Polymers and Composites

1
Polymers and Composites

• What is a Polymer
• Where do we use them???
• Examples
• How Do we Test them????

2
What is a Polymer

• What is a Polymer

A Polymer is a collection of mer units
generally arranged in a linear fashion, however
this can be modified to change the properties of
the polymer
This is a polymer. It's a very large molecule.
3
What is a Polymer

• Polymers this is a very large molecule
  containing hundreds to thousands of small
  molecular units called mers linked together in
  chains or unit like structures.
• Of the polymers used in the production of
  engineering materials plastics account for the
  highest majority of usage.
• It is common to divide
• polymers into distinct areas
• Thermosets
• Thermoplastics
• Rubbers and Elastomers

4
Polymer Basics

• Thermoplastics - melt on heating and are
  processed in this state by various methods
  including extrusion and moulding processes.
  Typical examples are polyethylene, polyvinyl
  chloride (PVC), polypropylene, and polystyrene.
• Thermosets - these are also called resins and
  include epoxy and phenolic resins, and
  polyurethane, once set they cannot be re-melted
  and reformed like the thermoplastics.
• Thermoplastics are more widely used then the
  thermosets.
• Rubbers and Elastomers form another group of he
  polymeric materials. Natural rubber are part of
  the group and polybudiene, and silicone rubber
  are elastomers

5
Polymer Basics

• Thermoplastics
• Polyethylene - containers, electrical
  insulation,blow moulded bottles (PET)
• PVC - (Note there are different blends of PVC) -
  uses include guttering,window frames, electrical
  conduit (Rigid PVC) - luggage, shoes, floor mats,
  garden hose (Plasticized PVC)
• Polystyrene - dials and knobs, appliance housings
• Polyacrylonitrile - sweaters and blankets

6
Polymer Basics

• Thermosets
• Phenolics - wiring devices, switch gear,
  connectors and relay systems. As binder materials
  in shell moulding.
• Epoxies - protective and decorative coatings. In
  fibre reinforced composite materials.
• Amino Resins (Urea and melamine) - melamine and
  urea soluble resins find application as adhesives
  in particle boards, boat hulls, flooring and
  furniture assembly.

7
Polymer Basics

• Elastomers
• Natural Rubber and Synthetic Rubber
• Styrene-butadiene rubber - tire threads
• Nitrile rubbers - fuel hoses gaskets
• Neoprene - wire and cable covering, industrial
  hosesand belts, automotive seals and diaphrams
• Silicone rubbers - sealents, gaskets, spark plug
  boots.

8
Polymer Bonding
Polymer materials rely on a covalent bond in this
case between the carbon and the hydrogen and also
on the secondary bonds that hold the chains of
molecules together.
Polyethelene Example
9
Polymer Arrangement (Linear)
Linear Polymers exist where the polymer chains
are arranged in a linear fashion. These can be
tangled ( like a bowl of Spagetti) or they can be
ordered (like building blocks)
10
Polymer Arrangement (Branched)
Linear branched polymers exist where side
reaction during polymerization cause branches to
form reducing the density of the polymer e.g.
LDPE
11
Polymer Arrangement (Network)
Network Arrangement occurs where a tri functional
mer unit is polymerized. These form thermosetting
plastics
12
Polymer Crystallinity

• In ceramics or metals, a crystalline solid
  comprises repeating unit cells that contain each
  of the component atoms in the material. Each unit
  cell is composed of one or more molecular units.
  In a polymer this is not possible the molecules
  are chains containing potentially millions of
  formula units. There is, however a repeating unit
  in a polymer - the monomer from which it was
  made. This must be the basis of both long and
  short-range order in a polymeric material.

13
Polymer Crystallinity

• Effects of Crystallinity
• The mechanical properties of all polymers are
  affected by the degree of crystallinity. The more
  crystallinity there is the stiffer, harder, less
  ductile more dense and less rubbery, more
  resistant to solvents and heat the polymer
  becomes. Increase in density is due to the more
  ordered packing in a highly crystalline
  structure. Optical properties are also affected
  by the degree of cyrstallinity, the reflected
  light between the crystalline and amorphous
  regions causes opaqueness.

14
Polymer Crystallinity

• A crystalline polymer really has two components
  the crystalline portion and the amorphous
  portion. The crystalline portion is in the
  lamellae, and the amorphous potion is outside the
  lamellae. If we look at a wide-angle picture of
  what a lamella looks like, we can see how the
  crystalline and amorphous portions are arranged.

15
Polymer Testing

• Why test Polymers ?????
• Mechanical and Physical Properties
• Polymer testing can take place using the
  following techniques
• Tensile Test
• MFI Melt Flow index
• DSC Differeential Scanning Calorimetry
• DMA Dynamic Mechanical Analysis
• TMA Thermomechanical Analysis

16
Polymer Tensile Test
17
Polymer Tensile Test
The graph shows the difference in behaviour of
polyethylene as a result of a different applied
strain rate. No cold drawing is observed at the
higher strain rate as it is not slow enough for
the polymer chains within the sample to
disentangle and reorganise themselves parallel to
the direction of applied stress at the lower
strain rate there is enough time for cold drawing
to occur.
18
Assessment of Polymer Flow

• Generally the manufacture of polymer components
  involves the melting and flow of the polymer.
  Typical processing routes are
• Injection Moulding
• Extrusion
• Blow Moulding
• All these involve flow and melting and so it must
  be examined.

19
Assessment of Polymer Flow

• Capillary Rheometry

  Capillary Rheometry measures apparent viscosity
(resistance to flow) over a broad range of shear
rates and at varied temperatures, which are
comparable to the conditions encountered in
molding, calendaring, extrusion, etc.  The data
is commonly used to determine processing
parameters, for lot-to-lot quality control, to
measure processing degradation, which could
reduce physical properties, and to study thermal
stability
20
Assessment of Polymer Flow
21
The MELT FLOW INDEXER is not dissimilar to the
capillary rheometer. It does operate at a fixed
point only and does not permit the assessment of
the material under normal extrusion conditions.
Both of these machines can show the problems of
'melt fracture' with the capillary rheometer
permitting the measurement of the critical shear
rate
Polymer Processing, Properties and Applications
Polymer Characterisation -- Melt flow indexer
Piston
Heaters
Molten polymer
?
Cut extrudate
Die swell
Extrudate
Melt flow rate MFR 600 x average weight of
cut-off (g) time interval between
cut-offs g/min.
22
Thermal Analysis

• Differential scanning calorimetry is a technique
  we use to study what happens to polymers when
  they're heated. We use it to study what we call
  the thermal transitions of a polymer. And what
  are thermal transitions? They're the changes that
  take place in a polymer when you heat it. The
  melting of a crystalline polymer is one example.
  The glass transition is also a thermal
  transition.
• The areas of interest on the generated DSC graph
  are
• Thermal Transition temperature
• Crystallization Temperature
• Melt Temperature

23
Thermal Analysis
24
DSC Graph
25
Glass Transition Temperature We can learn a lot
more than just a polymer's heat capacity with
DSC. After a certain temperature, our plot will
shift upward suddenly as shown below. This is the
glass transition temperature and the change in
heat capacity at that point causes the shift in
the heat flow and hence graph.
26
DSC Graph Explanation
27
Crystallinity Above the glass transition, the
polymers have a lot of mobility. When they reach
the right temperature, they will have gained
enough energy to move into very ordered
arrangements (Crystals). When polymers fall into
these crystalline arrangements, they give off
heat
28
DSC Graph Explanation
29
Glass Transition Temperature We can learn a lot
more than just a polymer's heat capacity with
DSC. After a certain temperature, our plot will
shift upward suddenly as shown below.
30
DSC Graph Explanation
31
Dynamic Mechanical Analysis
Dynamic Mechanical Analysis determines elastic
modulus (or storage modulus, G'), viscous modulus
(or loss modulus, G'') and damping coefficient
(Tan D) as a function of temperature, frequency
or time.  Results are typically provided as a
graphical plot of G', G'', and Tan D versus
temperature.  DMA identifies transition regions
in plastics, such as the glass transition, and
may be used for quality control or product
development.  DMA can recognize small transition
regions that are beyond the resolution of DSC
(Differential Scanning Calorimetry). 
32
Dynamic Mechanical Analysis
33
Dynamic Mechanical Analysis
Remember Storage modulus is an indicator of the
stiffness, loss modulus of the viscosity and the
peak in the Tan Delta curve represents the Tg of
the material.
Storage Modulus
Damping Coefficient
Loss Modulus
34
Thermogravimetric Analysis
Thermogravimetric Analysis or TGA is a type of
testing that is performed on samples to determine
changes in weight in relation to change in
temperature. TGA is commonly employed in research
and testing to determine characteristics of
materials such as polymers, to determine
degradation temperatures, absorbed moisture
content of materials, the level of inorganic and
organic components in materials, decomposition
points of explosives, and solvent residues.
35
Thermogravimetric Analysis
36
Thermogravimetric Analysis
37
Impact

•  The High Speed Impact test is used to determine
  toughness, load-deflection curves and total
  energy absorption of impact events. Since speed
  can be varied, it can simulate actual impact
  values at high-speeds.  . The data is often used
  to specify appropriate materials for applications
  involving impact.   Since many materials
  (especially thermoplastics) exhibit lower impact
  strength at reduced temperatures, it is sometimes
  appropriate to test materials at temperatures
  that simulate the intended end use environment.

38
Impact
39
Impact
40
Conclusions

• Polymers are Everywhere!!
• There are many different types
• The crystalline properties of the polymer affect
  performance
• Testing can be both Mechanical and Physical
• Other test methods exist

41
Glass Transition Temperature

• Have you ever left a plastic bucket or some other
  plastic object outside during the winter, and
  found that it cracks or breaks more easily than
  it would in the summer time? What you experienced
  was the phenomenon known as the glass transition
  . It is important to understand the consequences
  of glass transition in polymer performance i.e.
  increased heat capacity. DSC can help to do this
  by telling us the temperature at which the glass
  transition exists.

back