## 5 Applications Across Diverse Sectors
### New Materials
Poly(trimethylene terephthalate) (PTT), made from 1,3-propanediol and terephthalatic acid, exhibits high thermal stability and elastic recovery, with a renewable content of 37% from bio-sourced PDO. Polyether-derived polymers, including polyetherketone (PEK), polyetheretherketone (PEEK), and polyetherimide (PEI), are known for their exceptional mechanical performance and thermal stability. PEI is an amorphous engineering thermoplastic with excellent dimensional stability and heat resistance, making it suitable for injection-molded products and 3D printing applications. PEK, the first polyketone produced, offers high impact resistance and flame retardancy, although its initial production faced environmental challenges. PEEK is increasingly favored in chemical processing, aerospace, and biomedical applications due to its high melting point (335 \({}^{\circ}\)C) and biocompatibility. Polycarbonate (PC) is another important engineering thermoplastic derived from carbonic acid and polyhydroxy compounds. Known for its toughness, amorphous structure, and heat deflection temperature of 130 \({}^{\circ}\)C, PC also exhibits excellent resistance to scratches, ultraviolet radiation, and flame retardancy. The blending of engineering thermoplastics creates materials with enhanced mechanical properties and thermal stability. These blends allow for the development of diverse feedstock options suitable for a wide range of applications across medical, automotive, and consumer product sectors. Compatibilizing agents are often used to improve the compatibility of immiscible polymers, which is vital for maintaining mechanical performance. The blending strategies established in injection molding are now being adapted for additive manufacturing, facilitating the production of customized materials tailored to specific application needs. Fibers and fillers are often added to composites to enhance properties, increase renewability, reduce costs, and improve mechanical performance. Additionally, hybrid materials combining polymers with metal powders show potential in both biomedical implants and the electronics industry [17]. Additive manufacturing (AM) of composites offers significant advantages by streamlining the fabrication process and increasing automation, similar to traditional composite layering techniques. One of the key strengths of AM lies in its ability to precisely position fibers, which enables greater design flexibility and optimization within individual layers of a composite structure. The process typically begins with a client's design file, followed by data verification and production planning, where parameters like layer thickness and laser power are selected. This ensures that the final AM product is customized to meet specific requirements. AM without reinforcement involves the use of polymers, particularly thermoplastics, which behave uniquely during the printing process. These materials liquefy at high temperatures and solidify upon cooling. However, this process presents challenges such as shrinkage due to repeated heating and cooling cycles, and degradation risks at temperatures near the melting point. As a result, polymer-based AM materials are primarily suited for applications that require high strength, rigidity, and resistance to elevated temperatures. AM with reinforcement focuses on ceramic matrix composites (CMCs) and metal matrix composites (MMCs), which are widely used in industries like aerospace, biomedicine, and electronics. These composites offer high wear resistance and perform well at elevated temperatures. Selective laser melting (SLM) has proven effective in producing composite parts with enhanced mechanical properties, including improved hardness, fracture toughness, and wear resistance. Additionally, SLM-fabricated composites have demonstratedgood biocompatibility, making them highly suitable for advanced applications in fields such as biomedical implants and high-performance electronics.