Fine grinding of thermoplastics by high speed friction grinding assisted by guar gum

High speed friction grinding has been used to grind plant and food substances in water but never been explored for grinding of thermoplastics like polylactic acid (PLA), low and high density polyethylene and polypropylene. Such grinding was investigated in this work and was made possible by using 0.5% guar gum solution instead of just water because increasing the viscosity of water reduced their settling and the speed of passing through the grinder. Tensile, flexural, and impact strengths of the plastics were studied and higher grinding efficiency of PLA could be explained by its low elongation-at-break compared to low density polyethylene, high density polyethylene, and polypropylene. The microplastics (2000–45 μm) were studied for mass and particle size distributions and by scanning electron microscopy, ¹³C CP/MAS NMR, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. In addition, viscosity of guar gum and contact angles was measured. This new technology can produce finely ground microplastics (710–45 μm) for a variety of applications.     

Microhardness of rhombohedral crystals: Calcite and sodium nitrate

The variation of hardness of rhombohedral single crystals of calcite and sodium nitrate with quenching temperature is studied. Vickers and Knoop hardness numbers are determined from the indentations produced on freshly-cleaved crystal surfaces for various loads. The variation of hardness number with quenching temperature can be represented byHT _q ^k =constant where the exponentk is less than unity and its sign determines the nature of material.