Biomedical Engineering Reference
In-Depth Information
Fig. 11. FE-SEM micrographs of crack-tip region of PLA/PCL.
Fig. 12. FE-SEM micrograph of fracture surface of PLA/PCL.
In summary, it was shown that the fracture energy of PLA can be improved by blending
with PCL with unchanged biocompatible and bioabsorbable characteristics. This
improvement is considered to be achieved by stress relaxation and energy dissipation
mechanisms such as extensive multiple craze formation of continuous phase and creation of
extended fibril structures of dispersed phase. It is important to note that PLA/PCL
exhibited phase separation due to incompatibility of two components, and created voids
owing to removal of dispersed PCL phase. Those voids increased with increase of PCL
content. PLA/PCL exhibited craze-like deformation of continuous phase similar to neat PLA
during mode I fracture process, however, the size of the damage zone was much larger than
the PLA, corresponding to the higher
G
in
. PLA/PCL also showed creation of voids by PCL
phase separation within the fracture process region, and these voids were likely to be
extended at lower stress level, and therefore, decrease
G
in
due to local stress concentration.
4
.
Toughness improvement of PLA/PCL blend
4.1 Effect of LTI
As shown in the above section, blending with PCL successfully improved the fracture
energy of brittle PLA. It was, however, also found that the immiscibility of PLA and PCL
causes phase separation, and tends to lower the fracture energy especially when PCL
content increases. It has recently been found that the addition of lysine tri-isocyanate (LTI)
