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The glass-transition temperature T g of a material characterizes the range of temperatures over which this glass transition ... Polypropylene (PP atactic) −20 −4 [32]
In case of atactic polypropylene, the methyl group (-CH 3) is randomly aligned, alternating (alternating) for syndiotactic polypropylene and evenly for isotactic polypropylene. This has an impact on the crystallinity (amorphous or semi-crystalline) and the thermal properties (expressed as glass transition point T g and melting point T m ).
The Flory–Fox equation relates the number-average molecular weight, M n, to the glass transition temperature, T g, as shown below: =, where T g,∞ is the maximum glass transition temperature that can be achieved at a theoretical infinite molecular weight and K is an empirical parameter that is related to the free volume present in the polymer sample.
Crystal growth is achieved by the further addition of folded polymer chain segments and only occurs for temperatures below the melting temperature T m and above the glass transition temperature T g. Higher temperatures destroy the molecular arrangement and below the glass transition temperature, the movement of molecular chains is frozen. [6]
The onset temperature of the transition zone, moving from glassy to rubbery, is known as the glass transition temperature, or T g. In the 1940s Andrews and Tobolsky [ 6 ] showed that there was a simple relationship between temperature and time for the mechanical response of a polymer.
When the supercooled liquid is further cooled, it becomes a glass. [1] The temperature at which a polymer becomes a glass by fast cooling is called the glass transition temperature T g. At this temperature, viscosity reaches up to 10 13 poise depending upon cooling-rate.
The switching segments, on the other hand, are the segments with the ability to soften past a certain transition temperature (T trans) and are responsible for the temporary shape. In some cases this is the glass transition temperature (T g) and others the melting temperature (T m).
Glass-transition temperature - An increase in chain length often leads to an increase in the glass-transition temperature, T g. The increased chain length causes the chains to become more entangled at a given temperature. Therefore, the temperature does not need to be as low for the material to act as a solid.