Biomedical Engineering Reference
In-Depth Information
compensates to the increase of fracture energy due to the ductile deformation of PCL. This is
the reason for the slight improvement of
J
in
in PLA/PCL shown in Fig. 16. It is clearly seen
from Fig. 18(c) that cavities do not exist on the fracture surface of PLA/PCL/LTI, indicating
that the miscibility of PLA and PCL improves due to LTI addition. In addition, elongated
structures are more on PLA/PCL/LTI than PLA/PCL. Thus, extensive ductile deformation
associated with disappearance of cavitation is the primary mechanism of the dramatic
improvement of
J
in
.
(a)PLA
(b)PLA/PCL
(c)PLA/PCL/LTI
Fig. 18. FE-SEM microgprahs of fracture surfaces of PLA, PLA/PCL and PLA/PCL/LTI.
In summary, the miscibility between PLA and PCL is dramatically improved by introducing
LTI as an additive. The increase of molecular weight and the decrease of crystallinity with
increase of LTI content clearly indicate that crosslinks are generated by urethane bonds in
which the hydroxyl groups at the ends of PLA and PCL molecules react with the isocyanate
groups of LTI during molding process. Such microstructural modification results in the
dramatic improvement of the macroscopic fracture property,
J
in
.
4.2 Effect of annealing process on PLA/PCL/LTI
As described in the previous section, the immiscibility of PLA/PCL can be improved by
adding LTI as a compatibilizer, and as a result, the fracture energy of PLA/PCL is
