Preparation of rubber seed shell powder by planetary ball milling and its influence on the properties of starch foam

Abstract

Starch foam composites containing rubber seed shell particles of different sizes were prepared and characterized. The first objective was to prepare small particles of rubber seed shell using a planetary ball mill at different rotational speeds (300 and 600 rpm) and milling times (20, 40 and 60 min) to optimize the milling condition to achieve the smallest possible particle size. The second objective was to study the influence of the size of the rubber seed shell particles on the properties of the starch foam. Laser particle size analysis and morphological observation by scanning electron microscope (SEM) revealed the optimal milling condition to be 600 rpm for 40 min. The smallest average particle size obtained at this condition was 51.57 μm. Starch foam containing the smallest particles (GRS) exhibited greater flexural stress at maximum load and narrower cell size distribution and had a lower density than starch foam composite with crude rubber seed shell (CRS) at the same filler content. The small size and high surface area of GRS enabled a better dispersion of filler particles and the establishment of stronger interactions within the starch matrix. The change in the color parameters and whiteness values of the rubber seed shell particles can be attributed to exposure to the heat generated by ball milling and the reduction of the average particle size. The effect of the addition of GRS and CRS on the thermal properties of the composites was determined by simultaneous thermogravimetry – differential scanning calorimetry.