Abstract
Abstract The aim of the research was to identify the influence of different microencapsulated reaction time on the morphology, size, infrared spectral, thermal and micromechanical properties of melamine formaldehyde microspheres, synthesised with modified in situ polymerisation. Microspheres are microencapsulated particles with a blurred boundary of the core and shell due to their same composition. The synthesis of microspheres was paused after 1, 3, 9 and 15 h, and stopped after 23 h. The scanning electron microscopy and granulometric analysis were used to study the morphology and size of microspheres. Regardless of the reaction time, the produced microspheres were spherical in shape and with a rough surface. The average size of microspheres was almost identical (0.709–0.790 µm), while the volume size distribution curve of the particles became narrower with prolonged reaction time. The curing mechanism of melamine formaldehyde resin was studied using the Fourier-transform infrared spectroscopy and thermal analysis, and nano-indentation identification. The results revealed a slightly more crosslinked structure: with minimal (neglected) increased thermal weight loss (only up to 0.5%) and minor increased Young’s modulus (up to 2.3%). Using a nano-indenter, the hardness of synthesised particles improved by up to 14.8% after 23 h reaction time.
Highlights
Microcapsules usually consist of the core material and a shell
The results showed a noticeable impact of prolonged reaction time on the curing mechanism of the melamine formaldehyde (MF) resin, density of microspheres together with their mechanical and thermal stability, but an insignificant impact on the surface morphology and average size of the microspheres in suspension
Performed with the STA technique, the higher amount of denser crosslinking of the MF resin during the synthesis of particles was proven by high weight loss detection in the temperature region significant to the breakdown of methylene bridges for the particles produced with 23 h reaction time
Summary
Microcapsules usually consist of the core material and a shell. They are produced in a microencapsulation process, where droplets or tiny particles of the core material are surrounded by a coating shell or are embedded in a homogeneous or heterogeneous matrix. In situ polymerisation is a chemical encapsulation technique, in which the formation of the microcapsule shell takes place in a phase, i.e. water or oil phase, in which the core material is dispersed, and in the presence of a modifier, without which the formation of microcapsules would not be possible, since it acts as an emulsifier for the core material and as a catalyst for the formation of the microcapsule shell. This technique is used for the preparation of microcapsules with a melamine formaldehyde (MF) shell and various core materials. It is carried out in two phases: The first phase involves the formation of an emulsion between two immiscible substances (usually water and water-insoluble organic material), while the second phase is the polycondensation reaction (curing) of the shell material (amino groups in the case of MF) on the surface of the emulsified particles, resulting in the formation of microencapsulated particles with a constituted core and shell
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