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the stimuli-responsive self-healable materials. It provides details about the history, different types and importance of self-healable materials. The major focus is on recent examples of self-healing polymers that show response to various stimuli. The chapter ends with a discussion about aspects concerning the commercialization of SHSMs and challenges in the area.
Chapter 15 covers mechanically-induced SHSMs with novel characteristics for numerous applications. Various methods of producing these mechanically-induced SHSMs based on different types of materials are discussed.
Chapter 16 discusses SHSMs, their method of synthesis, and application in robotics. The focus of the chapter is on describing the chemistry of self-healing and the working principles. The various approaches of self-healing are also explained such as capsule-based, vascular, and intrinsic self-healing systems. The major focus is on the application of the material in the different sections of soft robots such as skin, actuator, electronics, and sensor.
Chapter 17 discusses the various methods of developing SHSMs for aerospace structural and high-temperature applications. Materials like fiber-reinforced polymers that alter the nature of the base matrix and ceramic matrix composites are described in detail along with intrinsic and extrinsic self-healing mechanisms.
Chapter 18 presents bioinspired, magnificent, nature-based, broadscope elements with numerous functions. These elements exhibit immense power to perceive, respond, and self-heal (autonomous healing). The discussion proceeds with a brief insight into SHSMs, coatings, their types, and the exploitation process used to extract their characteristic features to benefit humankind. This chapter sheds more light on examples dealing with self-healable materials with a notion to fabricate such self-healable materials with rapid exploration and a promising platform.
Chapter 19 introduces SHSMs as promising candidates for the fabrication of electronic devices, energy storage systems, and even sensors. The progress made in SHSMs research is detailed and the preparation mechanisms and properties of the self-healing processes are summarized. In terms of self-healing batteries, both macroscopic and microscopic SHSMs are introduced.
Chapter 20 focuses on self-healing in bleeding engineered composite structures. Additionally, materials with intrinsic and extrinsic self-healing properties are discussed. Moreover, various strategies like bioinspired, biomimetic and vascular networks, are described in detail. Also discussed are approaches for the synthesis of bleeding composite structures, along with their evolved properties, repairing mechanism, disadvantages, and advantages.
Chapter 21 provides a general overview of numerous materials with self-healing attributes. Greater emphasis is also placed on autonomic and non-autonomic types of SHSMs. The mechanism of action of these SHSMs are also highlighted.
Inamuddin, Mohd Imran Ahamed, Rajender Boddula and Tariq Altalhi
March 2021
1
Self-Healing Polymer Coatings
Facundo I. Altuna* and Cristina E. Hoppe †
Instituto de Investigaciones en Ciencia y Tecnología de Materiales (INTEMA), Universidad Nacional de Mar del Plata—CONICET, Mar del Plata, Argentina
Abstract
Traditional coatings made of thermosetting polymers could not be healed or mended because of their cross-linked structure, so damage implied the end of their service life cycle. This picture has dramatically changed since the first self-healing systems reports, moment in which this “disadvantage” of thermosets has started to vanish with the continuous increase in the availability of self-healing and recyclable thermosetting polymers. These advances constitute a breakthrough, as they would avoid replacement and catastrophic failure, encourage recycling and re-processing and prevent the generation of a considerable amount of waste, with obvious environmental and economic benefits. This chapter describes some of the more recent advances in the field of self-healing thermosetting polymers with potential application as coatings. Extrinsic self-healing thermosets use an external agent to perform the healing whereas intrinsic ones require the intervention of an external trigger for repair damage. The first part of the chapter describes the work in extrinsic self-healing thermosets, and the second part in intrinsic ones, with emphasis on polymeric networks with dynamic covalent bonds (DCBs). The most common strategies for the external triggering of intrinsic self-healing polymers are also described. Finally, challenges are discussed with the aim put in attaining the so expected end-user applications.
Keywords: Self-healing, thermosets, dynamic covalent bonds (DCBs), coatings, crosslinked polymers
1.1 Introduction
Traditionally, materials science and technology research has been a quest for improving one or several properties of any given class of materials, so that they can have an enhanced performance. With this aim, all kinds of materials from ceramics and metals to glasses and soft polymers are nowadays designed based on strong scientific knowledge. However, during their service life, materials can suffer damages with consequences that range from affecting the way in which the materials are supposed to work to catastrophically break down or, in the case of a damaged coating, leaving the substrate deprived from its protection. In such cases, besides all the relevant physicochemical, mechanical, thermal and other properties, it would be highly desirable that the material could be mended. Doing so, it would avoid its replacement and save lots of time and economic resources. It would also prevent the generation of a considerable amount of waste, with obvious environmental and economic benefits. With this purpose, the development of self-healing polymers is gaining momentum since the first works studying healing mechanisms in polymers were published about 40 years ago [1, 2]. Another leap forward followed with the design of self-healing polymeric systems containing vessels with healing agents [3, 4], which demonstrated autonomous healing ability.
Thermosetting polymers constitute one of the two great polymer groups according to the most usual polymers classification. They distinguish themselves from thermoplastic polymers—which form the other group—by their crosslinked structure, which provides them with a set of distinctive properties, such as an improved resistance to solvents and chemical reagents, good mechanical strength and thermal stability [5]. Owed to these properties their use as protective coatings, among other applications, has become very popular. Unfortunately and also because of its crosslinked structure, typical thermosetting polymers cannot be healed. This is their main disadvantage in comparison with thermoplastics, which can be not only healed but also reprocessed and recycled by applying the proper processing that often includes a thermal treatment [6, 7]. These differences, however, are starting to vanish, as proved by the continuously increasing number of systems based on self-healing and recyclable thermosetting polymers appearing in the scientific literature. The relevance of the role that self-healing materials and recyclable thermosets are called to play has been already highlighted by the World Economic Forum, which listed them among the Top 10 Emerging Technologies in 2013 and 2015 respectively [8, 9].
In this chapter, we will describe some of the more recent advances in the field of self-healing thermosetting polymers with potential application as coatings. One of the most popular classification of self-healing thermosets is between extrinsic and intrinsic healing systems [10, 11]. The category of extrinsic self-healing thermosets encompasses all those systems that make use of an external agent to perform the healing