1. Developing Biodegradable Plastics from Starch
The diversity and ubiquity of plastic biodegradable synthetic polymer like
products substantially testify to the polylactic acid (PLA) with varying
versatility of the special class of results. Starch is typically plasticised,
engineering materials known as destructured, and/or blended with other
polymers. However, the non- materials to form useful mechanical
biodegradability of these petrochemical- properties.
based materials has been a source of
environmental concerns and hence, the Experimental studies have demonstrated
driving force in the search for green that cassava starch could be used for
alternatives for which starch remains the making various types of packaging
frontliner. Starch is a natural biopolymer products. As a major source of starch in
consisting predominantly of two tropical and subtropical regions, cassava
polymer types of glucose namely is a promising raw material for the
amylose and amylopectin. The alpha development of biodegradable plastics in
linkage of amylose starch allows it to be these areas.
flexible and digestible.
Biodegradability of Starch Based
The advantages of starch for plastic Polymer
production include its renewability, good
oxygen barrier in the dry state, Starch is a linear polymer
abundance, low cost and (polysaccharide) made up of repeating
biodegradability. The longstanding quest glucose groups linked by glucosidic
of developing starch-based linkages in the 1-4 carbon positions. The
biodegradable plastics has witnessed the length of the starch chains will vary with
use of different starches in many forms plant source but in general the average
such as native granular starch, modified length is between 500 and 2000 glucose
starch, plasticized starch and in blends units.
with many synthetic polymers, both
biodegradable and non-biodegradable, Starch-based biodegradable plastics may
for the purpose of achieving cost have starch contents ranging from 10%
effectiveness and biodegradation to greater than 90%. Starch based
respectively. The type of starch and polymers can be based on crops such as
synthetic polymer as well as their corn (maize), wheat, cassava or potatoes.
relative proportions in the blends Starch content needs to exceed 60%
influence the properties of the resulting before significant material breakdown
plastic blends. occurs. As the starch content is
increased, the polymer composites
Starch has been used as fillers in starch- become more biodegradable and leave
filled polymer blends, thermoplastic less recalcitrant residues. Often, starch-
starch (TPS) (produced from the based polymers are blended with high-
combination of starch, plasticizer and performance polymers (e.g. aliphatic
thermomechanical energy), in the polyesters and polyvinyl alcohols) to
production of foamed starch and

2. achieve the necessary performance inorganic), processing conditions, all in
properties for different applications. the hope of realizing renewable
At lower starch contents (less than 60%) biodegradable substitutes for the
the starch particles act as weak links in petroleum based plastics.
the plastic matrix and are sites for
biological attack. This allows the
polymer matrix to disintegrate into small
fragments, but not for the entire polymer
structure to actually bio-degrade.
Biodegradation of starch based polymers
is a result of enzymatic attack at the
glucosidic linkages between the sugar
groups leading to a reduction in chain
length and the splitting off of sugar units
(monosaccharides, disaccharides and
oligosaccharides) that are readily utilised
in biochemical pathways. High starch
content plastics are highly hydrophilic
and readily disintegrate on contact with
water. This can be overcome through
blending, as the starch has free hydroxyl
groups which readily undergo a number
of reactions such as acetylation, Amit Singh (PG Dip Chem, BScEN, USP)
esterification and etherification. Lecturer in Chemistry
Fiji Institute of Technology
Email – singh_a@fit.ac.fj
There are several categories of
biodegradable starch-based polymers
including:
Thermoplastic starch products;
Starch synthetic aliphatic polyester
blends;
Starch PBS/PBSA polyester blends; and
Starch PVOH Blends.
Most starch-based composites exhibit
poor material properties such as tensile
strength, yield strength, stiffness and
elongation at break, and also poor
moisture stability. This therefore
requires more scientific inquiries
towards improving the properties of
these promising starch-based
biocomposites through starch
modification, use of compatibilizers and
reinforcements (both organic and