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 |
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Authors: | P Poornima Vijayan Debora Puglia P Jyotishkumar Jose M Kenny and Sabu Thomas |
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Affiliation: | (1) School of Chemical Sciences, Mahatma Gandhi University, Priyadarshini Hills P.O., Kottayam, Kerala, India;(2) Department of Civil and Environmental Engineering, Materials Engineering Centre, University of Perugia, Strada di Pentima 4, 05100 Terni, Italy;(3) Faculty of Applied Sciences, Universiti Teknologi MARA, 40450 Shah Alam, Selongor, Malaysia;(4) Center of Excellence for Polymer Materials and Technologies, Tehnoloski park 24, 1000 Ljubljana, Slovenia; |
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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. |
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