Polyamide 6 (PA6) thermoplastic composites have higher recyclability potential when compared to conventional thermoset composites. A disruptive liquid molding manufacturing technology named Thermoplastic Resin Transfer Molding (T-RTM) can be used for processing composites due to the low viscosity of the monomers and additives. In this process, polymerization, crystallization and shrinkage occur almost at the same time. If these phenomena are not controlled, they can compromise the reproducibility and homogeneity of the parts. This work studied the influence of packing pressure, as a process variable, throughout the filling and polymerization stages. To assess the process reproducibility and parts’ homogeneity, physical, thermal and mechanical properties were analyzed in different areas of neat PA6 and composite parts. This study showed that a two-stage packing pressure can be successfully used to increase parts’ homogeneity and process reproducibility. The use of 3.5 bar packing pressure during the polymerization stage resulted in mechanical properties with lower standard deviations, indicating a higher degree of homogeneity of the manufactured parts and higher process reproducibility. These results will be used for establishing the actual state of the technology and will be a base for future process optimization.

The automotive industry is engaged on the development of new vehicles with more sustainable and lightweight materials. Recent manufacturing technologies are being developed to respond to these challenges. Thermoplastic-Resin Transfer Moulding (T-RTM), a liquid moulding technology, emerged in this field has a promising approach for the manufacture of lightweight thermoplastic composites for structural applications. This process is based on the in-situ polymerisation of a thermoplastic monomer. This material is suitable for impregnation of continuous fibres and is prone to recycling, in opposition to conventional thermosetting composites. However, T-RTM remains a complex manufacturing technology mainly due to the instability of the resin in the presence of moisture or oxygen as well as thermal and pressure gradients within the mould. These gradients lead to non-uniform initial conditions for polymerisation along the mould cavity and, consequently, to a considerable variability in the T-RTM process. This study aims to contribute to the upscaling of this technology towards its industrial application, through the implementation of an innovative dynamic resin mixing and vibrational apparatuses designed to increase the homogeneity of the resin mixture after its injection into the mould. The parts’ homogeneity and process reproducibility were evaluated based on the statistical analysis of the mechanical and physical properties assessed in different areas of glass fibre-reinforced parts. This study has shown that both apparatuses can improve homogeneity regarding the mechanical behaviour and density of the parts. Furthermore, the dynamic mixing enhanced the polymerisation reactivity, assessed through dielectric analysis, compared to the standard T-RTM manufacturing method.

Climate changes are one of the main adversities of XXI century and can cause serious consequences on biodiversity preservation and available resources

Driven by increasingly stringent international environmental regulations, the automotive industry is investing considerable resources to reduce its carbon footprint. Lightweight design has emerged as a central strategy. This is particularly evident in the growing adoption of thermoplastic polymers for the production of aesthetic and functional parts. For structural applications, reinforced composites based on thermosetting materials have been explored, but with limitations on the recycling of end‐of‐life vehicles. Emerging structural composites based on thermoplastic matrices present a promising solution for a lightweight structural design, but they are still mainly in an experimental development stage. Manufacturing methods such as thermoplastic‐resin transfer molding (T‐RTM) can be a viable technology for manufacturing polyamide 6‐based parts, particularly with continuous fiber reinforcements. This article reviews the current state of the art in T‐RTM and identifies key opportunities, challenges, and research directions. The main recommendations are the development of new precursors with reduced sensitivity to moisture and oxygen, the design of new specific resin homogenization systems, deeper research into the complex polymerization process and improvements in injection and molding systems, as well as in sustainable recyclability strategies tailored to thermoplastic composites. Addressing these aspects is crucial for the industrial viability of T‐RTM in the automotive sector.