Abstract

The physicochemical properties of polymer nanocomposites (such as polymer/clay systems) are dependent on the properties of the polymer and filler, the reinforcement dimensionality, dispersion and orientation, and the nature of the interface between filler and matrix. Hence, thoroughly characterizing the morphology of those materials can lead to a better understanding of the behaviour of the final product and to improved design tools. The objective of performing TEM tomoghraphy (TEMT) on Poly lactic acid(PLA)/clay samples is to characterize their 3D microstructure, by obtaining the dispersion, distribution and orientation of the dimensions of the clays. This information cannot be elucidated from a qualitative TEM analysis or from conventional characterization techniques such as X-Ray diffraction. To carry out this work, nanocomposites obtained by extruding a PLA matrix and Cloisite 30B clays are used. The nanocomposites are obtained by using different extrusion shear rates. Shear rate favours the exfoliation of the clay particles and their dispersion, leading to nanocomposites with different microstructures and properties. Then, quantitative TEMT is performed to all the nanocomposites and the resulting 3D quantitative characterization is used for the comprehension of the mechanical behaviour of the nanocomposites.

Abstract

With the recent increase in the use of additive manufacturing (AM) in more and more challenging applications, the demands on the mechanical performance and sustainability of printed parts are increasing considerably. Among the different additive manufacturing technologies, fused filament fabrication (FFF) is the most widely used for thermoplastic materials. This work focuses on comparing the behaviour of parts obtained by FFF using a bio-based polyamide (BIOPA-11) reinforced with different types of fibres: short glass fibre (GF) and a fibrillar nanoclay (SEP, sepiolite). Different composites were prepared by melt process, converted into filaments used in FFF, and characterised the final parts. The thermal and mechanical properties obtained were systematically examined as a function of printing orientation, amount and type of fibre, accompanied by X-ray tomography image analysis of the internal parts of the pieces. As expected, anisotropic properties showed improvements in Young's Modulus and tensile strength in both composites with increasing amount of reinforcement, with respect to pure biopolyamide. However, the improvements in mechanical performance of the nanocomposites were very noticeable under many conditions (composition and direction of fabrication). The research shows that this is due to the stiffening mechanism, based on the polymorphism of BIOPA, which is induced by nanometric loadings. Additionally, the internal morphology of the nanocomposite parts showed small amounts of inter-filament cavitations, while the parts obtained from the GF composites showed irregular, intra-filament cavitations. Thus, the BIOPA11 nanomaterial parts are attractive in terms of properties, weight, cost reduction, and sustainability.