Variation of Glass Temperature With Pressure in Polypropylene.

Area of Science:

• Polymer Science
• Thermodynamics
• Materials Science

Background:

• The glass transition is a critical phenomenon in amorphous polymers, affecting their mechanical and thermal properties.
• Understanding how external factors like pressure influence the glass transition is crucial for material design and application.
• Previous studies have explored the glass transition of polypropylene, but its pressure dependence requires further thermodynamic investigation.

Purpose of the Study:

• To experimentally determine the variation of polypropylene's glass transition temperature with pressure (dT/dP).
• To investigate the thermodynamic principles governing the glass transition in polypropylene.
• To correlate experimental findings with established thermodynamic theories.

Main Methods:

• Measurement of polypropylene's specific volume as a function of temperature at various applied pressures.
• Calculation of the change in the coefficient of expansion (Δα) and specific heat (ΔC) at the glass transition temperature.
• Determination of the change in compressibility (Δβ) from the experimental data.

Main Results:

• The study found that the glass transition temperature of polypropylene increases with pressure (dT/dP).
• The experimentally determined dT/dP was found to be approximately equal to ΔC/Δα within experimental error.
• Calculated Δβ/Δα also showed equality with dT/dP, though this was shown to be an artifact of the experimental method.

Conclusions:

• Thermodynamic principles can be applied to the glass transition phenomenon in polypropylene.
• The observed relationship between dT/dP, ΔC/Δα, and Δβ/Δα provides insights into the thermodynamic nature of the glass transition.
• While the equality of dT/dP with Δβ/Δα holds, it is primarily a consequence of the experimental approach rather than solely a thermodynamic imperative.