Isophorone Diisocyanate (IPDI) Microencapsulation for Mono-Component Adhesives: Effect of the Active H and NCO Sources

Abstract

Polyurea/polyurethane (PUa/PU) shell microcapsules (MCs), containing high loadings of isophorone diisocyanate (IPDI) in the core, were developed to enable the production of mono-component, eco-friendly and safer adhesive formulations for the footwear industry. IPDI microencapsulation was obtained via oil–in–water (O/W) microemulsion combined with interfacial polymerization. A methylene diphenyl diisocyanate (MDI) compound (a commercial blend of monomeric and polymeric species), with higher reactivity than IPDI and low viscosity, was added to the O phase to competitively contribute to the shell formation, improving its quality. Four different active H sources were tested, aimed at achieving a high encapsulation yield. The successful encapsulation of IPDI was confirmed by Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA), while the MCs’ morphology and size distribution were assessed by scanning electron microscopy (SEM). The incorporation of a multifunctional isocyanate silane in the O phase, as “latent” active H source, led to the formation of impermeable PUa/PU-silica hybrid shell MCs with more than 60 wt.% of pure encapsulated IPDI. A proof-of-concept study shows high peeling strength and a structural type of failure of the adhesive joint, revealing an effective IPDI release. These new engineered MCs are found to be promising crosslinkers for mono-component adhesives for high demanding applications.

Hybrid shell microcapsules containing isophorone diisocyanate with high thermal and chemical stability for autonomous self‐healing of epoxy coatings

“…1522 cm −1 and COC at ca. 1214 cm −1 confirmed the presence of urethane and urea linkages, providing an evidence that the shell was composed by PUa/PU …”

“…Through the analysis of the size distribution of the MCs, using the Fiji software, it was possible to conclude that the MCs have an average diameter of 10 ± 1 μm in both cases [Figure (e)]. Since the key parameters that determine the size of MCs, namely, emulsification rate, stirring rate, and emulsifier concentration, were kept constant in all the syntheses, obtaining the same size of MCs was expected . Figure (a) demonstrates the absence of relevant aggregation in the case of H MCs.…”

“…This work aims at the encapsulation of IPDI in the core of small dimension MCs (5–30 μm) and follows a recent work from the group, in which encapsulation of IPDI using a commercially available oligomeric MDI source, Ongronat 2500, with higher reactivity than IPDI, was successfully achieved by a facile one‐pot method . In the previous work, four different active hydrogen sources were tested, namely, 3‐(2‐aminoethylamino) propyltrimethoxysilane (aminosilane) in combination with tetraethyl orthosilicate, diethylenetriamine, and 3‐(triethoxysilyl) propyl isocyanate (IPES), to form impermeable shell due to faster polymerization reactions and as a result, an increased encapsulation yield.…”

“…In the previous work, four different active hydrogen sources were tested, namely, 3‐(2‐aminoethylamino) propyltrimethoxysilane (aminosilane) in combination with tetraethyl orthosilicate, diethylenetriamine, and 3‐(triethoxysilyl) propyl isocyanate (IPES), to form impermeable shell due to faster polymerization reactions and as a result, an increased encapsulation yield. The previous work reported a pure IPDI encapsulation at 60 wt % in MCs with an average diameter of 80–95 μm, attained by employing IPES as “latent” active H source, which was an acceptable dimension for the envisaged application, namely, crosslinking agents in one‐component adhesive formulations. The shift to a new application, consisting of autonomous healing of epoxy coatings for corrosion protection, raised the need to reduce the size of MCs.…”

“…The organic moieties of the hybrid shells are formed by reaction of the NCO groups of the isocyanate compound with OH groups from water and silanol groups from HDMS and n ‐OTES (forming PUa/PU moieties), while the inorganic moieties of the hybrid shells are formed by reaction among silanol groups giving siloxane (or silica) moieties. The resulting shell is a hybrid material based on PUa/PU and silica …”