Microencapsulation of Isocyanates for Self-Healing Polymers

TLDR

Isocyanates can act as catalyst‑free healing agents in humid or wet environments. The study presents the preparation of a polyurethane prepolymer and microencapsulation of isophorone diisocyanate (IPDI) as a healing agent. Microcapsules containing reactive diisocyanate were fabricated by interfacial polymerization of polyurethane, yielding smooth spherical capsules 40–400 µm in diameter produced by controlling agitation rate (500–1500 rpm) following a power‑law relation. The capsules exhibit a constant wall‑to‑diameter ratio of ~0.05, high yields (~70 %) with 70 wt % liquid core, remain stable with only ~10 wt % IPDI loss after 6 months, and show brittle fracture with shell strength following a power‑law dependence on diameter.

Abstract

Microcapsules containing reactive diisocyanate for use in self-healing polymers are successfully fabricated via interfacial polymerization of polyurethane (PU). Isocyanates are potential catalyst-free healing agents for use in humid or wet environments. The preparation of PU prepolymer and microencapsulation of isophorone diisocyanate (IPDI) healing agent are presented. Smooth spherical microcapsules of 40−400 μm in diameter are produced by controlling agitation rate (500−1500 rpm) according to a power law relation (n = −2.24). The PU shell wall thickness varies linearly with capsule diameter, such that the capsules wall thickness to diameter ratio is constant (∼0.05). High yields (∼70%) of a free-flowing powder of IPDI/PU capsules are produced with a liquid core content of 70 wt % as determined by TGA analysis. The microcapsules are stable with only ∼10 wt % loss of IPDI detected after 6 months storage under ambient conditions. Direct mechanical compression testing of microcapsules reveals a brittle fracture mode and normalized shell wall strength that varies with capsule diameter in a power law fashion (n = −0.77).