|Ph.D Student||Kaully Tamar|
|Subject||Highly Filled Thermosetting Resins:|
Interfaces in Particulate Reinforced Composites
|Department||Department of Materials Science and Engineering||Supervisor||Professor Emeritus Arnon Siegmann (Deceased)|
|Full Thesis text|
Particulate polymer composites have become
attractive owing to their widespread applications. For some, it is desired to
obtain properties of interest through the use of high loadings without limiting
the processability or degrading the mechanical properties of the material.
The current work deals with the rheological and mechanical properties of highly filled particulate composites based on natural CaCO3 particles and polydimethylsyloxane (PDMS), liquid at room temperature and rubbery after crosslinked, as a binder; its interfaces structure and properties, and the role of particle size characteristics.
Capillary as well as dynamic rheometry was used for studying the effect of particle size distribution on the rheological properties of different filler content and particle size suspensions. It is shown that increased particle size and bimodal particle size distributions which improve packing density, reduce viscosity and enhance processability. A combined Farris-Chong model is suggested for improved prediction of bimodal suspensions viscosity.
The tensile and dynamic mechanical properties of composites (cross linked matrix polymer) of similar compositions were studied. The elastic modulus is shown to depend on particle packing efficiency, in good correlation with viscosity.
A series of fatty acids was used to modify the surface properties of the filler, to better understand the relationship between the interface structure and the rheological and mechanical behavior of the studied systems.
The surface energy of the raw and fatty acids treated filler was studied by inverse gas chromatography and the wicking method. The neat and treated liquid polymer and the crosslinked polymer surface properties were studied using an improved drop weight method and the contact angle method respectively. It is shown that the fatty acids hydrocarbon chains dissolve in the liquid polymer, and segregate to the surface of the crosslinked film.
The interface structure was analyzed as follows: The adsorbed layers composition by gas chromatography and thermal gravimetric analysis; the adsorbed layers structure by differential scanning calorimetry and the surface chemistry by XPS. It is shown that the adsorbed fatty acids arrange in an ordered structure characterized by an apparent melting.
The viscosity of the treated suspensions measured by capillary rheometry was markedly reduced, enabling a 4vol% increase in the maximal solid loading.
The reduced surface energy of the treated CaCO3 lead to lower matrix-filler adhesion as well as lower tensile modulus, strength and elongation at failure. Tan d values indicate higher PDMS chains mobility in the treated composites.