PP-sepiolite nanocomposites. Final properties improvement through processing optimization

RAQUEL MARTINI; SIMONE LA TEGOLA; ANDREA TERENZI; SILVIA BARBOSA; JOSÉ KENNY

Paris, Francia

Simposio; 5th International ECNP Conference on nanostructured polymers and nanocomposite; 2009

Polyethylene (PE) - sepiolite nanocomposites are very interesting materials because they combine their properties in a synergetic manner. Chemically, sepiolite is a hydrated magnesium silicate with the ideal formula Si12Mg8O30(OH)4(OH2)4.8H2O. Unlike other clays, is not a layered phyllosilicate, it contains needle-like particles instead of plate-like ones. In this sense, the use of sepiolite fillers improve processing, dimensional stability, mechanical strength and thermal resistance of polyethylene as well as, they allow controlling the rheological behavior of the polymer enhancing their stability under a wide temperature range. Due to its structure, usually described as a quincunx (an arrangement of five objects so placed that four occupy the corners and the fifth the centre of a square or rectangle) of talc-type sheets separated by parallel channels, these nanofillers have a high ability for liquid absorption and odor control. In this sense the PE/sepiolite nanocomposite could be used in waste treatments, industrial absorbents, moisture controls, etc.   In this work, a systematic study of mechanical was performed in order to investigate the influence of the sepiolite content and modification on the basic properties of PE. The nanocomposites were prepared in a laboratory twin screw extruder in two steps. Initially, a masterbatch containing 10 % of sepiolite was prepared and, in a second step, it was diluted up to final concentration desiderate and directly molded by injection in a bone form specimen (for mechanical properties). In this sense, either the distributive or dispersive mixing was improved. Samples with 1, 3, 5 and 10 wt % and using sepiolite with and without surface modification were prepared and tested.   Results show an important increment in elastic modulus and strength in all the samples tested with a slight decrement in the elongation at break, as expected. However, all the nanocomposites remain flexible and can be molded as films either by compression molding and film extrusion, maintaining the mechanical properties and the translucently. Up to 3% of sepiolite added the films remains with a color similar to pure PE, but for higher amount of sepiolite added, the translucently remains but the color lightly turns to beige. The color, translucently and repetitive values of mechanical properties, as well as, the well formed films obtained by extrusion cast molding, are ulterior proves of the well mixed obtained in all samples. For probe it, the amount of sepiolite in films were tested either by FTIR (by comparison of typical sepiolite/PE peaks) or by scanning electronic microscopy. Also the amount of exfoliation obtained in the nanofiller can be observed from the transmission electronic microscopy results provided.