Powder Characterization for a New Selective Laser Sintering Polypropylene Material (Laser PP CP 60) after Single Print Cycle Degradation

Abstract

Experiments were conducted to characterise a new polymeric powder (Laser PP CP 60) from Diamond Plastics GmbH used in selective laser sintering (SLS) additive manufacturing (AM). Three different batches of the powder were tested in the study; virgin powder, used powder, and a mixture (50% virgin: 50% used) powder. The three batches of powder were subjected to scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and melt flow index (MFI) testing. Scanning electron microscopy was used to determine the morphology of particles. The distribution of powder particle sizes was established by analysing the acquired SEM images using ImageJ software. Differential scanning calorimetry was used to determine the peak melting point, degree of crystallisation, and the sintering window of the powder. Thermogravimetric analysis was utilised to determine temperatures of degradation of the powder considered in the study. Lastly, MFI testing was used to determine the variation of flowability of the powder. It was found that the three batches of powder considered showed poor, but allowable morphology and particle size distribution. The sintering window of the virgin Laser PP CP 60 polypropylene powder increased after a single cycle of printing by 28%, from 21.04°C (virgin powder) to 26.95°C (used powder). The sintering window was lower than that for polyamide polymer, which might have contributed to the high shrinkage rates observed during processing of the material, as a narrow sintering window results in difficulties of regulating the cooling rate of the printed parts. The three batches of powder showed high degradation temperatures, which makes the material suitable for SLS processing. Finally, the three batches of powder showed low values of MFI, which indicates that the molten material has a high viscosity. This explains the difficulties experienced in processing the material.