In this work, inspired by the hierarchical
architecture of nacre, we have fabricated poly(propylene carbonate)
(PPC)/thermoplastic polyurethane (TPU) alternating multilayer films
via layer-multiplying coextrusion. Based on the glass transition at
around 37 °C of PPC, the multilayer films exhibited an outstanding
body heat-responsive shape-memory effect (SME) with high shape fixation
and recovery ratios (96.1 and 93.6%), much better than the conventional
cocontinuous blend with the same compositions. It was revealed that
the high phase continuity and abundantly two-dimensional interfaces
both capable of promoting stress transferring and load distribution
maximally contributed to the SME. Furthermore, the multilayer films
showed a superior recovery stress storage capacity and the force generated
by shape recovery allowed automatic expansion of the spiral in 37 °C
water and efficient lifting of a load 880 times its weight. Different
from the opacity of the blend, a high optical transparence was observed
in the multilayers because of the parallel assembly of transparent
PPC and TPU enabling light to directly pass through the films. Besides,
the nacre-like films had layer debonding and layer stepwise breaking
during stretching, resulting in a 90% increase in tensile strength,
a 70% increase in elongation at break, and onefold improvement in
yield stress, compared with those of the blend. Our approach paves
a new way for developing bioinspired structural materials with excellent
optical, mechanical, and shape-memory properties, which can be extended
to different amorphous polymers and elastomers. Also, the materials
presented herein have great potential in applications of biomedical
devices and soft robotics.
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