Structural Analysis of Polyethylene Terephthalates with Different Crystallinity using Reactive Pyrolysis GC-TOFMS and NMR
MSTips No. 400
Polyethylene terephthalate (PET) is a thermoplastic polyester that is obtained by polycondensation of ethylene glycol and terephthalic acid and has excellent transparency, toughness, rigidity, and heat resistance (Figure 1). PET can be roughly divided into two types, crystalline PET (C-PET) and amorphous PET (A-PET), depending on the processing method. C-PET has the characteristics of high strength and heat resistance due to the regular arrangement of the molecules in the crystallized part, which increases the density. A-PET is characterized by high impact strength and easy bending. However, the amorphous portion of A-PET slowly crystallizes due to long-term use and heat history, causing changes over time. Changes in density generate internal stress that cuts polymer chains, which can lead to deterioration in flexibility, impact resistance, strength, etc. Therefore, a polymer was devised in which about 30-40% of the ethylene glycol in PET was replaced with cyclohexanedimethanol, and this is called glycol-modified PET (G-PET, PETG) (Figure 2). G-PET is treated as an amorphous resin because the polymer does not crystallize even during the molding process.
In this application note, two types of commercially available PET resins are analyzed by reactive pyrolysis GC-TOFMS and NMR, and the results of analysis to determine whether they are PET or G-PET are reported.