Chemistry Reference
In-Depth Information
Fig. 3.15
Approachability of grafted and linear polymers to the particles in an effluent [
106
]
with acrylate esters, methacrylate esters and styrene results in thermoplastic grafts
and these are used in the preparation of starch-filled plastics because hydrophobic
grafted branches will make a graft copolymer more compatible with the plastic
matrix than unmodified starch. Plastics filled with the graft copolymers were easily
attacked by the common soil microorganisms and these plastics also exhibit higher
tensile strength and better appearance than those filled with unmodified starch. One
of the most promising polymer for this type of use is starch-g-poly(methyl methac-
rylate-
co
-acrylonitrile). Extrusion processing of granular starch-g-poly(methyl
acrylate) yields tough, leathery, translucent plastics, which maintain their integrity
when immersed in water for prolonged period of time.
Starch-graft-poly(acrylonitrile) and starch-graft-polymethacrylate can be
extruded for use as expanded packaging material or foamed protective packaging
material that can replace traditional expanded “polystyrene peanuts” [
107
]. Such
starch-based loose fills contain a variety of biodegradable polymers and additives
that will improve resiliency and compressibility and aid in processing. Low shear
conditions during extrusion produce loose fills that are both brittle and heavy,
regardless of the type of starch used. The process of the disordering of amylose
and amylopectin chains through the melting of crystallites taking place during
heating of starch with limited amounts of water is called “destructurised starch”
[
108
]. The latter is useful in the development of extrusion-blown films from starch
and poly(ethylene
co
-acrylic acid) graft copolymers. As much as 50 % of the weight
of starch can be incorporated into such composites, yet still retain acceptable
properties.
The use of such biodegradable films for agricultural mulching controls weeds
conserves soil moisture and heat for early cropping, and reduces nutrient leaching.
As the starch portion is utilised by the organism, the available surface area of the
