Self-Healing Poly(urea formaldehyde) Microcapsules: Synthesis and Characterization

Abstract

Smart coatings and smart polymers have been garnering great interest in recent times due to their novel characteristics, such as being self-restoring, self-cleaning, and self-healing. However, most self-healing materials have a low glass transition temperature (Tg) and are inadequate for the repair of advanced composites. Because of their low Tg, the conventional self-healing materials plasticize and weaken the composites. In this study, moderate to high temperature self-healing microcapsules, capable of healing and thus stopping crack propagation, are prepared. The microcapsules were prepared using a two-step process involving the synthesis of poly(urea formaldehyde) (PUF) prepolymer, followed by the encapsulation of hexamethylene diisocyanate (HDI) in an oil-in-water emulsion to form a crosslinked PUF shell. Diisocyanates are of particular interest as self-healing encapsulants because of their diversity of structure and fast rate of hydrolysis. Successful encapsulation was verified by Fourier transform infrared spectroscopy (FTIR) and optical microscopy. Thermogravimetric analysis (TGA) was used to characterize the thermal properties of microcapsules. The onset temperature for microcapsule degradation varied from 155 °C to 195 °C. Dynamic mechanical analysis (DMA) was used to determine the thermomechanical response of microcapsule/epoxy films. DMA showed that the glass transition temperature (Tg) of the epoxy/microcapsule composite was greater than the Tg for neat epoxy and varied between 34 and 65 °C. The TGA analysis of the epoxy/microcapsule composite shows that the thermal stability and char retention of the epoxy/microcapsule composite increased and the low temperature decomposition peak at 150 °C, associated with the microcapsule, disappeared after the DMA test, indicating the occurrence of a reaction between HDI and the epoxy to form a crosslinked polyurea network structure.

Microcapsules of Poly(butylene adipate-co-terephthalate) (PBAT) Loaded with Aliphatic Isocyanates for Adhesive Applications

“…The differences are due to a small polyurea formation, resulting from the NCO groups’ reaction with water (from the emulsion or from atmospheric humidity). These encapsulation percentages are on par with the most notable reported results for isocyanate encapsulation. − …”

Promising New Horizons in Medicine: Medical Advancements with Nanocomposite Manufacturing via 3D Printing

“…Flow rates and healing efficiency are affected by various factors, including optimizing the topology, establishing the gradient structure, and designing microfluidics. PMMA with urea-formaldehyde microcapsules, for example, has increased healing effectiveness by 87% despite the PMMA level being just 5% [305]. When it comes to 3D printing with recyclable polymers and composites, the options are almost limitless; nevertheless, the current recycling system sets constraints on material types, such as FDM filaments and DIW gels, among others.…”