3D/4D Printing of Thermoplastic Composite Materials

In 2021, 3D printing using fused filament deposition (FFF) will be the most widely used 3D printing technology, thanks to its simplicity and the low cost of equipment and raw materials, compared with other 3D printing technologies such as stereolithography or selective laser sintering. This technology has been the subject of numerous innovations in terms of the variety of materials that can be used, and in terms of improving the performance of these devices (precision, reproducibility, printing speed, etc.). What's more, the expiry of the FFF patent held by Stratasys ^® combined with the RepRap project (The Replicating Rapid Prototyper, a project aimed at developing a fleet of free, self-replicating printers, i.e. capable of printing the parts needed to build these same printers) has made FFF and 3D printing more widely available. In 2019, the 3D printing market was estimated at $13.8 billion, with a projection of $22.7 billion by 2024. Today, 3D printing has become a disruptive innovation present in a wide range of application sectors (automotive, aeronautics, space, medicine, robotics, construction, food industry, marine engineering...).

The main advantage of 3D printing compared with traditional manufacturing processes is its ability to shape finished products in very few steps, with almost infinite freedom of design, thus drastically reducing production costs and speeding up the process. However, the most widespread technology, molten filament deposition, suffers from certain limitations.

Firstly, this technology is very often restricted to the production of prototypes, due to a still incomplete understanding of the process-architecture-properties relationship leading to average mechanical properties. The development of high-performance FFF materials is therefore a major challenge for both academia and industry.

One solution is to modify the formulation of printed materials to include reinforcing fibers (continuous or discontinuous) to improve mechanical performance. In addition, the current environmental context is prompting us to change the way we design, select and manufacture materials. For example, composites reinforced with plant fibers or biocomposites are seen as a credible alternative to certain synthetic composites, particularly as part of an eco-design approach. What's more, 3D printing offers an incredible opportunity for biocomposites to develop for the first time on the same timescale as their synthetic counterparts.

Beyond the need for mechanical performance, the composites industry is expressing a growing need to develop multifunctional composite materials. In this context, 4D printing (3D printed materials with time-dependent properties, whose response...