Microencapsulation of reactive isocyanates for application in self-healing materials: a review

Tailoring Thermomechanical, Shape Memory and Self-Healing Properties of Furan-Based Polyketone via Diels-Alder Chemistry with Different Bismaleimide Crosslinkers

Furan/maleimide dynamic covalent chemistry has been extensively used to fabricate re-workable and self-healing thermosets. Understanding the relationship between crosslinker structure, network dynamics, and material final properties, however, remains a challenge. This study introduces self-healing and shape-memory thermosets derived from furan-functionalized polyketones (PKFU) crosslinked with aromatic bis-maleimides, i.e., 1,1'-(methylenedi-4,1-phenylene)bis-maleimide (BISM1) and bis(3-ethyl-5-methyl-4-maleimidophenyl)methane (BISM2), via a thermally reversible Diels-Alder reaction. Polyketones were chemically modified with furfurylamine through the Paal-Knorr reaction, achieving varying furan grafting ratios. The resulting networks, characterized by ATR-FTIR, 1H-NMR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and rheology, demonstrated tunable thermomechanical properties. BISM2-based thermosets exhibited enhanced thermal stability and reversibility over a broad temperature range (20-120 °C), with a shape recovery ratio of up to 89% and complete self-healing at 120 °C within 5 min. These findings highlight the potential of polyketone-based thermosets for applications requiring adaptive thermomechanical properties, efficient self-repair, and sustainability.

Bio-Microcapsules of Polybutylene Succinate (PBS) and Isocyanates: Towards Sustainable, Safer, and Efficient Adhesives

This work describes the encapsulation of three different aliphatic isocyanates to reduce the risks associated with isocyanates' direct handling. The use of bio-based polybutylene succinate (bio-PBS) increases the sustainability factor as it allows for the use of microcapsules (MCs) from renewable sources with biodegradable features. The three different MCs (MCs-Monomer, MCs-Trimer, and MCs-Polymer) are spherical, crack-free, and matrix-type, containing an isocyanate payload between 67 wt% and 70 wt%. Protection against environmental moisture was improved, resulting in losses of less than 10% for most cases after one month. The bio-PBS MCs were found to be suitable as crosslinking agents in high-performance adhesive formulations for the footwear industry. Adhesive joints with encapsulated isocyanate exhibited peel strength values ranging from 3.28 to 4.56 N/mm, well above the minimum requirements for the intended footwear application. Additionally, these joints demonstrated improved creep resistance compared to those using non-encapsulated isocyanates. In this context, the MCs-Trimer stood out, providing exceptional thermal robustness to the joints, as they showed no failure or opening at 90 °C, consistent with commercial adhesives. These results confirm that bio-PBS MCs can be excellent components for future adhesive formulations and that matrix-type MCs can also be utilised for this purpose.

Biodegradable Microcapsules of Poly(Butylene Adipate-co-Terephthalate) (PBAT) as Isocyanate Carriers and the Effect of the Process Parameters

Poly(butylene adipate-co-terephthalate) (PBAT), a biodegradable flexible, and tough polymer is herein used, for the first time, to encapsulate and protect isocyanate derivatives. Isocyanates are essential building blocks widely employed in the chemical industry for the production of high-performing materials. Microencapsulation of isocyanates eliminates the risks associated with their direct handling and protects them from moisture. In light of this, and having in mind eco-innovative products and sustainability, we present a straightforward process to encapsulate isophorone diisocyanate (IPDI) using this biodegradable polymer. Spherical and core-shell microcapsules (MCs) were produced by an emulsion system combined with the solvent evaporation method. The MCs present a regular surface, without holes or cracks, with a thin shell and high isocyanate loadings, up to 79 wt%. Additionally, the MCs showed very good isocyanate protection if not dispersed in organic or aqueous solutions. Effects of various process parameters were systematically studied, showing that a higher stirring speed (1000 rpm) and emulsifier amount (2.5 g), as well as a smaller PBAT amount (1.60 g), lead to smaller MCs and narrower size distribution.

High-Temperature Aroma Mitigation and Fragrance Analysis of Ethyl Cellulose/Silica Hybrid Microcapsules for Scented Fabrics

Microencapsulation can improve the thermal stability of a fragrance, and composite wall materials are one way to further improve the thermal stability of microcapsules. This paper presents a facile approach for cotton fabric coatings by using cellulose/silica hybrid microcapsules. Lavender fragrance oil-loaded cellulose/silica hybrid microcapsules were one-step synthesized via emulsion solvent diffusion. The prepared microcapsules were found to be spherical in shape with a particle size distribution between 500 to 1000 nm. Due to the slow releasing of lavender fragrance oil in the capsules, the fragrance loss rate of (3-aminopropyl)triethoxysilane (APTES)-, triethoxy(3-glycidyloxypropyl)silane (GPTES)-, and (3-aercaptopropyl)trie-thoxysilane (MPTES)- modified cellulose/silica hybrid microcapsules are 25.2%, 35.1%, and 16.7% after six hours at 120 °C. E-nose and gas chromatography–mass spectrometry (GCMS) studies found that the fragranced cotton fabrics had good retention of characteristic aromas. It provides the basis for the application of the heating treatment of cotton fabrics in sterilization, bleaching, printing, and other processes.

Preparation and Self-Healing Application of Isocyanate Prepolymer Microcapsules

In this study, we successfully manufactured polyurethane microcapsules containing isocyanate prepolymer as a core material for self-healing protection coatings via interfacial polymerization of a commercial polyurethane curing agent (Bayer L-75) and 1,4-butanediol (BDO) as a chain extender in an emulsion solution. With an optical microscope (OM) and a scanning electron microscope (SEM), the resulting microcapsules showed a spherical shape and an ideal structure with a smooth surface. Fourier transform infrared spectra (FTIR) showed that the core material was successfully encapsulated. Thermal gravimetric analysis (TGA) showed that the initial evaporation temperature of the microcapsules was 270 °C. In addition, we examined the influence of the concentration of the emulsifier and chain extender on the structure and morphology of the microcapsules. The results indicate that the optimal parameters of the microcapsule are an emulsifier concentration of 7.5% and a chain extender concentration of 15.38%. Microcapsules were added to the epoxy resin coating to verify the coating’s self-healing performance by a surface scratch test, and the results showed that the cracks could heal in 24 h. Furthermore, the self-healing coating had excellent corrosion resistance.