POLYMERS
Prof. Amita Chaudhary
Molecular Structure of Polymers• Linear
• High Density Polyethylene (HDPE), PVC, Nylon, Cotton
• Branched
• Low Density
Polyethylene (LDPE)
• Cross-linked
• Rubber
• Network
• Kevlar, Epoxy
COPOLYMERS
TACTICITY(Arrangement Of Side groups)
Geometrical isomerism of Polymers
• Configuration
The two types of polymer configurations are cis and trans.
These structures can not be changed by physical means (e.g. rotation).
The cis configuration arises when substituent groups are on the same side of a
carbon-carbon double bond.
Trans refers to the substituents on opposite sides of the double bond.
Conformation
• Conformation refers to order that arises from the rotation of molecules
about the single bonds:
• thermal fluctuation of the bond length (3%) and bond angle (3-5°) are small
at room temperature
• rotations around the bonds are well possible
COORDINATION POLYMERISATION
(Insertion polymerisation)
Zeigler – Natta catalyst
Ziegler-Natta Catalysis
Polymerization of propylene through action of the titanium
catalyst gives an isotactic product; whereas, a vanadium
based catalyst gives a syndiotactic product.
BIOPOLYMERS1. Starch
• Starch or amylum is a carbohydrate consisting of a large number of glucose units joined by
glycosidic bonds.
• It is a polysaccharide comprising glucose monomers joined in α 1,4 linkages.
• A white, granular, organic chemical that is produced by all green plants.
• A soft, white, tasteless powder that is insoluble in cold water, alcohol, or other solvents.
• The basic chemical formula of the starch molecule is (C6H10O5)n.
• The simplest form of starch is the linear polymer amylose; amylopectin is the branched
form.
α-1,4-glycosidic bonds
2. Cellulose- A polysaccharide consisting of a linear chain of several hundred to many thousands of β
linked D-glucose units.
- Formula: (C6H10O5)n
- Non- reducing carbohydrate.
- Insoluble in water.
Polymer Composite materials
Chapter-4
COMPOSITES
-Composite materials are engineered materials made from two or more
constituent materials that remain separate and distinct while forming a single
component
-Generally, one material forms a continuous matrix while the other provides the
reinforcement.
- The two materials must be chemically inert with respect to each other so no
interaction occurs upon heating until one of the components melts, an exception
to this condition is a small degree of inter diffusion at the reinforcement-matrix
interface to increase bonding
COMPOSITES
Can you think of any examples of where composites are used?
COMPOSITES
Composites can be found in:
-Boat hulls
-The aerospace industry (structural components as well as engines and motors)
-Automotive parts (panels, frames, dashboards, body repairs)
-Sinks, bathtubs, hot tubs, swimming pools
-Cement buildings, bridges
-Surfboards, snowboards, skis
-Golf clubs, fishing poles, hockey sticks
-Trees are technically composite materials, plywood
-Electrical boxes, circuit boards, contacts
-Everywhere
CONSTITUENTS OF COMPOSITES• Composite materials consist of two phases:
(i) Body constitutes or matrix phase
(ii) Structural constituents or dispersed phase or reinforcing materials
I. The properties of the constituents phases.
II. Concentration of constituents.
III. Their distribution and orientation.
For example:
Fibre glass reinforced plastic : Matrix- Plastic
Dispersed phase- fibre glass
Dispersed phase
Matrix
(continuous phase)
COMPOSITES
Composites can be classified by their matrix material which include:
-Metal matrix composites (MMC’s)
-Ceramic matrix composites (CMC’s)
-Polymer matrix composites (PMC’s) or sometimes referred to as organic
matrix composites (OMC’s)
(Polyamide(nylons), phenolics, epoxy, polysulphones and silicons)
Functions of matrix phase
Binds the reinforcing material
Protect the dispersed phase
Acts as a medium by which an externally applied load is transmitted and
distributes through the dispersed phase
Prevent from propagation of cracks by virtue of its relative softness and
plasticity
Properties of good matrix
Should be ductile
High bonding Strength with dispersed phase
Elastic modulus should be lower than dispersed phase
The dispersed phase (reinforcement)
Dispersed Phase
Fibre Particulate Flakes Whiskers
Glass Fibres Carbon Fibre Aramid Fibre
TYPES OF FIBERS
Some commonly used fibers for polymer matrix composites:
-Glass fibers
-Carbon fibers
-Aramid fibers
Fibre: Any polymer metal or ceramic that is drawn into long and thin filament.
Characterstics:
• High length to diameter ratio ( aspect ratio)
• High tensile strength and stiffness.
GLASS FIBERS
Produced by forcing out a melt glass through a small orifices and rapidly
pulling with subsequent cooling. Individual glass fiber called
monofilaments having diameter around 10µm.
Characteristics:
1. Chemically inert.
2. Very high strength.
3. Can be easily drawn into fibre.
4. Readily available and low cost.
5. Used in continuous form in catalyst activated thermosetting resins.
CARBON FIBERS-Carbon fibers are produced by pyrolysis of organic polymers such as about 90%
of the carbon fiber produced are made from polyacrylonitrile (PAN) and remaining
10% are made from rayon or petroleum pitch in an inert atmosphere.
monofilaments have diameter in the range of 5-10µm.
-High specific strength and stiffness
-Good resistance to moisture, acids, bases
“Carbon fiber composites are five times stronger than 1020 steel yet five times
lighter. In comparison to 6061 aluminum, carbon fiber composites are seven times
stronger and two times stiffer yet still 1.5 times lighter”
-Initially used exclusively by the aerospace industry they are becoming more and
more common in fields such as automotive, civil infrastructure, and paper
production.
ARAMID FIBERS
They are aromic polyamides (aramides) i.e. Nomex and
Kevlar.
Kevlar is p-phenylene terephthalamide. It is spun from a nematic liquid crystalline solution
using a jet wet spinning technique using sulphuric acid as solvent and cold water as
coagulant.
-They have the highest level of specific strength of all the common fibers.
- Retain mechanical properties in a wide temperature range (-200 to +200 0C).
-They are commonly used when a degree of impact resistance is required such as in ballistic
armour
- High tensile strengths and tensile moduli
- Resistant to combustion and stability at high temperature
- But prone to degradation by strong bases and acids.
- Weak in compression.
Particulates
Dispersed phase in particulate composites consists of particles
(metallic and non metallic)
- Improved performance at high temperature
- Wear and abrasion resistance
- Improved thermal and electrical conductivities
- Surface hardness is increased.
- Reduction in cost, shrinkage and friction.
Flakes
Two dimensional geometry.
Provide equal strength in all directions in their plane.
Mica flakes are used in electrical and heat insulating applications.
Whiskers
Very thin single crystals with high aspect ratio.
Show a high degree of crystalline perfection
High strength
Graphite, silicon carbide, silicon nitride and aluminium oxide.
COMPOSITES
PARTICLE REINFORCED
LARGE PARTICLE
DISPERSION STRENGTHENED
FIBRE REINFORCED
CONTINUOUS
GLASS FIBRES
CARBON FIBRES
ARAMID FIBRES
DISCONTINUOUS
ALIGNGED
RANDOMLY ORIENTED
STRUCTURAL
LAMINAR
SANDWICH PANELS
FIBRE REINFORCED COMPOSITES
(FRC)Property of FRC are affected by:
Length of fibers
Orientation of fibers
Concentration of fibers
1. Fibers length:
𝑙𝑐 = 𝑑𝜎𝑓
𝑇𝑐
Where:
𝑙𝑐 = Critical length of fiber
d = Fiber diameter
𝜎𝑓 = Tensile strength
𝑇𝑐 = Bond strength of matrixNote:
If 𝑙 >> 𝑙𝑐 or 𝑙 > 15𝑙𝑐 then the fibers are continuous fibers
If 𝑙 < 𝑙𝑐 , discontinuous or short fibers.
Generally length of the fiber is in the range of 20-150 time its diameter
The minimum length at which the center of the
fiber reaches the ultimate (tensile) strength sf,
when the matrix achieves the maximum shear
strength tm:
Laminar composite structure – conventional
Sandwich structure
Honeycomb sandwich structure
Structural Composite
ADVANCED POLYMERIC MATERIALS1. Polythene or polyethylene
- Low density polythene (LDPE)
It has branched structure
- High density polythene (HDPE)
It has a linear structure.
2. Saran:
- It is a copolymer of vinylidene chloride and vinyl chloride.
- As protective wrap for food.
Polyethylene or polytheneLow Density Polythene (LDP)
• Reaction involved:
n CH2=CH2
• Chemically inert, flexible, and poor
conductor of electricity.
• Used in insulation of electric wires, for
making squeeze bottles, toys and pipes.
High Density Polythene (HDP)
• Reaction involved:
n CH2=CH2 -(CH2-CH2-)n
• Chemically inert, tough and hard, high
tensile strength.
• Used in the manufacture of container,
bottles, housewares, etc.
350 – 570 K
1000 – 2000 atm,
traces of O2
330-350K
Zeigler – Natta
catalyst
3. Polyamide – Kevlar- Heating 1,4-benzenediamine and the acylchloride of benzene-1,4-dicarboxylic acid gives
the aramid Kevlar with loss of HCl.
- Used to make bullet-proof vests, protective helmets.
4. Polycarbonates – Lexan- Clear transparent, strong, and impact-resistant plastic
- Used
- Protective and everyday eye glasses
- CDs and DVDs
- Mobile phones
- Automobile dash panels and headlight and taillight lenses
- Helmets of Apollo-11 astronauts
6. Polyethylene Terephthalate (PET)- A linear thermoplastic polyester
- Formed from monomers terephthalic acid and ethylene glycol
- Used in food packaging, soft-drink bottles, photographic films, audio tapes, video tapes
- PET + cotton/wool give better wash/wear and crease-resistant properties to textiles.
Cyclist wearing a pair of spandex shorts and a cycling jersey
Polyurethanes:(-NHCOO-)- A major use in spandex fibers
- In athletic wear, paints, adhesives and foams.
Conductive Polymers
- Electrically conductive polymer contain electron donor and
electron acceptor groups.
- First conductive polymer- Polyacetylene
- Polyaniline (PAN), polypymole, polythiophene and poly(p-
Phenylene)
- Used in sensors, laser printing, solar cells, batteries etc.
Uses of Conductive polymers
1.Electrochromic displays
2.Polymeric electrodes for light weight batteries.
3.Coating
4.Sensors
5.Polymeric ferroelectric RAM
6.Artificial nerves, Brain cells.
7.Laser printing
8.Conductive adhesives.
8. Liquid Crystal Polymers (LCP)- Have highly aromatic structures. Ex: Vectra
- Used in electronic components, aerospace applications.
9. Epoxy Resins- basically polyether
- Obtained by condensation of epichlorohydrin with diphenylol propane.
- Used in surface- coating materials.
10. Thermocole It is a foamed-plastic, obtained by blowing air or gas through molten polystyrene or
polyurethane.
Light, strong and chemically inert.
Used as shock-proof material.
Compressive strength is 117-145 kg/cm2.
Can be used up to 55 0C.
Used for packing materials, insulation, protecting screens in radar and decorative
purposes