# Repair Performance of Self-Healing Microcapsule/Epoxy Resin Insulating Composite to Physical Damage
## 3 Results and Discussion  
### Repair Performance of Mechanical Damage  
#### 3.1.1 Structural Change of Scratch  
Figure 1 shows the OM results of pure epoxy resin and its composite. Compared with the pure epoxy resin, there are obvious microcapsules in composite. And the microcapsules have excellent dispersion in the epoxy resin matrix without obvious rupture. The excellent dispersion and intact morphology of microcapsule in the matrix can ensure the better repair effect of damage based on the less influence on the basic properties of matrix material.  
Figure 2 is the OM results of the scratch test. The composite without catalyst was added as the contrast to verify the repair effect to scratch damage more intuitively. The scratch could cause physical structural damage to epoxy resin insulating material. And the scratch width in pure epoxy resin had no obvious change after heating. The results indicate that the original epoxy resin insulating material does not have any self-healing ability to physical damage. Moreover, the influence of heating factor on the physical damage (such as scratch) in epoxy resin material is very small, which can be ignored.  
Figure 1: Morphology of epoxy resin samples. (**a**) Pure epoxy resin. (**b**) Microcapsule/epoxy resin composite.  
The scratch can destroy the microcapsules in the sample, resulting in the rupture of wall structure. And the heating condition would cause the core material to flow out. For the composite without catalyst, the unreacted DCPD was volatilized by heating. So, the scratch of this composite had no repair effect, which is similar to the pure epoxy resin. When the composite contained catalyst, its repair behavior is shown in Figure 3. The melted repairing agent (DCPD) flowed to the damaged area, contacted with the catalyst and reacted to form solid repair product (PDPCD) at the defect area. In other words, the microcapsule can fill the damage structure. Therefore, the scratch structure was reduced dramatically. If the scratch width is taken as the criterion of the repair efficiency, the self-healing rate is 70%-100%.  
Furthermore, infrared results (as shown in Figure 4) show that the filler in scratch is really the PDCPD (3050 cm-1 and 3003 cm-1 indicate = C-H, 2926 cm-1 and 2851 cm-1 indicate -CH2-, 1701 cm-1 and 1633 cm-1 indicate C=C) [26]. In addition, the carbon-carbon double bonds are retained after the reaction, which makes the stiffness and toughness of product reach an excellent balance. Thus, the good repair effect of the damaged part is ensured.  
Figure 2: Morphology of the scratch: (**a**) Unheated pure LDPE epoxy resin; (**b**) Heated pure epoxy resin for 30 min; (**c**) Heated pure epoxy resin for 60 min; (**d**) Unheated composite without catalyst; (**e**) Heated composite without catalyst for 30 min; (**f**) Heated composite without catalyst for 60 min; (**g**) Unheated composite; (**h**) Heated composite for 30 min; and (**i**) Heated composite for 60 min.  
The repair effect around the region of ruptured microcapsule is more obvious, and the scratch is almost completely repaired. The main reason is that the damage region near the microcapsule would contact a large number of core material preferentially. Moreover, the reaction rate of core material is relatively fast, leading to the repairing agent having already begun to react in the diffusion process. Furthermore, the comparison between Figure 2h,i shows that the reaction process of core material is concentrated in the first 30 min. It proves that the repair reaction speed is fast, which can better meet the timely requirement of damage treatment in insulating material. Thus, the repair ability of microcapsule can effectively and timely prevent the further deterioration of insulating material.  
In short, the obvious self-healing ability of composite to physical damage can be proved by the comparison of three groups of scratch experiments. The repair performance of insulating material to physical defects is realized, thus ensuring the reliable operation of electrical equipment.