Unit 12

POLYMERS
POLYMERS
Polymers are large molecules built from many smaller repeating units called monomers These monomers
bond covalently to form long chains giving polymers their unique properties. Polymerisation is the joining up
of many monomers to form a big molecule.
CLASSIFICATION
Polymers can be classified into two categories based on their synthesis: addition polymers and condensation
polymers.
1. ADDITION POLYMERS
FORMATION:
Addition polymers are formed by adding monomer units without losing the small molecules. Monomers
usually contain double or triple bonds that open and combine to form a polymer The number of carbon atoms
in these chains can vary from 4000 to 40,000.
REPEATING UNITS: For a polymer, a repeating unit is the same as a monomer, except that the double
bond is replaced by a single bond after polymerization.
EXAMPLES
(i) POLYTHYLENE (PE)
Monomer: CH2= CH2 ethylene
Repeating unit: — CH2—CH2 —
Formation
Ethene is the smallest hydrocarbon containing a carbon-carbon double bond Ethene molecules can join
together to produce very long chains. Part of the double bond is broken, and the electrons in it are used to
join neighbouring molecules. This process is called addition polymerisation.
At high temperatures and high pressures, the monomer ethene joins up to give a polymer called polyethylene
or polyethene.
H H H
H
n C C C C
H H
H H n
Ethene Polyethene

(ii) POLYPROPYLENE (PP)

Monomer: CH2=CH—CH3 propylene
Repeating unit: ̶ CH2 — CH(CH3) ̶̶̶ or
CH2 CH

CH3

Formation
H H H

n H2C C CH3 C CH

H n
CH3
Propylene
Polypropylene
(iii) POLYVINYLCHLORIDE (PVC)
Monomer (CH2=CHCI) Vinyl chloride
Repeating unit
H Cl
C C
H H

Formation
Chloroethene is an ethene molecule in which one of the hydrogen atoms is replaced by a chlorine atom. It is
called vinyl chloride. Ploymerising vinyl chloride gives polychloroethene. Its commercial name is
polyvinylchloride(PVC).

H H Cl
Cl
n C C C C
H H
H H n
Vinylchloride Polychloroethane

2. CONDENSATION POLYMERS
FORMATION:
Condensation polymers are formed in a condensation reaction where each time a bond is formed between
two monomers, a small molecule (often water) is released. polymers form in a different
Some way than addition polymers. If one monomer contains a -OH group and the other -H. then they can be
joined by eliminating a molecule of water. This reaction is called a condensation reaction. This type of
polymerisation process is called condensation polymerisation.
Repeating units:
In condensation polymers, the repeating unit usually consists of two different types of monomers, each of
which forms the polymer backbone with functional groups that react to form the polymer and release small
molecules.
Example: Polyesters such as polyethylene terephthalate (PET) are formed from terephthalic acid (HOOC-
CH-COOH) and ethylene glycol (HO-CH2-CH2-OH).
MAIN TYPES
Condensation polymers are usually polyamides or polyesters formed by the reaction of functional groups
(e.g. carboxyl and amino in polyamides or carboxyl and hydroxyl group in polyesters) with the removal of a
small molecule such as water
(i) POLYESTERS
Polyster such as polyethylene terephthalate (PET) are formed from terephthalic acid (HOOC-CH-COOH)
and ethylene glycol (HO-CH2-CH2-OH).
Monomers: terephthalic acid and ethylene glycol (a diol)
Repeating unit: —OC—CH—COO—CH2—CH2—O—
Released molecule: water (H₂O)
Uses: Polyester fibres are very strong and flexible and are used to make clothing. For example, terylene,
which can give permanent crease, useful for trousers.

(ii) POLYAMIDES
Polyamide such as nylon-6, 6 are formed from hexamethylenediamine (H₂N-(CH2)-NH2) and adipic acid
(HOOC-(CH2)-COOH).
Monomers: hexamethylenediamine and adipic acid
Repeating unit: -NH-(CH2)-NH-CO-(CH)-CO-
Released molecule: water (H₂O)

Uses: Nylon is used to make carpets, clothing, ropes that do not rot, and toothbrushes. Nylon is stronger
and durable than natural fibers such as cotton.

PET RECYCLING AND RE-POLYMERISATION

Condensation polymers generally have a higher potential for recycling compared to addition polymers.
Polyethylene terephthalate (PET) undergoes acid hydrolysis in the presence of strong acids such as sulphuric
acid (H₂SO₄) or hydrochloric acid (HCl) at high temperature (e.g., 200-250°C) and pressure. The reaction
breaks down the ester bonds in PET. This reaction produces the monomers from which PET is made i.e.,
terephthalic acid and ethylene glycol
The Chemical Reaction:
During acid hydrolysis:
1. The ester bonds (-COO-) in PET are cleaved.
2. Water molecules (H₂O) and the acid catalyst attack these bonds, breaking the polymer into smaller
molecules.
The reaction can be written as:
 n HOOC C6H4 COOH + nHO H2C CH2 OH
OOC C6H4 CH2 CH2 + (2n+1) H2O

Acid hydrolysis of PET is an essential step in recycling, as it allows recovery of pure monomers for reuse in
making new PET or other products. This process contributes to sustainability by reducing the need for raw
materials and minimizing plastic waste.

PET recycling flow diagram

PLASTICS
 The word "plastic" is derived from the Greek word "plastikos" which means "malleable" or
"moldable" and "plastos" meaning "mouldable."
 Plastics are synthetic materials made from organic polymers, such as PVC (polyvinyl chloride),
polyethylene (polyethylene), nylon, etc.
 These materials can be melted down and then transformed into solid or slightly flexible shapes. They
are also referred to as "long carbon chain polymers". The ability of a material to be moulded or
malleable during the manufacturing process means that it can be cast, pressed, or extruded into a
variety of forms, including film, fiber, sheet, tube, bottle, and box.
PROPERTIES OF PLASTICS
The properties of plastics are directly derived from the characteristics of the polymers they are made from.
Some of these are:
1. Molecular Structure
Polymer chains tend to be longer and more durable which can be (linear or branched. Branched polymers are
softer and more flexible. On the other hand, linear polymers are stronger and more rigid. Cross-linking is
also possible, with high cross-linking resulting in tough and heat-resistant plastics, such as vulcanized rubber.
2. Chemical Composition
Chemical composition is determined by the monomer type, which determines the plastic's properties. For
example, polyethylene (PE)is flexible and moisture-resistant, while polystyrene (PS) is stiff and brittle.
Additives such as plasticizers, stabilizers, and fillers can also enhance the plastic's properties, depending on
the processing conditions.
3. Temperature and Pressure
Conditions such as temperature and pressure during polymerisation and moulding affect the plastics'
crystalline structure, affecting properties like transparency, tensile strength, and melting poin
ENVIRONMENTAL IMPACT OF PLASTICS
Most plastics are highly resistant to degradation due to their strong carbon-carbon backbone. This leads to
long persistence to degradation. As plastics degrade slowly, they can break down into microplastics, which
are small particles that can contaminate water bodies. These microplastics are harmful to aquatic life and
human health.
Incineration
While incineration reduces plastic volume, it can release harmful chemicals and greenhouse gases if not
properly managed. Certain plastics, when burned, can emit toxic substances like dioxins and furans
IMPORTANCE OF POLYMERS IN THE TEXTILE INDUSTRY
Polymers are essential for the textile industry because they are versatile and can be used in a variety of
applications. The properties of polymers allow them to be used for a variety of purposes, from everyday
clothing to specialised industrial applications. Some of the most commonly used polymers in textiles, with
their specific characteristics are:
1. Polyester (PET): Durability, shrinking and stretching resistance, rapid drying, excellent colour
retention, etc. PET is used in clothing (for example, shirts and pants), home furnishing (for example, curtains
and bed linens) Industrial applications (ropes and tyre cords).
2. Nylon-6,6 (polyamide) has properties such as high strength, high elasticity, resistance to abrasion, and
chemical and oil resistance. It is commonly used in clothing. It can also be used as a part of blended fabrics
for different garments. It is also used for making tooth brushes, ropes that don't rot, carpets, and other
products.
3. PE (polyethylene) is lightweight, durable, and has properties such as good thermal insulation, water
resistance, chemical resistance, moisture resistance, mildew resistance, and other properties. Polyethene is
used for making trays, fruit juice containers, milk containers, crates, food packaging products, garbage bags,
toys, insulation for wires and cables, and housewares.
PROPERTIES OF PLASTICS AND THEIR IMPLICATIONS FOR DISPOSAL
The properties of plastics, while beneficial for their intended uses, create significant challenges for disposal.
Therefore, plastics cause numerous environmental issues. The following properties of plastics pose
implications for disposal.
1.Durability and Longevity
Plastics are made durable, which means that they can withstand a wide range of environmental conditions
without breaking down quickly. However, because of the same durability plastics can last hundreds or even
thousands of years in the environment. This makes them difficult to dispose off. After being disposed off,
plastic can end up in landfill sites or nature for an extended period of time, resulting in long-term problems
with waste management.
2. Lightweight Nature
Because plastics are lightweight, they can be easily packed and transported, but they can also be transported
by wind or water. This makes it easier for them to spread over long distances, which can lead to extensive
environmental pollution, particularly in marine environments.
3. Chemical Composition
The chemical composition of plastics can vary from one plastic material to another. Many plastic materials
contain additives to enhance their properties, such as stabilisers, plasticizers, flame retardants, etc. These
additives can leach materials into the environment, which can pose a risk to ecosystems and to human
health.
4. Recyclability
Some plastics can be recycled. However, their contamination, sorting issues, and economic constraints often
limit the amount that can be recycled. Many plastics cannot be recycled effectively, resulting in a large
portion of them going to landfill or being burned.

ENVIRONMENTAL CHALLENGES CAUSED BY PLASTICS

Many environmental challenges are caused by plastics. Some of these are as follows.
1. DISPOSAL OF PLASTICS IN LANDFILL SITES
The disposal of plastics in landfills has the following implications.
a) Space consumption in landfill
Plastics take up a lot of space in a landfill because of their size and resistance to compaction. This means
that landfills fill up quickly, leading to more landfilling and exacerbating land use issues.
b) Chemical leaching in soil
Over time, plastic in a landfill can leach dangerous chemicals into soil or groundwater.
c) Formation of microplastics
As plastic slowly decomposes in a landfill, it breaks down into smaller micro-plastic particles. Micro-
plastics can then seep into soils and water bodies and become a persistent environmental pollutant.
2. ACCUMULATION IN OCEANS
Plastics accumulate in ocean rings and build up into large floating debris, like the Pacific Garbage Patch.
Marine plastic pollution
Plastics are a major component of marine litter, and an estimated 8M tons of plastic are dumped into the
ocean each year.
Impact on marine animals
Plastics can also be ingested and entangled by marine animals, which often mistake plastic for food. This
can cause gastrointestinal blockage and even death.
Microplastics in food chain
Microplastics can enter the food chain, and once in the food supply, these pollutants can reach toxic levels
in humans.
3. FORMATION OF TOXIC GASES FROM BURNING
Incinerating plastics releases a variety of toxic gases and particulates. These substances are known to be
carcinogenic and can cause serious health problems for humans and animals.
Contribution to air pollution
Burning plastics contributes to air pollution, releasing greenhouse gases like carbon dioxide (CO₂) and
methane (CH4), which aggravate climate change.
Health risks
The emission of other pollutants can also cause respiratory problems, cardiovascular diseases, and other
health issues for populations living near incineration facilities.
Contamination from residual ash
The residual ash from burning plastics can contain toxic substances that, if not properly managed, can
contaminate soil and water sources. This further complicates the disposal process and poses additional
environmental risks.
NEED FOR SUSTAINABLE WASTE MANAGEMENT
Addressing these challenges requires comprehensive waste management strategies, increased recycling
efforts, and the development of more sustainable materials.