posted on 2022-03-18, 16:37authored byAndrew Anstey, Anthony V. Tuccitto, Patrick C. Lee, Chul B. Park
Polylactide
(PLA) resins are among the most desirable biopolymers
due to their biobased and compostable nature, excellent stiffness,
and tensile strength. However, the widespread application of PLA has
long been hindered by its inherent brittleness. While multiple routes
have been successfully developed for the toughening of PLA, this toughening
has always come at the cost of compromising the stiffness and strength
of the matrix. In this work, we report a robust and scalable method
for the development of PLA nanocomposites with an unprecedented combination
of stiffness and toughness. Using the in situ nanofibrillation
technique, we generated PLA composites containing nanofibrils of thermoplastic
polyester elastomer (TPEE). Due to the high aspect ratio of these
nanofibrils, they form physically percolated networks at low weight
fractions (∼2.8 wt %) which dramatically change the mechanical
behavior of the material. We found that, upon network formation, the
material transitions from brittle to ductile behavior, dramatically
increasing its toughness with only a marginal decrease in Young’s
modulus. We investigate the peculiar rheological behavior and crystallization
kinetics of these blends, and propose an extension of the critical
ligament thickness mechanism, wherein intrinsic toughening arises
at the fiber-matrix interface in the presence of entangled elastomer
networks.