Preparation and characterization of thermoplastic starch composites with fly ash modified by planetary ball milling.

Thermoplastic starch (TPS) composites were prepared containing different amounts of unmodified (UFA) or modified fly ash (MFA) powder. The modification of the fly ash was carried out by dry grinding UFA in a planetary ball mill at various speeds and grinding times. The particle size of the fly ash was determined with a laser particle size analyzer and a scanning electron microscope (SEM). It was found that the particle size of the UFA decreased from 59.60 μm to 13.17 μm after grinding for 1 h at 400 rpm. Both UFA and MFA powder were incorporated in a thermoplastic starch. The mechanical properties, water resistance, degradation under simulated weathering conditions and thermal properties of the TPS and the composites were characterized. The maximum tensile strength (7.78 MPa) was obtained in a composite with 2.50% of MFA. This value is about 9 times higher than the tensile strength of the TPS and 2 times higher than that of a TPS/UFA composite with 15.00% UFA. In addition, composites with MFA showed improved water resistance and delayed degradation compared to the TPS and the composites with UFA. The presence of UFA or MFA had a slight effect on the thermal stability of the samples. However, fly ash promoted the final phase of the thermal decomposition of starch indicating a possible catalytic activity.