Chemistry Reference
In-Depth Information
Synthetic Pathways
Examples
Thermoplastic starch (TPS)
Extraction and modification of
natural polymers in plants
Cellulose derivatives
Rubber
Polyamides
Polyurethanes
Polyesters
Polymerization of
bio-monomers
Bioplastics
Polylactic acid
Extraction of polymers
produced by microorganisms
Polyhydroxylalkanoates (PHA family)
FIGURE 13.4
Flow chart of different pathways used to synthesize bioplastics.
the material. When polyisoprene is vulcanized with heat and sulfur, the resulting
product is very useful in commercial products such as tires
[5]
.
13.3.1.2
Starch
Starch, in its native form, is a granular structure. This form of starch is incorpo-
rated into plastics as a type of filler
[14]
. Starch is heavily used in food proces-
sing, such as cereal, snacks, canned goods, frozen food, dairy products, and much
more. Starch is also used in a variety of industries such as adhesives, mining,
metal, paper, cosmetics and pharmaceutical, construction, and textile in many pro-
ducts. In order to use starch as the polymer for a bioplastic application, the poly-
mer structures amylose and amylopectin are extracted. Extraction occurs by
disrupting the granular structure by solubilization of the starch granules in water
at elevated temperatures, called gelatinization
[4,15]
. In the presence of water the
granules swell and eventually burst, leading to the release of polymer into the sur-
rounding water. Products used for a range of applications can be obtained depend-
ing on the level of destruction of the granule caused by the water content, time,
and temperature of the extraction. For starch to be able to be classified as a plas-
tic, usable interchangeably with traditional plastics, it must undergo further pro-
cessing before it is classified as thermoplastic starch.
Thermoplastic starch (TPS) is defined as destructurized or gelatinized starch
that is combined with one or more additives (plasticizer) to produce a material
that can be treated like other thermoplastic polymers
[16]
. Common plasticizers
used are glycerol, sorbitol, polyethylene glycol, or other polyols that are added to
the extracted polymer. The plasticizers are able to separate the melting tempera-
ture from the thermal degradation temperature to allow the extracted polymers to
be processed using conventional machines, such as extrusion and injection mold-
ing. The resulting material is expelled from the extrusion die as a homogeneous
molten phase and then pelletized after cooling. Thermoplastic starch blended
