Abstract
Hydrolytic degradation of commercially available 3D printing filament, i.e. poly (lactic acid) with broad molecular weight distribution was induced by incubating 3D-printed parts in deionized water at 3 temperatures. Small changes in orthogonal dimensions occurred due to relaxation of printing stresses, but no mass or volume loss were detected over the time-frame of the experiments. Molecular weight decreased while polydispersity remained constant. The most sensitive measure of degradation was found to be nondestructive, small-amplitude oscillatory tensile measurements. A rapid decay of tensile storage modulus was found with an exponential decay time constant of about an hour. This work demonstrates that practical monitoring of commercially available PLA degradation can be achieve with linear viscoelastic measurements of modulus.
Highlights
The recognition of the impact of plastic waste on the health of the planet, as well as the finite quantity of fossil fuels has motivated research into more sustainable plastics
The cyclic dimer of lactic acid, known as lactide, can undergo ring-opening polymerization (ROP) to form high molar mass poly(lactic acid) (PLA).(Masutani & Kimura, 2018; Mehta, Kumar, Bhunia, & Upadhyay, 2005) The biodegradability of PLA can be attributed to ester linkages within the backbone that are susceptible to hydrolytic cleavage
Water sorption into the dogbone samples of this study generated via 3D printing will be much more rapid than would be observed in samples produced via a mold where macropores are not present
Summary
The recognition of the impact of plastic waste on the health of the planet, as well as the finite quantity of fossil fuels has motivated research into more sustainable plastics. The cyclic dimer of lactic acid, known as lactide, can undergo ring-opening polymerization (ROP) to form high molar mass PLA.(Masutani & Kimura, 2018; Mehta, Kumar, Bhunia, & Upadhyay, 2005) The biodegradability of PLA can be attributed to ester linkages within the backbone that are susceptible to hydrolytic cleavage Another advantage of PLA over fossil-fuel-derived polymers is lower carbon dioxide emissions over its lifecycle.(Vink, Rábago, Glassner, & Gruber, 2003) It can even serve as a carbon sink if it is produced with renewable energy.(Jamshidian et al, 2010; Vink & Davies, 2015) PLA has superior modulus to rigid polyolefin polymers, but poorer toughness.(Dorgan, Lehermeier, & Mang, 2000) It melts at a much lower temperature than sdr.ideasspread.org. The primary degradation product of PLA is lactic acid, which can further degrade into carbon dioxide and water and be excreted through the kidneys or exhaled. Biomedical applications of PLA consist of screws, plates, drug delivery, grafts, cavity filling, bone scaffolds, and stents; it can be spun into fibers for sutures.(Abd Alsaheb et al, 2015; Chen et al, 2016; Narayanan, Vernekar, Kuyinu, & Laurencin, 2016; Tyler, Gullotti, Mangraviti, Utsuki, & Brem, 2016) The reason for such a wide array of applications comes from the ability to manipulate its properties by controlling stereochemistry and incorporating copolymers,(Becker, Pounder, & Dove, 2010) adding fillers,(Raquez, Habibi, Murariu, & Dubois, 2013) or tuning processing conditions, all of which can have significant impact on crystallinity.(Anderson, Schreck, & Hillmyer, 2008; Rasal, Janorkar, & Hirt, 2010) the longer term impact of processing, especially via FDM, on degradation has not been examined, to the best of our knowledge
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