Dispersion mechanisms of carbon black in
an elastomer under shear
Veronique Collin* et Edith Peuvrel Disdier
Ecole des Mines de Paris, Centre de Mise en Forme des Materiaux
UMR CNRS/Ecole des Mines de Paris 7635
BP 207, 06905
edith.disdier@ensmp.fr
* Present address: Lafarge Centre de Recherche, rue du Montmurier 95
BP 15, 38291 St
Quentin
Silica and carbon
black are traditionally used as reinforcing filler in rubber applications
(tires and technical rubber parts). These types of filler present a multiscale organisation. The filler is introduced as
pellets (100 micrometer to the millimetre size) in the matrix. These pellets
are agglomerates constituted by smaller entities which are aggregates,
themselves resulting from the aggregation of elementary particles. During the
mixing operation of the filler, the elastomer and
other constituents (vulcanising agent, oil, antioxidant), the filler is
dispersed in the matrix, that is its size is reduced down to the smallest
attainable size (aggregate size), and spatially distributed in the matrix. A
good dispersion and a good distribution of the filler in the matrix are a
necessary condition for a reinforced material. Although mixing filler particles
in a matrix is a common operation, the elementary mechanisms responsible for
the size reduction of the filler are not fully understood. One way to optimise
this state would be to be able to observe inside the mixer what happens, which
is not possible. Rheo-optical techniques were
recently shown as a good tool to investigate in-situ dispersion but in a
simpler flow (shear).
In this work, we
studied the elementary mechanisms of dispersion (rupture and erosion) of
commercial carbon blacks in a SBR matrix using a transparent counter-rotating
shear cell coupled to an optical microscope in order to observe in-situ during
the shear the behaviour of a carbon black pellet suspended in a SBR matrix. The
effect of hydrodynamic parameters (quantity of strain units, applied shear
stress, pellet size) and intrinsic parameters of the carbon black (structure,
specific area) was investigated. This study led to the determination of a
critical condition for rupture and a mastercurve for
erosion kinetics. The mechanisms of dispersion will be discussed.
This work was part of
a project supported by the European Community in the framework of the Competitive
and Sustainable Growth program. The authors wish to thank all the partners
including Harburg-Freudenberger Maschinenbau
GmbH, Michelin, Snecma Propulsion Solide,
Optigrade-TechPro, Polyflow,
Cesame (U.C. Louvain) and T.U. Lodz for their
collaboration in this project.