Page 282 - Biodegradable Polyesters

260 10 Highly Toughened Polylactide-Based Materials through Melt-Blending Techniques

2 wt% within PLA/ethylene-methyl acrylate-glycidyl methacrylate rubber blends
to counteract the negative effect of the rubber on modulus. In this work, most
of the clay was encapsulated in the rubber phase with some clay locating at the
PLA/rubber interface and in the PLA matrix. Accordingly, the best balance of
stiffness–toughness properties was reached at 10 wt% of rubber that exhibited
the highest level of exfoliation.
Jiang et al. [168] investigated PLA ternary composites containing both PBAT
and rigid nanoparticles, that is, montmorillonite clay (MMT) or nanosized
precipitated calcium carbonate (NPCC). Using maleic anhydride-grafted PLA
(PLA-g-MA) as a compatibilizer, the elongation at break of the ternary compos-
ites was substantially increased, possibly owing to improved dispersion of the
nanoparticles. From this study, the toughness increase by MA grafting afforded
the better-balanced overall performance for the PLA-based composite containing
10 wt% of PBAT and 2.5 wt% of MMT with a 16.5-fold increase in elongation
at break than that of neat PLA. Further investigations by Liu et al. reported the
improvement of toughness of PLA/basalt fiber composites through the addition
of (PEO-g-MA) or ethylene-propylene-diene rubber (EPDM-g-MA) grafted
with maleic anhydride and ethylene-acrylate-glycidyl methacrylate copolymer
(EAGMA) [169]. It was shown that EAGMA was more effective in toughening
PLA/basalt fiber composites than PEO-g-MA and EPDM-g-MA, reaching an
unnotched Charpy impact strength of 33.7 kJ m −2 when the content of basalt
fibers and EAGMA are both set to 20 wt%. Finally, PLA/MMT nanocomposites
toughened with maleated styrene-ethylene/butylene-styrene (SEBS-g-MA) were
studied by Leu et al. [170]. Overall, the PLA/MMT (2 wt%)/SEBS-g-MA (5 phr)
exhibited balanced properties with significant increase in elongation at break
and notched Izod impact strength (22% and 7.2 kJ m −2 compared to 10% and
3.6 kJ m −2 for the binary PLA/MMT blend). They found that these improvements
result from a mixture of the intercalated and exfoliated structure of MMT
coexisting in the PLA matrix, together with some encapsulation of MMT by
SEBS-g-MA (Figure 10.19). In this field, Nuñez et al. [171] focused on the study of
the effectiveness of two grafted polymers (SEBS-g-MA and PE-g-MA) as compat-
ibilizing agents in ternary blends with PLA as matrix phase, LLDPE as dispersed
phase, and sepiolite clay as filler. It was found that the presence of sepiolite at the
PLA/LLDPE interface and in the PLA matrix phase reduces the effectiveness of
these compatibilizing agents, resulting in elongation at break lower than those
of the blends without clay. Nevertheless, a yield stress and higher elongation at
break and toughness were obtained in these blends compared with neat PLA.
Many other investigations on the co-addition of soft elastomers and rigid
particles within PLA can be also found in the literature. For instance, high
mechanical performances were reported through the addition of cellulose
nanocrystals within PLA/NR blend. From this study, different morphologies
upon the nanocrystal modifications were evidenced, which strongly influenced
the affinity toward the polymers and their ultimate properties [172]. PLA-based
wood–plastic composites with polyhydroxyanoates (PHAs) were reported by
Qiang et al. [173], reaching a notched Charpy impact strength of 105.3 kJ m −2 in