Civil Engineering Reference
In-Depth Information
(PHB) is biocompatible, biodegradable and thermoplastic, but has high melting tem-
perature and thermal instability. BC/PHB nanocomposites were prepared by both
soaking BC membranes with PHB chloroform solutions followed by drying [173, 174]
and by
in situ
modii cation of BC during biosynthesis [175]. Similar improvements in
terms of mechanical properties (tensile strength of up to 55 MPa for 50% wt of PHB)
and thermal stability were observed in the nanocomposites prepared by impregnation.
h e nanocomposites prepared by addition of PHB during BC biosynthesis showed also
considerable improvements on the tensile strength compared to the neat PHB, however
since the membranes were analyzed as such, without any post processing to promote
the dif usion of the PHB particles inside the BC nanostructure, the results are certainly
not truly representative due the high heterogeneity of the nanocomposite membranes,
as in fact revealed by SEM analysis. BC/poly(3-hydroxybutyrate-
co
-4-hydroxybutyr-
ate) porous nanocomposite scaf olds were prepared by freeze-drying and using tril uo-
roacetic acid as co-solvent [176]. In this case both PHB and BC were dissolved and
therefore the tridimensional structure of BC was destroyed. Field Emission Scanning
Electron Microscopy (FESEM) analysis revealed that the obtained nanocomposite scaf-
folds have a tridimensional network structure with multi-distribution of pore size. Cell
compatibility tests showed that they are bioactive and may be suitable for cell adhesion/
attachment suggesting their potential application for wound dressing and tissue engi-
neering. Although PHAs are quite hydrophobic polymers, only one study investigated
the acetylation of BC microcrystals as a way to improve compatibility with poly(3-
hydroxyoctanoate) [177]. Acetylated BC microcrystals and poly(3-hydroxyoctanoate)
were physically blended and solvent casted into nanocomposite i lms which demon-
strated improved mechanical properties and biocompatibility (50-110% higher cell
proliferation) in comparison with the neat polymer.
BC has also been used as a reinforcing agent for poly(ε-caprolactone) matrix [178],
another biodegradable polyester produced from renewable resources. h e nanocompos-
ites were prepared by melt-compounding and showed improved mechanical performance
when compared with the neat biodegradable polyester matrix. In a dif erent study, BC
nanoparticles were topochemically modii ed with poly(ε-caprolactone), via ring open-
ing polymerization, as a strategy to improve the compatibility between BC nanoparticles
and poly(ε-caprolactone) matrix in the corresponding thermoplastic nanocomposites
[179]. However, the thermal analysis results did not indicated a signii cant enhancement
in nanocomposite particle-matrix interactions with this surface grat ing.
BC-reinforced unsaturated polyester resin nanocomposites were prepared using
vinyl triethoxysilane-modii ed BC i bers by the resin transfer molding (RTM) meth-
odology [180]. h e X-Ray photoelectron spectroscopy (XPS) analysis revealed that
chemical bonding was formed between the matrix and the modii ed BC i bers which
resulted in composites with improved mechanical properties.
h e group of Yano developed a very stimulating class of optically transparent BC
nanocomposites by impregnation of BC sheets with dif erent acrylic (as well as epoxy
and phenol-formaldehyde) resins under vacuum [181-184]. h ese nanocomposite
materials showed high transmittances (more than 80% in the range 500-800 nm) despite
the high i bers contents (such as 60 wt%), low sensitivity to refractive index of the
matrices, low thermal expansion and good mechanical properties, thus making them
excellent candidates for a variety of applications, such as substrates for l exible displays,
