Crosslinking of an epoxy with a mixed amine as a function of stoichiometry. II. Final properties via dynamic mechanical spectroscopy

Abstract

SynopsisVariation of the epoxy/curing agent ratio for a system containing a diglycidyl ether of bisphenol-A (DGEBA) and a mixed aromatic amine was found to have a significant effect on the cure kinetics and final dynamic mechanical properties of both the neat resin and glass reinforced epoxy. For a partial B-stage cure to an ultimate C-stage cure, optimum cure temperatures were obtained as a function of stoichiometry. For the ultimately cured (C-stage) resin, the molecular weight between crosslinks ( M , ) passed through a minimum, and both the glass transition temperature ( T,) and a secondary (sub-T,) transition passed through a maximum at the stoichiometric ratio. In addition, the activation energy of the ultimately cured resin passed through a maximum at or near the stoichiometric ratio for both the Tg and sub-T, transitions.

Treatment of advanced colorectal carcinoma with oxaliplatin and capecitabine

“…The d.c. conductivity was obtained from the diameters of the depressed semicircles in a plot between 299 and 495 K. The relation between σ and T was found to follow equation (3): where A is the preexponential factor, k the Boltzmann constant, and E c the activation energy. Figure 2 shows that C 11 , C 12 , and C 13 behaved almost similarly in respect to the characteristic that a more rapid increase of conductivity in both cases occurred above the temperature T e , where the temperature T e is defined8–13 by T e = ( T g + Δ T ). Figure 2 indicates the T e for C 11 , C 12 , and C 13 as 166.9, 127, and 107.1°C, respectively.…”

Anhydride Cured Bio‐Based Epoxy Resin: Effect of Moisture on Thermal and Mechanical Properties

“…The cross‐linking density of the resins ( v e ) and the average molecular weight of network‐chains between the cross‐linking points ( M c ) were evaluated from the storage modulus in the rubbery plateau according to the relationship given in Equation where E ′ is the tensile storage modulus in rubbery plateau (160 °C), v e is the cross‐linking density, k is the Boltzmann constant, ρ is the density, R is the gas constant and T is the temperature in Kelvin corresponding to the storage modulus value (rubbery plateau) …”

Static and Dynamic Mechanical Analysis of Coir Fiber/Montmorillonite Nanoclay-Filled Novolac/Epoxy Hybrid Nanocomposites

“…It is evident from this observations that ENR offers more rigid networks after curing, its fiber-matrix interaction is strong compared to that of DGEBA-based nanocomposite that has lower stress at maximum load and also a lower T g compared to that of 20 and 35 % ENR-based composites. The possible explanation may be the synergistic effect of good fiber-matrix interaction attributed to DGEBA and higher extent of crosslinking to the presence of ENR (Otaigbe 1991;Wingard and Beatty 1990). Figure 7 shows tan δ versus temperature plots for different nanocomposites.…”

“…The improvement in thermomechanical properties was observed by the introduction of modified montmorillonite into the blends of laboratory prepared ENR and DGEBA resin. For characterization of polymeric materials such as homopolymers, copolymers, terpolymers, blends, and composites and their evaluation for consideration in stress and safety sensitive applications, dynamic mechanical analysis (DMA) at a selected fixed frequency over a range of temperature has advanced as an increasingly useful technique (Ghosh et al 2003;Otaigbe 1991;Wingard and Beatty 1990). Dynamic mechanical tests, in general, give more information than other tests about a composite material.…”