Melt
blending of homopolymers is an effective way to achieve an
attractive combination of polymer properties. Dynamic vulcanization
of fatty-acid-based polyester polyol with glycerol and poly(
l
-lactic acid) (PLLA) in the presence of hexamethylene diisocyanate
(HDI) was performed with the aim of toughening PLLA. The dynamic vulcanization
in an internal mixer led to the formation of a PLLA/PU biobased blend.
Melt torque, Fourier transform infrared (FTIR), and gel fraction analysis
demonstrated the successful formation of cross-linked polyurethane
(PU) inside the PLLA matrix. Scanning electron microscopy (SEM) analysis
showed that the PLLA/PU blends exhibit a sea–island morphology.
Gel fraction analysis revealed that a rubbery phase was formed inside
the PLLA matrix, which was insoluble in chloroform. FTIR analysis
of the insoluble part shows the appearance of an absorption band centered
at 1758 cm
–1
, related to the crystalline carbonyl
vibration of the PLLA component, thus suggesting the partial involvement
of PLLA chains in the cross-linking reaction. The overall content
of the PU phase in the blends significantly affected the mechanical
properties, thermal stability, and crystallization behavior of the
materials. The overall crystallization rate of PLLA was noticeably
decreased by the incorporation of PU. At the same time, polarized
light optical microscopy (PLOM) analysis revealed that the presence
of the PU rubbery phase inside the PLLA matrix promoted PLLA nucleation.
With the formation of the PU network, the impact strength showed a
remarkable increase while Young’s modulus correspondingly decreased.
The blends showed slightly reduced thermal stability compared to the
neat PLLA.
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