Otimização da síntese de microcápsulas poliméricas de poli (ureia-formaldeído) (PUF) preenchidas de com 5-etilideno-2- norboneno (ENB) para autorreparo usando metodologia de planejamento fatorial

Abstract

The study of self-healing materials has grown progressively in recent decades due to the demand for highly durable materials. In this work, poly(urea-formaldehyde) (PUF) microcapsules filled with 5-ethylidene-2-norbonene (ENB) were prepared by in situ emulsion polymerization. This work is part of a sequential experimental design strategy, where significant parameters were initially selected from the results of a Plackett Burman (PB) design performed previously, in order to realize a 2 4-1 fractional factorial design. The parameters selected included the agitation speed, the poly (ethylene-alt-maleic anhydride) (EMA) content (emulsifier), the reaction pH and the drops of 1-octanol (inhibitor of bubble formation during the synthesis). Then, to carry out the full factorial design aiming to optimize the synthesis process, only the 1-octanol variable was not selected. The responses analyzed were yield, encapsulate content, medium diameter of microcapsules, stability and thermal degradation. After conducting the full factorial design, representative mathematical models of the process were obtained for the medium diameter, stability and thermal degradation, for a 90% confidence level. To define the optimal condition for producing microcapsules, the medium diameter response variable was taken into consideration based on the mathematical model obtained after statistical analysis, and a joint evaluation was carried out based on the yield results, encapsulate content, stability, and thermal degradation. Thus, using the response surface methodology (RSM), it was concluded that the synthesis condition (PUF/ENB 2) at 700 RPM agitation speed, reaction pH of 3.0 and EMA content added in solution of 0.425 g, is inserted within the optimized region of the synthesis process, resulting in microcapsules with adequate morphological properties, such as regular shell surface, little U/F residue, average diameter around 80 µm, narrow diameter distribution, in addition to good yield and encapsulated content results.