Curing studies of bisphenol a based bismaleimide and cloisite 15a nanoclay blends using differential scanning calorimetry and model‐free kinetics

Abstract

Blends of 2,2-bis[4-(4-maleimidophenoxy phenyl)]propane [bismaleimide (BMIX)] with different proportions (1,2,3,4,5,7, and 9%) of the nanoclay Cloisite 15a were prepared with ultrasonication. Fourier transform infrared studies reveal the existence of interactions between the clay particles and the imide rings in BMIX. The difference in the melting characteristics and the decrease in the curing window caused by the incorporation of the clay particles in BMIX, as evidenced by detailed differential scanning calorimetry investigations, confirmed the existence of interactions between the nanoclay particles and BMIX molecules. The Flynn-Wall-Ozawa, Vyazovkin, and Friedman kinetics methods were used to calculate the activation energies (E a 's) for the curing of the BMIX materials. E a for the polymerization varied, depending not only on the amount of clay loaded in the BMIX but also on the extent of the curing reaction. Because of the loss of interaction between the clay platelets and the imide rings of BMIX, a decrease in E a at higher reaction extents was noted when there was lower clay loadings (1-4% Cloisite 15a) in BMIX. A reversal in the previous behavior was noted at higher clay loadings (7 and 9% Cloisite 15a) in BMIX and was attributed to the restriction of the molecular mobility due to the presence of increased concentrations of clay platelets and the decreased availability of reaction sites for polymerization. These two opposing factors played were equal at the optimum level of Cloisite 15a loading (5%) in BMIX, which was reflected in the constancy of E a variation noted with increasing reaction extent. Figure 6. SEM images of the (A) thermally cured BMIX and (B) BMIX þ 5% Cloisite 15a. ARTICLE WWW.MATERIALSVIEWS.COM WILEYONLINELIBRARY.COM/APP

Indane‐based bismaleimide and cloisite 15a nanoclay blends: Kinetics of thermal curing and degradation of particulate nanocomposites

“…The incorporation of cloisite 15a nanoclay in BMII does not affect the melting point of BMII but the enthalpy of fusion is decreased. Previous investigations indicated that the clay particles affects the melting point of BMIX and the enthalpy of fusion drastically and it provides a very good evidence for the interaction existing between the cloisite 15a clay and BMIX in the melting stage itself. In this case, the results prove that the clay particles do not have much interaction with the BMII in the blends itself, but the clay particles interact with the material, when it was heated.…”

“…This led to higher activation energy values. So, the apparent activation energy for the polymerization was comparatively higher at the final stages of polymerization in comparison to the initial polymerization. The rapid decrease in the activation energy at higher reaction extent ( α > 0.8) levels could be explained by the change in the reaction mechanism from kinetically controlled to diffusion controlled and the monomer molecules became frozen in their positions in the glassy state and this resulted in a virtual cessation of the reaction, the chemical reactions were considerably reduced.…”

“…But, the enthalpy of curing decreases by the addition of clay (2 phr) and the value further decreases as clay content increases from 2 to 4 phr and the variation was noted in the enthalpy of curing of epoxy nanocomposites for different heating rates. Previous investigations showed that the clay particles decreases the onset, maximum and endset curing temperatures of BMIX and it is led to the interaction of olefinic bond present in the cyclic imide part of BMIX and the cloisite 15a nanoclay. Here, there is no characteristic change in the onset, maximum, and endset temperature of curing and there is only an abrupt change in the enthalpy of curing.…”

“…The band at 694 cm −1 corresponds to the –OCN< bending vibration of maleimide ring is also affected by the addition of cloisite 15a nanoclay. Previous investigations of cloisite 15a loaded bismaleimide (2,2‐bis[4‐(4‐maleimidophenoxy phenyl)]propane) blends indicated that the clay particles affects only the cyclic imide ring stretching of BMIX and in the thermally cured system the clay particles affects the cyclic imide ring and COC stretching (middle part) of the polyBMIX system. From this one can conclude that whatever be the bismaleimide, loading of cloisite 15a nanoclay particles affects the aromatic spacer part and maleimide rings present in the thermally cured bismaleimide systems.…”

“…The apparent activation energy for the polymerization of the blends and thermal degradation of the polymers were obtained using three model free kinetic [Flynn‐Wall‐Ozawa (FWO), Vyazovkin (VYZ), and Friedman (FRD)] methods. The added nanoclay particles influence the thermal curing behavior of BMIX and slightly decrease the degradation temperature of polyBMIX .…”