Environmental Engineering Reference
In-Depth Information
A bio-derived plastic on the other hand is biopolymer that is chemically
modified to improve its properties. Cellulose from plants can be acetylated
to yield cellulose acetate, the bio-derived plastic used in cigarette filters.
It can also be xanthated and extruded into cellophane (or Rayon), a
bio-derived plastic. Chitin, a biopolymer from crab shells, can be processed
(by converting the amide functionalities into amine functionalities) into its
amine analog to obtain a bio-derived plastic, chitosan.
A bio-based polymer on the other hand is a man-made polymer where the
starting materials or raw materials (but not the polymer itself) are derived
from living organisms (generally plants). These renewable feedstocks are
used to make polymers varieties that are identical in chemistry to
conventional fossil fuel-based plastics.
Despite the fact that they are chemically identical, it is possible to
analytically identify bio-based plastics apart from identical fossil fuel-based
plastics. Carbon dioxide in air has two isotopic forms of carbon, 12 CO 2
and 14 CO 2 , in equilibrium with each other, and plastics derived from plant
sources will therefore have both these isotopes. Any 14 C isotopic carbon in
fossil fuel deposits, however, had long decayed over the millions of years
since their formation (half-life of 14 C is 5730 years) into 12 C and fossil fuels,
and plastics made from them do not have significant levels of 14 C. Burning a
sample of plastic and measuring the ratio { 14 C/ 12 C} in the CO 2 using liquid
scintillation counting or isotope-ratio mass spectrometry therefore provide
a test as to the origin of the plastic (ASTM D 6866).
The distinction between bio-based and conventional plastics is based on
the source of feedstock and should not be confused with “biodegradable
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