Sustainable Plastics - January/February 2022 - 29

bioplastics
oils contain active functional
groups in the fatty acid chain,
such as the hydroxyl group in
castor oil or the epoxy resin in
vernonia oil, which can be used
for polymerization.
The naturally occurring hyPolymers
of
the future
Over the past 50 years, the use and production of synthetic
polymers have increased exponentially. While most are
derived from non-renewable fossil fuel-based raw materials
such as coal, oil and natural gas, the industry has grown
increasingly aware that, if it is to keep pace with the ongoing
shifts in societal attitudes, alternative feedstocks must be
sought to produce polymers fi t for the future.
I
s it possible to produce
sustainable polymers
that address the needs
of consumers and do not
harm neither the environment
nor the economy, yet provide
the same performance as conventional
polymers at competitive
cost? It's a challenge
that researchers, raw materials
manufacturers and other
stakeholders around the world
have taken on with interesting
results. Among others, renewably
sourced polymers have
been derived from biomass
such as lignin, cellulose, starch
and plant oils, and even directly
through the utilisation and
conversion of carbon dioxide.
Below, we've touched briefly
on three areas that look to be
promising for the development
of new, sustainable polymers.
Direct utilisation of CO2
Researchers have long been
interested in using greenhouse
gases such as carbon dioxide
(CO2) to produce useful and
valuable polymers. An abundant,
inexpensive and nontoxic
biorenewable resource, CO2 is
an attractive raw material for the
synthesis of polymers, including,
for example, polycarbonate.
Such sustainable polymers
can be produced by alternating
copolymerization of epoxy
compounds, usually cyclohexene
oxide and carbon dioxide.
However, the eff iciency of the
coupling reaction of oxiranes
and CO2 is highly dependent
on the catalyst. Research is ongoing
into the development of
eff icient catalysts for the formation
of copolymers from carbon
dioxide and epoxides.
Lignin-based polymers
Lignin is the second most
abundant biopolymer on the
planet after cellulose. Lignin
has many properties ideal for
polymers, such as high thermal
stability, biodegradability,
antioxidant and antimicrobial
behaviour, and relative abundance,
but it can also be used
as low-cost reinforcement for
polymer composite applications.
Studies on lignin-reinforced
polystyrene (PS) composites,
for example, in which
the surface of the lignin was
modified with appropriate
technology to make it compatible
with other polymer materials,
show that the addition of
lignin can improve mechanical
properties such as the flexural
modulus and shear modulus of
the mixture. Lignin could also
be modified - using diff erent
transition metal cations such
as Fe (III), Ni (II) and Co (II) -
to prepare polystyrene polymer
composites for packaging
applications. The research of
lignin-reinforced polymer composites
is still in its infancy.
However, as an alternative to
traditional reinforced materials,
lignin-reinforced polymer composites
have great market potential
and prospective future.
Polymers derived from
vegetable oil
Vegetable oils are esters of glycerol
and various fatty acids, usually
containing 8 to 24 carbon
atoms and 0 to 7 carbon-carbon
double bonds. Some vegetable
droxyl group makes castor
oil suitable for polyurethanes
production without any modification.
Castor oil is a nonfood-grade
raw material widely
used in industrial production.
PU is widely used in coatings,
adhesives, sealants, elastomers
and foams. Due to the uniform
distribution of hydroxyl groups
in the castor oil main chain, the
generated PU has a uniform
cross-linked structure, essential
for good mechanical properties
and thermal stability.
Conclusion
Three potential feedstock options
for developing new, renewably
sourced sustainable
polymers have been only very
briefly highlighted, and much
work remains to be done before
such materials can become
more mainstream. Nonetheless,
the share of bioplastics in the
total plastics industry, while tiny,
is currently growing. Speaking
at the 16th EUBP conference,
François de Bie, chairman of
European Bioplastics, noted
that " before 2026, the share of
bioplastics in the total global
production of plastics will pass
the 2% mark for the first time " -
a milestone.
We live in a world of materials
made from synthetic polymers,
which have become an integral
part of modern life and the
global economy. But concerns
about fossil resource depletion,
disposal and related end-of-life
issues, as well as government
policies, are impacting attitudes
and changing the way plastics
are viewed. Sustainable
polymers that are designed
to address the environmental
challenges inherent with traditional
petroleum-based polymers,
while maintaining the
exceptional performance these
materials bring to our everyday
lives, are a crucial part of the future
of plastics.
Contributed by Dr. Raj
Shah, Qincheng Yu and
Gabby Massoud.
January/February 2022
29
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