Influence Of Silanized Hollow Glass Microspheres On Thermal, Rheological And Mechanical Properties Of Poly(?-Caprolactone) Composites For Rotational Molding

In this work we report on the thermal, rheological and mechanical properties of composites prepared by mixing hollow glass microspheres (HGM), as such or surface modified by treatment with (3-aminopropyl) triethoxysilane (APTES) [1], with poly(?-caprolactone) (PCL). The silanization treatment implies a good dispersion of filler within the matrix and an enhanced filler-polymer adhesion as testified by scanning electron microscope observations [2]. The crystallization of PCL/HGM composites at different filler concentrations (from 10 to 25 wt%) was investigated by differential scanning calorimetry under isothermal and dynamic conditions. The results showed that the HGM acted as nucleating agent, as confirmed by a remarkable reduction of the crystallization time. This effect was observed as a function of the HGM amount in the composites. Moreover, the silanization of glass microspheres enabled even faster crystallization rates. The effect of HGM on the thermal stability and degradation of the composites was studied by thermogravimetric experiments. The presence of HGM as such leads to an increase in the thermal stability of the composites compared to neat PCL. Conversely, the composites filled with silanized HGM show a decrease of thermo-oxidative stability because of the presence of less stable APTES anchored onto HGM surface. Reinforcing PCL with HGM involved an increase in both storage modulus and complex viscosity as observed through rheological tests. A pseudo solid-like behavior, characterized by a plateau of storage modulus at low frequencies, in the presence of 20 wt% silanized HGM highlighted a stronger filler-matrix interactions. The addition of HGM also affected the mechanical properties. Tensile tests showed a high increase of Young's modulus and a decrease of elongation at break with a consequent reduction of ductility for all composites compared to neat PCL. Nevertheless, the composites filled with the modified HGM, characterized by an increase of the tensile strength, pointed out the important role played by the silane in improving the filler-matrix adhesion. This is a remarkable result, considering that the addition of 20 wt% HGM implies a decrease of density by about 23% compared to neat PCL. Finally, PCL/HGM composites were firstly proven to be successfully processed by rotational molding, both at laboratory and industrial scale