Highly filled natural CaCO3 composites, III. Filler surface treatment and its structure

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. Improved properties and higher solid loading can be achieved using surface active agents. The current work deals with the structure and properties of interfaces in highly filled particulate composites based on natural CaCO3 particles and polydimethylsiloxane (PDMS) as a binder. A series of fatty acids was used to modify the surface properties of the filler, changing the interfacial properties and better understand the relationship between the interface structure and the rheological and mechanical behavior of the studied systems. This part of the work describes the surface properties and surface energy characterization of the raw and fatty acids treated filler, studied by inverse gas chromatography and the wicking method. The neat and treated prepolymer was studied using an improved drop weight method and the polymer films surface properties were studied using the contact angle method. It is shown that the fatty acids' hydrocarbon chains dissolve in the prepolymer, and segregate to the surface of the polymerized film. The interface structure was analyzed as follows: the adsorbed layers composition through gas chromatography and thermogravimetric analysis; the adsorbed layers structure through differential scanning calorimetric analysis and the surface chemistry by XPS. It is shown that the adsorbed fatty acids arrange in an ordered structure characterized by an apparent melting peak.