Self-Healing EPDM Rubbers with Highly Stable and Mechanically-Enhanced Urea-Formaldehyde (UF) Microcapsules Prepared by Multi-Step In Situ Polymerization

Abstract

The mechanically-enhanced urea-formaldehyde (UF) microcapsules are developed through a multi-step in situ polymerization method. Optical microscope (OM) and field emission scanning electron microscope (FE-SEM) prove that the microcapsules, 147.4 μm in diameter with a shell thickness of 600 nm, are well-formed. From 1H-nuclear magnetic resonance (1H-NMR) analysis, we found that dicyclopentadiene (DCPD), a self-healing agent encapsulated by the microcapsules, occupies ca. 40.3 %(v/v) of the internal volume of a single capsule. These microcapsules are mixed with EPDM (ethylene-propylene-diene-monomer) and Grubbs’ catalyst via a solution mixing method, and universal testing machine (UTM) tests show that the composites with mechanically-enhanced microcapsules has ca. 47% higher toughness than the composites with conventionally prepared UF microcapsules, which is attributed to the improved mechanical stability of the microcapsule. When the EPDM/microcapsule rubber composites are notched, Fourier-transform infrared (FT-IR) spectroscopy shows that DCPD leaks from the broken microcapsule to the damaged site and flows to fill the notched valley, and self-heals as it is cured by Grubbs’ catalyst. The self-healing efficiency depends on the capsule concentration in the EPDM matrix. However, the self-healed EPDM/microcapsule rubber composite with over 15 wt% microcapsule shows an almost full recovery of the mechanical strength and 100% healing efficiency.

Preparation and Application of Latent Microcapsule Catalysts in One-Component Silicone Rubber Curing

“…There are various methods for the preparation of microcapsules, which can be divided into three categories based on the molding mechanism of microcapsules: physical, − chemical, − and physicochemical methods. − The physicochemical method is the most widely used technology and is mainly represented by the solvent evaporation method, which is more effective in controlling the process parameters. , Generally, the solvent evaporation method includes encapsulation of the catalyst and evaporation of the volatile solvent process. The encapsulation process consists of two steps, with the first step being the preparation of a stable oil-in-water emulsion.…”

Preparation and performance improvement of a dual‐component microcapsule self‐healing system for silicone rubber insulating material

“…The microcapsule self-healing technology has many applications in repairing mechanical damage inside polymer materials. Healing agent systems based on dicyclopentadiene (DCPD) [18,19], epoxy resin [20], polydimethylsiloxane (PDMS) [21], and others have been developed [22,23]. Singleshell and multi-shell microcapsules with polyurethane (PU), poly(urea-formaldehyde) (PUF), and poly(melamine-formaldehyde) (PMF) as shell materials have been prepared [24][25][26].…”

Preparation and Self-Healing Application of Isocyanate Prepolymer Microcapsules

“…Microcapsule healing materials [1][2][3][4][5] have attracted increasing attention and have been widely researched, especially since the first-generation healing system reported by White et al [6] This is mainly because the microcapsule healing materials can provide instant feedback to external signals from the outside [7][8][9][10][11], complete the healing automatically and significantly extend the service life [12][13][14][15][16]. As reported in previous work [17,18], healing reagents must be encapsulated in capsules before being added to self-healing coatings to offer the self-healing functions [19].…”