A Design-Driven Strategy for the Development of Polypropylene Composites Tailored for 3D Printing ^†

Despite growing interest in additive manufacturing for polymers, its industrial application is limited by a lack of suitable materials. In particular, Fused Filament Fabrication (FFF) relies primarily on amorphous or low-crystalline thermoplastics, most of which are not specifically functionalised. Although polypropylene (PP) is a widely used commodity, it still represents a challenge for FFF applications, mainly due to its semicrystalline nature and unfavourable rheological behaviour.

In this work, an effective strategy for obtaining 3D printable PP-based materials is proposed, also considering the possibility of exploiting the FFF technology for the obtainment of items endowed with specific functionalities and for upcycling purposes.

Firstly, a detailed rheological and thermal characterization of a series of PPs (both homopolymers and heterophasic copolymers) characterized by different viscosities and the presence of fillers allowed for highlighting important microstructure/processabilty relationships, providing critical features for the design and development of 3D printable PP-based materials.

In the second step of this research, several kinds of micro- and nano-fillers were introduced within PP with the aim of endowing the 3D-printed samples with superior mechanical properties, flame retardancy, or thermal conductivity.

Finally, recycled PP (r-PP) recovered from different streams was valorized through the formulation of filaments for FFF processes. In this context, on the basis of the know-how acquired in previous research about PP printability, the formulation of r-PP deriving from municipal solid waste, e-waste, or protective single-use face masks was optimized through the introduction of different types of fillers in order to adjust the rheological and thermal characteristics of the material for achieving a successful FFF process.

The obtained results show that a proper modification of r-PP microstructure and a close optimization of the processing parameters allow for profitably, enhancing the added value of r-PP and contributing to sustainable manufacturing practices.