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Abstract
Composites are used in a variety of applications due to their excellent properties. However, structural polymers are sensitive and susceptible to thermal and mechanical damage in form of micro-cracks, which are onset to grow deep within the structure where detection and repair are practically impossible. To overcome these problems, broad range of self-healing structures have emerged. This technology has led to an increase in the material’s lifetime and safety while reducing the repair and replacement costs. Capsule-based healing systems are a well-known technology that has many uses in smart protective coatings, dental composites, concrete components, and generally for polymer and fiber-reinforced composites. This article summarizes the research work on the capsule-based self-healing system over the last two decades. In this regard, after a brief introduction, various types of microencapsulation-based methods used in healing systems are classified. After explaining the manufacturing process of capsules, parameters affecting the microencapsulation quality particularly, agitation rate, core to shell weight ratio, monomer viscosity, solvent property, reaction time, temperature, pH, and U/F ratio are explained in detail. Finally, the most common healing efficiency evaluation methods are described. This review provides the reader with an overview of achievements to date, and insight into future development for industrial and engineering applications.
Graphical Abstract
| Abbreviations | ||
| 2MZ-Azine | = | 2,4-diamino-6[-2-methyl-imidazolyl(1)]-ethyl-cis-triazine |
| 2PhI | = | 2-phenyl Imidazole |
| BGE | = | N-butyl Glycidyl Ether |
| CAI | = | Compression After Impact |
| CB | = | Carbon Black |
| CC | = | Compliance Calibration |
| CNS | = | Calcium hydroxide (Ca(OH) ) Nano-spherulites |
| CNTs | = | Carbon Nanotubes |
| DCB | = | Double Cantilever Beam |
| DCM | = | Dichloromethane |
| DCPD | = | Dicyclopentadiene |
| DGEBA | = | Diglycidyl Ether of Bisphenol A |
| DTHP | = | Diglycidyl Tetrahydro-o-Phthalate |
| EDA | = | Ethylenediamine |
| ENB | = | Ethylidene Norbornene |
| EPA | = | Ethyl Phenyl Acetate |
| FCG | = | Fatigue Crack Growing |
| FRP | = | Fiber-Reinforced Polymer |
| GHS | = | Globally Harmonized System of the Classification and Labeling of Chemicals |
| GO | = | Graphene Oxide |
| HGFs | = | Hollow Glass Fibers |
| IPDI | = | Isophorone Diisocyanate |
| MBT | = | Modified Beam Theory |
| MCC | = | Modified Compliance Calibration |
| MF | = | Melamine-Formaldehyde |
| MWCNT | = | Multi-Walled Carbon Nanotube |
| NaCMC | = | Carboxymethyl Cellulose |
| O/W | = | Oil-in-Water |
| PA | = | Phenyl Acetate |
| PAA | = | Phthalic Anhydride |
| PAANa | = | Sodium Polyacrylate |
| PCL | = | Polycaprolactone |
| PCP | = | Polycyclopentadiene |
| PDA | = | Polydopamine |
| PDMS | = | Poly (Dimethyl-Siloxane) |
| PEA | = | Polyetheramine |
| PhCl | = | Chlorobenzene |
| PMCs | = | Polymer Matrix Composites |
| PMMA | = | Poly (Methyl-Methacrylate) |
| PMUF | = | Poly (Melamine-Urea-Formaldehyde) |
| PU | = | Polyurethane |
| PVA | = | Polyvinyl Alcohol |
| ROMP | = | Ring-Opening Metathesis Polymerization |
| SEM | = | Scanning Electron Microscope |
| SENB | = | Single-Edge Notched Bending |
| SIFs | = | Stress Intensity Factors |
| SWCNT | = | Single-Wall Carbon Nanotube |
| TDCB | = | Trapped Double Cantilever Beam |
| TGA | = | Thermogravimetric Analysis |
| UF | = | Urea-Formaldehyde |
| UFM | = | UF Microcapsules |
| W/O | = | Water-in-Oil |
| W/O/W | = | Water-in-Oil-in-Water |
| Nomenclature | ||
| = | Healing efficiency | |
| = | Critical stress intensity factor (Mode I) | |
| = | Crack length | |
| = | Crack opening displacement | |
| = | Specimen length | |
| = | Specimen width | |
| = | Specimen thickness | |
| = | Critical fracture load | |
| = | Young's modulus | |
| = | Compliance | |
| = | Critical energy release rate (Mode-I) | |
| = | Internal work (Strain energy) | |
| = | Number of Fatigue cycles | |