PREPREG AGING IN RELATION TO TACK

Thermoanalytical measurements and tack tests were both performed using a commercially available carbon fiber/epoxy prepreg system (Hercules 3501-6) to examine changes caused by aging as they affect handling and processability of thermosetting matrix-based composites. Combining these techniques, a relationship between prepreg bulk and surface characteristics in relation to aging was investigated. Isothermal kinetic studies at low temperatures showed maximum conversions (alpha(m)) that increased with increasing cure temperatures. In addition, a linear relationship between glass transition temperatures (T(g)) and conversions (alpha) was observed regardless of aging (or cure) temperatures. Energy of separation of prepreg stacks, which may be viewed as a measure of prepreg tack, showed a maximum value at a specific temperature. The maximum energy of separation was observed in the temperature range of 20-25-degrees-C above the glass transition temperature for a given sample. However, the maximum energy of separation values decreased with increasing aging times (or conversions), implying that prepreg tack was a viscoelastic property rather than a viscous property of the resin matrix in the prepreg.