Page 245 - Biodegradable Polyesters

9.3 Effect of Hydrogen Bonding in Polymer Blends on Nano-Morphology 223

(a) (b)

Figure 9.5 SEM micrographs of PLA prepared from PVA/PLA (80/20 by wt%) blend after
extraction of PVA with water at (a) lower magnification (individual not interconnected
microfibrils) and (b) higher magnification (nanofibrillar nanoporous 3-D network).
The experience gained with microfibrillar scaffolds based on PET was further
used to develop PLA-based microfibrillar scaffolds [25]. Following the basic con-
cept of the MFC approach, an appropriate second blend component was selected.
It should have a melting temperature close to that of PLA and be thermodynami-
cally nonmiscible with PLA, exhibiting good drawing properties. Poly(vinyl alco-
hol) (PVA) was found to be a suitable candidate. After melt blending, the drawing
was performed in a continuous manner and the fine filaments obtained were sub-
merged in water for a couple of hours. The residue was a thin film (Figure 9.5a),
the SEM inspection of which showed microfibrillar structure.
Surprising results regarding the intimate structure were found at higher mag-
nifications – instead of individual microfibrils, a nanofibrillar nanoporous 3-D
structure was observed (Figure 9.5b). Such a spatial arrangement of microfibrils
results in the formation of extremely porous material where the pores have sizes
in the nano-range (Figure 9.5b). In other words, one deals in the present case with
biodegradable (PLA-based) nanofibrillar nanoporous scaffolds distinguished by
an extremely high specific surface. What is of particular importance in this case is
the fact that the scaffolds were prepared in a way excluding any contact with any
organic solvents or other toxic components as the extraction of PVA was carried
out by means of water only.
The same approach was applied to other biodegradable polymers, important for
biomedical applications, such as PHB and poly(caprolacton) (PCL). The morphol-
ogy of the scaffold materials of these polymers is demonstrated in Figure 9.6.

9.3
Effect of Hydrogen Bonding in Polymer Blends on Nano-Morphology

An interesting question arises at this point: what could be the reason for obtaining
of two completely different nano-morphologies of nano-sized polyesters when
blended with polyolefins (PP or PE, e.g., Figure 9.4) or PVA as a second blend