Abstract
This work is part of the research on the reinforcement of elastomeric materials with high aspect ratio fillers. The aim is to orient the reinforcing fillers in a direction to obtain anisotropic mechanical properties, in order to better understand the relationship between structure and mechanical properties of initially anisotropic elastomers. Cellulose microfibrils (MFC) have particularly suitable characteristics, i.e. high elastic modulus, two nanometre dimensions, high aspect ratio and high specific surface area. To enable the formation of strong bonds with the matrix, a coupling agent was grafted onto the surface of the MFCs. The grafted MFCs were then incorporated into a Styrene Butadiene Matrix (SBR), and a fabrication protocol was developed to orient the MFCs uniaxially in SBR films. Several MFC fractions between 10 vol.% and 20 vol.% were used. Specimens were cut at 0° (INIT0), 45° (INIT45) and 90° (INIT90) to the main direction of orientation of the MFCs. Tensile tests revealed a hyper-viscoelastic, initially anisotropic behaviour with the presence of a strong Mullins accommodation. An increase in the slope of the stress-strain curves is observed the more the fibres are initially aligned towards the tensile direction. At the same time, a decrease in stress at break and strain at break is observed. The different initial orientations of the MFC also highlighted the anisotropy of the Mullins effect in cyclic tests. X-ray diffraction measurements under strain showed the rotation of the MFCs, initially misaligned with respect to the tensile direction, during deformation. Different rotation regimes of the MFCs were observed for the different initial orientations. In particular, a much greater rotation was observed for the INIT90 specimens than for the INIT45 and INIT0 specimens.
