Isothermal cure kinetics

The isothermal cure kinetics of a series of TGMDA/DDS resin formulations were investigated over the temperature range 121°-187°C. Figure 4 illustrates data obtained for the resin TGMDA/DDS(25%) at 177°C. During the early stage of cure prior to the onset of... 

Conversion of the mixed system to the B-stage cure condition to yield Isothermal cure kinetics. 

Sourour, S., Kamal, M. R. Differential scanning calorimetry of epoxy cure isothermal cure kinetics, Thermochimica Acta, 14, 41 (1976)... 

Since non-isothermal cure is of practical importance in cure control, one would like to extend the cure model to include non-isothermal cure kinetics. This modification is shown below ... 

Isothermal Cure Kinetics of an Epoxy Resin Prepreg... 

The isothermal cure kinetics of a glass fiber-epoxy resin prepreg is investigated using high performance liquid chromatography (HPLC) and differential scanning calorimetry (DSC). The... 

The isothermal cure kinetics were evaluated using the following equation (3)... 

There are correlations between isothermal cure kinetics parameters determined by DSC and compositional parameters determined by HPIX. 

The isothermal cure kinetics of the prepreg has characteristics similar to those reported for th.e neat resin (5). Rutocatalysis and diffusion control are observed and similar heats of reaction and activation energies are determined. The extents of reaction at the gel point estimated by DSC and torsional braid analysis of the neat resin(s) correspond to values determined gravlmetrlcally in this study. The low value of the reaction ratio dlcy/enoxy at the lower curing temperatures would explain the unreacted dicy noted by Schneider et. al ( ). 

The viscoelastic and thermal properties of fully and partially cured DGEBA epoxy resin composites were smdied modified with montmorillonite nanoclay exposed to UV radiation. Samples were fabricated and cured to 80 % conversion (partially cured) based on isothermal cure kinetic smdies. Influence of 1-3 wt% loading of montmorillonite nanoclay on the cure behavior and development of physical properties of these composites were evaluated. Results of the smdy revealed that for optimization of modified epoxy composite properties, a different curing cycle was necessary due to interaction of different amounts of nanoclay and epoxy molecules. Addition of nanoclay increased the viscoelastic properties, storage modulus and activation energy of decomposition of partially cured samples evolved over exposure time, while fuUy cured samples degraded over the same period. 

Isothermal differential scanning calorimetry (DSC) measurements were carried out to investigate the curing kinetics [85]. Conversion vs time curves of DGEBPA-PACP systems prepared with 1 wt % of catalyst and without catalyst at identical curing temperature are overlaid in Fig. 31. 

To obtain the cure kinetic parameters K, m, and n, cure rate and cure state must be measured simultaneously. This is most commonly accomplished by thermal analysis techniques such as DSC. In isothermal DSC testing several different isothermal cures are analyzed to develop the temperature dependence of the kinetic parameters. With the temperature dependence of the kinetic parameters known, the degree of cure can be predicted for any temperature history by integration of Equation 8.5. 

Fig. 24. Change of the dynamic Young modulus E (solid lines) during isothermal cure at different Tcu . DGER-mPhDA (P = 1) dotted lines are the kinetic curves from Fig. 1...

A generalized kinetic model of cure is developed from the aspect of relaxation phenomena. The model not only can predict modulus and viscosity during the cure cycle under isothermal and non-isothermal cure conditions, but also takes into account filler effects on cure behavior. The increase of carbon black filler loading tends to accelerate the cure reaction and also broadens the relaxation spectrum. The presence of filler reduces the activation energy of viscous flow, but has little effect on the activation energy of the cure reaction. 

A generalized kinetic model of cure has been developed from the aspect of relaxation phenomenon. The model not only can predict isothermal and non-isothermal cure curves using modulus and viscosity data, but also allows us to take into account the effect of filler on cure behavior. The prediction of viscosity and modulus values during the cure cycle allows one to preprogram cure in order to improve the material processing and end-product performance. The important findings of this study... 

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