Separation of PE/PS in-situ reactive blends with near critical n-pentane (6 pag)

M. DIAZ; G. MABE; E. BRIGNOLE; S. BARBOSA,

Versalles, France

Simposio; 6th International Symposium on Supercritical Fluids - ISSF 2003; 2003

In-situ compatibilized polymer blends are very important commercial materials for the improvement of the blend final properties. It is obtained by the in situ generation of a copolymer, which enhances the dispersed phase morphology parameters (particle size, size distribution, and interparticle distance), and interface adhesion. The characterization of this copolymer depends on achieving a clear separation from the raw copolymers involved in the blend. When the raw materials are high molecular weight commercial grades polymers, this separation is very difficult by traditional selective solvent extractions (like Soxhlet at atmospheric pressure). The use of high-pressure/temperature fluid extraction is an interesting alternative to obtain the complete separation. In this way, polymer/copolymer solubilization can be tuned trough changes in parameters like pressure, temperature, etc. In this work, a polymer blend components separation using high-pressure near critical fluid is proposed. The system analyzed was PE/PS/PE-g-PS/ using n-pentane as solvent. PE-g-PS was in-situ generated by a low cost Friedel-Crafts reaction in melt form. Studies were carried out in cylindrical cell were small samples 50-100 mg of polymer blends, confined in a basket made with a Teflon microporous filter were placed in contact with the solvent at temperatures between 373 to 473 K and pressures in the range of 200 to 500 bar. The thermoplastic blend phase separation experiments were performed for physical mixtures of PE/PS in different ratios and for the PE/PS/PE-g-.PS mixtures. The mass solubilized was determined by weight difference. The soluble fractions were collected by rapid expansion of the superheated n-pentane. Both samples soluble and insoluble fraction were collected and analyzed by: a) size exclusion chromatography and scanning electron microscopy. The results obtained indicated that this separation approach allows the study of the copolymers formation and morphology.