Page 230 - Biodegradable Polyesters

208 8 Systematic Development of Electrospun PLA/PCL Fiber Hybrid Mats

(X = 12.6%) while 15% HMW PCL mats possess the lowest mass loss with
c
highly crystalline phases (X = 70.9%) (Table 8.3). Besides, the difference in mass
c
loss tends to be enlarged on increasing the PCL concentration for PLA/PCL
blends. This phenomenon can be ascribed to the increase of fiber diameter
and simultaneously the reduction of porosity on fiber surface at the high PCL
concentration. The lower fiber porosity decreases the overall PBS penetration
to fiber cores while the large fiber diameters reduce the surface areas in contact
with PBS.

8.9
Conclusions

This chapter examined the impact of various polymeric solution parameters
such as solution viscosity, PCL molecular weight, PCL concentration, blend
ratio of PLA/PCL and solvent type on morphological structures, fiber diam-
eters, thermal properties, degree of crystallinity, drug release rate as well as
fiber biodegradation. The focus in terms of material formulation lies in 9 and
15 wt%/v HMW PCL and 15 wt%/v LMW PCL blended with PLA (fixed at
8 wt%/v) solution at five blend ratios, dissolved in a wide range of cosolvents
including chloroform (CHCl )/acetone (C H O), chloroform (CHCl )/methanol
3
6
3
3
(MeOH), and DCM/N, N-dimethylformamide. It is indicated that increasing the
molecular weight and PCL concentration has led to a significant enhancement
in the solution viscosity, resulting in uniform bead-free fibers, particularly at
blend ratio 1/1 for PLA/PCL. The fibers for all PLA/PCL blend ratios that
generated from DCM/DMF, were smaller compared to those produced from
the chloroform/methanol system. The fibers produced by employing the chloro-
form/methanol cosolvent system created better uniformity of fibrous structures
compared with DCM/DMF and chloroform/acetone cosolvents. When dissolved
in chloroform/methanol, the X of PLA:15% HMW PCL fibers (blend ratio: 1/1)
c
was higher and completely different from those for PLA/9% HMW PCL and
PLA/15% HMW PCL at blend ratios of 1/1 and 3/1, respectively. Mixing LMW
PCL with PLA causes a significant decline in the X and T of PCL in contrast to
c m
HMW PCL counterpart despite a remarkable increase in the T of PLA. More-
c
over, the use of chloroform/methanol cosolvents causes moderate decreases in
the X and T compared with those based on DCM/DMF cosolvent, which arises
c c
from the fast evaporation of methanol. Decreasing HMW PCL concentration
from 15 to 9 wt%/v within the blends was found to contribute to the decrease
of the T for PCL. When PLA/PCL fibers were used in place of individual PLA
g
or PCL fibers, good miscibility between PLA and PCL within the blends is well
confirmed by both the variations of T , T ,and T as well as the shift of the
g m c
carbonyl stretching band to higher wave numbers. This is particularly the case for
PLA/15% HMW PCL (blend ratio: 1/1) when dissolved in chloroform/methanol
system. The drug release rate and biodegradation behavior of PLA/9% HMW
PCL fiber mats was higher than that of PLA/15% HMW PCL counterparts.