Nanoscale fibrillar crystals of PET from dilute quiescent solution

The crystallization behavior of poly(ethylene terephthalate) (PET, IV∼2 dL/g) from solution in biphenyl-diphenyl ether mixed solvent is examined. Reversible gelation of the polymer solution is observed during cooling of the solutions. Light scattering and DSC analysis are used to follow the heating and cooling processes, thus determining the crystallization temperature and the melting point, which are found to be nearly independent of the polymer concentration (0.25-5%). High degree of crystallization (>50%) is observed in the PET crystallized from the solution at 170 °C. Morphological characteristics of the crystals obtained after solvent removal are determined by WAXD, FTIR, SEM and TEM examination. The crystallization of PET into unique high aspect ratio fibrillar morphology during cooling of the solutions explains their gelation even at low PET concentration. Thin films made from the thus obtained PET could be drawn five times at 250 °C, resulting in only moderate values of modulus and strength.