Semicrystalline polymers physical aging

Figure 3.5 shows the temperature variation of H for the four above mentioned polymers, namely PMMA, PVAc, PET and PEEK. In the case of the two amorphous polymers (PMMA and PVAc) H decreases with T and the Tg value can he clearly identified with a hend in the 7/ vs T plot. However, the two semicrystalline materials quenched into the amorphous state (PET and PEEK) show an apparent maximum just before the glass transition takes place. Also, in the case of PET tested immediately after quenching it is observed that H increases with T above room temperature. These phenomena will be discussed in Section 3.3 in the light of the physical ageing undergone by the above polymers. It is seen that H follows an exponential decrease as a function of T given by (see eq. (2.5))... 

Struik, L. C. E., The mechanical and physical aging of semicrystalline polymers 1, Polymer, 28, 1521-1533 (1987a). 

In amorphous polymers the physical aging takes place atTp -F 30°C erases the glassy structure. In semicrystalline polymers,... 

The effects of structural recovery are not limited to fully amorphous materials. In semicrystalline polymers, the amorphous regions physically age in a similar manner to the process in fully amorphous materials. Obviously, however, the change in properties will be only a fraction of that found in fully amorphous materials since the amount of amorphous material makes up only a fraction of the... 

Similar to many semicrystalline polymers, PLA exhibits both Tg and 7j . The Tg of PLA can range from 35 to 60°C depending on molecular weight, the presence of plasticizers, physical aging, polymer architecture, and degree of crystallinity [14]. Above Tg PLA is rubbery, while below Tg it becomes a glass, but it is still able to creep until it is cooled to its 3 transition temperature at approximately —45°C, below which it behaves like a brittle polymer [15]. In applications where mechanical properties are important, such as packaging... 

Struik C. E. Leen. The mechanical behavior and physical ageing of semicrystalline polymers 2. Polymer. 28 no. 9 (1987) 1534-1542. 

The effects of structmal recovery are not limited to fully amorphous materials. In semicrystalline polymers, the amorphous regions physically age in a similar... 

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