Effect of uncoated calcium carbonate and stearic acid coated calcium carbonate on mechanical,thermal and structural properties of poly(butylene terephthalate) (PBT)/calcium carbonate composites

PBT/CaCO₃ composites were prepared in a single screw extruder with particle content varying from 0–30% by weight. The influence of surface treatment of the particles, with and without stearic acid (SA), on the mechanical, thermal and structural properties was studied. The experiments included tensile tests, impact tests, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy. The composite systems containing SA coated CaCO₃ were found to exhibit better mechanical properties as compared to composite systems containing uncoated CaCO₃, with the S3 system (20% of SA coated CaCO₃) exhibiting best combination of mechanical properties. Thermal study revealed that particle type and content had no influence on the melting temperature but the crystallization temperature, % crystallinity and thermal stability increased on increasing the CaCO₃ content in PBT matrix. Morphological observation indicated that in PBT composites containing SA coated CaCO₃, the coupling agent favours a better polymer filler interaction rendering inorganic polymer interface compatible, which is also evident from better mechanical and thermal properties.