Recycling and rheology of poly(lactic acid) (PLA) to make foams using supercritical fluid
Biodegradable plastics are thought to be the possible directions in managing plastic pollutions. Unfortunately, they are not recycled in most countries since they are designed to decompose even though recycling is a more pragmatic method than landfill or incineration. Thus, it is more constructive t...
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Veröffentlicht in: | Physics of fluids (1994) 2021-06, Vol.33 (6) |
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Format: | Artikel |
Sprache: | eng |
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Zusammenfassung: | Biodegradable plastics are thought to be the possible directions in managing plastic
pollutions. Unfortunately, they are not recycled in most countries since they are designed
to decompose even though recycling is a more pragmatic method than landfill or
incineration. Thus, it is more constructive to develop methods to recycle biodegradable
plastics or to develop biodegradable yet recyclable plastics. In this study, we used
cutlery with a composite of poly(lactic acid) (PLA) and talc. The possibility to recycle
it to make foams was studied even though it will have lowered mechanical strength from the
recycling process as it is less significant for this product. Tensile properties of solid
PLA and foams showed no significant decrease in the strength up to three processes of
compression molding and foaming. We performed shear rheometry to determine the thermal
stability and dependences of the complex viscosity on frequency and temperature. The
magnitude of the complex viscosity dramatically increased with decreasing frequency and
such an upturn increased with temperature, but time-temperature superposition was valid at
high temperatures. The extensional rheometry showed no strain hardening, but physical
foaming using supercritical carbon dioxide (CO2) could still occur, and the
operating conditions to obtain various foamed structures were determined. We also compared
the effects of one-directional against three-dimensional expansion. Overall, the
concentration of CO2 in PLA and crystallinity of the foams are the two key
variables to describe the bulkiness of foams. Surprisingly, the lower the CO2
concentration, the bulkier the foams at any sorption temperature and pressure. |
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ISSN: | 1070-6631 1089-7666 |
DOI: | 10.1063/5.0050649 |