Dissolution mechanism of polymers in high pressure–high temperature n‐alkanes—Application to blends separation

The use of a high temperature–high pressure near critical solvent is an interesting alternative to dissolve high‐molecular‐weight polyolefins with alkanes. This characteristic allows their separation from the blends with other polymers. In the present work, the polymer dissolution of commercial polypropylene (PP) and polystyrene (PS) in n‐alkanes at high pressure and high temperature is analyzed. The comprehension of the different polymer dissolution behaviors and solvent affinities clarifies the understanding of the mechanism of PP/PS physical blend separation under these conditions. The PP dissolution in n‐pentane and n‐heptane was interpreted in terms of chain disentanglement and solvent diffusion. A mathematical model is proposed to predict the experimental results and to calculate mass transfer coefficients in order to quantify the PS barrier effects. It is possible to assess the effect of the temperature on the pure PP solubilization using these coefficients. In blends separation, it was demonstrated that the PS, insoluble at the same conditions, hinders the PP diffusion. As the PS blend content increases, the separation efficiency decreases. Particularly, mass transfer coefficient increases with PP content while PS is the matrix (PS barrier decreases). Afterwards, PP has no ulterior barriers and mass coefficient remains constant. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers