Crystallinity of pure and nucleated PET

Pure and Al(OH)3-containing PET films were prepared, quenched, and subsequently annealed under identical conditions. The level of crystallinity of the films was determined by three methods: density measurements, X-ray crystallinity determination, and measurements by IR of the relative concentration of trans OCCO conformation in the polymer. For pure PET it was found that the percentage crystallinity measured in annealed samples by X-ray and IR is about the same. The density measurements agree with these techniques only when the amorphous density is taken as 1.348 g/cm3. In the case of quenched pure PET, a 7% correction to the concentration of trans conformation must be introduced (in agreement with recent literature) to fit the IR results to the X-ray and density data. Annealed PET containing Al(OH)3 crystallizes to about the same level as annealed pure PET. The agreement between X-ray and IR data is reasonably good. In the quenched PET/Al(OH)3 there exists a higher level of trans conformation (enhanced order), probably resulting from adsorption of relatively extended PET chain segments on the surface of the hydroxide particles. These extended units may possibly serve as nucleation sites for PET crystallization upon cooling from the melt.