Effect of glycidylisobutyl–POSS on the thermal degradation of the epoxy resin

Abstract

In this study, polyhedral oligomeric silsesquioxane glycidylisobutyl-POSS was dispersed in an epoxy resin (DGEBA) using ultrasound, and the thermal degradation was investigated by the Flynn-Wall-Ozawa and Criado methods using thermogravimetric analysis. The TEM analysis indicated higher polyhedral oligomeric silsesquioxane (POSS) dispersion in spherical shape. The POSS dispersion was associated with the formation of micelles as a result of their hybrid character. The addition of POSS did not change the degradation of the resin until *380°C, and above this temperature, increase in the thermal stability was observed. The kinetic results revealed that the addition of POSS decreased E a values primarily to 10 % POSS and did not affect the mechanism of degradation for all contents. The reduction in E a was associated with the easier breaking of bonds at the interface of the DGEBA/POSS nanocomposite. The thermodynamic parameters suggested an increased ''degree of arrangement'' for the formation of an active complex during the degradation process and corroborate the lower E a values. The results suggest that the addition of POSS is able to cause an effect of thermal barrier at higher temperatures without affecting the homogeneity of the microstructure of the cured resin.

Evaluation of the Mechanic and Electrochemical Properties of an Epoxy Coating with Addition of Different Polyhedral Oligomeric Silsesquioxanes (POSS) Applied on Substrate of Low Alloy Steel

“…So, the clusters formation is faster. The contrary occurs with the sample DGEBA/POSSocta, due to a higher concentration of glycidyl radicals, and the formation of dispersed and spherical clusters is compromised, leading to the appearance of lamellar structures 10,16,18 .…”

“…The increase in the nanocomposites hardness is justified by some authors, due to the formation of cross-links with the polymer chains and the epoxy resin, the functionality of POSStri and POSSocta makes the chains mobility difficult, possibly presenting free spaces, as well as forming clusters which makes the film more rigid. This rigidity may possibly be associated with the epoxy resin chains movement to be restricted by the presence of the POSS nanocages, due to its functionality, leading to a higher resistance to deformation 10,18,32,33 . This rigidity of the system containing POSStri is an aggravating factor for the low electrochemical resistance, when compared to the other systems studied, mainly in the first hours of contact with the electrolyte, since this coating facilitates the permeation of the electrolyte.…”

“…This hardness increase of the system containing POSSocta can be related to the movement of the epoxy resin chains be restricted due to the presence of the POSSocta nanocages, and the formation of agglomerates, because of the high functionality, occasioning higher resistance to deformation and, consequently, higher hardness 10,18,32 . Meanwhile, the system containing POSSmono is more flexible when compared to the sample containing POSSocta, due to the lower functionality, which promotes more mobility of the polymeric chains and, thus, an efficient dispersion, obtaining a more homogeneous film 18,31,33 .…”

“…The high functionality of POSSocta does not facilitates the chains mobility, presenting free spaces, in addition to the formation of agglomerates, which makes the film more rigid 10,18,32 . Pistor et al also point out that the increase of POSS concentration makes the nanocomposite less flexible 10 .…”

Influence of the functionality of polyhedral oligomeric silsesquioxane–POSS containing glycidyl groups on the dispersion and interaction with epoxy nanocomposites

“…The TGA analyses (TGA50 -Shimadzu) were performed under a N 2 atmosphere, from 238C to 830 C. Approximately 10 mg of each sample was used in each analysis at heating rates of 208C min 21 . Figure 2 shows the TEM images for the nanocomposites containing the different POSS compounds studied.…”