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The purpose of this investigation is to develop a facile method to encapsulate a sunlight-curable silicone-based resin into a melamine–urea–formaldehyde (MUF) shell in the presence of polyvinylpyrrolidone (PVP) as an emulsifier. These microcapsules can be used in self-healing coating formulations.

MUF microcapsules containing a sunlight-curable core (methacryloxypropyl-terminated polydimethylsiloxane, MAT-PDMS) have been fabricated by means of in situ polymerisation of an oil-in-water emulsion using PVP as an efficient and environmentally advantageous stabiliser. The effects of agitation rate and PVP concentration on the microencapsulation process have been investigated using optical microscopy (OM) and scanning electron microscopy (SEM). The chemical structure and thermal stability of the microcapsules have been studied using Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA). The solvent resistance of the microcapsules has been determined as well.

It has been revealed that the pH of the reaction mixture remained almost constant during the reaction, which simplified the process. It has also been observed that the microencapsulation yield improved and the microcapsules’ surface morphology became smoother when a high PVP content was used. With an increase in stirring rate from 600 to 1,200 rpm, the surface roughness and the average particle size decreased. The mean diameter of the prepared microcapsules ranged from 32.1 to 327.1 µm depending on the synthesis conditions. It was demonstrated that the microcapsules had a high capacity for MAT-PDMS encapsulation (more than 88 Wt.%). The solvent stability of the microcapsules against different polar, semi-polar and non-polar solvents was also evaluated.

This research is limited to the encapsulation of a hydrophobic and sunlight curable liquid (such as MAT-PDMS) by means of in situ polymerisation of amino resins.

The results can be used by researchers working on the fabrication of microcapsules for applications such as drugs, electrophoretic inks, electrophoretic displays, intumescent fire-retardant coatings and self-healing materials.

In self-healing coatings, healing agents which can be cured by UV irradiation or sunlight are envisaged attractive because they are catalyst-free, environmentally friendly and relatively inexpensive. PVP is an environmentally friendly emulsifier. The prepared microcapsules can be used in self-healing coatings to help in reducing maintenance costs for buildings and steel structures.

The novel aspect of this work is the development of a sunlight-curable silicone-based resin that was encapsulated in a MUF shell in the presence of PVP. A simple method was used to fabricate MUF microcapsules containing MAT-PDMS without the need to control pH during the reaction. Conventional methods for the preparation of amino resin microcapsules require an intensive and precise pH control to obtain favourable microcapsules. MAT-PDMS can be cured by sunlight and is catalyst-free, environmentally friendly and relatively inexpensive.

The purpose of this work was to express a facile method to fabricate microcapsules containing linseed oil with melamine-urea-formaldehyde (MUF) shell in the presence of polyvinylpyrrolidone (PVP) as an emulsifier. These microcapsules may be used in self-healing coating formulations.

In this work, different types of PVP (i.e., PVP with different molecular weights or K values) were used as emulsifiers and colloid protectors to encapsulate linseed oil in an MUF shell. Moreover, the effect of agitation rate on the morphology of the microcapsules was investigated. Microcapsule morphology and particle size distribution were evaluated using optical microscopy and scanning electron microscopy. Thermal studies were performed using a thermo-gravimetric analysis technique and chemical structure of materials was characterized by using Fourier transform infrared analysis.

In this work, microcapsules with a regular spherical shape and a shell thickness of about 330 nm were fabricated. The results revealed that the use of PVP in the fabrication of MUF could facilitate the synthesis process by eliminating the necessity of pH control during the reaction. In fact, the pH of the reaction media must be precisely controlled in conventional processes. The yield of microencapsulation was found to be 86.5 per cent when a high molecular weight of PVP (PVP K-90) was used. It was also found that the surface morphology of microcapsules became smoother when PVP K-90 was used. The results showed that the surface roughness and the average particle size decreased with an increase in stirring intensity. Mean diameter of the prepared microcapsules ranged from 34 to 346 μmin for various synthesis conditions.

This work is limited to the encapsulation of a hydrophobic liquid (such as linseed oil) by an in situ polymerisation of amino resins.

The presented results can be used by researchers (in academia and industry) who are working in the field of fabrication microcapsules, in various applications such as pharmaceuticals, electrophoretic displays, textiles, carbonless copy papers, cosmetics, printing and self-healing materials.

PVP is considered as an environmentally friendly emulsifier. Therefore, this process is less harmful to the environment. In addition, the prepared microcapsules may be used in self-healing coatings, which helps in reducing maintenance costs for buildings and steel structures.

Ethylene maleic anhydride and styrene maleic anhydride are usually used as emulsifiers in conventional methods for the preparation of amino resin microcapsules. These methods require an intensive and precise pH control to obtain favourable microcapsules, while in the present research, a facile method was used to fabricate MUF microcapsules containing linseed oil without needing any pH control during the reaction.