UNIPLANAR DEFORMATION OF ISOTACTIC POLYPROPYLENE .1. DRAW CHARACTERISTICS

Isotactic polypropylene (iPP) (M(w) = 2.9 x 10(5)) has been deformed in uniaxial compression by forging at several constant temperatures from 20 to 140-degrees-C. A relation between draw efficiency and the formation of the smectic phase during deformation has been examined over a wide range of compression draw ratios (approximately 50). At a forging temperature below the smectic-phase stability limit temperature (T(s)), the efficiency of draw, parallel to the uniplanar direction, was high (approximately 97%) and independent of the compression ratio, pressure and draw temperature (T(d)). The relation between the compression yield energy (E(y)) and T(d) has also been examined. E(y), the area under the compressive stress strain curve up to the yield point, as a function of T(d) was found to consist of two linear components of different slope. These two linear relations arose from the glassy and crystalline phases. The intercept temperature (T(d) at zero yield energy for the glassy phase has been evaluated to understand compression drawability. Above T(i), the achievable compression ratio (CR) increased steadily with T(d). At a given T(d), the CR increased with increasing applied pressure, and this tendency was more prominent above T(i). The T(i) moved higher as the compression rate was increased.