Optimisationof charge ratios for ball milling synthesis: agglomeration and refinement of coconut shells

Abstract

Agglomeration is an attractionof fine particles for one another due to their high surface energy,leading to formation of particle colonies known as agglomerates. When a polymeric or metallic matrix is reinforced with particles, agglomerates usually createregions of discontinuity or weak particle adhesion withinthe matrix and degrademechanical properties of the resultingcomposites. In ball-milling synthesis of nanoparticles, formation of agglomerates can be controlled through optimisation of milling parameters. In this study, coconut shell (lignocellulosic) nanoparticles weresynthesised by varyingthe charge ratios from 2.5 to 40 at constant milling duration (70 hours), speed in terms ofdrum/vial rotation (194 revolution per minute) and ball sizes (5-60 mm). Assessment ofthe effects ofcharge ratios (CRs) on the morphologies and particles sizes of uncarbonised coconut shell nanoparticles (UCSnp) was studied. The synthesised UCSnp were characterised using electron microscopy and X-ray diffractometry(XRD). The results showedvariousmorphologies and orientations of UCSnp with changesintheCRs. Size determination using XRD and SEM revealed a reduction in particle size as the CR increased up to a valueof 10. At higher CRs,further reduction in the average particle size was not observable. This could be linked to a balance between particlerefinement and agglomeration at these higher CRs. Although particle agglomeration was apparent above CRvaluesof 10, sizes of the UCSnp obtained abovethisCRswere much smaller than the initial size (37 μm) of the coconut shell precursor particles. Thisaffirmed the ball milling synthesis as a particle refinement process,but not a coarsening/agglomeration process. The resultsobtained from statistical analyses show agreement with experimental results.

Keywords

• Electron microscopy
• Surface energy
• X-ray study
• Agglomerates
• Synthesis