Environmental Engineering Reference
In-Depth Information
polymers” (discussed in Chapter 6 ). Biodegradability is merely a property
or functionality of a plastic material. Both bio-based and conventional
polymers can be biodegradable or nonbiodegradable in the environment as
illustrated in Table 4.9 . As “nonbiodegradable” is strictly a misnomer (see
Chapter 6 ), the term “durable” is used in its place.
Table 4.9 Selected Examples of the Three Classes of Plastics
Durable
Readily biodegradable
Conventional PE, PP, PS, PET,
PVC
Poly(caprolactone), poly(butylene
succinate/adipate), copolymers of
poly(butylene succinate)
Bio-derived Cellulose esters,
cellulose ethers
Rayon, cellophane, chitosan, gelatin,
gluten (wheat), zein (corn), pectin
Bio-based
Bio-PET, bio-PE,
biopolyamide 11,
biopolyamide 610
Poly(lactic acid)—compostable
Biopolymers Lignin, humus
Cellulose, starch, chitin, pullulan,
zein
Using renewable feedstock to make plastics is a key dictum in
environmental sustainability. An abundance of biomass that can be used
as raw material is available. Of the 170 billion tons of biomass produced
annually by nature, less than 4% is used by humans (mostly for food and
wood-based industries (Thoen and Busch, 2006)). The first bio-derived
plastic, celluloid, was invented back in 1860 followed by a few others in the
1940s. But with the discovery of oil, these inventions were never developed
into commercial scale. With future shortage of fossil fuels, the time is ripe to
exploit bio-based and bio-derived technologies (Momani, 2009).
The savings in primary energy and avoided CO 2 emissions in using
bio-based feedstock compared to conventional petroleum feedstock are
significant. For instance, the GHG emission for conventional PET in a
cradle-to-grave LCA estimate was 3.36 (kg equiv. CO 2 /kg plastic). The
corresponding number for bio-based PET was 2.34-2.67 (kg equiv. CO 2 /kg
plastic), depending on feedstock used (Shen et al., 2012).
 
 
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