Microcapsules with low content of formaldehyde: preparation and characterization

In the research reported here, an in situ polymerization process has been used to produce melamine formaldehyde microcapsules containing an oil-based industrial precursor. Here the microcapsules were produced with a low formaldehyde to melamine molar ratio (0.20 0.49) compared to previous literature reports (2.30-5.50). The properties of the microcapsules such as morphology, particle diameter and distribution, wall thickness, mechanical strength, and encapsulation efficiency were characterized, and it was found that the wall thickness and mechanical properties of microcapsules were modulated as a function of formaldehyde to melamine (F/M) molar ratio. The wall thickness of the microcapsules measured by transmission electron microscopy (TEM) increased from 80 +/- 1.9 to 308 +/- 1.7 nm (285 +/- 2.4% increase) when the F/M molar ratio was increased from 0.20 to 0.49 (145% increase), and the nominal rupture stress of the microcapsules measured by a micromanipulation technique increased from 1.3 +/- 0.1 to 4.2 +/- 0.4 MPa (223 +/- 11.5% increase). In contrast, when the F/M molar ratio increased from 0.49 to 2.30 (369%), the wall thickness of microcapsules only increased by 14 perpendicular to 0.8% and the nominal rupture stress of the microcapsules only increased by 66 perpendicular to 12.8%. Thus, it has been shown that significant reduction in the levels of formaldehyde content is possible from previous literature reports, whilst only marginally reducing the mechanical properties, and still maintaining the encapsulation efficiency of similar to 75%.