Effect of nanoclay and carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) rubber on the reaction induced phase separation and cure kinetics of an epoxy/cyclic anhydride system

Abstract

The effects of nano clay, carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) liquid rubber and the combination of both on the cure kinetics of diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin/nadic methyl anhydride were studied. Cure kinetics studies were carried out by performing dynamic and isothermal differential scanning calorimetric (DSC) experiments. The dynamic DSC experiments were carried out at four different heating rates. Dynamic kinetic modeling was performed using Kissinger and Ozawa approaches. Since these methods are based exclusively on the maximum rate of cure, which occurs approximately at the beginning of the cure reaction, the activation energy calculated using these methods is valid only for the initial stage of the cure. The clay (3 phr) filled epoxy system has an activation energy 24 % lower than the unfilled system. The role of the surfactant chemistry on the initial stage of the cure reaction was also studied. A plausible reaction mechanism which involves the effect of the nanoclay surfactant as an accelerator of the cure reaction was proposed. The phase separated CTBN rubber hindered the cure reaction and has 3 % higher activation energy for epoxy/CTBN system than the unfilled system. In the ternary epoxy/3 phr clay/15 phr CTBN system, the accelerating effect of clay on cure was highlighted. The cure activation observed in the presence of clay overshadows the hindrance created by the phase separated CTBN. Isothermal DSC scans were carried out at five different temperatures. The experimental datas showed an autocatalytic behavior of the reaction, and the isothermal modeling was carried out by Kamal autocatalytic model. The results showed a very good agreement within the whole conversion range for the unfilled and all the filled systems. The evolution of the morphology and phase separation was also studied using optical and scanning electron microscope. Faster cure reaction resulted in smaller phase-separated CTBN particles in epoxy/clay/CTBN ternary system as compared with those observed in epoxy/ CTBN binary blend.

Liquid-rubber-modified epoxy/clay nanocomposites: effect of dispersion methods on morphology and ultimate properties

“…The lowest domain diameter was shown by epoxy/clay/CTBN nanocomposite prepared by sonication technique. The catalytic action of the nanoclay as confirmed from our previously reported calorimetric [31] and rheological [26] studies provides early network formation and faster attainment of gel point. The proposed reason behind the catalytic activity of nanoclay is that the trace amount of water in the curing system undergoes autoprotolysis at elevated temperatures and thus dissociated OH anions thermally cleave the N-C bond of the trimethyl stearyl ammonium.…”

“…Due to the fast gelation in epoxy/clay/CTBN system, the phase-separated CTBN domains do not get much time to grow and coalesce and therefore result in smaller CTBN domains. Moreover, the clay platelet which surrounds the rubber domains does not allow further coalescence [31]. The substantial change in size and shape of the phase-separated CTBN particles was evident from the AFM images (Fig.…”

Cellulose nanocrystal reinforced liquid natural rubber toughened unsaturated polyester: Effects of filler content and surface treatment on its morphological, thermal, mechanical, and viscoelastic properties

“…The incorporation of inorganic nanoparticles has indeed been shown to simultaneously increase the toughness, Young's modulus, strength, and T g of polyester [5][6][7][8][9][10], although in some cases, the T g of the nanocomposite was decreased [4]. The resulting hybrid polyester nanocomposites have found a wide range of applications, notably as joint adhesives for which toughness is a crucial property [11].…”

Curing kinetics of nanostructured epoxy blends toughened with epoxidized carboxyl-terminated liquid rubber

“…The addition of fillers to the epoxy resin systems will alter their morphology and curing kinetics [23][24][25][26][27]. Vijayan et al [26] have investigated the effects of nanoclay and carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) rubber on the reaction induced phase separation and curing kinetics of an epoxy/cyclic anhydride system using dynamic and isothermal differential scanning calorimetry (DSC), and found that nanoclay surfactant accelerated the cure reaction, whereas the phase-separated CTBN hindered the cure reaction.…”

“…Vijayan et al [26] have investigated the effects of nanoclay and carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) rubber on the reaction induced phase separation and curing kinetics of an epoxy/cyclic anhydride system using dynamic and isothermal differential scanning calorimetry (DSC), and found that nanoclay surfactant accelerated the cure reaction, whereas the phase-separated CTBN hindered the cure reaction. In another study investigating the effects of the epoxidation degree and content of epoxidized polystyrene-block-polybutadiene star copolymer on the final properties and curing behavior of nanostructured thermosetting system, Serrano et al have shown that the final morphology was influenced by the competitive kinetics between phase separation and polymerization [28].…”