Monoj Pramanik

Cure kinetics of several epoxy–amine systems at ambient and high temperatures

Epoxy-crosslinker curing reactions and the extent of the reactions are critical parameters that influence the performance of each epoxy system. The curing of an epoxy prepolymer with an amine functional group may be accompanied by side reactions such as etherification. Commercial epoxy prepolymers were cured with different commercial amines at ambient as well as at elevated temperatures. Singularly, only epoxy–amine reactions were observed with diglycidyl ether of bisphenol-A (DGEBA)-based epoxides in our research even upon post-curing at 200°C. Etherification side reaction was found to occur at a cure temperature of 200°C in epoxides possessing a tertiary amine moiety. A combined goal of our research was to understand the effect of tougheners on the cure of epoxy–amine blend. To discern the effect of tougheners on the cure, core–shell rubber (CSR) particles were incorporated into the epoxy–amine blend. It was observed that CSR particles did not restrict the system from proceeding to complete reaction of epoxy moieties. Besides, CSR particles were found to accelerate the epoxy-amine reaction at a lower level of epoxy conversion. The lower activation energy of epoxy–amine reaction of CSR incorporated system compared to control supported the catalytic effect of CSR particles on the epoxy-amine reaction of epoxy prepolymer and amine blends.

Molecular weight effects on the mechanical properties of novel epoxy thermoplastics

A series of epoxy thermoplastics (ETPs) with varying molecular weights were synthesized from a difunctional diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin and an aromatic secondary diamine. The materials possessed glass transition temperatures varying between 73.61 and 85.36°C. The ETP series was characterized for fracture toughness, flexural, and compression properties. In general, fracture properties increased with increasing molecular weight and yet were consistently shown to decrease when higher molecular weight values were the result of increased branching. Flexural ultimate strength and strain-at-break increased with increasing molecular weight while flexural modulus decreased to a plateau. Compression properties were relatively unaffected by changes in molecular weight over the range of materials synthesized.

A rapid quantitative protocol for measuring carbon nanotube degree of dispersion in a waterborne epoxy–amine matrix material

The available literature makes it very clear that accurate measurements of carbon nanotube dispersion quality are very complicated and the typical characterization is neither simple nor reliable. Most methods to quantify carbon nanotube dispersion reported in the literature require investigator-chosen assumptions or software interpretations that are impractical at best and misleading at worst for facile application. Herein, we report on the use of visible light absorption-based method(s) and validate that these were quantitative for discerning dispersibility differences for MWCNTs with three distinct surface chemistry modifications and concentration levels blended with polymeric materials. Ultimately, the dispersion quality was quantified via the trendline slope of the thickness-normalized absorbance values as a function of MWCNT concentration. Extremely poor dispersions were represented by statistically insignificant slope trendlines. Our data revealed that hydroxyl surface modification increased MWCNT dispersibility by a factor of ~2.8 and ~2.6 compared to the as-received MWCNT formulations via the absorption and the blackness methods, respectively. These results support and quantifiably validate that simple optical blackness values directly measured the degree of dispersion for MWCNTs in coatings applied to substrates, and our data support that this is a simple and effective quality control metric.