This effort has
been pursued for a long time and it now appears to be bearing significant
fruit. Our petrochemical based plastics
industry was driven by a huge supply of convenient feed stocks and it really
was often the first solution. Replacing them
with equal and safer or better is appropriate.
There certainly
are plastics we need to see removed from the supply chain although that will
take this type of replacement and the additional regulatory case. This also shows us just how long it can take
to implement. We forget that the age of
plastics arose slowly rather than fast and the quality we expect today is actually
fairly recent.
All good and
this is a good update.
Creating
Renewable Plastics That Don’t Cost the Earth
Imagine a future where
packaging is made entirely from waste material and biodegrades to harmless
by-products. Or where your home’s cavity wall insulation foam is made from
captured CO2 emissions. Or where construction materials, vehicle components,
and engineering plastics are sophisticated biological composites comprised of
tough cellulose fibers embedded in naturally derived polymers.
Such inventions are
already entering the mainstream, driven by considerable consumer and economic
pressure to replace conventional plastics (made from petrochemicals) with new materials
derived from natural sources, such as plants or gases like CO2. Sustainable
polymers like these offer some intriguing advantages over conventional
petrochemical polymers, most of which were discovered more than 50 years ago.
Sustainable polymers are
made from natural raw materials. Although that does not in itself mean they are
any greener than conventional materials, over the whole lifecycle of
manufacture, use, and disposal they can provide substantial gains. This is
particularly obvious when they’re made from waste materials. For example, if
CO2 emissions from power stations are used to make insulation foam, this
represents a means to lock-up carbon emissions and also put them to long-term
use insulating homes, thus reducing emissions further.
Another key aspect of
sustainable polymers is that they naturally contain oxygen in the form of
oxides of carbon, carbon dioxide, or carbohydrate for example. Petrochemicals
are hydrocarbons (reduced forms of carbon), which means oxygen must be added to
them, a process that often requires the use of toxic reagents or catalysts.
Some bio-derived
polymers (although not all) are biodegradable. This can be an advantage in
situations where recycling is not an option, such as in some packaging or
agricultural applications. In most other cases they are recyclable—although
it’s important to ensure new bio-polymers don’t contaminate conventional
plastics recycling streams.
The sophisticated
structures of natural materials could bring improvements in the properties of new
polymers. Using the natural chemistry of renewable resources more cleverly has
to be a future goal, for example with built-in degradation, improved barrier
properties for airtight packaging, and enhanced biodegradability, strength, or
heat resistance.
Plastic From Plants
Polylactic acid, or PLA,
is a sustainable polymer derived from cornstarch that has been on the market
for a decade, mainly as disposable packaging. An important aspect of PLA
chemistry is its chain tacticity—the arrangement of its polymer chains. By
changing the stereochemistry of the molecules—the patterns in which they’re
arranged—different properties can be emphasized.
Our team at Imperial
College London has developed a new catalyst to prepare a new, more
heat-resistant form of PLA that will widen the range of uses PLA can be put to.
Producing the new material cost-effectively will be the next challenge, but
this class of material could replace common tough polyesters currently used for
such things as housings for household appliances.
Adding cellulose,
nature’s reinforcing agent, to polymers to improve strength is a method that
aims to mimic the way plants and trees generate the strength to support their
structures. Composite materials like this, with cellulose fibers reinforcing a
matrix or resin composed of a naturally derived polymer, could deliver
materials tough enough even for the vehicle industry, where bioplastics have
struggled to match the properties of petrochemical plastics and resins.
Making Solid CO2 Gains
Other research has
focused on polymers created from feedstocks other than cornstarch. For example,
Hillmyer and Tolman in Minneapolis have reported an interesting class of
thermoplastic elastics prepared from the ester lactide and an extract of
menthol from spearmint. In Konstanz, Germany, Mecking and co-workers have
developed efficient chemical processes to transform natural fatty acids (which
are the well known polyunsaturates found in oil crops such as rapeseed) into
polymers with properties similar to polyethylene.
Many companies and
academic research groups worldwide are working intensively on how to create
processes that will sequester as much CO2 as possible. At Imperial College
London, we have developed an intriguing class of catalysts, based on
inexpensive zinc and magnesium, which use CO2 very productively at pressures as
low as one atmosphere and using carbon dioxide that is heavily contaminated
with water.
Such naturally derived
polymers clearly have a bright future, with some materials already commercially
available and others arriving in the next three to five years. The pace of
research in this area is rapid and accelerating. Today, the major use is in
packaging, but longer term these materials will expand into most if not all
markets that plastics currently rule.
Charlotte Williams is professor of Chemistry at Imperial College
London. This article was originally published at The Conversation,
www.theconversation.com
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