Abstract
Self-healing strategies including intrinsic and extrinsic self-healing are commonly used for polymeric materials to restore their appearance and properties upon damage. Unlike intrinsic self-healing tactics where recovery is based on reversible chemical or physical bonds, extrinsic self-healing approaches rely on a secondary phase to acquire the self-healing functionality. Understanding the impacts of the secondary phase on both healing performance and matrix properties is important for rational system design. In this work, self-healing coating systems were prepared by blending a bio-based epoxy from diglycidyl ether of diphenolate esters (DGEDP) with thermoplastic polyurethane (TPU) prepolymers. Such systems exhibit polymerization induced phase separation morphology that controls coating mechanical and healing properties. Structure–property analysis indicates that the degree of phase separation is controlled by tuning the TPU prepolymer molecular weight. Increasing the TPU prepolymer molecular weight results in a highly phase separated morphology that is preferable for mechanical performances but undesirable for healing functionality. In this case, diffusion of TPU prepolymers during healing is restricted by the epoxy network rigidity and chain entanglement. Low molecular weight TPU prepolymers tend to phase mix with the epoxy matrix during curing, resulting in the formation of a flexible epoxy network that benefits TPU flow while decreasing Tg and mechanical properties. This work describes a rational strategy to develop self-healing coatings with controlled morphology to extend their functions and tailor their properties for specific applications.
Highlights
Motivated by extending material lifetime through restoring performance upon damage, research aimed at developing self-healing polymers that self-repair is growing [1,2,3,4]
This work reveals that the epoxy–thermoplastic polyurethane (TPU). Morphology, which determines both mechanical and self-healing work reveals that the epoxy–TPU morphology, which determines both mechanical and self-healing performance, can be rationally tuned by the selection of a TPU prepolymer with the appropriate
This work reveals that the epoxy–TPU morphology, which determines both mechanical and self-healing performance, can be rationally tuned by the selection of a TPU prepolymer with the appropriate molecular weight
Summary
Motivated by extending material lifetime through restoring performance upon damage, research aimed at developing self-healing polymers that self-repair is growing [1,2,3,4]. Extrinsic self-healing systems require the incorporation of external healing components such as catalysts or thermoplastic additives in the system [17,18,19,20,21,22]. These healing agents can be encapsulated or form blends during material. To achieve the self-healing functionality, the external healing component must diffuse to the damage site to mend the crack. A highly transparent self-healing coating with facile process ability and good mechanical properties was obtained by blending epoxy with thermoplastic polyurethane (TPU). The self-healing mechanism was analyzed through correlations with epoxy matrix relaxation behavior and TPU chain diffusion
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