|M.Sc Student||Dzhanaev Grab Olga|
|Subject||Characterization of Expandable Thermoplastic Microsphere|
|Department||Department of Chemical Engineering||Supervisors||Professor Yachin Cohen|
|Dr. Eric Assouline|
|Full Thesis text|
Thermally expandable microspheres are polymeric particles with a core/shell structure. Upon heating, the pressure of the encapsulated gas increases and the thermoplastic shell softens. When the temperature is above the glass transition temperature of the polymeric shell, and when the internal pressure is high enough to overcome the yield strength of the polymer shell, an expansion will occur. These thermoplastic microspheres are used in various applications, especially as a lightweight filler.
The main purpose of this study was to pruduce a rigid free-standing foam based on thermoplastic microspheres with no resin added.
Expancel microspheres from AkzoNobel were used with a polyacrylonitrile shell encapsulating an isobutene gas. Optimal conditions for producing a foam with highest compression strength were studied with consideration of the different parameters that may influence the properties of the final product. Besides the parameters of time and temperature of preparation, the storage time and conditions until testing, and test conditions were found to have a great influence on the obtained mechanical properties of the samples. Optimal mechanical properties were obtained for the shortest preparation time that results in free-standing stable foam sample at each investigated temperature. The highest compression strength was obtained for the highest preparation temperature of 200°C. Using SEM images, it was concluded that the mechanism of foam creation can be divided into two steps: in the first few minutes the capsules expansion, and then the welding process of the capsules which duration increases as the preparation temperature decreases. Due to the motivation of applying the foam as a core material in sandwich structures of composites, the volume of accessible pores of the foam were examined as well. From the obtained results, even if the resin from the composite skins of the sandwich structure would fill up all of the open pores of the foam, the mass of the foam will increase only by several percentage points, resulting in a lightweight sandwich structure.