1. Polyester/melamine-fumed silica nanocomposites : Influence of the BET specific surface of silica
E. JACQUELOT1, J. GALY1, JF. GERARD1, A. ROCHE1, E. FOUISSAC2, E. CHEVET2, D. VERCHERE3
1Laboratoire des Matériaux Macromoléculaires IMP/UMR CNRS 5627, INSA Lyon, Villeurbanne cedex (France)
2Becker Industrie, 40 rue du champ de mars BP 34, Montbrison cedex (France)
3Sollac Montataire (groupe Arcelor), 1 route de Saint Leu, BP 30109, Montataire cedex (France)
Objectives: develop new coil-coating formulations based on nanofillers in order to improve the surface properties (hardness, scratch and abrasion resistance, …)
Coil-coating Process
Materials
Matrix
Polyester/melamine based formulation from Becker Industrie Co.
Nanofillers
4 grades of fumed hydrophilic silica were used with different specific surface area (BET)
Fumed silica Si O OH H
Synthesis Process
Processing of nanocomposites
Introduction of the fumed silica (0 to 30 wt%) by the means of dispersing process using a TurbodispersorTM
Free standing films were prepared using a bar coater on the surface of a PTFE-coated substrates
(20 m thick resulting films)
Rheological behavior of formulations (i.e. before reactive drying)
Experiments: Shear rate ramp from 0.03 up to 3,000 s-1 ;Steady state flow mode (20°C)
At low shear significant increase of the viscosity (the higher the specific surface area is, the higher the viscosity is)
- Due to ‘nanofiller effect’ i.e. the interfacial interactions between hydrophilic fumed silica surface and polar components of the matrix as well as particle-particle interactions.
- Increase of interfacial interactions with the specific surface area
=> Nevertheless, the ability of design coating for the coil-coating process is not affected as the nanocomposite formulations display a huge shear thinning behavior
Shear rate experiment performed on nanocomposite formulations: grade 3 grade 2 grade 1 neat matrix
Dynamic mechanical behavior of nanocomposite free films
Experiment: Tension mode , 1 Hz from –50 to 150 °C (thickness: 20m)
Difference of moduli in the glassy state of nanocomposite coatings with the introduction of nanofillers
Changes of E’ are more clearly evidenced for T > 30°C i.e. in the rubbery state
tan  vs. temperature for cured films : neat matrix grade 1 grade 2 grade 3 grade 4
E’ vs. temperature for cured films: neat matrix grade 1 grade 2 grade 3 grade 4
No shift in tan  peak position with the introduction of nanofillers
Large effect of interfacial interactions on the polymer chains dynamics
Reduction of the tan delta amplitude with increasing the amount of interfacial interactions, i.e. specific surface
Processing consequences
Morphology of nanocomposite free films
Depending of the mixing protocol, two similar formulations (same amount of silica grade) can lead to very different dispersions and morphology
Experiment: Transmission Electron Microscopy on ultramicrotomed samples
homogeneous
flocculated morphology
Visualisation of initial aggregates of fumed silica
=> Good dispersion in the polymer matrix
Important parameter for controlling the physical properties of the nanocomposites is the way the fumed silica is introduced
Conclusion
Introduction of silica nanofillers lead to a huge increase of the viscosity of the formulation at low shear rate (the higher the specific surface area is , the higher the viscosity is) due to the large changes of the polymer chain dynamics associated with the increase of interfacial interactions
Dispersion of fumed silica in polyester/melamine-based formulations may result homogeneous at a nanometer scale