Viscoelastic behaviour of polymethyl methacrylate networks with different crosslinking degrees

The influence of the cross-linking degree on the dynamics of the segmental motions close to the glass transition of poly(methyl methacrylate), PMMA, networks was investigated by three different mechanical spectroscopy techniques: thermally stimulated recovery (TSR), dynamic mechanical analysis (DMA), and creep. The application of the time-temperature superposition principle to isothermal DMA and creep results permitted to successfully construct master curves for PMMA networks with distinct cross-linking degrees. The former results were fitted to the KWW equation. The obtained variation of âKWW for the distinct networks indicated that the relaxation curves tend to broaden as the cross-linking degree increases. TSR results clearly revealed a significant shift of the R-relaxation to longer times and a broader relaxation as the cross-linking degree increases, what was also observed by DMA and creep. A change from a Vogel to an Arrhenius behavior was detected by the three techniques with the decrease of temperature below Tg. The temperature dependence of the apparent activation energies (Ea) was calculated from DMA, creep, and TSR experiments; above Tg a good agreement was seen between the Ea values for all the techniques. Furthermore, the effect of the cross-linking degree on the fragility of PMMA networks was evaluated. For these materials an increase of fragility with increasing cross-linking degree was observed

Mathematical and Experimental Modelling of Adsorption in Fixed Bed. II. Experimental Investigation of Nonisothermal Single Solute Adsorption and Adsorber Simulation

The adsorption separation process of n -heptane on a molecular sieve in a fixed bed adsorber is investigated. Experimental concentration and temperature breakthrough curves are obtained using different gas inlet concentration and temperature, different bed length and gas mixture flow rate. The mentioned experimental data are simulated a priori by means of a two-phase mathematical model. The model parameter values used in the simulations are estimated either through available semiempirical correlations or by independent experimental runs. An example of predicted and experimental concentration and temperature breakthrough curves comparison is presented