Thermal properties of poly(l-lactide)/olive stone flour composites

Thermal properties of poly(l-lactide)/olive stone flour (PLLA/OSF) composites were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) using dynamic heating regime. PLLA was blended with various amount of OSF using Brabender plastograph and pressed in a hydraulic hot press. DSC analysis showed that the glass transition temperature and the melting temperature of PLLA in the composites remained the same, while the cold crystallization temperature decreased. The crystallinity of PLLA was changed, too. SEM analysis confirmed weak interactions between polymer matrix and the filler. According to TG analysis, PLLA decomposes in one step, PLLA/OSF composites in two and OSF in three degradation steps. As the amount of OSF increases, thermal stability of PLLA decreases. At conversion higher than 0.7 char formation is probably responsible for higher Ea values of nonisothermal degradation of PLLA composites compared to pure PLLA.