Effect of self-nucleation on the crystallization kinetics and the microstructure of polypropylene parts manufactured by Laser Powder Bed Fusion

Laser Powder Bed Fusion (LPBF) of thermoplastic polymers is an additive manufacturing (AM) technique experiencing a remarkable growth in the recent years. Nowadays most widely used materials are polyamides (PA12, PA11…) but massively available LPBF-compatible polyolefin powders recently arrived on market. The need understanding crystallization process for these new essential and this was addressed present work. Isothermal non-isothermal kinetics investigated by differential scanning calorimetry parts microstructure analyzed using polarized light optical microscopy, electron transmission microscopy wide-angle X-rays diffraction experiments. It shown that it important to consider significant nucleating effect sub-surface layers solidification during building stage. Indeed, half-crystallization times PP material consistent with experimental observations time range LPBF only if occurs from self-nucleated molten state. Evidence presence nuclei were given thanks microscopic (WAXD) techniques. Alternate patterns very finely microstructured, oriented transcrystalline regions isotropic spherulitic every 100 µm (i.e. layer thickness printing) highlighted.