Rheology Behavior of Sepiolite-PE Nanocomposites

MARTINI, RAQUEL EVANGELINA; TERENZI, ANDREA; KENNY, JOSÉ MARÍA; BARBOSA, SILVIA ELENA

Madrid

Conferencia; VI International ENCP Conference on Nanostructure Polymers and Nanocomposites; 2010

CSIC

The use of nanoclays in thermoplastic matrix results in material with enhanced properties. This fact results in new and important applications of them. In particular these applications point both to improve functionalities of the matrix, mechanical properties and other final properties like thermal and fire resistance, barrier properties, etc. These properties are strong dependent on the clay concentration and disposition into the final part. The processing operation of these materials, usually performed in melt, determines the final orientation, distribution and intercalation of nanoparticles because they involve the flow of nanoclay suspensions. Then, the understanding of the relations between the nanoclay structure in the suspension and its rheological properties is a key step in the design and implementation of processing operations in order to improve the final properties of a nanocomposite.   The rheological properties of nanocomposites are strongly associated with their structure. Particularly, the transient response of these materials permits to analyze several structural variables, like nanoparticles orientation, concentration, interaction between them and with the matrix, etc. Rheological behavior has strong dependence with the clay dispersion and intercalation, as well. In this work, the transient rheological material functions of nanofibers suspensions constituted by sepiolite and linear low density polyethylene are measured and analyzed. Sepiolite is a hydrated magnesium silicate with the ideal formula Si12Mg8O30(OH)4(OH2)4.8H2O. It is not a layered phyllosilicate, it’s structure can be considered a quincunx of talc type sheets. The particular arrangement of atoms produces a needle-like structure, instead of typical plate-like one. Then this clay particles could be consider as nanofibers with length/diameter ratio higher than 100. It was measured from scanning electron microscopy micrographs.  The nanofibers motion in shear flow is analyzed in order to elucidate the final structure obtained. The study is focused on the relation between orientation and rheological properties for suspensions with different sepiolite concentration. The study shows that the rheological properties of the suspension, measured during the start up of steady shear flow, can be used also for the determination of the dispersion grade. The first normal stress coefficient is the property to measure in order to determine whether or not the suspension contains micro o nano particles of sepiolite, then permits to analyze the exfoliation grade. It was found that the normal stress coefficients can show negative or positive values depending on the particles exfoliation.