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Extrinsic and Intrinsic Approaches to Self‐Healing Polymers and Polymer Composites
Ming Qiu Zhang and Min Zhi Rong
Materials Science Institute, Zhongshan University Guangzhou, China
This edition first published 2022
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Preface
The global study of self‐healing polymers and polymer composites started roughly at the beginning of this century based on the consensus that it represents a next‐generation technology, which would greatly improve the performance of products, including, but not limited to, their reliability and durability. Two decades have past since then. When summarizing the present status, we find there has not yet been a landmark example of a commercial application. It turns out that our prediction of the development of the newly emerging innovation made in our book Self‐Healing Polymers and Polymer Composites, which was published by Wiley in 2011, was too optimistic. Nowadays, scientists are still working hard in both theoretical and applied research. In this context, an updated book is necessary to reflect the latest achievements, which fits with the vigor and vitality of the study activities.
Being involved in the early stage of the research, we witnessed the evolution track of the movement. In general, the strategies of self‐healing polymers and polymer composites are classified into two categories: extrinsic and intrinsic. The former makes use of the healing vessels (e.g. microcapsules, micropipelines, and vascular networks) embedded in the target materials to be repaired, which would be broken upon damaging the materials, releasing fluidic healing agent to the cracked sites and rebinding the cracks via chemical/physical interactions across the interface. In contrast, the latter operates by means of reversible intra‐ and/or intermacromolecular interactions, and no additional healing agent is required. A few groups investigated intrinsic self‐healing of polymers as early as the 1970s from the angle of polymer physics. Entanglement of molecular chains acted as the main mechanism of wound healing. In 2001, Professor Scott White and his coworkers at the University of Illinois at Urbana‐Champaign published a paper about self‐healing in terms of healing capsules. Afterwards, extrinsic self‐healing attracted plenty of research interest worldwide. In the meantime, intrinsic self‐healing via chemical reversible covalent and non‐covalent interactions grew so fast that it was ahead of extrinsic self‐healing once again with respect to the materials species and properties to be restored. Nevertheless, chemistry has made a greater contribution this time, as more and more chemists have become involved, focusing on molecular design and synthesis as well as functionalities recovery. Intrinsic self‐healing ability has been a standard feature of materials in some cases. In addition, the development of intrinsic self‐healing has created other new accompanying techniques, such as reprocessing, reshaping and recycling, topology rearrangement, and processing difficult‐to‐process materials of traditionally non‐reworkable thermosetting polymers. The new possibilities go beyond the scope of classic polymer engineering and enrich the measures of material diversification.
The style of writing and organization of our abovementioned book is followed herein, so that this book will provide the reader with an overall view of the ongoing research, and more importantly, inspiration for the development of novel materials and functionalities.
Chapter 1 serves as an introduction to the field of self‐healing polymers and polymer composites. In addition to the general scope, the achievements
