Page 279 - Biodegradable Polyesters

10.2 Polylactide Strengthening and Strategies 257

PLA

PLA + 17%pds Biomax strong

Figure 10.16 Transparency of PLA and a PLA blend containing 17wt% Biomax Strong
obtained by melt-processing.

It is worth pointing out that the use of impact modifiers in PLA can be accom-
panied by some decrease of both tensile strength and modulus. Other approaches
have thereby been proposed to enhance both impact and tensile properties of
PLA-based materials by combining impact strengtheners with nanoparticles, the
formation of interpenetrated networks and annealing process/crystallinity extend
as discussed below.

10.2.3
Nanoparticle-Mediated Compatibilization Process

The morphology of a two-phase system is usually a result of the equilibrium
between the breakup and coalescence of dispersed domains in the flow field [143].
To achieve a control over the morphology and therefore the performances of the
resulting melt blends, compatibilization routes are required, namely, via the use of
organic compatibilizers such as block or graft copolymers either pre-synthesized
or generated in situ during flow-induced processes [144–146]. The function of
a compatibilizer is twice: (i) as a dispersant to reduce the characteristic size of
the heterogeneous morphology upon the suppression of coalescence and (ii) as a
coupling agent to provide significantly improved adhesion between the continu-
ous and dispersed phase in the blend [147, 148]. In the case of in situ generated
compatibilizers, Macosko et al. [149] reported that the compatibilization extent
depends on the interfacial area created during processing flows. Unfortunately,
the extent of interfacial area is scarcely addressed in the existing literature
due to the difficulty in controlling the compatibilization process during melt
processing [149–152]. However, it appears that, if well controlled, the interfacial
area could greatly increase on 3 orders of magnitude at the early stage of mixing,
that is, less than 2 min, affording an elegant way to tailor the morphology of
polymer blends, and therefore, to tune up the material performances on purpose
[149–152]. Meanwhile, other compatibilization methods have been reported
upon the addition of nanoparticles into immiscible polymer blends [153–157].
Nanoparticles act specifically by localizing at the interface of both polymeric