**Abstract**

In order to overcome the challenges and limitations related to conventional maintenance and repair methods in structural composites during service, the concept of self-healing for polymeric materials has been developed in the last decades. Inspired by biological systems, ideal self-healing materials must be able to repair damages continuously during the service life of the component, recovering its performance. Several techniques have been proposed in the last years to manufacture self-healing polymers and fiber-reinforced composites to provide healing of microcracks in the composite structure without or with less intervention, extending service life and safety of the components and reducing maintenance time and cost. This book chapter proposes an overview of the most promising self-healing approaches for thermoset and polymer matrix composites developed in recent year.

**Keywords:** advanced materials, thermoset polymers, polymer matrix composites, self-healing, mendable resin

## **1. Introduction**

Polymers and polymer matrix composites (PMCs) have been extensively used for a variety of structural applications due their combination of high mechanical properties and light weight savings as major benefit. During service, the operating environment often exposes these materials to severe variations in mechanical loading and environmental conditions. Such conditions induce damages and can cause the formation of microcracks. These matrix damage can lead to the coalesce and growth of larger cracks, which compromise mechanical performance and integrity of the material inside its structure, where detection and external intervention are difficult and/or impracticable. Non-destructive testing methods are generally used for inspection of components during operation. However, internal microcracks can be difficult to repair [1, 2]. To overcome the challenges related to the repair of these internal damages in thermoset matrix and FRP, self-healing materials have been proposed in the decades as an alternative to conventional repair methods.

Ideal self-healing materials are designed to present the ability repair themselves, using resources inherently available to them. The recovery of performance can be full or partial and occurs during the service life of the component with minimal or no external intervention. These materials can provide the healing of invisible

microcracks in the composite structure and can be an alternative to non-effective conventional maintenance methods to extend service life and safety of the components in addition to reducing maintenance time and cost [1, 3, 4].

Inspired by biological systems, the self-healing of synthetic materials occurs in three steps. Initially, the healing mechanism is triggered by the damage. In the second step, the healing agent, that is, the material responsible to repair the damage, is transported to the damaged area. Lastly, the repair process takes place, recovering the crack. The time and efficiency of the recovery depend on the self-healing mechanism used [5, 6].

Different types of self-healing mechanisms are described in literature for all types of materials. Polymeric materials are reported as promising for self-healing, and the self-healing ability can be introduced by chemical modification or exposure to physical or thermal conditions. The glass transition temperature (Tg), the chain mobility, and the chemical structure are important parameters to be considered during the design of the self-healing system and can influence the success of the healing ability [7].

In this scenario, self-healing polymeric materials represent a new class of materials and have attracted great attention in the past decades. Studies have been developed to better understanding of the self-healing ability, the mechanisms, and how to overcome the challenges of processing and the limitations of each system. In the last decades, a significant increase in the amount of research about self-healing polymers is reported. **Figure 1** shows the growth of the number of papers published on the topic of self-healing polymeric materials since 2000.

Several mechanisms are employed to obtain self-healing polymeric materials and each mechanism presents advantages, limitations, and challenges in formulation. In this review article, principles and developments in self-healing thermoset matrix and fiber reinforced polymers were presented.

**Figure 1.** *Number of published papers according to science direct searched by "polymers self-healing".*
