Miscibility Studies and Phase Diagrams

The polyethylenes with higher functionality were soluble in epoxy resin and required lower temperamre and time for forming homogeneous blend systems. The miscibility of the polymers was dependent on the type of epoxy resin also. Cycloaliphatic epoxy resin showed more miscibility with the polymers compared to DGEBA resin and phase separation occurred in these blend systems as a result of crystallization of PE. Upper critical solution temperature (UCST) behavior was 

The presence of hardener hexahydrophthalic anhydride (HHPA) in the blends completely changed the miscibility behavior of the blends. All the blends became heterogeneous upon adding HHPA. The phase behavior of the ternary blends was evident from the phase diagrams given in Fig. 21.2. 

Comparing the phase diagrams of AC 540 modified DGEBA epoxy resin and hardener HHPA showed that the oxidized homopolymer with an acid functionality of 2.0 (AC 5120) was more miscible in epoxy resin and the RVP grafted AC 5120 had comparable miscibility as that of AC 5120. Similarly, ethylene acrylic acid-vinyl acetate terpolymer (AC 1450) was less miscible in epoxy resin compared to AC 5120 due to less chemical interaction with epoxy resin. Thus, the miscibility of the blends was reduced by the addition of HHPA to various blend systems. 

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