This article demonstrates the synthesis of lactic acid oligomer-grafted-chitosan (OLLA-g-CH), a nanoamphiphilic molecule, by in situ condensation polymerization and its effective use as a nanofiller for improvement in multiple properties of poly(lactic acid) (PLA) films, essential for stringent food packaging applications. Fourier transform infrared spectroscopy (FTIR) analysis shows the presence of amide-ester bond at 1539 cm(-1), which confirms the structural grafting of OLLA chains with chitosan molecules. This nanoamphiphilic OLLA-g-CH molecule act as surfactant containing hydrophilic chitosan head and hydrophobic OLLA tails with average size in the range of ∼2-4 nm. Prepared PLA/OLLA-g-CH bionanocomposite films appear with uniform dispersion of nanoamphiphilic OLLA-g-CH molecules with self-assembled micelles having size as low as ∼20 nm and as high as ∼150 nm with core-shell morphology in PLA matrix. This nanofiller is found very effective toward significant reduction in oxygen permeability (OP) by ∼10-fold due to the reduction in solubility of oxygen molecules and improvement in crystal nucleation density due to availability of nanonucleating sites. Ultimate tensile strength (UTS) of PLA/OLLA-g-CH bionanocomposite films are relatively comparable to that of PLA, however, elongation at break is improved significantly. The onset of thermal degradation of PLA/(OLLA-g-CH) films is also found comparable to that of PLA film. The glass transition temperature (Tg) of bionanocomposites is decreased by more than 18 °C with increase in OLLA-g-CH loading, which indicates the improved plasticization characteristics of PLA matrix. The crystallization kinetics suggest nonthree dimensional truncated spherical structures, which is controlled by the combination of thermal and athermal instantaneous nucleations. POM analysis suggested that the spherulite growth of PLA is improved significantly with the addition of OLLA-g-CH. The reduction in Tg of PLA with improvement in elongation at break and multifold reduction in oxygen permeability offers this bionanocomposite films, a promising candidate for stringent food packaging applications.
The worldwide demand for additive manufacturing (AM) is increasing due to its ability to produce more challenging customized objects based on the process parameters for engineering applications.
Nanobiocomposites
with balanced mechanical characteristics are
fabricated from poly(lactic acid) (PLA)/poly(butylene succinate) (PBS)blend
at a weight ratio of 80/20 in association with varying concentrations
of functionalized chitosan (
F
CH) through reactive
extrusion at a temperature of 185 °C. The combined effect of
F
CH and dicumyl peroxide (DCP) showed insignificant change
in tensile strength with a remarkable increase in % elongation at
break (∼45%) values. Addition of DCP also caused increase in
the molecular weight (
M
w
∼ 22%)
of the PLA/PBS/1D
F
CH nanobiocomposite, which is attributed
to the cross-linking/branching effect of
F
CH on the
polymers. The interfacial polymer–filler adhesion is also improved,
which is observed from the field-emission scanning electron microscopy
images of PLA/PBS/1D
F
CH. For PLA/PBS/1D
F
CH, the crystallization rate and nucleation density of PLA are increased
because of cross-linked/branched structures are developed, which
acted as nucleating sites. Therefore, the present work facilitates
a simple extrusion processing with a combination of balanced thermal
and mechanical properties, improved hydrophobicity (∼27%),
and UV-C-blocking efficiency, which draw the possibility for the utilization
of the ecofriendly nanobiocomposite in the packing of UV-sensitive
materials on a commercial level.
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