Title

Chemical modification of the carbon/polymer interface in the MY720/DDS/carbon system

Date of Completion

January 1990

Keywords

Chemistry, Polymer|Engineering, Materials Science

Degree

Ph.D.

Abstract

Acidic functionality on the oxidized carbon surface modifies the course process of the tetrafunctional epoxy resin MY720 (largely tetra-gly-cidyldiaminodiphenylmethane, TGDDM) crosslinked with diaminodiphenylsulfone (DDS). In the early stages of the cure, the rate of consumption of TGDDM and DDS and the rate of the 1:1 adduct are increased, together with an increase in the production of ether functionality. These chemical changes are associated with an increase in exotherm, and increase in gel fraction, and preferential adsorption of the amine curing agent on the carbon surface. During the middle stages of the cure, the acidic carbon surface has a slight retarding effect on the cure; but, on the completion of the later stages of the cure, the effect of the carbon surface functionality, such as the total cure exotherm and the final glass transition temperature, diminishes. The acidic carbon surface effect on the uncatalyzed cure is attributed to the acceleration of the primary amine-epoxide reaction, which, in turn, facilitates the etherification reaction of TGDDM. Basic functionality on the carbon surface has much less effect on the initial cure.^ In the catalyzed MY720/DDS system by boron trifluride-ethylamine (BF$\sb3$EA), the cure reactions is affected in a complex fashion by the presence of the oxidized carbon surface. The acidic nature of the carbon surface activates the latent catalyst, leading to an increase in the rate of epoxy consumption, and an acceleration of epoxide-epoxide reaction. However, at high humidities, or very low resin contents, the increased affinity of the oxidized carbon surface for water can lead to destruction of the catalyst and retardation of the cure. The changes in cure kinetics necessitate an increase in the conversion of low temperature cure. The main chemical effect during the cure is an increase in the number of the epoxy-epoxy sequences in the crosslinked network leading to a longer vitrification time. The chemical effects of the carbon surface are greatest in the early stages of the cure, and are most noticeable at relatively low loading of polymer. ^