Toughening Polylactide with Graft-Block Polymers

Bongjoon Lee, Michael J Maher, Haley J. Schibur, Marc A. Hillmyer, Frank S Bates

Research output: Contribution to journalArticlepeer-review

Abstract

Poly[(styrene-alt-N-hydroxyethylmaleimide)-ran-(styrene-alt-N-ethylmaleimide)]-graft-[poly(4-methylcaprolactone)-block-poly((±)-lactide)] (g-ML) graft-block polymers containing 50 vol % poly((±)-lactide) (PLA or L) were mixed with a commercial PLA homopolymer to modify the brittle mechanical behavior of this industrially compostable plastic. Various graft architectures, including linear, tri-arm, and tetra-arm polymer backbones, were prepared using a grafting-from method. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) revealed that the pure g-MLs form a lamellar morphology where the degree of long-range order is dictated by the polymer architecture. When melt-blended with PLA at low concentrations, the g-MLs formed well-dispersed nanoscale particles within the PLA matrix, yielding moldable plastics with high optical transparency. The tensile toughness of the PLA/g-ML blends was substantially enhanced over that of pure PLA using g-ML concentrations as low as 5 wt % and exhibited average strains at break of 280% following 2 days of aging at room temperature; pure PLA failed at a 7% strain. The elastic modulus, yield stress, and transparency of the toughened plastic were virtually unaffected by the low concentration of rubbery poly(4-methylcaprolactone) (M) domains and the formation of well-dispersed nanoscale particles. Graft-block polymers were shown to toughen PLA more efficiently than a linear triblock copolymer analogue LML, which produced a strain at break of 105% at a loading of 5 wt %. Blending g-ML into PLA significantly delays the onset of physical aging and the onset of the ductile-to-brittle (DTB) transition, which depends on the concentration of g-ML utilized.

Original languageEnglish (US)
JournalACS Applied Polymer Materials
DOIs
StatePublished - Mar 31 2022

Bibliographical note

Funding Information:
Support for this work was provided by the National Science Foundation (NSF) Center for Sustainable Polymers (CHE-1901635) at the University of Minnesota. Parts of this work were carried out in the Characterization Facility at the University of Minnesota, which receives partial support from the NSF through the MRSEC program (DMR-2011401).

Publisher Copyright:
© 2022 American Chemical Society.

Keywords

  • graft polymer
  • physical aging
  • polymer micelles
  • polymer toughening
  • sustainable polymers

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