329
19
Chitin and Chitosan
Chitin is the structural polysaccharide of invertebrates and is found in industrial significant
amounts mainly in the shells of crustaceans.
It is thus a waste product of the food industry.
Chitosan is the derivative of chitin produced by
deacetylation and has primary amino groups
(7 Chap. 9).
In contrast to chitin, chitosan is soluble in
organic acids, and therefore more comfortable
to be processed. Chitin can be converted
analogously to regenerated cellulose via the corresponding xanthogenate (7 Sect. 7.3). Both can
be used to produce films, foils, fibers and other
molded parts. Chitin and chitosan have the most
important fields of application as bioplastics in
the manufacture of antibacterial medical products, e.g. as wound pads, catheters and sutures.
Collagens
The term collagen comprises the scaffold proteins (scleroproteins), which are the most common proteins in the human and animal organism
with a proportion of up to 30%. They are found
in the skin, muscles, bones, connective tissue,
tendons, cartilage and teeth. It is estimated that
there are about 30 different types of collagen,
which differ in their amino acid composition
(primary structure) and their spatial arrangement (secondary and tertiary structure, 7 Chap.
14). Hence, the most diverse tasks in the body
can be addressed. The structure of collagens from
the single strands via micro- and macrofibrils to
individual fibers is similar to that of cellulose in
wood.
The most important collagen-based biopolymer of humanity is leather, which has been
used for clothing as long as humankind itself.
The most industrially important leather comes
from cattle, whose skin is treated as slaughter waste in an elaborate process to become
leather: i.e. tanning. There are several types of
tanning, in which mineral tanning with chrome
salts is applied to over 90% of the leather. Tanning makes the leather durable and workable.
It then has excellent properties that make it a
high-priced product for shoes, clothing, car and
furniture upholstery and other everyday items
(. Fig. 19.5).
Another important application of collagen
as a biopolymer is the production of sausage
viscose. It can also be processed into films
(cellophane) which can be mixed with glycerol as a plasticizer and used as packaging
material for food, for instance. The use of
regenerated cellulose as a material for artificial casings in sausage production is also of
significance.
5 Cellulose esters, such as cellulose acetate,
are also of importance. It is used as fibers,
e.g. in cigarette filters, and as film, e.g. for
food packaging. Cellulose nitrate, the ester
with nitric acid, mixed with camphor gives
celluloid, which is regarded as the first thermoplastic. Historically, it was introduced as
a replacement for billiard balls made of ivory
and later used as a film carrier. Today, table
tennis balls are still made of this material.
Lignin
The use of lignin in the plastics sector was presented in 7 Sect. 11.4.2.
Starch
The use of starch, the structure and occurrence
of which have already been discussed in detail in
7 Chap. 8, for the production of bioplastics can
principally be achieved in two ways:
5 Indirect use: Starch is used as a basic fermentation material for the production of, e.g.
lactic acid or polyhydroxyalkanoates.
5 Direct use: Starch is used directly to produce
various bioplastics.
The indirect use of starch for the production of
bioplastics is explained elsewhere in this chapter. Bioplastics produced directly from starch
include, for example, partially fermented starch
plastics. These have the advantage that they
can be produced from waste streams, e.g. from
potato treatment with subsequent cleaning.
The starch is partly converted into lactic acid
by naturally occurring lactic acid bacteria and
then dried to 10% residual water content and
extruded after the addition of certain additives.
These bioplastics still play a comparatively minor
role. There are also thermoplastic starches and the
starch blends based on them, which have already
been discussed in 7 Chap. 8. Native or thermoplastic starch mixed with reinforcing fibers
results in starch composites, which can be processed by injection molding.
19.2 · Biopolymer Representatives
19
Chitin and Chitosan
Chitin is the structural polysaccharide of invertebrates and is found in industrial significant
amounts mainly in the shells of crustaceans.
It is thus a waste product of the food industry.
Chitosan is the derivative of chitin produced by
deacetylation and has primary amino groups
(7 Chap. 9).
In contrast to chitin, chitosan is soluble in
organic acids, and therefore more comfortable
to be processed. Chitin can be converted
analogously to regenerated cellulose via the corresponding xanthogenate (7 Sect. 7.3). Both can
be used to produce films, foils, fibers and other
molded parts. Chitin and chitosan have the most
important fields of application as bioplastics in
the manufacture of antibacterial medical products, e.g. as wound pads, catheters and sutures.
Collagens
The term collagen comprises the scaffold proteins (scleroproteins), which are the most common proteins in the human and animal organism
with a proportion of up to 30%. They are found
in the skin, muscles, bones, connective tissue,
tendons, cartilage and teeth. It is estimated that
there are about 30 different types of collagen,
which differ in their amino acid composition
(primary structure) and their spatial arrangement (secondary and tertiary structure, 7 Chap.
14). Hence, the most diverse tasks in the body
can be addressed. The structure of collagens from
the single strands via micro- and macrofibrils to
individual fibers is similar to that of cellulose in
wood.
The most important collagen-based biopolymer of humanity is leather, which has been
used for clothing as long as humankind itself.
The most industrially important leather comes
from cattle, whose skin is treated as slaughter waste in an elaborate process to become
leather: i.e. tanning. There are several types of
tanning, in which mineral tanning with chrome
salts is applied to over 90% of the leather. Tanning makes the leather durable and workable.
It then has excellent properties that make it a
high-priced product for shoes, clothing, car and
furniture upholstery and other everyday items
(. Fig. 19.5).
Another important application of collagen
as a biopolymer is the production of sausage
viscose. It can also be processed into films
(cellophane) which can be mixed with glycerol as a plasticizer and used as packaging
material for food, for instance. The use of
regenerated cellulose as a material for artificial casings in sausage production is also of
significance.
5 Cellulose esters, such as cellulose acetate,
are also of importance. It is used as fibers,
e.g. in cigarette filters, and as film, e.g. for
food packaging. Cellulose nitrate, the ester
with nitric acid, mixed with camphor gives
celluloid, which is regarded as the first thermoplastic. Historically, it was introduced as
a replacement for billiard balls made of ivory
and later used as a film carrier. Today, table
tennis balls are still made of this material.
Lignin
The use of lignin in the plastics sector was presented in 7 Sect. 11.4.2.
Starch
The use of starch, the structure and occurrence
of which have already been discussed in detail in
7 Chap. 8, for the production of bioplastics can
principally be achieved in two ways:
5 Indirect use: Starch is used as a basic fermentation material for the production of, e.g.
lactic acid or polyhydroxyalkanoates.
5 Direct use: Starch is used directly to produce
various bioplastics.
The indirect use of starch for the production of
bioplastics is explained elsewhere in this chapter. Bioplastics produced directly from starch
include, for example, partially fermented starch
plastics. These have the advantage that they
can be produced from waste streams, e.g. from
potato treatment with subsequent cleaning.
The starch is partly converted into lactic acid
by naturally occurring lactic acid bacteria and
then dried to 10% residual water content and
extruded after the addition of certain additives.
These bioplastics still play a comparatively minor
role. There are also thermoplastic starches and the
starch blends based on them, which have already
been discussed in 7 Chap. 8. Native or thermoplastic starch mixed with reinforcing fibers
results in starch composites, which can be processed by injection molding.
19.2 · Biopolymer Representatives