Transcript Slide 1

Thermoplastic Materials
(Engineering Plastics)
• High strength and stiffness; some may require
reinforcement
• Retention of mechanical properties over a wide range of
temperature (esp. at high temp)
• Toughness that is sufficient to incidental impact (occur
during applications)
• Dimensional stability throughout the temperature range
of normal use
• Easy to shape and finish
Engineering Plastics
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Other properties for specific applications;
Abrasion resistance
Extended fatigue life
Lubricity
Electrical properties, etc
Engineering Plastics
• Examples
– Polyamides/nylon, TP polyester,
polycarbonate, PMMA, fluoropolymer, etc
Polyamides or Nylon (PA)
• Refer to polymer repeating units
for PA
• Subscript a and b indicates that in
nylon family the CH2 groups can
vary from 1 particular nylon type to
another
• The polarity of the amide group
makes nylon sensitive to polar
solvent such as water (absorptivity
of water is a problem in processing
because nylon resin must be dried
before any processing process)
• Tensile strength and modulus can
decrease by 20% with water
absorption
Polymer repeating units for polyamides
Specific Nylon Types
• Number of carbons in the
molecular sections between
amide groups determine
various types of nylon
• For example, if the nylon is
made from a six-carbon
diamine (a), and a 12carbon diacid (b), the
resulting polyamide namely
nylon (6/12) or nylon-sixtwelve
• Polyamide can also be
formed by one monomer
with amine group on one
end and an acid group on
the other (c), namely nylon
(6)
Aramid
• Contain amide group with benzene rings
between them
• This polymer has been given a generic
name of aramid. When made into fiber, the
materials is called kevlar
• The aramids are nonburning, solvent
resistant, and very high melting
Thermoplastic Polyesters (PBT/PET)
• Example; polyethylene
terephthalate (PET) &
polybutylene terephthalate (PBT)
• PET used for soft drink bottle
(tough & inexpensive), high
performance film (magnatic
tapes, etc) and fiber (textile)
• PBT- easier processing because
it crystallizes more rapidly than
PET
• The mechanical properties of
PBT are lower than PET
• Applications of PBT- slide
bearing, roller bearing, gear,
protective headgear, etc.
Polymer repeating unit for the most
common thermoplastic Polyester
where m can be 1 (for PET)
and 2 (for PBT)
Properties of PBT & PET
• Contain polar carbon-oxygen double bond, but
the percentage is small for entire molecules,
thus it has low moisture absorptivity
• low moisture absorptivity give consistent
electrical properties- led to numerous electrical
applications (lamp socket, switches, connectors,
etc)
• Excellent dimensional stability
• Melts of PBT & PET are of medium viscosity
compared to other engineering plastics
Polycarbonate (PC)
• Formed by condensation
polymerization, resulting in a
carbon that is bonded to three
oxygen (characteristics of
carbonate)
• Large, complex and aromatic
structure- noncrystalline yet it is
nearlly strong as highly crystalline
nylon
• Can be used continuously up to
135C
• Unique combination of properties;
high optical clarity and toughness
• Applications; camera bodies, hair
dryer, safety helmets, pump
impellers, etc
Polymer repeating unit for PC
Try to relate the PC structure
with its properties!!!
Acrylic (PAN, PMMA)
• Acrylic group is dominated by 2 resins,
polyacrylonitrile (PAN) (used for blending
with other resin and fiber)and PMMA
(used for molding)
• PMMA compete with other engineering
thermoplastic
• PMMA is atactic, thus amorphous
• Most important property-optical clarity
(92% light transmittance)-the highest of
any plastic materials
• The lowest sensitivity to UV light of other
plastics, low oxidation sensitivity, whether
resistance
Polymer repeating
unit for PMMA
Acrylic (PMMA)
• Shows better initial & long term optical
properties (compete with PC), but not as tough
as PC.
• Excellent optical properties- windshields (in
planes and helicopter), outdoor sign, automobile
tail-light, compact disc, etc
• PMMA scratch easily (solved with coated grade)
• PMMA has a significant advantage in price
compared to PC
Fluoropolymer
• The presence of fluorine in the
polymer-results in unique physical,
mechanical & chemical properties
• Teflon- DuPont brand name
• Flourine is the most electronegative
of the element, and strongly attracts
electron to it- thus forming very stable
bond with low chemical reactivitynonstick property
• Chemical inertness and lack of
bonding important in nonstick coating
application on pan
Polymer repeating unit
for polytetrafluoroethylene
(PTFE)
Fluoropolymer
• Applications; medical devices, industrial roller for
printing, photocopying, process guide and dies
• Superior solvent resistance (not attack by
solvent at operating condition)
• Nonflammable-used in electrical insulation
• Presence of fluorine atom results in problem in
toxicity if fluoropolymer decomposes.
• Service temp; 260C
Thermoplastic in Medical
Applications
• Every day, plastics are involved in critical surgeries, lifesaving efforts, and routine medical procedures.
• Plastic materials can be sterilized hundreds of times
without degradation.
• Lightweight plastics are used to form replacement joints,
non-surgical supports, and therapy equipment.
• Clear plastics provide visibility for transfusions,
surgeries, and diagnostic equipment of all kinds.
• And plastics can be machined, molded, or formed into
almost any shape imaginable.
Polysulfone
• One of the first high temperature
thermoplastic materials to be sterilizable
by all techniques
• polysulfone meets the demanding
requirements of FDA and USP. The
availability of a clear grade makes this
material the only choice for sterilizable
vacuum-formed medical equipment.
UHMW-PE (Ultra High Molecular
Weight Polyethylene)
• The diverse uses of lot-controlled UHMW-PE
range from standard wear applications to
implantable products.
• Biocompatibility, self-lubrication, and wear
resistance are among the major requirements of
articulating surfaces made from UHMW-PE.
• The biological response to UHMW in soft tissue
and bone has been well characterized by a
history of clinical use.
Polyetherimide
• Because of its superior physical properties
and its ability to withstand a wide spectrum
of sterilization methods, Ultem is often
specified as the material of choice in
demanding reusable medical device
applications.
Surgical Blades and Medical
Blades
• are demanding critical components
• wide range of applications such as catheter cutting
blades, endoscopic blades, diagnostic, orthopedic,
plastic surgeries, lasik blades, laproscopic blades, and
skin grafting blades
• surgical blade is tough to produce with the high level of
sharpness required for cutting human tissue
Bone Saw
Surgical Blades
Surgical Blades and Medical
Blades
• This surgical instrument is manufacture under
the highest standards of sharpness, consistency
and durability.
• Originally the blades were made of uncoated
stainless steel
• However, one problem resulted was tissue
sticking to the blade
• To overcome this problem, coat the blade with
nonstick material
What is the suitable thermoplastic material to create
nonstick coating on the surgical blade???
Aspect of structure that influence
properties
• Structure within the Mer
• Structure within the molecules
• Structure between molecules
Structure within the Mer
• Include elements involved and bond
energy, the bulkiness of the mer, side
groups, etc.
– Example;
• bond energy determine the thermal decomposition
• Flexibility and bulkiness of mer- influence
crystallinity
Structure within the molecules
• Include stereoisomerism, branching,
molecular weight and distribution, end
groups, etc
– Example;
• Stereoisomers of PP; isotactic, synditactic &
atactic- influence crustallinity
• Branching- long or short; rarely or frequently along
a chain
Structure between molecules
• The interactions between polymer
molecules have strong influence on
properties
• Example; cross linking, secondary bonding
and crystallinity
– Example
• Crosslinking- network is produced by joining short
chain
• Secondary bonding- Van der Waals bond
Properties of polymer
• Thermal properties
– Dimensional stability- Tg (noncrystalline
portion of the polymer change from glassy to
rubbery)
– Thermal decomposition- occur when primary
covalent bonds are ruptured
– Thermal expansion
– Thermal conductivity
Properties of polymer
• Mechanical properties; it is categorized
based on (also can be categorized based
on tensile, impact, flexural, etc);
– Stiffness
– Strength
– Toughness
Properties of polymer
• Chemical properties
– Solubility- in various solvent
– Permeability to gases or other molecules
– Chemical resistance towards chemicals,
environment & radiation
Properties of polymer
• Electrical & Optical properties
– Dielectric properties- most polymers are good
insulators, able to store electrical charge
effectively, thus serving as good dielectric
– Conductivity- most polymers are poor
conductors, because primary chemical
bonding is covalent- thus no free electron or
ion to conduct charge
– Optical properties such as color, transparency,
etc