Studies on recyclability of polyhydroxybutyrate‐co‐valerate bioplastic: Multiple melt processing and performance evaluations

Abstract

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

Mechanical Recycling of Poly(3-Hydroxybutyrate-co-3-Hydroxyvalerate)/Polylactide Based Blends

“…The changes in M w and M n are in agreement with the enhancement of PHBV chain mobility, explaining the increasing of crystallinity (see later). The same phenomenon was reported by Zaverl et al [20], when the reprocessing cycles reduce the molecular weight of PHBV due to chain scissions. This finding is also consistent with rheological data indicating a large reduction in the complex viscosity of PHBV with increasing the number of reprocessing cycles [20].…”

“…The same phenomenon was reported by Zaverl et al [20], when the reprocessing cycles reduce the molecular weight of PHBV due to chain scissions. This finding is also consistent with rheological data indicating a large reduction in the complex viscosity of PHBV with increasing the number of reprocessing cycles [20]. Nevertheless, a smaller decrease is observed for M n and of PLA compared to those of PHBV.…”

“…This indicates that PHBV could be recycled without significant degradation in the thermomechanical properties, as reported by Zaverl and al. [20]. For PLA, the storage modulus after the first cycle presents below PLA T g (60°C) a constant value equal to 2,500 MPa which decreases by about 20 % after six repeated reprocessing cycles (Fig.…”

“…Polymer recycling is one of the most important subjects of the current industry, besides producing biodegradable polymers, to increase the proportion of environment friendly materials. In the United States alone, recycling is done for more than 2 billion pounds of polymers [20]. However, the reprocessing and the recycling of polymers induce adverse effects on the final properties due to the degradation caused by mechanical shear forces coupled to thermal effects [21].…”

“…Zaverl and al. [20] studied the recyclability of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) with multiple melt processing (five cycles), using a twin screw extrusion followed by injection molding. The authors showed that the molecular weight of the polymer does not drastically decrease; however, a drop was observed after the third cycle, and set value of thermal decomposition decreased very slightly.…”