Transcript Slide 1

EBB 220/3
ADAVANCED POLYMERIC
MATERIALS
DR AZURA A.RASHID
Room 2.19
School of Materials And Mineral Resources Engineering,
Universiti Sains Malaysia, 14300 Nibong Tebal, P. Pinang
Malaysia
Introduction

A number of new polymers having unique and
desirable combinations of properties have been
developed over the past several years.

This include:
 A niches
in new technologies and/or
 A satisfactorily

replaced other materials
Some of these include:
 Ultrahigh
molecular weight polyethylene (UHMWPE)
 Liquid crystal polymers (LCPs)
 Thermoplastic elastomers (TPe)
 Nanotechnology
Ultrahigh Molecular Weight Polyethylene
(UHMWPE)

Ultrahigh molecular weight polyethylene (UHMWPE) is
a linear polyethylene that has an extremely high
molecular weight.

Its typical Mw is approximately 4 x 106 g/mol greater
than that of highdensity polyethylene

UHMWPE in fibre form has trade name ‘spectra’

This material has a relatively low melting temperature
its mechanical properties diminish rapidly with
increasing temperature.
UHMWPE Characteristics

Some of the extraordinary characteristics of this
material are as follows:
1.
2.
3.
4.
5.
6.
7.
8.
An extremely high impact resistance.
Outstanding resistance to wear and abrasion.
A very low coefficient of friction.
A self-lubricating and nonstick surface.
Very good chemical resistance.
Excellent low-temperature properties.
Outstanding sound damping and energy
absorption characteristics.
Electrically insulating and excellent dielectric
properties.

This unusual combination of properties leads to
numerous and diverse applications for this
material, including:










bullet-proof vests,
composite military helmets,
fishing line,
ski bottom surfaces,
golf ball cores,
bowling alley and ice skating rink surfaces,
biomedical blood filters,
marking pen nibs,
bulk material handling equipment (for coal, grain,
cement, gravel, etc.),
bushings, pump impellers, and valve gaskets.
Liquid crystal polymers (LCPs)

The liquid crystal polymers (LCPs)  are a group of
chemically complex and structurally distinct materials that
have unique properties and are utilized in diverse
applications.

LCPs are composed of extended, rod-shaped, and rigid
molecules.

In terms of molecular arrangement  these materials do not
fall within any of conventional liquid, amorphous, crystalline,
semicrystalline classifications   as a new state of matterthe liquid crystalline state, being neither crystalline nor
liquid.

In the melt (or liquid) condition LCP molecules can
become aligned in highly ordered configurations.

As solids  this molecular alignment remains, and form in
domain structures having characteristic intermolecular
spacing.
Semi crystalline
liquid
solid
Amorphous
Liquid crystals
Advantages of LCP











High Heat Resistance
Flame Retardant
Chemical Resistance
Dimensional Stability
Moldability
Heat Aging Resistance
Adhesion
Low Viscosity
Weldable
Low Cost
weatherability.
Disadvantages of LCP




Form weak weld lines
Highly anisotropic
properties
Drying required before
processing
High Z-axis thermal
expansion coefficient
Processing and fabrication of LCP

The following may be said about their processing and
fabrication characteristics:
1.
All conventional processing techniques available for
thermoplastic materials may be used.
2.
Extremely low shrinkage and warpage during molding.
3.
Exceptional dimensional repeatability from part to part.
4.
Low melt viscosity, which permits molding of thin sections
and/or complex shapes.
5.
Low heats of fusion; this results in rapid melting and
subsequent cooling, which shortens molding cycle times.
6.
Anisotropic finished-part properties; molecular orientation
effects are produced from melt flow during molding.
Typical LCP applications










Electrical/Electronic Applications
Automotive Applications
Parts, Engineering
Containers, Food
Appliances
Industrial Applications
Connectors
Optical Applications
Parts, Thin-walled
medical equipment industry (in components
to be repeatedly sterilized), in photocopiers.
Thermoplastic Elastomers (TPe)

Thermoplastic elastomers  elatosplastic are polymers
that combine the processibility of thermoplastics and
the functional performance of conventional elastomers.

Block copolymer that possess elastic properties within a
certain range of temperature e.g from room
temperature -70°C.

The elastic properties are due to physical crosslinks
resulting from secondary inter molecules forces such as
hydrogen bonding.

These crosslinks disappear when heated above certain
temperature and reform immediately on cooling to
develop elastic properties.

Of the several varieties of TPEs  one of the best
known and widely used is a block copolymer consisting
of block segments of a hard and rigid thermoplastic
elastomer.

These are dissimilar and incompatible with each other 
they act as individual phase.

The dominant soft segments  are flexible, amorphous
and have low Tg

The hard segments  have high Tm, and tend to
aggregate at ordinary temperatures into a rigid domains
to form physically effective pseudo crosslinks.

When the block copolymer is heated to the processing
temperature  the forces that bind hard segments
together will be destroyed.

It is then possible to process the polymer as a
conventional thermoplastics the macromolecules are
no longer bound together.

On cooling the hard segments re-associate into rigid
domains and material shows elastomeric properties once
again

Suitable solvents also able to destroy the pseudo
crosslinks  when solvent is evaporated the hard
segments re-associate into rigid domains.

The properties of block copolymers can be adjusted by

Varying the ratio of the monomers

Varying the lengths of hard and soft segments.

The polymers become harder and stiffer  as the ratio
of the hard to soft phase is increased.

The upper service temperature of the block copolymers
 depend on the softening point of the hard phase.

The low temperature properties and fluid resistance 
controlled largely by the soft segments.
Rigid domain (physical
crosslinking)
Soft amorphous domain
Morphology of thermoplastic elastomer
Advantages of TPes

The practical advantages of TPes include:
1.
Little or no compounding is required. Most TPes are
“ready to use”materials  eliminating batch to batch
variations compared to conventional elastomers
compounding.
2.
Easy processing  can be processed on conventional
thermoplastic equipments (e.g blow molding, injection
molding etc)  very fast processing with lowered costs.
3.
TPE parts may be reformed into other shapes  The
scrap can be easily recycled results in lower production
cost.
4.
Product consistency is better than comparable
vulcanized elastomer  higher productivity
5.
Very easy to colour with many types of pigments or dyes
and less skilled labour is needed
Disadvantages of TPe

The disadvantages of TPes including:
1.
They melt at elevated temperatures with results 
not suitable for applications requiring brief
exposures beyond the upper service
2.
They may require drying before processing  not a
common step with conventional elastomer but in
fabrication of thermoplastic products.
3.
There is a limited number of low modulus
compound
4.
They have higher compression set and less
thermal stability  do not allow these materials to
be used in areas where compression set is
important and the working conditions are critical.

E.g: at temperatures above normal and at high strain
Nanotechnology

The design, characterization, production and application
of structures, devices and systems by  controlling
shape and size at the nanoscale.

The understanding and control of matter at dimensions
of roughly 1 to 100 nanometers  where unique
phenomena enable novel applications.

Eight to ten atoms span one nanometer (nm)  The
human hair is approximately 70,000 to 80,000 nm thick.

It becomes dominant when the nanometer size range is
reached  Materials reduced to the nanoscale can
suddenly show very different properties compared to
what they show on a macroscale.
Applications & potential benefits

With nanotechnology, a large set of materials with distinct
properties (optical, electrical, or magnetic) can be fabricated.

Nanotechnologically improved products rely on a change in
the physical properties when the feature sizes are shrunk.


Nanoparticles for example take advantage of their dramatically
increased surface area to volume ratio.

When brought into a bulk material, nanoparticles can strongly
influence the mechanical properties, such as the stiffness or
elasticity.

E.g., traditional polymers can be reinforced by nanoparticles
resulting in novel materials e.g. as lightweight replacements for
metals.
Such nanotechnologically
 enhanced materials will enable a weight reduction
 accompanied by an increase in stability and
 an improved functionality.
Example of applications

Medicine

The biological and medical research communities have exploited
the unique properties of nanomaterials for various applications
(e.g., contrast agents for cell imaging and therapeutics for treating
cancer)’

Functionalities can be added to nanomaterials by interfacing them
with biological molecules or structures.

The size of nanomaterials is similar to that of most biological
molecules and structures; therefore, nanomaterials can be useful
for both in vivo and in vitro biomedical research and applications.

Tissue engineering

Nanotechnology can help to reproduce or to repair damaged tissue 
called “tissue engineering” makes use of artificially stimulated cell
proliferation by using suitable nanomaterial-based scaffolds and
growth factors.

Tissue engineering might replace today’s conventional treatments, e.g.
transplantation of organs or artificial implants.

Energy

The most advanced nanotechnology projects related to energy are:
storage, conversion, manufacturing improvements by reducing
materials and process rates,

energy saving e.g. by better thermal insulation, and enhance
renewable energies sources

Household

The most prominent application of nanotechnology in the household
is self-cleaning or “easy-to-clean” surfaces on ceramics or glasses

Common household equipment like flat irons has improved
smoothness and heat-resistance due to nanoceramic particles.

Optics

The first sunglasses using protective and antireflective ultrathin
polymer coatings are on the market.

For optics, nanotechnology also offers scratch resistant coatings
based on nanocomposites.

Textiles

The use of engineered nanofibers already makes clothes water- and
stain-repellent or wrinkle-free.

Textiles with a nanotechnological finish can be washed less frequently
and at lower temperatures.

Nanotechnology has been used to integrate tiny carbon particles
membrane and guarantee full-surface protection from electrostatic
charges for the wearer.

Sports

Tennis rackets with carbon nanotubes have an increased torsion and
flex resistance.

The rackets are more rigid than current carbon rackets and pack
more power.

Long-lasting tennis-balls are made by coating the inner core with clay
polymer nanocomposites.

These tennis-balls have twice the lifetime of conventional balls.
Example of the exams question

What is liquid crystal polymers?

Discuss the advantages of thermoplastic
elastomer.

What are the benefits of nanotechnologhy?