Abstract
The accumulation of marine debris in the oceans has been escalating. There is an urgent need to develop new technologies that efficiently record and transmit ocean data without contributing to ocean pollution. In this study, the behaviour of Polylactic Acid (PLA) and Polylactic Acid-Polyhydroxyalkanoate (PLA-PHA) in marine environments was analysed in order to assess biodegradability in marine applications. 3D Printed samples were submerged completely in seawater and cyclically in a salt spray chamber. Their change in mechanical properties was evaluated by conducting uniaxial tension tests after submersion periods of up to 45 days and failure regions were observed in microscope. Contrarily to PLA’s behaviour, PLA-PHA’s samples suffered embrittlement and registered losses in elongation at break of around 10-18%. The alignment of salt crystals and other impurities in the failure regions suggests that embrittlement could be related with environmental stress cracking resulting from the penetration of those impurities into the polymer. Such inclusions originate residual stresses which lead to a faster and more brittle failure. Embrittlement could also be related to an increase in crystallinity caused by chain scission of amorphous regions by means of chemical degradation. Further evaluation of changes in molecular weight should be conducted to confirm the latter.
Highlights
The behaviour of Polylactic Acid (PLA) and Polylactic Acid-Polyhydroxyalkanoate (PLA-PHA) in marine environments was analysed in order to assess biodegradability in marine applications. 3D Printed samples were submerged completely in seawater and cyclically in a salt spray chamber
We report the changes in mechanical properties and failure behaviour of 3D printed PLA and PLA-PHA samples when exposed to two different marine environments: complete submersion in seawater and cyclic submersion in a salt spray chamber for up to 45 days and 15 wet/dry cycles, respectively
The change in behaviour was sharper for sample submitted to the salt spray chamber than for the one submerged in seawater: PLA-PHA80 showed great increases in the Ultimate Tensile Strength (UTS) of around 6 MPa during the first 10 salinity cycles, accounting for 40% of the initial value, and PLA-PHA40 saw a decrease of 18% in elongation
Summary
Today we face the consequences of demographical growth. Around 2.4 million metric tons of plastic are trapped in garbage patches spread all over the world [1]. Thousands of active measuring instruments are required to create a clear image and, given the quantitative nature of such task, there is a constant need for designs that integrate new materials and techniques that will improve the environmental impact of ocean drifters Within this scope, the biopolymer Polylactic Acid (PLA) has been a focus of extensive research and has been identified as an eco-friendly alternative to traditional plastics. We report the changes in mechanical properties and failure behaviour of 3D printed PLA and PLA-PHA samples when exposed to two different marine environments: complete submersion in seawater and cyclic submersion in a salt spray chamber for up to 45 days and 15 wet/dry cycles, respectively. Uniaxial Tensile Tests and Microscopic Observation were used to evaluate the change in mechanical properties and failure behaviour
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