Changes to the physicochemical characteristics of wheat straw by mechanical ultrafine grinding

To investigate changes on the physicochemical characteristics of wheat straw by mechanical ultrafine grinding, wheat straw powders of four different particle sizes and distributions were produced using a sieve-based Retsch ZM100 grind mill and CJM-SY-B ultrafine vibration grind mill. Changes on the microstructure and physicochemical characteristics of the different powders were assessed by scanning electron microscopy, X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis and relevant standard laboratory analysis methods. Ultrafine grinding reduced the crystallite size and crystallinity of the wheat straw. New surfaces were exposed on the ultrafine powder with high levels of cellulose/hemicelluloses components but there was no apparent change in chemical structure. Wheat straw powders were smaller in size but had a higher bulk density (from 0.19 to 0.54 g/mL) and angle of repose (from 46.02A degrees to 55.61A degrees) and slide (from 37.26A degrees to 41.00A degrees). The hydration properties (water-holding capacity and swelling capacity) decreased with reduction in particle size of the wheat straw. Both the sieve-based and ultrafine powder exhibited a good ability to remove Pb2+ and Cd2+ and there was marginal improvement when using the ultrafine powder. The thermal stability of the ultrafine powder measured by thermogravimetric analysis decreased significantly because of the low cellulose crystallinity.