In contrast to PP and PE, the DSC results show that the recycling of blow molded PET bottles (by extrusion-pelletizing and then injection-molding into tensile specimens), if subjected to thermal cycles of the processes, has a positive effect on crystallization and in turn on mechanical properties (Fann et al., 1996). Avila (2001) and Mancini and Zanin (1999) reported similar results. The reason is that the secondary bonds between chains are attacked when subjected to thermal cycling rather than the chain length of recycled PET decreasing, retaining a less amorphous (more crystalline) structure.