Development of PBT/recycled PET binary blends

In this thesis study, twin-screw extruder (TSE) was used for producing PBT/recycled PET blends. Injection molding was used to prepare testing specimens. Raw materials and extruded pellets were dried in an oven overnight to avoid further degradation in the presence of moisture during extrusion and injection molding processes. A commercial chain extender with Joncryl ADR 4468 ® trade name was used in the blends. Joncryl is a multi-functional styrene acrylic oligomer with epoxy functional groups. First of all, 0.05, 0.25, 0.40 and 0.80 wt% of Joncryl was physically mixed with recycled PET flakes and extruded to obtain extended recycled PET. During blending, 25, 50 and 75 wt% of recycled PET flakes was physically mixed with PBT and extruded. Addition of Joncryl into the blends was carried out via two different extrusion method. In the first method, which was named as all together method, PBT, recycled PET flakes and Joncryl were physically mixed and extruded all together to the pellets from a hopper. In the second method, which was named as premixing method, recycled PET flakes were extended with Joncryl in extrusion previously. Extended PET pellets were dried in an oven overnight, and then physically mixed with PBT at certain ratios and extruded from a hopper to obtain final blends. In this thesis study, the effect of vaiorus concentrations of recycled PET on PBT/recycled PET binary blends were investigated. Furthermore, the effect of different blending methods on the final blend performances were examined. Various concentrations of chain extender additive was used in both production methods. As an example, PBT/recycled PET were blended and extruded at 75:25 ratios. Addition of chain extender is carried out by using two different processing methods, as mentioned above. In the all together method, 0.2 wt% of chaine extender was physically blended with around 75 wt% of PBT and 25 wt% of recycled PET flakes and extruded all together from a hopper. In the premixing method, recycled PET flakes were blended with 0.8 wt% Joncryl and extruded from a hopper. After drying, 25 wt% of this masterbatch was blended with 75 wt% of PBT and extruded from a hopper. The final Joncryl content was adjusted to be 0.2 wt% as in the first method. Only in 50:50 and 25:75 PBT/recycled PET blends, effect of different chain extender concentrations on the blend properties were examined. To achieve the final 0.2 wt% content of chain extender also in 50:50 and 25:75 PBT/r-PET blends, extended recycled PET with 0.4 and 0.25 wt% of chaine extender was used, respectively. Only in 50:50 and 25:75 PBT/recycled PET blends, effect of different final Joncryl concentrations on the blend properties were examined. The extended r-PET with 0.8 wt% of chain extender mixed with PBT at the ratios of 25, 50 and 75 wt%. Effect of this premix concentration on the blend properties were also investigated. Thermal degradation, crystallization behavior, viscoelastic properties, tensile and impact properties of the blends were investigated. Thermal properties and crystallization behavior of the blends were investigated by using thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). Dynamic mechanical analysis (DMA) and melt flow index (MFI) was used for investigation of viscoelastic properties of the blends. Tensile strength and modulus was obtained from tensile testing. Impact strengths of the blends were obtained from Izod notched impact testing. In thermal analysis, nucleation point effect of chain extender were observed in branched r-PET molecules. All blends either with chain extender or not showed single glass transition temperature during first and second heating cycled in DSC, which could be attributed to miscibility at amorphous state. Separate crystal melting temperatures in first heating cycle turned into a single peak with some shoulders in second heating, consequently miscibility could be observed depending on cooling rate. At constant chain extender concentration, blends prepared with all-together mixing method showed higher crystallinity. In DMA analysis, blends prepared with pre-mixing method showed higher storage modulus. Complex viscosity also supported the same behavior. Damping values from tan delta graphs was relevant with impact resistance of the materials. Increasing amount of chain extender decreased melt flow rate in MFI analysis, consequently increased melt strength by increasing molecular weight. All blends prepared by all together mixing method showed lower melt flow rate. E modulus and tensile strength of all blends was in the same range and was not affected from the compositions, chain extender concentration or processing strategies.