The Influence of Low Shear Microbore Extrusion on the Properties of High Molecular Weight Poly(l-Lactic Acid) for Medical Tubing Applications

Brian Dillon; Patrick Doran; Evert Fuenmayor; Andrew V Healy; Noel M Gately; Ian Major; John G Lyons

doi:10.3390/polym11040710

The Influence of Low Shear Microbore Extrusion on the Properties of High Molecular Weight Poly(l-Lactic Acid) for Medical Tubing Applications

Polymers (Basel). 2019 Apr 18;11(4):710. doi: 10.3390/polym11040710.

Authors

Brian Dillon¹, Patrick Doran², Evert Fuenmayor³, Andrew V Healy⁴, Noel M Gately⁵, Ian Major⁶, John G Lyons⁷

Affiliations

¹ Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland. A00237890@student.ait.ie.
² Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland. patrickdoran@ait.ie.
³ Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland. e.fuenmayor@research.ait.ie.
⁴ Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland. andrewhealy@research.ait.ie.
⁵ Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland. n.gately@ait.ie.
⁶ Materials Research Institute, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone and Co. Westmeath, Ireland. imajor@ait.ie.
⁷ Faculty of Engineering and Informatics, Athlone Institute of Technology, Dublin Road, Bunnavally, Athlone, Co. Westmeath, Ireland. slyons@ait.ie.

Abstract

Biodegradable polymers play a crucial role in the medical device field, with a broad range of applications such as suturing, drug delivery, tissue engineering, scaffolding, orthopaedics, and fixation devices. Poly-l-lactic acid (PLLA) is one of the most commonly used and investigated biodegradable polymers. The objective of this study was to determine the influence low shear microbore extrusion exerts on the properties of high molecular weight PLLA for medical tubing applications. Results showed that even at low shear rates there was a considerable reduction in molecular weight (M_n = 7-18%) during processing, with a further loss (M_n 11%) associated with resin drying. An increase in melt residence time from ~4 mins to ~6 mins, translated into a 12% greater reduction in molecular weight. The degradation mechanism was determined to be thermal and resulted in a ~22-fold increase in residual monomer. The differences in molecular weight between both batches had no effect on the materials thermal or morphological properties. However, it did affect its mechanical properties, with a significant impact on tensile strength and modulus. Interestingly there was no effect on the elongational proprieties of the tubing. There was also an observed temperature-dependence of mechanical properties below the glass transition temperature.

Keywords: Bioabsorbable polymers; crystallinity; low shear; microbore extrusion; molecular weight; poly-l-lactic acid; residence time; residual monomer.