# Thermoforming Process Effect on Performances of Thermoplastic/Recycled Carbon Fiber Composites
## 1 Introduction  
The development of carbon fiber-reinforced composites (CFRC) has attracted significant attention in recent decades, primarily because of their lightweight and superior mechanical properties like high specific strength and stiffness, corrosion and fatigue resistance [1, 2]. Due to their excellent properties, they are widely used in many fields, such as in construction [3], the aeronautic sector [4], and the automotive sector [5], with both thermoset and thermoplastic matrices [6, 7]. The growth in the production and use of CFs inevitably leads to high amounts of CF composite waste. Indeed, global CFRP waste is foreseen to reach up to 20 kilotons annually by 2025 [8]. The difficulty with the thermoset matrix is that it cannot be melted and reused, which represents a recycling problem. Most of this waste is either incierated or landfilled, even though the European Waste Framework Directive states that landfills are the least preferred option for CF composite disposal [9]. As a solution, thermoplastic composites appear to be the most viable option because they can be melted and reshaped multiple times without significantly altering their chemical structure [10]. Several methods are used to reclaim CFs from thermoplastic composite waste, ranging from electromagnetic to thermal and thermochemical methods [11, 12]. Recycled carbon fibers are typically in a discontinuous and random form due to the cutting process during composite manufacturing and the size reduction during recycling. From the recycling processes of carbon fibers, rCFs are obtained with mechanical properties that are not too far from those of virgin fibers. [PERSON] et al. [13] proposed an electrochemical method for recycling carbon fiber from carbon fiber-reinforced polymer (CFRP). The test on rCF shows that the maximum tensile strength of the reclaimed carbon fiber is 80% that of the virgin carbon fibers (VCF). [PERSON] et al. [14] recovered carbon fiber from epoxy with the steam thermolysis method. The results show that reclaimed resin (or residue) free carbon fibers retained more or less over 90% of their original tensile strength. The tensile strength of rCF could reach approximately 80-95% of virgin carbon fibers (VCF) [15]. Among the manufacturing technologies applicable to the rCF, it is worth considering infusion molding, extrusion/compression, and 3D printing [16; 17; 18]. Developing recycled carbon fiber-reinforced composites (rCFRCs) and utilizing non-woven fibrous mats infused with resin is possible. These mats can be produced using different techniques such as wet-laid, air-laid and carding processes. The air-laid process is a dry laying technique in which individual fibers are evenly dispersed in an airstream and then directed toward a permeable screen or conveyor, where the fibers are deposited randomly in the form of a web. The resulting nonwoven mat is essentially isotropic in nature with a three-dimensional structure where the areal weight ranges from 150 to 200 g/m\({}^{2}\)[19]. The process of producing wet-laid nonwovens is similar to papermaking. The fibers are mixed with water or a suitable solvent to form a fiber/water mixture. The mixture is then transferred to a head box, forming a continuous isotropic nonwoven web. The water is drained from the web and moved forward via a forming belt at this stage. Finally, the web is dried using the heaters and rolled up using a take-up system [20]. When fibers are randomly oriented, in-plane material isotropy can be expected. Carding is a mechanical process in which the discontinuous carbon fibers agglomerates are placed in a series of rotating cylinders covered with wire or pins that work to align and separate the fibers. During this phase, resin can be added to infuse the fibers. The resin-impregnated fibers are then laid in layers, forming mats with a specific fiber orientation [21]. Carding allows the production of anisotropic nonwoven composites, unlike the previous processes.