The Effect of the Functionalizing Agent Type on Processability, Mechanical and Thermal Properties of Polypropylene-Based Composites

The aim of this study is to monitor the influence of the addition of glass fibers (GFs) treated with polydimethylsiloxane (PDMS) and aminopropyltrimethoxysilane (APTMS) on processability and mechanical and thermal properties of polypropylene. The composites based on PP/GFs were processed on a twin screw extruder-granulator, using 20% glass fibers, relative to the polymer mixture (PP/PP-g-MA). Composite granules obtained by extrusion were used in order to determine flow indices and the values obtained demonstrate that the addition of 20% GFs does not raise serious processability problems (viscosity of the mixture does not vary very widely). Thermal stability tests under load - HDT demonstrate that the best thermal stability is that of the composite reinforced with GFs-PDMS. Mechanical tests also demonstrate that tensile strength, resistance to bending, modulus and elongation at break are superior for the composite reinforced with PP/GFs-PDMS compared with the one reinforced with GFs-APTMS. This can be attributed to the fact that there is a better compatibility between polydimethylsiloxane-treated fibers and the polypropylene matrix compared with those functionalized with aminopropyltrimethoxysilane. Moreover, glass fibers treated with polydimethylsiloxane are more stable to changes in temperature and pressure that the composite is subjected to during processing. TG-DSC results demonstrate a higher thermal stability of the composite with the addition of functionalized fibers.