  In this work, the preparation of nanocomposites based on poly(L-lactide) PLLA
and graphite nanoplatelets (GNP) was assessed, by applying, for the first time,
the reactive extrusion (REX) polymerization approach, which is considered a low
environmental impact method to prepare polymer systems and which allows an easy
scalability. In particular, ad hoc synthesized molecules, constituted by a
pyrene end group and a poly (D-lactide) (PDLA) chain (Pyr-D), capable of
interacting with the surface of GNP layers as well as forming stereoblocks
during the ring opening polymerization (ROP) of L-lactide, were used. The
nanocomposites were synthesized by adding to L-lactide the GNP/initiator
system, prepared by dispersing the graphite in the acetone/Pyr-D solution,
which was dried after the sonication process. DSC and X-ray diffraction
measurements evidenced the stereocomplexation of the systems synthesized by
using the pyrene-based initiators, whose extent turned out to depend on the
PDLA chain length. All the prepared nanocomposites - including those
synthesized starting from a classical initiator, that is 1-dodecanol - retained
similar electrical conductivity, whereas the thermal conductivity was found to
increase in the stereocomplexed samples. Preferential localization of
stereocomplexed PLA close to the interface with GNP was demonstrated by
Scanning Probe Microscopy (SPM) techniques, supporting for an important role of
local crystallinity in the thermal conductivity of the nanocomposites.
