Elastomer-modified epoxy curing effects

Oh B S, Kim H S and Ma P (1996) The effect of rubber on stress-whitening in DDS-cured epoxies, in Toughened Plastics IT. Novel approaches in science and engineering, Advances in Chemistry Series 252 (Eds. Riew CK and Kinloch AJ) American Chemical Society, Washington, DC, pp.111-118. Lee H and Neville K (1967) Handbook of epoxy resins, McGraw-Hill, New York, pp. 17-11. Pearson R A and Yee A F (1989) Toughening mechanisms in elastomer-modified epoxies, J Mater Sci 24 2571-2580. 

To assess the effect of elastomer degradation on composite performance, additional composites were fabricated with the same 121°C cure epoxy without any addition of the elastomer (211. The expansion behavior of the modified epoxy composite was similar to the toughened material. For electron doses less than 10 rads the CTE of the toughened and untoughened composites were essentially the same which suggests that the epoxy matrix and not the elastomeric component controls the thermal expansion behavior. 

Consequent to documentation surrounding methods of employing reactive nitrile elastomers to modify epoxy resins is a growing body of literature which serves to characterize and elucidate these systems. Such topics as morphology in the cured and uncured state, transitions from toughening to flexlbilization, viscoelastic effects, equilibrium physical properties and phase structure are available to the investigator (12-17). 

The carboxyl terminated polybutadiene (C-3000) is about equally effective to CTBN in heat distortion temperature and impact but considerably less effective in strength. From the haze data (the percent haze of ERL-4221 modified with 10 phr of CTBN and C-3000 were 17 and 85% respectively) it is quite clear that this elastomer (C-3000) is highly incompatible with the epoxy-hardener system in the cured state. A 2000 molecular weight polybutadiene elastomer, containing no carboxyl groups, was completely incompatible with the epoxy system and segregated in the cured state. 

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