3D printing by fused filament deposition (FFF) is in 2021 the most widely used 3D printing technology due to its simplicity, low cost of equipment and raw material compared to other 3D printing technologies such as as stereolithography or selective laser sintering. This technology has been the subject of many innovations concerning the variety of materials that can be used or even with regard to improving the performance of these devices (precision, reproducibility, printing speed, etc.). In addition, the expiry of the patent on the FFF held by Stratasys® combined with the RepRap project (The Replicating Rapid Prototyper, a project aimed at developing a fleet of free and self-replicating printers, that is to say capable of printing the parts necessary for the construction of these same printers) has made it possible to widely democratize the FFF and more widely 3D printing. Thus, in 2019 the 3D printing market was estimated at 13.8 billion dollars with a projection of 22.7 billion dollars by 2024. 3D printing has now become a disruptive innovation present in many many application sectors (automotive, aeronautics, space, medicine, robotics, building, food industry, marine engineering, etc.).
The main advantage of 3D printing compared to traditional production processes is its ability to shape finished products in very few steps with almost infinite freedom in terms of design, thus reducing production costs. production drastically and speed up the process. However, the most widespread technology, the removal of molten filament, 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. Thus, the development of high-performance materials developed by FFF is a major challenge in both the academic and industrial fields.
One of the solutions envisaged is the modification of the formulation of the printed materials in order to add reinforcement fibers (continuous or discontinuous) to improve the mechanical performance. In addition, the current environmental context is pushing us to change the way we design, select and manufacture materials. Thus, composites reinforced with plant fibers or biocomposites are considered to be a credible alternative to certain synthetic composites, particularly within the framework of an eco-design approach. Furthermore, 3D printing is an incredible opportunity for biocomposites to grow for the first time on the same time scale as their synthetic counterparts.
Beyond the need for mechanical performance, the composites industry expresses a growing need to develop multifunctional composite materials. In this context, 4D printing (3D printed materials with time-dependent properties, whose response is driven by their architecture and actuated by an external stimulus) was first introduced in 2013 by S. Tibbits . This new paradigm is often inspired by the functioning of biological structures. It makes it possible to develop so-called programmable materials and structures by controlling their architecture established during implementation. They are then able to change shape (morphing) sequentially or not, to self-assemble or self-repair… The modification of the properties of the structure in 4D printing can be autonomous or actively triggered by external stimulation (variation in temperature, electric current, humidity, pH, etc.).
This article presents a state of the art of 3D and 4D printing of organic matrix composite materials reinforced with synthetic and natural fibers (continuous and discontinuous) for structural and multifunctional applications.
