Biobased polylactic acid (PLA) foam
packaging has been commercialized
as an alternative to conventional polystyrene (PS) foam. However,
PLA’s low glass transition temperature results in its inherently
poor heat resistance and in turn limits the application to cold-fill
packaging. In this study, low-density PLA foam sheet was extruded
using an industry-scale tandem extrusion line and subsequently laminated
with a PLA film casted from a high heat deflection temperature (HDT)
PLA resin with a very low d-lactide monomer content (i.e.,
∼0.4 mol %). Experimental results reveal that the crystallization
behaviors of PLA foam sheets were sensitive to both thermoforming
temperature and process-induced strain. Furthermore, this work has
demonstrated that heat-resistant biodegradable PLA foam sheets could
be realized by laminating them with solid films made of high-HDT PLA
to serve as environmentally sustainable alternatives to PS foams in
hot-fill packaging applications.
Styryldiphenylbismuth (SDB) has been copolymerized with
vinylbenzylphosphonate ester
(VBP) and methyl methacrylate (MMA) producing highly radiopaque
copolymers and
terpolymers. The phosphoryl ester groups were also converted to
phosphonic acids and the
polymers were characterized. Thermal analysis of the co- and
terpolymers yielded single
glass transition temperatures in the range 60−100 °C.
Poly(styryldiphenylbismuth vinylbenzylphosphonate ester) copolymer is thermally stable up to 255 °C
and degrades at ca.
285 °C, producing bismuth crystallites within the partially degraded
polymer matrix.
Radiopacities of the polymers were compared to aluminum standards
and were found to be
proportional to the bismuth contents. It was found that ca. 16 mol
% (or 31.6 wt %) of
styryldiphenylbismuth in the terpolymer of SDB, VBP, and MMA has double
the radiopacity
of aluminum.
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