Page 274 - Biodegradable Polyesters

252 10 Highly Toughened Polylactide-Based Materials through Melt-Blending Techniques

(a) (b) (c)

HV spot det pressure mag WD 20 μm HV spot det pressure mag WD 20 μm HV spot det pressure mag WD 20 μm
15 00 kv 3.0 ETD 6 76e-g Torr 5 000 x 10 6 mm 15 00 kv 3.0 ETD 6 04e-6 Torr 5 000 x 12 3 mm 15 00 kv 3.0 ETD 4 61e-6 Torr 5 000 x 11 3 mm
Figure 10.14 Morphologies (a), 80/15/5 wt/wt/wt% (b), and
of impact-fractured surface of 80/5/15 wt/wt/wt% (c). Reproduced with per-
PLA/EBA–GMA/EMAA–Zn blends adja- mission from Ref. [113] © 2011, John Wiley
cent to the notch: 80/20/0 wt/wt/wt% and sons.
A commercially available ethylene/acrylate impact modifier was also inves-
tigated by Taib et al., highlighting plastic deformation in the form of matrix
shear yielding due to rubber cavitation. This retarded crack initiation and
propagation, leading to an improved impact strength of PLA (reaching 14 kJ m −2
at 10 wt% and 28 kJ m −2 with a partial break at 20 wt%) [115]. Afrifah and
Matuana [116] investigated the toughening mechanisms of PLA blended with an
ethylene/acrylate copolymer (EAC) to show a mode of fracture through crazing
or microcracking and debonding of impact modifier particles with the matrix,
resulting in brittle failure at low content. Nevertheless, higher impact modifier
content than 10 wt% revealed fracture mechanisms including impact modifier
debonding, fibrillation, crack bridging, and matrix shear yielding, resulting in a
ductile behavior (Figure 10.15). Interestingly, a continuous increase in impact
strength was observed by increasing the impact modifier concentrations from
−1
−1
0wt% (17Jm ) to 20wt% (88Jm ) after which it increased at a lower rate
−1
−1
to 30 wt% (118 J m ) and then increased sharply at 40 wt% (348 J m ). This
represented about sevenfold increase over the impact strength of the blend with
30 wt% of EAC [116].
Another study regarding biosourced PLA blends with different contents of
poly(ethylene oxide-b-amide-12) (PEBA) was investigated by Han et al. [117]. The
authors have found that the impact triggered not only the generation of fibrils

(a) (b) (c)

Figure 10.15 Morphologies of impact-fractured surfaces of PLA-based materials containing
10 wt% (a), 20 wt% (b), and 30 wt% (c) of EAC. Reproduced with permission from Ref. [116]
© 2010, John Wiley and sons.