Modelling Sorption Thermodynamics and Mass Transport of n-Hexane in a Propylene-Ethylene Elastomer

Abstract

Optimization of post polymerization processes of polyolefin elastomers (POE) involving solvents is of considerable industrial interest. To this aim, experimental determination and theoretical interpretation of the thermodynamics and mass transport properties of POE-solvent mixtures is relevant. Sorption behavior of n-hexane vapor in a commercial propylene-ethylene elastomer (V8880 VistamaxxTM from ExxonMobil, Machelen, Belgium) is addressed here, determining experimentally the sorption isotherms at temperatures ranging from 115 to 140 °C and pressure values of n-hexane vapor up to 1 atm. Sorption isotherms have been interpreted using a Non Random Lattice Fluid (NRLF) Equation of State model retrieving, from data fitting, the value of the binary interaction parameter for the n-hexane/V8880 system. Both the cases of temperature-independent and of temperature-dependent binary interaction parameter have been considered. Sorption kinetics was also investigated at different pressures and has been interpreted using a Fick’s model determining values of the mutual diffusivity as a function of temperature and of n-hexane/V8880 mixture composition. From these values, n-hexane intra-diffusion coefficient has been calculated interpreting its dependence on mixture concentration and temperature by a semi-empiric model based on free volume arguments.

Expanded Beads of High Melt Strength Polypropylene Moldable at Low Steam Pressure by Foam Extrusion

“…The observation of the exiting strands supplies important insights into the non-linear rheological behavior (e.g., die swell) that are directly linked to the extrusion of the material through the die plate for bead production. In particular, the observed die swell is used to calculate the first normal stresses difference, N 1 , (shown in Figure 2 b), using the empirical equations [ 25 , 26 , 27 ]: where are the shear stresses at the wall and the die swell is defined as the ratio between the diameter of the polymer strand and the capillary diameter. It is worth noting that the swell measurements, B , can be considered independent of the geometry because the capillary design is characterized by Dr/D < 20 and L/D = 21 (where Dr is the diameter of the cylindrical reservoir) [ 27 ].…”

Continuous 3D Printing of Hierarchically Structured Microfoamed Objects

“…Here, one can promote desorption so as to generate a nonuniform blowing agent profile within the filament that, in turn, allows to obtain custom cellular morphologies in the foaming zone. [ 22–25 ] If this is not wanted, a negligible desorption might be also achieved. Desorption can be effectively controlled by modulating the residence time () of the polymer in this zone.…”

“…Desorption can be effectively controlled by modulating the residence time () of the polymer in this zone. [ 25,26 ]…”

“…With such proposed setup, a fast and gram-size analysis of the so-called foamability map [23][24][25] for a specific polymer can be conducted in a very efficient way. The 3D foam printer is, indeed, a fast and economical tool for characterizing new formulations, blowing agents, and processing conditions, as also shown in Figure 4.…”

An Experimental and Numerical Investigation on Bubble Growth in Polymeric Foams

“…These operations are interconnected and their interplay strongly affects the cell morphology and, thus, the properties of the final product. For instance, the number of bubbles nucleating in step 2 grows exponentially with the amount of blowing gas solubilized in step 1 [ 7 ]. In addition, for polymers that have the ability to crystallize, the bubble growth in step 3 and foam setting in step 4 depend on the amount of solubilized blowing gas because of the plasticization effect that this has on the polymer and on its influence on polymer crystallization rate and temperature [ 8 ].…”