Structure et propriétés de nanocomposites polypropylène/argile lamellaire préparés par mélange à l'état fondu

摘要

The present PhD work deals with the relationships between melt processing conditions and the structure of polypropylene-layered silicate nanocomposites, as well as the influence of the dispersion state on the mechanical properties of nanocomposites. This study is based on experimental results. Structural analysis are performed using rheology, X-ray diffraction and electron microscopy.Internal mixer studies revealed that the increase of compatibilizer (PP-g-MA) content simultaneously leads to enhanced nanoscale dispersion and increased brittleness of the nanocomposites. A significantly higher dispersion was stated using a masterbatch method, as opposed to direct blending method. Co-rotating twin screw extrusion experiments allowed to highlight the effect of screw rotation speed (N), feed rate (Q) and barrel temperature (TrÈg) on the degree of dispersion. The influence of these three parameters on the nanocomposites structure can be described using the specific mechanical energy (SME) as a single processing parameter. Exfoliation is clearly promoted by the increase of the SME until it reaches a critical value. Above that threshold, the degree of exfoliation levels off and improvement of the dispersion state cannot be obtained through the optimization of processing conditions anymore. A relationship between the Youngís modulus of the nanocomposites and the exfoliation level has been established. Twin screw extrusion simulation software (LUDOVIC©) was used to calculate the evolution of processing data along the screw profile. From these results, a correlation between the progression of the dispersion state along the extrusion profile and the SME was found. Eventually, rheological investigation on the thixotropic behaviour of nanocomposites enabled to emphasize that time-temperature superposition principle doesn't systematically hold true for nanocomposites because of their structure aging.