A Novel Method for the Production of
Biodegradable Polylactic Acid (PLA) from
Municipal Food Waste
The system is designed as a total material
recycling process for municipal food waste, with
minimal environmental emissions and energy
savings. It has also the potential to produce
from MSW a valuable, renewable product that
can substitute for currently produced nonrenewable,
petrochemical polymers.
Introduction
The production of plastics and articles
produced from them is expanding systematically
since they are cheap, lucrative,
light weight, coloured, durable
and consume less energy for production.
But simultaneously the amount
of waste is increasing because the
majority of conventional plastics are
resistant to the long-lasting action of
weather and/or drastic biological conditions
and not degradable. Both recycling
and combustion are processes,
which permit only a partial
solution of the above mentioned problems.
In the recent years, intensive
investigations into biodegradable
polymers have been undertaken. It
seems that one polymer which may
meet our requirements and replace the
majority of popular plastics on market
is Poly Lactic Acid (PLA).
Municipal Solid Wastes (MSWs),
including food waste, are usually in-cinerated or landfilled,
but these processes
generate many unnecessary
problems. Incineration
facilities can be
damaged by temperature
fluctuations when food
waste with high water
content is burnt in a
semi-continuous process.
In addition, it is difficult
to recover energy
from such waste incineration
processes because
the heating value
of food waste is low.
Further, landfill space is very limited,
and uncontrolled fermentation of organic
wastes in landfills causes secondary
problems, such as methane
emissions.
Treatment of biological solid
waste via microbiological processes
improves these wastes and reduces
the need for both landfill space and
fuel used in waste incineration. Direct
composting and methane fermentation,
which produce fertilities and
biogas, are the alternative ways to reuse
food waste, but these processes
have been applied only in rural areas.
On the other hand, there are economical
ways and means for converting
solid waste into natural Lactic acid
from which biodegradable polylactic
acid can be manufactured.
Lactic acid has both hydroxyl and
carboxyl groups with one chiral carbon
atom, and are widely used in food,
pharmaceutical, and in general, chemical
industries. In addition, Lactic acid can be polymerized to produce the
biodegradable and recyclable polyester
polylactic acid (PLA) which is considered
a potential substitute for plastics
manufactured from petrochemicals.
Although the ester bond of Poly-
L-Lactate (PLLA) is susceptible to
some enzyme, including proteinase
and lipases, and PLLA has been recognized
as a biodegradable plastic, its
biodegradation in soil is rather slow
and depends on morphology and
thickness. Therefore, PLLA may better
be developed as a chemically recyclable
plastic with an appropriate collection
system for the used materials
and not as a single-use plastic. Recently
the production of PLLA from
cornstarch has been taken up in the
industrial scale by Cargill-Dow and
many other companies in the world.
Such materials are expected to come
into worldwide use, but PLLA and
other-plant derived plastics are costly,
thus preventing their widespread application.
In addition, the process uses
corn starch feedstock, which is also a
source of food for human and other
animals.
Figure - 1 shows schematic diagram
for the production of Lactic acid
from municipal solid waste.
....contd.
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