Page 289 - Biodegradable Polyesters

10.3 Crystallization-Induced Toughness and Morphological Control 267

researchers have also investigated the combination of an active nucleating agent
and impact modifier as an effective method to simultaneously improve the
crystallization and the impact toughness of PLA-based blends. For instance,
higher tensile and especially impact toughness within PLA/NR blends are
reached by promoting higher crytallinity and smaller spherulites in the presence
of nucleating agents [203]. Surprisingly, Jain et al. [204] investigated the talc
loading on phase morphology and resulting properties of PLA/PCL blends to find
that talc not only acts as a nucleating agent but also improves the compatibility
and adhesion between the dispersed phase and the matrix. Further, Bai et al.
′
′′
[205] utilized a highly active nucleating agent N,N ,N -tricyclohexyl-1,3,5-
benzene-tricarboxylamide (TMC-328) to tailor the crystallization of PLA matrix
within the rubber-toughened PLA/PCL blends, highlighting a linear relationship
between PLA crystallinity and impact toughness (Figure 10.24). From this study,
it is believed that PLA crystals provide a path for the propagation of shear
yielding deformation required for effective impact energy dissipation. Especially,
the PLA/PCL (80/20 wt/wt%) blend containing 0.3 wt% of nucleating agent
−2
shown impact strength of 28.9 kJ m , more than 13-fold over that of neat PLA.
Another investigation by Bai et al. [206] further highlighted that toughening of
PLA/PCL blends is only efficient if matrix crystallinity and particle size are well
matched. With the significant increase of matrix crystallinity, an evident decrease

(a) (b)

7/13/2011 HV mag WD mode 60 μm 7/13/2011 HV mag WD mode 5 μm
6:36:55 PM 10.00 kv 2 000x 12 0 mm SE 6:38:04 PM 10.00 kv 20 000x 12 0 mm SE
(c) (d)

50 μm 5 μm
7/13/2011 HV mag WD mode 7/13/2011 HV mag WD mode
6:46:04 PM 10.00 kv 2 000x 11 6 mm SE 6:48:17 PM 10.00 kv 20 000x 11 6 mm SE
′
′′
Figure 10.24 Morphologies of (N,N ,N -tricyclohexyl-1,3,5-benzene-
impact-fractured surfaces of PLA/PCL tricarboxylamide) as a nucleating agent (c, d).
85/15 wt/wt% (a, b) and corresponding Reproduced with permission from Ref. [205]
blend containing 0.5 wt% of TMC-328 © 2012, American chemical society.