Enhanced Mechancial Properties in Uniaxially Stretched Films of Diblock Polymer Modified Poly(L-lactide)

Semicrystalline poly(L-lactide) (PLLA) is a bio-sourced, compostable alternative to conventional plastics

but lacks the toughness required for many applications. Chain alignment via uniaxially stretching

significantly toughens PLLA in the machine direction (MD) but leaves the transverse direction (TD)

brittle. This work reports uniaxially stretched films of PLLA blended with 3 wt% poly(ethylene oxide)-b-

poly(butylene oxide) (PEO-PBO/PLLA) with increased toughness in both MD and TD. Tensile testing in

the MD showed toughness in both PLLA and PEO-PBO/PLLA, with shear yielding as the primary

mechanism of deformation. In the TD, by contrast, PEO-PBO/PLLA films outperformed PLLA and

deformed uniformly by crazing. Faster stretching was shown to enhance the mechanical properties of

both MD and TD and was correlated with greater degrees of crystallinity and crystallite alignment

determined by wide-angle X-ray scattering. Increasing the stretching rate from 2 %s ^-1 to 100 %s ^-1

increased the yield stress in the MD from 76 MPa to 95 MPa, while in the TD elongation at break was

increased from 12 % to 36 %, exceeding that of the MD. In summary, this work presents uniaxially-

stretched but biaxially-toughened PEO-PBO/PLLA as a more sustainable alternative to conventional

plastics.