Conclusions
The size of PLLA spherulites increased dramatically with
annealing temperature in PLLA/PEO (80/20) and (50/50) blends.
The breadth and PEO content of the interpherulitic layers were
found to be much larger for the (50/50) blend than for the (80/20)
blend. The size of the intraspherulite PEO-rich domains was also
much larger for the (50/50) blend than for the (80/20) blend. The
toughness of PLLAwas significantly improved by the blending with
PEO and was shown to be closely related to the morphology of the
blends. The isothermal crystallization temperature of the PLLA/PEO
(80/20) and (50/50) blends produced opposite effects on their
impact toughness. For the neat PLLA and PLLA/PEO (80/20) blends,
the impact toughness decreased with increasing spherulite size,
whereas the impact energy of the (50/50) blend improved
remarkably with crystallization temperature, and therefore with
spherulite size. This latter effect is suggested to be due to a synergism
of greater plasticity within the spherulites and plasticity and
multiple microcracking along interspherulite boundaries.