Pressure Dependence of the Glass Transition in Atactic and Isotactic Polypropylene

Abstract

The segmental relaxation process in atactic and isotactic polypropylene (PP) is studied over the temperature (258-323 K) and pressure (0-300 MPa) ranges by means of dielectric spectroscopy. The combined dielectric and equation of state data provide a means of disentangling the relative influence of thermal energy and density on the glass "transition". Thermal energy is the controlling parameter of the segmental dynamics in both atactic and isotactic PP as inferred by the values of the ratio of the apparent activation energies at constant pressure and volume (0.72 and 0.63, respectively). Despite the common origin of the segmental dynamics, the relaxation times of the isotactic polymer exhibit higher pressure sensitivity due to the increasing crystallinity on pressurization.

Pressure influence on crystallization kinetics during injection molding

“…The T m pressure dependence law obtained is close to that described by Fulchiron et al (2001) who used a dilatometry measurement method and to that described by Mezghani and Phillips (1998) who used the Hoffmann-Weeks method. The T g pressure dependence law obtained is lower to that described by Gitsas and Floudas (2008), for the same polymer (iPP). The obtained results show considerable pressure influence on the crystallization rate and then on the cooling duration of molded parts.…”

“…Fig. 13) pressure dependence is lower with respect to the value given by Gitsas and Floudas (2008). In Fig.…”

Acoustic properties of Kel F-800 copolymer up to 85 GPa

“…This can be seen as plausible by noting the empirical dependence of γ on the glass transition temperature T g as outlined by Warfield et al, in which large values of T g correspond to values of γ close to 1, 21 and considering that T g tends to grow dramatically larger with even small increases in pressure. [22][23][24] A plot of 1/υ 2 B vs. pressure is shown in Fig. 5.…”

Complete relaxation map of polypropylene: radiation-induced modification as dielectric probe

“…The origins of these relaxations have been studied in the past, mainly by mechanical measurements. However, a few dielectric studies are also available [4,[9][10][11]. Although some detailed molecular assignments are still open to debate, the reality of the basic relaxation processes is clear.…”