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Influence of Annealing and Biaxial Expansion on the Properties of Poly(l-Lactic Acid) Medical Tubing

1
Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone, N37 HD68 Co. Westmeath, Ireland
2
Faculty of Engineering and Informatics, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone, N37 HD68 Co. Westmeath, Ireland
*
Author to whom correspondence should be addressed.
Polymers 2019, 11(7), 1172; https://doi.org/10.3390/polym11071172
Received: 11 June 2019 / Revised: 4 July 2019 / Accepted: 5 July 2019 / Published: 11 July 2019
(This article belongs to the Special Issue Biopolymers and Biobased Polymers: Chemistry and Engineering)
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Abstract

Poly-l-lactic acid (PLLA) is one of the most common bioabsorbable materials in the medical device field. However, its use in load-bearing applications is limited due to its inferior mechanical properties when compared to many of the competing metal-based permanent and bioabsorbable materials. The objective of this study was to directly compare the influence of both annealing and biaxial expansion processes to improve the material properties of PLLA. Results showed that both annealing and biaxial expansion led to an overall increase in crystallinity and that the crystallites formed during both processes were in the α’ and α forms. 2D-WAXS patterns showed that the preferred orientation of crystallites formed during annealing was parallel to the circumferential direction. While biaxial expansion resulted in orientation in both axial and circumferential directions, with relatively equal sized crystals in both directions, Da (112 Å) and Dc (97 Å). The expansion process had the most profound effect on mechanical performance, with a 65% increase in Young’s modulus, a 45% increase in maximum tensile stress and an 18-fold increase in strain at maximum load. These results indicate that biaxially expanding PLLA at a temperature above Tcc is possible, due to the high strain rates associated with stretch blow moulding. View Full-Text
Keywords: bioabsorbable polymers; poly-l-lactic acid; annealing; biaxial expansion; orientation; crystallinity; strain rate bioabsorbable polymers; poly-l-lactic acid; annealing; biaxial expansion; orientation; crystallinity; strain rate
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Dillon, B.; Doran, P.; Fuenmayor, E.; Healy, A.V.; Gately, N.M.; Major, I.; Lyons, J.G. Influence of Annealing and Biaxial Expansion on the Properties of Poly(l-Lactic Acid) Medical Tubing. Polymers 2019, 11, 1172.

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