Biphasic systems linear crystalline polymers and their properties

5 Biphasic systems linear crystalline polymers and their properties 

Linear crystalline polymers always contain a fraction of amorphous material. For this reason they are usually considered biphasic systems. They show the typical transitions of amorphous polymers (glass and secondary) but also the common transitions of crystalline polymers (polymorphic, order-disorder, melting). Mechanical and physical properties of this category of polymers depend on morphology and amorphous/crystalline ratio, but also on the molecular mobility of the amorphous phase. 

29 Schematic representation of E-T curve for a generic crystalline polymer. 

In the proximity of T, there is a mechanical collapse owing to gradual crystallite fusion (Braun, 2005). 

The behaviour described in the previous section occurs in thermoplastic polymers, where the single molecules are bondedtogether by thermosensitive intermolecular attractive forces (van der Waals, dipole-dipole, hydrogen bonding). Crosslinked polymers (thermosetting polymers) show a different behaviour owing to primary bonds between main chains. These types of bonds are not thermosensitive and they limit viscous flows. The segments of chain, included between transversal bonds, are obstructed in their movement. 

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