In fl uence of sub-monolayer quantities of carbon nanoparticles on the melting and crystallization behavior of polyamide 12 powders for additive manufacturing

In this paper, the influence of 0.005 vol% and 0.05 vol% of carbon nanoparticles on the surface of polyamide 12 powder particles by dry coating and colloidal additivation is evaluated in great detail concerning thermal and microstructural properties. The dispersion of the nanoparticles on the polymer surface influences the flowability of the feedstock powder already during the additivation process. When analyzing the composite powders dynamically and isothermally with fast scanning and differential scanning calorimetry, carbon nanoparticles influence the crystallization behavior of the feedstock material significantly by acting as nucleation seeds, already at a few percent of a monolayer coating, while showing no effect on the fast heating process. The difference in calorimetric properties and crystallization behavior between the additivation methods of different abrasive forces is discussed. The surface-additivated carbon nanoparticles significantly increase the crystalline area by up to a threefold and the crystallization rate by up to a hundredfold. Furthermore, they change the crystal growth from a typical twoto three-dimensional growth of spherulites to a oneto two-dimensional growth of ellipsoidal impinged lamellar structures. Between 0.005 vol% and 0.05 vol% of well-dispersed carbon nanoparticles should be added to polyamide 12 to trigger an anisotropic heterogeneous nucleation while avoiding agglomerates. (c) 2021 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).