Selective laser sintering (SLS) is a powder bed fusion technology that uses a laser source to melt selected regions of a polymer powder bed based on 3D model data. Components with complex geometry are then obtained using a layer-by-layer strategy. This additive manufacturing technology is a very complex process in which various multiphysical phenomena and different mechanisms occur and greatly influence both the quality and performance of printed parts. This review describes the physical phenomena involved in the SLS process such as powder spreading, the interaction between laser beam and powder bed, polymer melting, coalescence of fused powder and its densification, and polymer crystallization. Moreover, the main characterization approaches that can be useful to investigate the starting material properties are reported and discussed.

Blends based on poly(lactic acid) and low-density polyethylene were compatibilized exploiting an innovative strategy involving the introduction of different mixtures of two sustainable liquid surfactants characterized by dissimilar hydrophilic-lipophilic ratios. The compatibilization method was first applied on blends made of virgin polymers, aiming at assessing the surfactant mixture inducing a more significant morphology refinement. Besides, to verify the effectiveness of the selected compatibilizers on recycled materials, the same process was carried out on blends based on reprocessed polymers. Interestingly, the compatibilization caused a significant microstructure modification, with a decrease of 54% of the mean size of the dispersed particles, in the case of virgin polymers-based blends, with a consequent increase of 19% of the dynamic elastic modulus. On the other hand, in the case of reprocessed polymers-based blends, a different compatibilizer efficiency was observed, as the noncompatibilized blend showed amore regular microstructure compared to the compatibilized counterpart.

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