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 deg C with strain. These results are interpreted as an increase in phase mixing. After annealing at 100 deg C, the Tg decreases to a baseline value of -63 deg 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 deg C with strain. After annealing, the Tg value at the high strain level is about 4 deg 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 deg C. The Tg at the impact center after an annealing cycle is about 4 deg C greater than the baseline value, indicating somewhat less than full reversal of the mixing.