Study of the matrix-filler interface in PLA/Mg composites manufactured by Material Extrusion using a colloidal feedstock

The aim of this paper is to investigate the evolution of a matrix-filler interface during the processing of novel composites formed by a matrix of polylactic acid (PLA) and Mg particles, when they are manufactured by Materials Extrusion. The particles addition to the PLA was carried out through the preparation of a Magnesium stable suspension in the polymer solution. To improve the Mg dispersion, the surfaces of the particles were previously modified by the adsorption of dispersants, namely Polyethylenimine (PEI) and Cetyltrimethylammonium bromide (CTAB) in aqueous suspension. The physical and mechanical characterization of PLA/Mg composites show that the Mg surface modification is the key to its successful dispersion due to the formation of ionic interactions between the dispersants and the matrix. This is favoured by the seeding effect of the PEI-modified Mg particles over the PLA re-precipitation during the composite shaping. Moreover, a PEI-PLA covalent bond appeared in the printed scaffolds as a consequence of the temperature applied (165 degrees C) during extrusion and printing. Consequently, the matrix-filler strengthened interface improved the extrusion process and permits the printing of 3D customized pieces. At the same time, particle agglomeration and the nozzle blocking is prevented.