Thermal characterization of polyesters blends.
Rosario Bretas, Marcelo Farah
E. S.
Brazil

Keywords: crystallization kinetics, Poliesters, blends

---

Today, a common and economical way to develop new polymeric materials is to blend them in order to obtain synergistic properties. Polyesters are known to have excellent mechanical properties; blending two polyesters can improve these properties. However, they are extremely dependent of the crystallization kinetics and miscibility. In this work, three polyesters, polybutylene terephthalate, PBT, polytrimethylene terephthalate, PTT and polyethylene terephthalate, PET were chosen to develop binary blends, in a weight ratio of 50/50. The blends, PET/PTT, PTT/PBT and PET/PBT were prepared by twin screw extrusion using a Werner & Pflediener ZSK30 twin extruder, with a low mixture profile. The extruded pellets were dried at 150 C for 5 h. Differential scanning calorimetry measurements were done in the blends in a TA Instruments Q100 to study their crystallization kinetics. The samples were heated at 20 C/min to 270 C, kept at this last temperature during 5 min and cooled at 50 C/min to their corresponding crystallization temperatures, Tc. Isothermal crystallization was then monitored. The blends PET/PTT and PET/PBT showed double crystallization peaks up to 207 C. Avrami analyses were done in all the isothermal runs, after deconvolution. For the homopolymers, n was found between 2.5-3.5. It was found, in the blend PET/PBT, that PBT had a lower crystallization rate than the homopolymer while the PET had a higher crystallization rate than the homopolymer. In the blend PET/PTT, both polymers had lower crystallization rates than the homopolymers.