Composite materials future relies on achieving lighter parts through integrating sustainable materials, with bio-based and/or circular materials in reinforced thermoplastics. To meet the requirements of various industrial applications, Poly Ether Ether Ketone (PEEK) and biodegradable PolyLactic Acid (PLA) matrices can be reinforced by reclaimed carbon fibers and biodegradable flax fibers. However, the mechanical behavior of composites is heavily influenced by the quality of the interface and the presence of defects and voids, this would imply a required control at the stage of composite manufacturing. Despite their significance, mechanisms governing interface and void formation at the microscales and mesoscales remain insufficiently explored and understood. The adhesion phenomena at the fiber / matrix interface depends on different properties of the constituents. The most influent ones still must be identified. Moreover, the effect of temperature should be considered since the polymer can be exposed to high temperatures during the interface formation. Furthermore, the crystallinity and the induced mechanical properties of the produced fiber / matrix interface will be studied. The DUINTACOS project aims to address this gap by allowing a deep understanding of interface formation in fiber-reinforced thermoplastic tapes, seeking to minimize micro voids, that is a requirement to obtain a high-quality composite structure.