Influência das variáveis de síntese nas propriedades de microcápsulas de PUF/ENB utilizando planejamento Plackett-Burman

Abstract

Polymers and polymer composites are constantly susceptible to damage, due to the appearance of microcracks, that can compromise the structure, as well as the life of the material during use. Thus, self-healing systems have been increasingly studied and the use of polymeric microcapsules is one of the effective solutions for repairing damage during application, eliminating the need to remove the component for repair, reducing costs. In this work, poly(urea-formaldehyde) (PUF) microcapsules with 5-ethylidene-2-norbornene (ENB) core material were prepared by in situ polymerization. The Placket-Burman (PB) experimental design tool was used to perform a statistical analysis of the synthesis process variables effect on the properties of the microcapsules obtained. Among the factors manipulated are the stirring speed, pH, content of poly(ethylene-alt-maleic anhydride) (EMA) (emulsifier), molar ratio of urea/formaldehyde monomers (U/F), ammonium chloride and resorcinol (stabilizer) and 1-octanol drops (bubble inhibitor). The evaluated response variables were the average diameter of the microcapsules, the yield, the encapsulated content, the microcapsule wall roughness, the thermal stability and the degradation temperature. It was observed that, of all the parameters analyzed, the agitation speed and the EMA content were the ones that most exerted significant effects on the analyzed response variables, at a confidence level of 90%. Microcapsules with larger diameters were obtained when agitation and EMA content were at the lower level of the PB design. On the other hand, the thermal stability and the degradation temperature of the microcapsules increased with the agitation and the EMA content. Furthermore, the high significance of curvature in Pareto charts of some analyzed response variables indicated that microcapsules with satisfactory properties can be obtained in the central points. With regard to yield and encapsulated content, the analyzed parameters did not present a significant statistically effect, at a confidence level of 90%, however, at a confidence level of around 85%, it was possible to observe that some variables were significant. Finally, it was possible to conclude that microcapsules with different characteristics can be obtained by controlling the synthesis parameters. Through experimental design it was possible to understand the influence of these factors on the analyzed response variables.