‐0 rating in the UL‐94 test. Moreover, the flame‐retardant mechanism is investigated by thermogravimetric analysis/infrared spectrometry (TG‐IR) and scanning electron microscopy (SEM), which can be summarized into two aspects: the quenching effect of phosphorus‐containing radicals and diluting effect of nonflammable gases in the gas phase, and the barrier effect of char layer in the condensed phase.

Synthesis and Characterization of Fluorinated Acrylic Polymer and the Properties of Epoxy Thermosets Modified With It

A novel fluorinated acrylic polymer poly(2,2,3,4,4,4-hexafluorobutyl methacrylate)-r-poly(glycidyl methacrylate) (PHFMA-r-PGMA) was synthesized and used to modify the general performances of epoxy resin. Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance spectroscopy (1H-NMR) successfully verified the synthesis of PHFMA-r-PGMA. In order to study the effect of epoxy groups in PHFMA-r-PGMA on the properties of modified epoxy resin, corresponding fluoropolymer without epoxy group (PHFMA) was also prepared, and the properties of epoxy thermosets modified by two kinds of fluoropolymers were comparatively studied. The contact angle measurements indicated that the PHFMA-r-PGMA and PHFMA modified thermosets both showed considerable hydrophobicity and lipophobicity. For further comparison, it was also found that the thermosets modified by PHFMA-r-PGMA had a little worse hydrophobicity and lipophobicity but better surface stability than which modified by PHFMA because the epoxy groups in PHFMA-r-PGMA “locked” more fluoropolymers in the bulk matrix of the thermosets, but PHFMA was more freely able to migrate to the surface of the thermosets. SEM images of the fracture surface of PHFMA-r-PGMA and PHFMA modified epoxy thermosets displayed “irregular ripples” or “protuberant island” structures, which suggesting both of these two copolymers could significantly toughen epoxy resin. The results of differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the thermosets modified by PHFMA-r-PGMA had better thermal stability than which modified by PHFMA due to the higher crosslinking density between PHFMA-r-PGMA and epoxy resin because of the epoxy groups in PHFMA-r-PGMA. The mechanical properties were investigated by tensile testing and impact testing. Although the tensile strength of the PHFMA-r-PGMA and PHFMA modified epoxy thermosets both declined slightly with growing the content of fluoropolymers, the elongation at break and impact strength both increased first and then decreased in the meantime, which indicated that the two kinds of modified thermosets had better toughness than pure epoxy resin. It may be because the macro-phase separation between the long fluorine carbon chain segments and epoxy resin during curing could absorb the impact energy effectively.

Morphology and fracture toughness of nanostructured epoxy thermosets containing macromolecular miktobrushes composed of poly(ε-caprolactone) and polydimethylsiloxane side chains

In this work, we investigated the nanostructures and mechanical properties of epoxy thermosets containing a macromolecular miktobrush composed of poly(e-caprolactone) (PCL) and polydimethylsiloxane (PDMS) side chains. The novel macromolecular miktobrush was synthesized via the combination of reversible addition–fragmentation chain transfer and ring-opening polymerizations. In the brush-like copolymer the molar ratio of PCL to PDMS was controlled to be 1:1 and the length of PCL chains was controlled to be close to that of PDMS chains (i.e., L PDMS = 1000). The densely grafted miktobrush copolymer was incorporated into epoxy and the nanostructured thermosets were obtained as evidenced by means of transmission electron microscopy and dynamic mechanical thermal analysis. The results of small-angle X-ray scattering showed that the formation of nanostructures in the thermosets followed a self-assembly mechanism. The measurement of critical stress intensity factor (K 1C) showed that the nanostructured thermosets displayed the improved fracture toughness owing to the formation of nanostructures.

Study on the Properties of Epoxy Thermosets Cured by ImHBPs under Lower Temperature

The 2-methylimidazole (Im) -terminated hyperbranched polyesters (ImHBPs) with different generations were prepared and used in diglycidyl ether of bisphenol A (DGEBA) as curing agents and tougheners in this work. It was found that the ImHBPs had better latent property than Im which indicated that the ImHBPs were proper to be used as low temperature curing agent in epoxy curing system. It was also found that the tensile strength, the flexural strength and impact strength of epoxy thermosets cured by ImHBPs under 90 were much higher than those of CYD-128/2-methylimidazole thermoset, which indicated that the ImHBPs obviously improved the mechanical properties of epoxy thermosets, and the thermoset cured by ImHBP with two generation had the best performance among the thermosets.

The effects of monophenol chain terminators on the structure–property relationships of controlled epoxy networks

AbstractFive families of new controlled epoxy thermosets (CENs) using three monophenol chain terminators were prepared to study systematic changes in the structure and amount of the monophenol and the initial molecular weight between crosslinks (Mc,i) on the properties of epoxy thermosets. Glass transition temperature (Tg) decreases with monophenol mole fraction (χ) in proportion to both the concentration and flexibility of the chain terminator. Distinct serial relations for Tg depression were observed for the three Mc,i families. Dynamic mechanical analysis (DMA) shows significant perturbations of the relaxation behavior with added terminator as evidenced by decrease in peak tan δ and in post Tg damping. The rubbery coefficients of thermal expansion (CTE) increases with monophenol concentration only at χ > 0.05 and shows distinct curvature versus temperature, but is largely invariant with monophenol flexibility. The thermal stability of terminated CENs decreases only slightly with χ and little difference was found with monophenol structure. Most surprisingly, fracture toughness decreases markedly and discontinuously with χ depending on Mc,i. The values of the critical monophenol concentration at which fracture toughness markedly decreases (χc) are inversely proportional to Mc,i but are independent of monophenol flexibility. No correlation of χc with any of the calculated network structure parameters was apparent. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1632–1640, 2008