Recyclability of the bioplastic polyhydroxybutyrate‐co‐valerate (PHBV) was studied with multiple melt processing (five cycles), with their performances evaluated. A batch of PHBV was processed with a twin screw extrusion followed by injection molding. This operation was repeated five times and samples were collected from each cycle for characterization. For each cycle, the mechanical properties were characterized with tensile, flexural, and impact testing, along with dynamic mechanical analysis. The results showed that the mechanical properties are maintained for four cycles; but in the fifth cycle, there was slight decrease in the properties. Gel permeation chromatography studies revealed that the molecular weight of the polymer does not decrease drastically; however, a drop was observed after third, fourth, and fifth cycle (8.7% decrease after third cycle, 13.5% decrease after fourth cycle, and 16.6% decrease after fifth cycle). The differential scanning calorimeter showed that the glass transition and melting temperatures did not change upon reprocessing, but the degree of crystallinity was reduced as a consequence of melt processing. The thermal gravimetric analysis showed that the onset value of thermal decomposition decreased very slightly. It was observed by Fourier transform infrared spectroscopy that the chemical structure of PHBV was maintained without any side chain reaction during processing. Scanning electron microscopy studies from the fractured surfaces of Cycles 1 and 5 confirmed that the uniformity of PHBV surfaces was maintained after five cycles, coinciding with the mechanical tests. The density measurements revealed that there was no change in the density of PHBV. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

This work studies the effect of processing parameters on mechanical properties and material distribution of co-injected polymer blends within a complex mold shape. A partially bio-sourced blend of poly(butylene terephthalate) and poly(trimethylene terephthalate) PTT/PBT was used for the core, with a tough biodegradable blend of poly (butylene succinate) and poly (butylene adipate-co-terephthalate) PBS/PBAT for the skin. A 1 =2 factorial design of experiments is used to identify significant processing parameters from skin and core melt temperatures, injection speed and pressure, and mold temperature. Interactions between the processing effects are considered, and the resulting statistical data produced accurate linear models indicating that the co-injection of the two blends can be controlled. Impact strength of the normally brittle PTT/PBT blend is shown to increase significantly with co-injection and variations in core to skin volume ratios to have a determining role in the overall impact strength. Scanning electron microscope images were taken of co-injected tensile samples with the PBS/PBAT skin dissolved displaying variations of mechanical interlocking occurring between the two blends.

As tatistical experimental design method known as the Taguchi method was utilized to optimize the injection molding processes of poly(butylene terephthalate) (PBT) and poly(trimethylene terephthalate) (PTT) blends. Impact strength was taken as the optimized property. The significant parameters included mold temperature, injection pressure, holding pressure, injection time and holding temperature. Results of the Taguchi analysis gave mold temperatures as major influencing factor on the impact strength. The optimal processing conditions were determined through the Taguchi method giving an increase of 13.7 %i ni mpact strength for the blend. Further analysis was done to distinguish the blends dependency on temperature. Differential scanning calorimetry curves indicated the presence of recrystallization peaks that were dependent on the temperature profile the sample had received prior to testing. Polarized optical microscopy was used to show the different sphereulitic growth patterns under varying isothermal conditions. It was seen that at 90 8 Csphereulitic growth contained pockets of different sized spereulites. AFM imaging was also used to indicate differences in blended polymer morphology.