How environmental factors affect the structure of polymers

1. ENVIRONMENTAL BEHAVIOUR OF
POLYMERS
HNC/D Applied Chemistry
Polymer Chemistry
By Sabrina Lee

2. DEGRADATION
WHAT IS DEGRADATION?
Degradation is a type of organic chemical reaction in which a
compound is converted into a simpler compound. [1]
EXAMPLES OF DEGRADATION?
Examples of degradation include environmental degradation e.g. the
hole in the o-zone layer caused by car emissions and pollution (physical)
and chemical degradation.

3. DEGRADATION IN POLYMERS
POLYMER DEGRADATION
Degradation in polymers refers to a change in the properties of a
polymer under the influence of one or more environmental factors
FACTORS
 Heat
 Light
 Chemicals – Acids, Alkalis and some salts

4. IS DEGRADATION DESIRED OR UNDESIRED?
Are the changes in the properties of a polymer due to degradation
desired or undesired?
UNDESIRABLE CHANGES
X Cracking
X Chemical disintegration of
products
DESIRABLE CHANGES
 Biodegradation – deliberately
lowering the molecular
weight of a polymer for
recycling, often termed
“aging”.

5. TYPES OF DEGRADATION IN POLYMERS
PHOTOINDUCED DEGRADATION
Degraded by photolysis to give a lower molecular weight – often via
visible light or UV, X-rays or gamma rays.
THERMAL DEGRADATION
Degraded by thermolysis at high temperatures to give monomers, oils,
gases and water.
Includes: Pyrolysis, Hydrogenation and Gasification
CHEMICAL DEGRADATION
Degraded by solvolysis and mainly hydrolysis to lower molecular weight

6. ANTI-DEGRADANTS
WHAT ARE ANTI-DEGRADANTS?
Deterioration inhibitor in rubber compounds to deter the aging of rubber
products
HOW DO THEY WORK?
Anti-degradants cover the surface of the rubber product to prevent
direct contact between rubber and oxygen, thus preventing the
degradation, or “aging” of the product i.e. wax products

7. EXAMPLES OF WAXES
ANIMAL WAXES
Beeswax
Chinese wax
Lanolin (wool wax)
Shellac wax
VEGETABLE WAXES
Bayberry wax
Carnauba wax
Castor wax
Jojoba oil
Soy wax
MINERAL WAXES
Ceresin waxes
Montan wax
Ozocerite
Peat waxes
PETROLEUM WAXES
Paraffin wax
Microcrystalline wax
Petroleum jelly
SYNTHETIC WAXES
Polyethylene waxes
Chemically modified waxes
Substituted amide waxes
Polymerised α-olefins

8. ENVIRONMENTAL DEGRADATION
WHAT IS ENVIRONMENTAL DEGRADATION?
• The deterioration of the environment through depletion of resources,
such as air, water and soil.
• The destruction of ecosystems and the extinction of wildlife
• When natural habitats are destroyed or natural resources are
depleted, the environment is degraded.

9. FACTORS OF ENVIRONMENTAL
DEGRADATION
NATURAL FACTORS
• Droughts
• Storms – e.g. hurricanes,
tornadoes, volcanic eruptions
These factors lead to land
degradation caused by erosion.
HUMAN FACTORS
• Deforestation
• Industrialisation
• Urbanisation
These factors lead
to water, air and
land pollution.
[3]

10. ENVIRONMENTAL STRESS CRACKING (ESC)
[2]
WHAT IS ESC?
• Unexpected brittle failure of thermoplastic
polymers
• Accounts for 15-30% of all plastic
component failures in service
• Caused by exposure to liquid chemicals
• Occurs mostly in amorphous, brittle
polymers like polystyrene and
polycarbonate

11. ESC AND POLYMER DEGRADATION
ESC and polymer degradation are not the same thing.
Polymer degradation involves breaking polymer bonds, whereas ESC
does not.
ESC breaks the secondary linkages between polymers instead.

12. EXAMPLES OF ESC
ESC is seen in various polymers from plastic drinking glasses to the
automotive industry.
The need to resist ESC in the automotive industry is high as a number of
different polymers are subjected to a number of fluids.
Examples:
• Petrol
• Brake fluid
• Windscreen cleaning solution

13. HOW DOES STRUCTURE AFFECT
REACTIVITY?
The structure of a polymer depends upon various factors:
• Number of branches (methyl groups)
• Type of branching – long or short branched polymers
• Number of cross links within a polymer
All of these factors contribute to physical and mechanical properties of a
polymer.

14. HOW DOES STRUCTURE AFFECT
REACTIVITY? (Cont.)
BRANCHING
• Branching makes a polymer less dense resulting in low tensile strength
and low melting points.
• Branching also reduces the free volume of a polymer, resulting in a
higher glass-transition temperature, Tg.

15. HOW DOES STRUCTURE AFFECT
REACTIVITY? (Cont.)
CROSS LINKING
Cross linkage is described as a short side chain of atoms linking two
longer chains in a polymeric material [1]. Cross links can either be
covalent or ionic bonds.
Polymers with a high enough degree of cross-linking have "memory."
When the polymer is stretched, the cross-links prevent the individual
chains from sliding past each other. The chains may straighten out, but
once the stress is removed they return to their original position and the
object returns to its original shape.

16. HOW DOES STRUCTURE AFFECT
REACTIVITY? (Cont.)
FUNCTIONAL GROUPS
Different functional groups can affect a polymers properties by
• Different groups lending the polymer to ionic or hydrogen bonding,
depending upon where the bond is formed, resulting in higher tensile
strength and crystalline melting points.
• Amides or carbonyl groups form hydrogen bonds between adjacent
chains while polymers such as Ethene have no permanent dipole,
resulting in VDW forces which are much weaker. Hydrogen bonding is
stronger than VDW, resulting in higher MP & tensile strengths.

17. REFERENCES
[1]
Oxford Dictionary of Chemistry
Sixth Edition
Published 2008
Edited by John Daintith
[2]
http://upload.wikimedia.org/wikipedia/en/thumb/4/42/Crazes1.jpg/4
17px-Crazes1.jpg
[3]
http://thenovocastrian.files.wordpress.com/2012/07/urbanisation.jpg