Civil Engineering Reference
In-Depth Information
leading studies reported the preparation of transparent nanocomposites by adding a
BC pellicle to a chloroform PLA solution followed by drying during several days [155].
h e tensile strength and Young´s modulus of the nanocomposites increased by 203%
and 146%, respectively, when matched with the neat PLA matrix. However, the use of
an extremely injurious organic solvent and the limited adhesion between an aliphatic
polyester matrix and BC nanoi brils could limit to a great extent their potential appli-
cation in biomedical devices and food packaging. In order to surpass this constraint,
novel transparent nanocomposites prepared by the simple and green mechanical com-
pounding of PLA and acetylated BC nanoi brils were developed (Figure 2.18) [156].
h ese nanocomposites showed improved mechanical properties (increments of about
40% and 25% in the Young´s modulus and tensile strength for a 6% loading), thermal
stability and water resistance.
In a more fundamental vein, Zhang
et al.
[157] studied the coni ned crystallization
behavior of PLA/acetylated BC nanocomposites prepared by compression molding. h e
results indicated that acetylated BC favored the crystallization of PLA at higher tempera-
tures. In a similar mode, Quero
et al.
[158] investigated the micromechanical properties
of laminated BC/PLA nanocomposites by Raman spectroscopy as a mean to understand
the fundamental stress-transfer processes in these nanocomposites and as a tool to select
appropriate processing and volume fraction of the i bers. Results showed that Young´s
modulus and stress at failure of PLA i lms were found to increase by 100 and 315%,
respectively, for 18% volume fraction of BC and BC membranes cultured for 3 days
exhibited enhanced interaction with PLA because of their higher total surface area.
Martínez-Sanz
et al.
[159] optimized the dispersion of BC nanowhiskers into PLA,
also by melt compounding, via their pre-incorporation into PLA i bers by electrospin-
ning or a poly(ethylene vinyl-alcohol) copolymer by solution co-precipitation. In an
additional study, poly(glycidyl methacrylate) grat ed BC nanowhiskers, prepared by
means of a redox-initiated free radical copolymerization reaction, were incorporated
as i llers into a PLA matrix by solvent casting followed by compressing molding [160].
h is grat ing approach improved both matrix-i ller adhesion and the dispersion of the
BC nanowhiskers (only for loading up to 3 wt%) and reduced the oxygen permeability
of PLA for low relative humidity conditions.
h e research group of Bismarck has been also exploring the surface functionaliza-
tion of BC as a road to create PLA nanocomposites with upgraded properties. h e
functionalization with various organic acids rendered BC nanoi bers hydrophobic
[161, 162] and resulted in better interfacial adhesion between PLA and BC [163]. In
100
80
60
40
PLA
PLA-BCA c1
PLA-BCA c4
PLA-BCA c6
20
0
400
700
nm
Figure 2.18
Images of acetylated BC/PLA transparent nanocomposites and corresponding transmittance
in the visible region. Reproduced with permission from [156].
