Biopolymer

1. INTRODUCTION
 Biopolymers are polymers that are
biodegradable.
 The input materials for the production of these
polymers may be either renewable (based on
agricultural plant or animal products) or
synthetic.
 There are four main types of biopolymer based
respectively on:
1. Starch
2. Sugar
3.Cellulose
4.Synthetic materials

2. BIOPOLYMERS
 Biopolymers are polymers produced by living
organisms.
 Cellulose and starch, proteins and peptides
and DNA and RNA are all examples of
biopolymers, in which the monomeric units,
respectively, are sugars, amino acids, and
nuclotides.
 Cellulose is both the most common biopolymer
and the most common organic compound on
Earth.
 About 33 percent of all plant matter is cellulose
(the cellulose content of cotton is 90 percent
and that of wood is 50 percent).

3. BIOPOLYMERS CLASSIFICATIONS
 Depending to the evolution of the synthesis process,
different classifications of the different bio- polymers
have been proposed.
 We have 4 different categories.
 Only 3 categories (a to c) are obtained from
renewable resources:
 Polymers from biomass such as the Agropolymers
from agro-resources (e.g., starch, cellulose),
 Polymers obtained by microbial production, e.g., the
polyhydroxy-alkanoates,

4.  Polymers conventionally and chemically synthesised
and whose monomers are obtained from agro-
resources, e.g., the polylacticacid.
 Polymers whose monomers and polymers are
obtained conventionally, by chemical synthesis.
 We can also classify these different biodegradable
polymers into two main families: the agro (category
a) and the biodegradable polyesters (categories b to
d).


6. BIOPOLYMERS VERSUS POLYMERS
 A major but defining difference between polymers and
biopolymers can be found in their structures.
 Polymers, including biopolymers, are made of repetitive
units called monomers.
 Biopolymers often have a well defined structure, though
this is not a defining characteristic (example:ligno-
cellulose):
 The exact chemical composition and the sequence in
which these units are arranged is called the primary
structure in the case of proteins.
 Many biopolymers spontaneously fold into characteristic
compact shapes as well as secondary structure and
tertiary structure, which determine their biological
functions and depend in a complicated way on their
primary structures.
 Structural biology is the study of the structural properties
of the biopolymers.


7.  In contrast most synthetic polymers have much
simpler and more random (or stochastic) structures.
 This fact leads to a molecular mass distribution that
is missing in biopolymers.
 In fact, as their synthesis is controlled by a template
directed process in most in vivo systems all
biopolymers of a type (say one specific protein) are
all alike: they all contain the similar sequences and
numbers of monomers and thus all have the same
mass.
 This phenomenon is called monodispersity in
contrast to the polydispersity encountered in
synthetic polymers.
 As a result biopolymers have a polydispersity
indexof 1.

8. CONCEPTS: BIODEGRADABILITY AND COMPOSTABILITY
 According to ASTM standard D-5488-94d,
biodegradable means capable of undergoing
decomposition into carbon dioxide, methane water,
inorganic compounds, or biomass in which the
predominant mechanisms is the enzymatic action of
micro-organisms that can be measured by standard
tests, over a specific period of time, reflecting
available disposal conditions.
 There are different media (liquid, inert or compost
medium) to analyse biodegradability.
Compostability is material biodegradability using
compost medium.
 Biodegradation is the degradation of an organic
material caused by biological activity - mainly
microorganisms' enzymatic action. This leads to a
significant change in the material chemical
structure.

9.  The end-products are carbon dioxide, new biomass
and water (in the presence of oxygen: aerobic) or
methane (oxygen absent: anaerobic), as defined in
the European Standard EN 13432:2000.
 Unfortunately, depending on the standard used
(ASTM, EN), different composting conditions
(humidity, temperature cycle) must be realised to
determine the compostability level.
 Then, it is difficult to compare the results using
different standard conditions.
 We must also take into account the amount of
mineralization as well as the nature of the residue left
after biodegradation .
 The accumulation of contaminations with toxic
residues and chemical reactions of biodegradation
can cause plant growth inhibition in these products,
which must serve as fertilizers.

10.  Actually the key issue is to determine for these by-
products, the environment toxicity level which is
called the eco-toxicity .
 Some general rules enable the estimating of the
biodegradability evolution.
 An increase of parameters such as the hydrophobic
character, the macromolecular weight, the
crystallinity or the size of spherulites decreases
biodegradability .
 On the contrary, the presence of polysaccharides
(blends) favours biodegradation.

11. ADVANTAGES OF BIOPOLYMERS
 Besides being available on a sustainable basis, biopolymers
have several economic and environmental advantages.
 Biopolymers could also prove an asset to waste processing.
 For example, replacing the polyethylene used in coated papers
by a biopolymer could help eliminate plastic scraps occurring in
compost.
 Consumers have a lively interest in biopolymers too.
 Conventional plastics are often seen as environmentally
unfriendly. Sustainable plastics could therefore provide an
image advantage.
 The major advantage of biodegradable packaging is that it can
be composted.
 But the biodegradability of raw materials does not necessarily
mean that the product or package made from them (e.g. coated
paper) is itself compostable.
Biopolymers can also have advantages for waste processing.

12.  Coated paper (with e.g. polyethylene) is a major
problem product for composting.
 Although such materials are usually banned from
inclusion in organic waste under separate collection
schemes, some of them usually end up nonetheless
in the mix.
 The paper decomposes but small scraps of plastic
are left over in the compost.
 The adoption of biopolymers for this purpose would
solve the problem.
Widespread interest for biopolymers among
consumers.
 Conventional plastics are environmentally unfriendly
in the public perception.
 Sustainability can provide an image benefit.

13. DISADVANTAGE OF BIOPOLYMERS
 A disadvantage of chemical modification of
biopolymer is however that the biodegradability
of the polymer may be adversely affected.
 Therefore it is often necessary to seek a
compromise between the desired material
properties and biodegradability.

14.  The environmental benefits of biodegradable
packaging must be reflected in cost advantages, if
large-scale applications are to become feasible.
 In the short term, it would be preferable to
communicate the functional advantages of
biodegradable packaging rather than its
compostability.

15. RENEWABILITY AND SUSTAINABLE DEVELOPMENT
 Renewability is linked to the concept of sustainable
development.
 The use of annually renewable biomass, like wheat,
must be understood in a complete carbon cycle.
 This concept is based on the development and the
manufacture of products based on renewable and
biodegradable resources: starch, cellulose,etc.
 By collecting and composting biodegradable plastic
wastes, we can generate much-needed carbon-rich
compost: humic materials.
 These valuable soil amendments can go back to the
farmland and reinitiate the carbon cycle.
 Besides, composting is an increasingly key point to
maintain the susbstainability of the agricultural
system by reducing the consumption of chemical
fertilizers.

16. DIFFERENT BIOPOLYMERS
 Polypeptides
 The convention for a polypeptide is to list its
constituent amino acid residues as they occur
from the amino terminus to the carboxylic acid
terminus.
 The amino acid residues are always joined by
peptide bonds.
 Proteins though used colloquially to refer to any
polypeptide, refers to larger or fully functional
forms and can consist of several polypeptide
chains as well as single chains.
 Proteins can also be modified to include non-
peptide components, such as saccharide chains
and lipids.

17.  Nucleic acids
 The convention for a nucleic acid sequence is to list
the nucleotides as they occur from the 5' end to the
3' end of the polymer chain, where 5' and 3' refer to
the numbering of carbons around the ribose ring
which participate in forming the phosphate diester
linkages of the chain.
 Such a sequence is called the primary structure of
the biopolymer.

18.  Sugars
 Sugar-based biopolymers are often difficult with
regards to convention.
 Sugar polymers can be linear or branched are
typically joined with glycosidic bonds .
 However, the exact placement of the linkage can vary
and the orientation of the linking functional groups is
also important, resulting in α- and β-glycosidic bonds
with numbering definitive of the linking carbons'
location in the ring.
 In addition, many saccharide units can undergo
various chemical modification, such as amination,
and can even form parts of other molecules, such as
glycoproteins.

19.  Poly-hydroxybutyrate-co-hydroxyvalerate
 (PHBV) is a copolymer of 3-hydroxybutanoic acid and
3-hydroxypentanoic acid, in which the monomer
units are connected by ester linkages.
The properties of PHBV vary according to the ratio of
both the acids.
 3-hydroxybutanoic acid provides stiffness and 3-
hydroxypentanoic acid imparts flexibility to the
copolymer.
 It is used in specialty packaging, orthopaedic devices
and even in controlled drug release.
 When a drug is put into a capsule of PHBV it is
released only after the polymer is degraded.
 PHBV also undergoes bacterial degradation in the
environment.

21. POLYLACTIC ACID
 Polylactic acid or polylactide (PLA) is a
biodegradable,thermoplastic aliphatic polyester
derived from renewable sources such as corn, starch
(in the U.S.) or sugarcanes(rest of world).
 Although PLA has been known for more than a
century, it has only been of commercial interest in
recent years, in light of its biodegradability.

23. 
Bacterial fermentation is used to produce lactic acid from
corn starch or cane sugar.
 However, lactic acid cannot be directly polymerized to a useful
product, because each polymerization reaction generates one
molecule of water, the presence of which degrades the forming
polymer chain to the point that only very low molecular weights
are observed.
 Instead, lactic acid is oligomerised and then catalytically
dimerised to make the cyclic lactide monomer.
 Although dimerization also generates water, it can be separated
prior to polymerization.
 PLA of high molecular weight is produced from the lactide
monomer by ring opening polymerisation using most commonly
a stannous octoate catalyst.

24. APPLICATIONS FOR BIODEGRADABLE POLYMERS
 Agriculture field:
 Agricultural applications for biopolymers are not
limited to film covers.
 Containers such as biodegradable plant pots and
disposable composting containers and bags are also
made of biopolymers.
 Fertilizer and chemical storage bags which are
biodegradable are also made of biopolymers.
 Young plants which are particularly susceptible to
frost may be covered with a thin Ecoflex film.
 At the end of the growing season, the film can be
worked back into the soil, where it will be broken
down by the appropriate microorganisms.
 Therefore, plastic films that begin to degrade in
average soil conditions after approximately one
month are ideal candidates as crop mulches.

25.  Medical Field:
 The biopolymers used in medical applications must
be compatible with the tissue they are found in, and
may or may not be expected to break down after a
given
time period.
 Development of biopolymers with adhesion sites that
act as cell hosts in giving shapes that mimic different
organs.
 Artificial bone material which adheres and integrates
onto bone in
 the human body. The most commonly employed
substance in this area is called Bioglass .
 Another application for biopolymers is in controlled
release delivery ofmedications. The bioactive
material releases medication at a rate determined by
its enzymatic degradation .


26.  PLA materials were developed for medical devices
such as resorbable screws, sutures, and pins.
 These materials reduce the risk of tissue reactions to
the devices, shorten recovery times, and decrease
the number of doctor visits needed by patients.

27.  Automotive field:
 Biobased cars are lighter, making them a more
economical choice for consumers, as fuel costs are
reduced.
Natural fibres are substituted for glass fibres as
reinforcement materials in plastic parts of
automobiles and commercial vehicles.
 Natural fibres (from flax or hemp) are usually applied
in formed interior parts.

28.  Others:
 Biopolymer starch (gelatin-based) fat replacers
possess fat-like characteristics of smooth, short
plastic textures that remain highly viscous after
melting.
 Biopolymer materials are currently incorporated into
adhesives, paints, engine lubricants, and
construction materials .
 Biodegradable golf tees and fishing hooks have also
been invented.
 Ecoflex is a fully biodegradable plastic material that
was introduced to consumers by BASF in 2001. The
material is resistant to water and grease, making it
appropriate for use as a hygienic disposable
wrapping, fit to decompose in normal composting
systems.
 Consequently, Ecoflex has found a number of
applications as a packaging wrap.

29.  Depart, the polyvinyl alcohol is used in hospital
laundry bags which are“washed away” allowing
sanitary laundering of soiled laundry, as well as
applications as disposable food service items,
agricultural products, and catheter bags
 Biodegradable plastic films may be employed as
garbage bags, disposable cutlery and plates, food
packaging, and shipping materials.

30. ORIGIN AND DESCRIPTION OF BIOBASED POLYMERS
 Biobased polymers may be divided into three main
categories based on their origin and production:
 Category 1. Polymers directly extracted/removed
from biomass. Examples are polysaccharides such
as starch and cellulose and proteins like
 casein and gluten.
 Category 2. Polymers produced by classical
chemical synthesis using renewable biobased
monomers.
 Exampleis polylactic acid, a biopolyester
polymerised from lactic acid monomers.
 The monomers themselves may be produced via
fermentation of carbohydrate feedstock.

31.  Category 3. Polymers produced by microorganisms
or genetically modified bacteria.
This group of biobased polymers consists mainly of
the polyhydroxyalkonoates, but
 developments with bacterial cellulose are in
progress.
 Category 1
 The principal polysaccharides are cellulose, starch,
gums, and chitosan.

32.  Starch, the storage polysaccharide of cereals,
legumes and tubers, is a renewable and widely
available raw material suitable for a variety of
industrial uses.
 As a packaging material, starch alone does not form
films with adequate mechanical
 properties (high percentage elongation, tensile and
flexural strength) unless it is first treated by either
plastization, blending with other materials, genetic or
chemical modification or combinations of the above
approaches.
 Corn is the primary source of starch, although
considerable amounts of starch are also produced
from potato, wheat and rice starch.
 Starch is economically competitive with petroleum
and has been used in several methods forpreparing
compostable plastics.
 Common plasticizers for hydrophilic polymers, such
as starch,are glycerol and other low molecularweight
– polyhydroxy –compounds, polyethers and urea.
 .

33.  Plasticizers lower the water activity, thereby limiting
microbial growth.
 Cellulose:
 Cellulose is the most abundantly occurring natural
polymer on earth and is an almost linear polymer of
anhydroglucose.
 Because of its regular structure and array of
hydroxyl groups,it tends to form strongly hydrogen
bonded crystalline microfibrils and fibres and is most
familiar in the form of paper or cardboard in the
packaging context.
 Cellulose is a cheap raw material, but difficult to use
because of its hydrophilic nature, insolubility and
crystalline structure.

34.  To make cellulose or cellophane film, cellulose is
dissolved in an aggressive, toxic mixture of sodium
hydroxide and carbon disulphide (“Xanthation”) and
then recast into sulphuric acid.
 The cellophane produced is very hydrophilic and,
therefore, moisture sensitive, but it has good
mechanical properties.
 It is,however, not thermoplastic owing to the fact that
the theoretical melt temperature is above the
degradation temperature, and therefore cannot be
heat-sealed.

35. Chitin:
 Chitin is a naturally occurring macromolecule In
present.
 the exoskeleton of invertebrates and represents the
second most abundant polysaccharide resource after
cellulose.
 In general,chitosan has numerous uses; flocculant,
clarifier, thickener, gasselective membrane, plant
disease resistance promoter, wound healing
promoting agent and antimicrobial agent.
 Chitosan also readily forms films and, in general,
produces materials with very high gas barrier, and it
has been widely used for the production of edible
coating.
 Furthermore, chitosan may very likely be used as
coatings for other biobased polymers lacking gas
barrier properties.
 However, as with other polysaccharide based
polymers, care must be taken for moist conditions.

36.  Proteins:
 Proteins can be divided into proteins from plant
origin (e.g.gluten, soy, pea and potato) and proteins
from animal origin (e.g. casein, whey, collagen,
keratin).
 A protein is considered to be a random copolymer of
amino acids and the side chains are highly suitable
for chemical modification which is helpful to the
material engineer when tailoring the required
properties of the packaging material.
 Due to their excellent gas barrier properties,
materials based on proteins are highly suitable for
packaging purposes.
 However, like starch plastics mechanical and gas
properties are influenced by the relative humidity due
to their hydrophilic nature.
 One of the ways to modify protein properties is by
chemical modification.

37.  Casein:
 Casein is a milk-derived protein.
 It is easily processable due to its random coil
structure.
 Upon processing with suitable plasticizers at
temperatures of 80–100 °C, materials can be made
with mechanical performance varying from stiff and
brittle to flexible and tough performance.
 Casein melts are highly stretchable making them
suitable for film blowing.
 In general, casein films have an opaque appearance.
 The main drawback of casein is its relatively high
price.
 Casein was used as a thermoset plastic for buttons
in the 1940’s and 50’s.
 It is still used today for bottle labelling because of its
excellent adhesive properties.

38.  Gluten:
 Gluten is the main storage protein in wheat and corn.
 Wheat is an important cereal crop because of its
ability to form a viscoelastic dough.
 Mechanical treatment of gluten leads to disulfide
bridge formation formed by the amino acid cysteine
which is relative abundant in gluten.
 Processing temperatures are, depending on the
plasticizer contents, in the range of 70–100 °C.
 Mechanical properties may vary in the same range as
those for caseins.
 Gluten plastics exhibit high gloss (polypropylene
like) and show good resistance to water under
certain conditions.
 They do not dissolve in water, but they do absorb
water during immersion.

39.  Due to its abundance and low price, research on the
use of gluten in edible films, adhesives, or for
thermoplastic applications is currently being carried
out.
 Soy proteins are commercially available as soy flour,
soy concentrate.
 And soy isolate, all differing in protein content.
 The most successful applications of soy proteins is
the use in adhesives, inks and paper coatings.