Polyethylene Final Properties Improvement by Grafting of Styrene in Supercritical Media

MARTINI, RAQUEL EVANGELINA; BRIGNOLE, ESTEBAN ALBERTO; BARBOSA, SILVIA ELENA

Bordeaux, Francia

Simposio; 9th International Symposium on Supercritical Fluids; 2009

ISSF

The use of near and supercritical fluids, as solvent aid in polymer processing and polymer chemistry, has been incremented from the last decade. They can have gas-like diffusivities, which have important implications for reaction kinetics, as well as liquid-like densities, allowing solvation of many compounds. On the other hand, macromonomer cationic copolymerization is a growing field of synthetic polymer chemistry. Friedel-Crafts alkylation involves the alkylation of an aromatic ring and an alkyl halide using a strong Lewis acid catalyst. It can be applied to obtain a copolymer from an aromatic monomer and polyethylene (PE) chains as a macromonomer. In the present work a novel method of copolymerization is proposed. Near critical n-heptane is used as reaction medium and swelling agent for the copolymerization of PE with styrene monomer using AlCl3 as catalyst. The reaction was performed in a stirred batch reactor at 140 oC and 150 bar. It was determined that PE is completely solubilized in the n-heptane at high pressure-high temperature conditions. In this way, it is expected that using near critical n-heptane as reaction medium, PE chains and the catalyst will be more available to react each other. The copolymerization reaction was corroborated analyzing the reaction products after a careful pure polystyrene separation by selective soxhlet extraction using tetrahydrofuran. The copolymer obtained was characterized and polystyrene grafted quantified by a combination of techniques like nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The oxygen barrier of grafted PE films was improved in a 30% respect to pure PE, when around of 7 % of styrene was grafted. Tensile mechanical properties of the same samples show that although the rigidity lightly increases, the grafted PE could be processed as films because the elongation at break remains around of 260%.