THE EFFECT OF MECHANICAL DEFORMATION ON THE GLASS TRANSITION TEMPERATURE OF POLYUREA

The glass transition temperature (Tg) of a polyurea (Versathane P1000) is shown to be a function of mechanical strain and strain rate. For low strain rate (10−1/s), tensile testing, Tg values increase from −58 to −52 °C with strain. These results are interpreted as an increase in phase mixing. After annealing at 100 °C, the Tg decreases to a baseline value of −63 °C as an indication that the strain induced phase mixing is reversible. For one dimensional plate impact experiments, the Tg increases from −58 to −54 °C with strain. After annealing, the Tg value at the high strain level is about 4 °C higher than the baseline value. The impact may have caused some permanent change in the morphology. For a conical‐shaped steel impact experiment, Tg values also increase with strain from −58 to −50 °C. The Tg at the impact center after an annealing cycle is about 4 °C greater than the baseline value, indicating somewhat less than full reversal of the mixing.