A degradable polymer to replace PLA?

Packaging Professional magazine
,
17 Jul 2011

A polymer that could
replace PLA and lead to
more degradable plastic
bags is being spearheaded by
chemists at the University of
Florida, USA.

PhD student chemists Ryan
Martin and Stephen Miller
synthesised polyesteracetal
(PEA) using vanillic acid, derived
from vanillin, a lignin-based
by-product of the paper pulping
industry. They claim the material
is better suited to modern
environmental demands than
other disposable plastics. ‘PLA
is the current market leading
green plastic, but it is essentially
a century-old material,’ says
Martin. ‘PEAs, however, are
21st century materials and are
thoughtfully designed on the
molecular scale.’

The main strength of PEA,
according to Martin, lies in its
superior degradation properties,
achieved using strategically
placed degradable functional
groups along the polymer chain
that allow for more facile degradation
under landfill or ocean
conditions. ‘Previous materials,
including PLA, degrade under
normal environmental conditions
in approximately 500-1000
years. The PEA breaks down in
as little as five to ten years. This
timescale is really a sweet
spot that would allow for a
disposable material to mitigate
the trash crisis while still serving
a useful lifetime.

‘Degradation studies were
performed at ambient temperature
under a range of pH
conditions, as well as in the
Atlantic Ocean.

The impact PEAs could
have on the US$400 bln/year
disposable plastics industry is
significant, says Martin. Made
from biomass or agricultural
waste, PEAs ‘have a green birth,
a useful life, and a green death,
and have properties that are on
par with, or better than, existing
materials’. He adds that the
material can be produced on a
similar cost scale as PLA. Martin
continues that as oil becomes
increasingly scarce and costly,
PEAs could eventually capture
the market of petroleum-based
plastics such as PE, PP, PS,
and PET.

Plastic staying power

Though Martin applauds the
intentions behind initiatives
to get people to stop using plastic bags, he cannot see
them being a success in
the long-term. ‘Plastics are
popular materials because
of their extreme convenience.
Getting consumers to stop
using plastic bags is counterconvenient,
and therefore
not likely to be a sustainable
long-term solution. The best-case
scenario is one in
which the materials we have
come to love are reinvented
to retain their usefulness
and convenience, while
being produced in an
increasingly thoughtful and
responsible way.’

Furthermore, he claims
that PEA, though made
under the same conditions
as PLA, has a higher
glass transition temperature,
(meaning it could replace
polystyrene cups, unlike PLA,
which deforms) improved
optical clarity, and decreased
brittleness. ‘We believe this
is largely due to increased
anomeric interactions associated
with the acetal groups,
and this will be described
in further detail in an
upcoming literature publication,’
notes Martin.