Chemistry Reference
In-Depth Information
occurred. Nevertheless, the low cost of this polyester and its rapid bio-
degradation properties have promoted continued interest in its develop-
ment.
27-28,33,46
There are certain problems associated with these polyesters:
they are highly hydrophilic (water sensitivity) and exhibit high brittleness.
Both of these conditions have limited their use.
7.3
Ingredients and Cost of Bio-plastics
7.3.1 The Cost of Current Bio-plastics
Polylactic acid is the one of the most popular bio-plastics in today's market,
being manufactured from fermented plant starch (usually corn).
10,48
PLA is
often considered an alternative to petroleum-based plastics but it has some
major disadvantages such as poor mechanical performance, especially at
high temperatures and in wet environments, poor bio-degradability and a
relatively high price versus petroleum-based polyolefins.
48
In order to im-
prove the mechanical and thermal properties of PLA, commercial additives
are included with PLA during processing.
10
PLA could be employed as a
substitute for PS.
49
The price of PLA has declined considerably over the years
from US$2.00 per lb in 2005
48
to around US$1.00 per lb in 2007.
10
The price
of other ''green'' thermoplastics is considerably more than petroleum-based
plastics. For comparative purposes the current costs of petroleum-based
plastics are shown in Table 7.2.
For example, bio-based PE is about 50% more expensive than petroleum
PE (US$1.50-1.80 per lb versus US$1.04-1.23 per lb).
50
Similarly, bio-based
Table 7.2 Prices of petroleum-based plastics.
Cost/U$ per lb
a
Plastic
Thermoplastic:
High Density Polyethylene (HDPE)
1.04-1.23
Low Density Polyethylene (LDPE)
1.15-1.14
Linear Low Density Polyethylene (LLDPE)
0.97-1.28
Polystyrene (PS)
1.27-1.77
Polyvinyl Chloride (PVC)
0.94-1.12
Polypropylene (PP)
1.15-1.60
Acylonitrile Butadiene Styrene (ABS)
1.15-1.70
Acrylic
1.25-1.30
Polyethylene terephthalate (PET)
97-1.12
Thermoset:
Epoxy 1.00-2.97
Melamine molding compound 1.35-1.75
Phenolic 0.75-0.85
Polyester unsaturated 1.71-2.65
Polyurethane isocyanates 1.05-1.20
Urea molding compound 0.95-1.10
Vinyl ester 2.04-2.37
a
Prices presented were obtained from a current plastic resin price chart
accessed 02/02/14.
54
