Huang, Wei; (2025) Digital light 3D/4D printing of multifunctional polymers. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis focuses on advancing digital light processing (DLP)-based 3D/4D printing by addressing critical limitations of traditional 3D-printed polymers, such as low mechanical strength (less than 25 MPa), lack of reparability, and limited functionality. Novel strategies were developed to overcome these challenges, including the rational design of soft and hard polymer domains, the use of sustainable cellulose to enable shape-morphing functionality, and the integration of selfhealing and photothermal features into 4D printing systems, all of which contribute to sustainable development through optimized polymer networks. First, a robust and 3D-printable polymer system (ACMO-Zn-MUA polymer composites) was developed, achieving exceptional mechanical properties (e.g., with tensile strength up to 49 MPa), alongside self-healing and recyclability. These attributes were attained through a molecular design that combined two distinct polymer domains cross-linked by dual dynamic chemical bonds. The resulting 3D-printed structures—honeycomb, re-entrant, and chiral lattices—demonstrated the ability to restore structural integrity and stiffness after damage, indicating their potential in applications necessitating prolonged service life and minimal maintenance, such as aerospace structures, biological tissues, and electronic devices. Extending the capabilities of 3D-printed polymers, this thesis further explored shape-morphing functionalities using sustainable cellulose. The developed shape-memory polymer system (i.e., the SMPCs with sugar-beet pulp (SBP)) integrated ductile, cellulose-rich domains with a glassy polymer matrix, yielding materials with tuneable actuation behaviour. The use of cellulose, a renewable resource, also enhanced the potential sustainability of these smart materials. Furthermore, a rational modulation method was employed to combine shape-memory and selfhealing capabilities within a multifunctional polymer system (i.e., the healable and stretchable SMPCs with lignin-containing polyurethane acrylate (LPUA)). This system blended a polymerbased framework with an elastic lubricant featuring hydrogen bonds, collectively enhancing selfhealing, stretchability, and shape-recovery properties. Additionally, photothermal properties were embedded through the strategic inclusion of novel cross-linkers functionalized with sustainable lignin, enabling remote actuation. These advancements were particularly exemplified in aerospace applications, where the materials can perform effectively in environments devoid of robust propulsion systems and inaccessible to human intervention. The reparability, stretchability, remote4 controllability, and mechanical robustness of the polymer system offer substantial benefits for actuation practices, potentially streamlining maintenance processes and reducing associated costs. Overall, this research pushes the boundaries of traditional 3D-printed polymers by modulating polymer systems that combine robustness with cutting-edge functionalities, such as shapememory-assisted self-healing and photothermal responsiveness). These developments not only deepen the scientific understanding of 3D and 4D printing technologies but also pave the way for future innovations in the creation of smart materials across diverse applications.

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