Thermally stimulated current (TSC) was used to study molecular relaxations in polyethylene terephthalate (PET) bottles. Unstretched PET film, which was used as a model for the bottle preform, exhibited two peaks at 77 and 90oC that correspond to the a and r relaxation processes, respectively. The bottles exhibited only the r relaxation, which is located within the temperature range for blow molding PET bottles. The a peak is associated with the main glass transition temperature (Tg) and the r peak may be associated with a second Tg. The second Tg is attributed to a 'constrained state', which shows dipolar behavior. Heat-shrinkage behavior was examined at 90 oC. The maximum TSC (Im) of the r peak decreased with increasing heat set temperature, and with decreasing shrinkage. Bottles blown at 113 oC showed a lower Im and shrinkage than those blown at 103 oC for equivalent heat set temperatures. The higher blowing temperature allowed a higher stretch speed that produced higher crystallinity bottles with self-heat generation during rapid deformation. A relationship between the shrinkage mechanism and the dipole relaxation was proposed.
Keywords: TSC; PET bottle; r peak; relaxation time; blow condition; shrinkage.
Rahmat Satoto
Keywords: TSC; PET bottle; r peak; relaxation time; blow condition; shrinkage.
Rahmat Satoto
