MODIFICATION OF POLYETHYLENE PROPERTIES BY STYRENE GRAFTING USING N-ALKANES AT HIGH PRESSURE AS REACTION MEDIA

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

Barcelona, España

Conferencia; 11th European Meeting on Supercritical Fluids; 2008

CSIC, España

In the last years, the most significant trends in the field of plastics are changing focusing in the final material use. The compromise between economy and technique requirement satisfaction is frequently reached, by development of materials with predeterminate properties, based in commodity plastics [1]. Particularly, the copolymers are molecules generated by chemical reaction, containing two o more monomers in their chains, and generally they have a synergetic combination of properties respect to the homopolymer ones. For this reason, they are used in applications as adhesives, paints, coatings, emulsifiers, biomedical materials, etc. [1, 2]. The introduction of new functional groups to a polymer can modified some properties as hydrophilicity, dyeability, permeability, antimicrobial activity, adhesion, etc. [3]. Particularly, the introduction of aromatic rings to the PE chains changes the polarity and the inert character of the material. Consequently, the material became easier to be stained, dyed and printed. Also, the permeability respect to the water, carbonic anhydride and oxygen, suffer modifications and can be tailored focusing in a specific properties desirables in the packaging and textile industries. On the other hand, in last years, the use of near and super critical fluid as solvent or as processing agent in the polymer technology area increased. The main advantages of the use of this kind of fluids are the diffusivity increment and the viscosity and superficial tension decrement [4]. In this work, the copolymerization of styrene onto polyethylene (PE), using near critical n-alkanes as reaction media is proposed. The reaction is a Friedel-Crafts alkylation and the catalyst was aluminum chloride (AlCl3). By this reaction, a hydrocarbon chain can be chemically bonded to the styrene ring through an aromatic electrophilic substitution. The principal advantage of this method of reaction is that the high molecular weight PE, is solubilized by alkanes at near critical conditions, and then, the polymer chains are more available to react than in a melt blend. The reaction occurrence was corroborated by nuclear magnetic resonance (13C-NMR), Fourier transform infrared spectroscopy (FTIR), after a careful phase separation of the reaction product by selective soxhlet extraction using tetrahydrofuran (THF). Besides of FTIR, differential scanning calorimetry (DSC), size exclusion chromatography (SEC), scanning electron microscopy (SEM) were the techniques used for characterization of the reaction products and quantification of the polystyrene copolymerized. The water and oxygen permeability of this material obtained were measured and compared with those of the virgin PE. The effect of the amount of catalyst added was studied varying the content from 1 to 5-wt% of AlCl3 at the same PE/styrene ratio. [1] R. Hudson Commodity Plastics - As Engineering Materials? RAPRA Report. Shawbury: Rapra Tech. LTD, 1994. [2] A.H. Trivedi, S. Kwak, S. Lee, Polym. Eng. Sci. 2001, 41, 1923-1937. [3] T.F. Bash, H.G. Karian, In Handbook of Polypropylene and Polypropylene Composites; Karian, H.G., Ed.; Marcel Dekker: New York, 1999. [4] C.F. Kirby, M.A. Mc Hugh, Chem. Rev. 1999, 99, 565-602.