Tailoring mechanical and functional properties of Thermoplastic Polyurethane (TPU) filaments for additive manufacturing: A review of blends and additives

Abstract

Thermoplastic polyurethane (TPU) is widely used in additive manufacturing (AM) and is known for its notable flexibility. However, its applications are restricted by its low stiffness, poor thermal stability, hygroscopic nature, and processing challenges in AM. Modifying specific formulations of TPU with blends and additives can overcome these limitations. Existing studies have reviewed TPU printing parameters, modifications, and applications, but the relationships between formulations, microstructural development and resulting properties remain insufficiently integrated. Thus, this paper analyses the processing-microstructure-property framework for TPU. The review begins by outlining the processing behaviour of TPU, emphasizing material diversity, processing optimization, and polymer immiscibility. It then reviews commonly used blends and additives in TPU systems, including polylactic acid (PLA), polycaprolactone (PCL) and acrylonitrile butadiene styrene (ABS), as well as additives such as fillers, compatibilizers and plasticizers. The literature demonstrates that polymer blending enables the alteration of properties such as stiffness, toughness and shape memory behavior, while additives modify compatibility, processability and functionality. Nonetheless, these improvements are highly dependent on composition and microstructural development, such as phase morphology, interlayer adhesion, crystallinity, and filler dispersion. Material incompatibility and filler agglomeration can otherwise limit material modifications. This paper also considers the application of TPU-based 3D printing in four (4) sectors, namely medical devices, electronics and sensors, non-pneumatic tires (NPT), and textiles and sports equipment. The final section highlights emerging directions, including sustainability, bio-based, and recyclable TPUs with multi-material and 4D printing capabilities. For future research, this paper provides a framework that connects material formulation and processing to microstructural development and final properties for designing smart, high performance and sustainable TPU-based additive manufacturing.