P. M. Remiro

Design of morphology in PMMA‐modified epoxy resins by control of curing conditions. I. Phase behavior

Rheokinetic and phase separation behavior of diglycidylether of bisphenol-A–4,4′-diaminodiphenyl methane epoxy mixtures, modified with a constant amount (15 wt %) of poly(methyl methacrylate) (PMMA), have been investigated. Stoichiometric epoxy/amine mixtures precured at 80°C several times presented various levels of miscibility. Differential scanning calorimetry (DSC) and dynamic mechanic thermal analysis were used for rheokinetic studies of curing and also for testing the thermal behavior of the fully cured mixtures. Phase separation, through curing, was simultaneously studied by transmission optical microscopy and DSC, showing an excellent correlation between the results obtained with both techniques.

Influence of curing conditions on the morphologies of a PMMA-modified epoxy matrix

The effect of curing conditions such as time and temperature on the morphology developed in a diglycidyl ether of bisphenol-A epoxy resin cured with diamino diphenyl methane, and modified with 15 wt% poly(methyl methacrylate), has been investigated. The reacting mixtures were precured at 80°C for a period of time ranging from 2 to 7 h, afterwards they were cured at 140°C and finally postcured at 200°C. The mixtures were opaque or transparent depending on the precuring time. Dynamic mechanical thermal analysis suggested that all mixtures were heterogeneous. However, phase separation occurred for all precuring times but to a lesser extent for samples precured for 5, 6 or 7 h than for those precured for shorter time intervals at 80°C. Two phases were clearly distinguished by atomic force microscopy, in all mixtures. The phase size was controlled, on one hand, by the time the phases had to grow, i.e. the interval between the cloud and gel points, and on the other hand, by the viscosity of the reacting mixture at the moment of phase separation.

The effect of crosslinking and miscibility on the thermal degradation of an uncured and an amine-cured epoxy resin blended with poly(ε-caprolactone)

The results of an investigation concerning the thermal behaviour of an uncured and an amine-cured diglycidyl ether of bisphenol-A (DGEBA) epoxy resin blended with poly(e-caprolactone) (PCL) are reported. The nature and extent of degradation were analysed by means of integral (TGA) and derivative (DTG) thermogravimetry. The decomposition kinetics of both uncured and cured blends were elucidated by the Coats and Redfern equation. Pure PCL has been seen to be more thermally stable than uncured DGEBA, but more unstable than cured DGEBA. For uncured blends, thermogravimetric curves clearly displayed more than one degradation step, while for the cured blends essentially a single weight loss step was observed. The cured blends showed enhanced thermal stability and char formation when compared to the corresponding uncured ones of identical DGEBA/PCL ratio. Besides, it has also been evidenced that although the uncured blends are miscible and the cured ones are immiscible, both systems exhibited negative deviations of the apparent activation energy from the additivity rule.

Miscibility and Crystallization of an Amine-Cured Epoxy Resin Modified with Crystalline Poly(ε-caprolactone)

Blends of diglicidyl ether of bisphenol-A, DGEBA, and poly(e-caprolactone), PCL, were cured with 4,4′-diaminodiphenyl sulfone, DDS, and analyzed by differential scanning calorimetry, DSC, in order to study the effect of curing on the miscibility and crystallization behavior of the crystallizable component. The spherulitic morphology of PCL was investigated by thermal microscopy. The results indicate a change in the miscibility state resulting from curing. Likewise, at all the temperatures studied a marked difference in crystallization behavior and morphology between the uncured and the cured systems was observed. These differences are attributed to the multiphase nature of the cured blends versus the homogeneous character of the uncured ones.

Properties of a Vinyl Ester Resin Modified with a Liquid Polymer

A vinyl ester (VE) resin was modified with different concentrations of a liquid polymer, polyoxypropylenetriamine (POPTA), in order to study the changes produced during curing and in its final properties. Fourier transform infrared spectroscopy (FTIR) measurements were made to obtain both the styrene and vinyl ester unsaturations conversions during the cure of the resin. The glass transition region was analysed by dynamic mechanical thermal analysis (DMTA), which showed the constancy of glass transition temperature with modifier content. The mechanical properties of the mixtures were also analysed and the results have been related to the flexural behaviour of the cured neat resin.