1. Amorphous and Semi-Crystalline Engineering Thermoplastics
Materials, properties and applications.
Prepared by the IAPD Education Committee (Module 4)
Presented courtesy of Modern Plastics Inc.
The IAPD Plastics Primer, Module 4

2. The IAPD Plastics Primer, Module 4
In Module 4, you will learn about amorphous and semi-crystalline engineering thermoplastics.
As in past modules, we will touch on the materials, properties and applications. We will start with the amorphous engineering plastics.
The IAPD Plastics Primer, Module 4

3. Amorphous Engineering Thermoplastics Key Characteristics
Moderate cost, strength and temperature resistance
Good impact resistance
Translucency
Good dimensional stability
Excellent optical qualities
The IAPD Plastics Primer, Module 4

4. Amorphous Engineering Thermoplastics Materials
Polycarbonate (PC)
Polyphenylene Oxide (PPO)
Polyphenelyne Ether (PPE)
Thermoplastic Urethane (TPU)
These are the materials that fall under the amorphous engineering thermoplastic heading.
We will go through each of these individually in more detail.
The IAPD Plastics Primer, Module 4

5. Polycarbonate (PC) Strengths
Excellent clarity
Excellent toughness
Good heat resistance
Excellent electrical properties
Intrinsic flame-retardancy
Excellent strength
Polycarbonate (PC) is an amorphous thermoplastic that was developed in 1957.
It is characterized by excellent impact strength, glass like transparency, and
high dimensional stability up to just below its glass-transition temperature of
150oC/302oF.
PC is extremely strong — over 250 times stronger than glass and 30 times stronger
than acrylic.
Additional strengths to the ones listed above are: low water absorption, high
dimensional accuracy out of the mold, good creep resistance, high impact strength, very
good dimensional stability and good dielectric properties.
The IAPD Plastics Primer, Module 4

6. Polycarbonate (PC) Limitations
Continual exposure to hot water causes gradual embitterment
Most aromatic solvents, esters and ketones can cause crazing and cracking
A few limitations exist as well with PC. Long-term exposure to humidity or
water at high temperature is not advisable for PC. It tends to yellow with exposure to
ultraviolet light and is sensitive to environmental stress cracking by some chemicals
(i.e., solvents and fatty substances). It is subject to scratching and other forms of surface
wear. Its notch sensitivity requires designs to avoid small notch radii.
Modifying PC overcomes some of these limitations, expanding its use significantly.
Principal modifications include copolymerization, variation of chain stoppers, branching,
blending, and the use of performance additives and fillers.
The IAPD Plastics Primer, Module 4

7. Polycarbonate (PC) Applications
Vandal resistant windows
Machine guards
Outdoor signs
Sky lights
Backboards
Bike, roller blading protective wear
Most PC grades are for injection molding. Specialized PC ranges from very-high-flow
resins for optical data storage to extrusion grades for sheet, film and profiles.
Incorporating glass fibers improves the modulus and dimensional stability of PC and
reduces creep, shrinkage, and the coefficient of thermal expansion. Impact modified PC
offers low-temperature ductility and reduced notch-sensitivity. Recently, high-flow
impact-modified grades have been thin-wall molded into miniature cell phone and
battery housings.
PC has an outstanding combination of engineering properties and processing versatility
that make it ideal for many applications, including safety glazing, light covers,
automotive headlamp lenses, water bottles, compact discs, and housings for electrical
applications.
The IAPD Plastics Primer, Module 4

8. Modified Polyphenylene Oxide (Mod PPO) Modified Polyphenylene Ether (Mod PPE) Key Characteristics
High dielectric strength
Available in FDA compliant grades
Less expensive than polycarbonate (PC)
Good chemical resistance to strong acids, bases and water
Wide range of processing
Good creep resistance
Compatibility with PS results in wide range of high-temperature, tough, stable products.
Modified PPO and PPE are available in FDA compliant grades and both PPO and PPE
are moderately priced.
A major limitation of these materials is that they require high processing temperatures.
The IAPD Plastics Primer, Module 4

9. Modified Polyphenylene Oxide (Mod PPO) Modified Polyphenylene Ether (Mod PPE) Applications
Electrical housings in appliance, computers, business equipment, etc.
Water purification equipment parts
Insulators
Gears
The IAPD Plastics Primer, Module 4

10. Thermoplastic Polyurethane (TPU) Key Characteristics
Wide range of service temperatures
Wide range of harness options
Excellent tear resistance
Excellent compression strength
Excellent resistance to non polar solvents
Excellent electrical properties
Excellent abrasion resistance
High tensile strength
Thermoplastic polyurethane (TPU) is part of the thermoplastic elastomer (TPE) family.
TPEs combine the processing advantages of thermoplastics with the properties of vulcanized rubber.
When heated, TPEs melt and can be formed into complex shapes using standard thermoplastic melt
processing equipment. As solids, they are soft, flexible and resilient like rubber and can be decorated,
reground and reprocessed without significant property loss.
Multi block polymers with crystalline hard segments are produced by various condensation reactions
to form a polymeric unit structure (A-B) of hard A and soft B segments. The crystalline A segments
are hard and rigid in behavior while the amorphous B segments are soft and elastic. Properties depend
on the lengths of the hard and soft segments which is determined by selecting appropriate polymers.
Most TPEs are two-phase systems, normally produced in polymerization reactors or melt mixing
compounders where the hard plastic phase is chemically or mechanically coupled with a soft
elastomeric phase. Traditional TPEs are categorized into three types: (1) block copolymers;
(2) hard polymer/elastomer combinations; and (3) multi block polymers with crystalline hard segments.
TPUs fall into the third category.
Isoplast is the trade name for TPU.
The IAPD Plastics Primer, Module 4

11. Thermoplastic Polyurethane (TPU) Applications
Impact resistant housings
Valves
Water filter caps
Geophysical cable spacer
TPUs replace many special rubbers. TPU applications include footwear, gears, rolls,
wheels, belting, apparel, adhesives, sealants, laminating films, magnetic media binders
and medical tubing.
New grades offer improved stability food contact approval non-halogen content for
wire and cable, more elasticity and film breathability.
Reinforced TPUs find use in applications that require excellent dimensional stability like
gears and agricultural parts. Blends and alloys of TPUs are used in blow-molded boots
for steering gear assemblies, grease seals, drive belts and hydraulic hoses.
Replacement of thermoset rubber offers the greatest growth potential for thermoplastic
elastomers. Transportation and general industry elastomer applications consume the
most tonnage. Growth markets include medical, construction and consumer products.
The IAPD Plastics Primer, Module 4

12. Semi-Crystalline Engineering Thermoplastics Key Characteristics
Moderate cost, strength
Moderate temperature resistance
Good chemical resistance
Good bearing and wear properties
Low COF
Difficult to bond
This section describes the properties associated with the group defined as semi-crystalline engineered thermoplastics.
The IAPD Plastics Primer, Module 4

13. Semi-Crystalline Engineering Thermoplastics Materials
Polyamide (PA) — Nylon
Polyoxymethylene (POM) — Acetal
Polyethylene terephthalate (PET)
Polybutylene terephthalate (PBT)
Ultra high molecular weight polyethylene
(UHMW-PE)
These are the materials in the semi-crystalline engineering thermoplastic category.
We’ll go through each of these individually in more detail.
The IAPD Plastics Primer, Module 4

14. Nylon (PA) Strengths Good strength Good toughness Fair heat resistance
Good chemical resistance
Low COF
Polyamides, popularly know as nylon, once a trademarked name, are among the most versatile and
durable of the plastics. They are also considered to be the first engineering thermoplastics.
Polyamides are primarily crystalline resins, but amorphous and semi-crystalline versions are
available. They are called polyamides because they contain an amide group as a recurring part of
their molecular chains. Polyamides are manufactured through two different routes: combining
adipic acid and hexamethylene diamine yields polyamide 66; polymerizing caprolactam yields
polyamide 6. Different types of polyamides are identified by a nomenclature which corresponds
to the number of carbon atoms in their monomers. In addition to polyamide 66 and 6, there are 69,
610, 613, 11, 12, 46 and 1212.
From the perspective of design and performance, polyamide 66 and 6 are largely interchangeable in
their end uses, with a few exceptions. These two forms of polyamide make up the majority of all
polyamide sales.
Because of their strength, toughness and heat and chemical resistance, they have found uses in a
wide variety of applications.
Polyamides are available in a variety of grades, including general purpose, which can be reinforced
or unreinforced; impact-modified grades, reinforced or unreinforced, but with superior impact
resistance; and reduced moisture grades, available as glass and/or mineral reinforced or both
reinforced and impact modified. There are also flame retardant grades and grades for
medical devices.
The IAPD Plastics Primer, Module 4

15. Nylon (PA) Limitations
Strong acidic environments
Areas where moisture absorption is of concern
Areas experiencing high operating temperatures
When nylon absorbs moisture the tensile strength and hardness decline, however,
the toughness increases.
Methods of manufacture are limited to extrusion, casting, injection molding and
rotational molding.
All methods of manufacture provide for a wide range of available grades,
however, each method does yield some benefit in cost depending on profile
shape, component size and quantity required.
The IAPD Plastics Primer, Module 4

16. Nylon (PA) Applications
Film
Automotive
Electrical/electronics
Consumer goods
The North American market for polyamides can be divided into four major segments.
The largest is extruded film, made from polyamide 6. Film manufacturers utilize the material
due to its generally lower crystallinity. Primary applications include food packaging such as
sausage casings and clear wrap. In a particularly out of the ordinary application, polyamide
film is used to package freeze-dried meal components astronauts take on space shuttle
missions. A subset of the extruded polyamide market is its use in sheathing for cables and wires.
The second largest market segment is the automotive industry. This is the largest market for
polyamide 66, with polyamide 6 as a close second. The resins are used interchangeably,
except in a few applications. Applications include bearings and bushings; wheels and cams;
washers, guides, sprockets and sheaves.
The third largest segment is the electrical/electronics market where polyamides are used
for injection molded connectors, switches and housings.
The fourth largest market is consumer applications. Principally, power tool housings,
but including other applications ranging from textiles to fishing line.
Additional applications include slides, gears and pile driving pads.
The IAPD Plastics Primer, Module 4

17. Cast PA vs. Extruded PA
Extruded nylon can be produced in almost any grade
Cast nylon grades are limited to Type 6, Type 6 1/2 and some Type 12
Generally Nylon 6/6 and Nylon 6 (cast or extruded) are interchangeable in most applications (physical property differences are minor)
Nylon 6/6 is stronger and stiffer than Nylon 6, and has more resistance to compression
Nylon 6 has better elongation values than Nylon 6/6, providing better ductility
Cast Nylon can be produced in large profiles and custom shapes, and is generally less expensive than extruded grades
Cast and extruded nylon have some differences that are highlighted above.
Next we’ll cover the semi-crystalline engineering thermoplastic — polyoxymethylene
(POM), better known as acetal.
The IAPD Plastics Primer, Module 4

18. Acetal (POM) Strengths
Good dimensional stability
Good wear resistance
Excellent strength
Excellent stiffness
Good rigidity
Low moisture absorption
Low COF
Acetals are highly crystalline thermoplastic engineering resins that offer high mechanical properties and
resist many chemicals. Acetals are known for their high strength, fatigue and creep resistance,
resilience, surface hardness, lubricity, toughness and excellent solvent and gasoline resistance.
Acetal resins are polymerized from formaldehyde. Acetal’s proper name is polyoxymethylene (POM).
A high degree of crystallinity makes acetals stiffer and stronger than most thermoplastics, yet they
are tough at ambient and low temperatures. Good dimensional stability is a key property. At
room temperature, acetals yield after strains of eight to 10 percent. Below this, they recover even
after repeat loading.
Acetals absorb little water, minimizing its effect on their physical properties. They resist neutral oils,
grease, petroleum-based fuels and many organic solvents. Acetal copolymers resist alkalies, but
oxidizing agents and strong acids attack acetals.
Specialized acetal grades offer features such as high melt flow rates for thinwall molding, improved
extrudability, low porosity important for machined parts, lubricants to reduce wear rates, UV-stabilizers
to prevent sunlight induced brittleness, impact modifiers to increase toughness, and reinforcements to
improve strength.
Acetal copolymers are noted for their high resistance to gasoline and diesel fuel, including types
containing methanol and ethanol, as well as grease, oil, brake fluid and coolants. Acetal copolymers
are practically impervious to swelling when in contact with these substances, resulting in
extremely high dimensional stability.
Acetals can be injection molded, blow molded and extruded as sheet and profiles. Standard processing
equipment is used and predrying of pellets is not required when proper storage conditions are used.
Regrind can be used, but is not recommended if optimum properties are needed.
The IAPD Plastics Primer, Module 4

19. Acetal (POM) Limitations
Centerline porosity in copolymers
Using copolymer in hot water environments (boiling/steam)
Strong acidic environments
Strong alkali environments
Areas experiencing high operating temperatures
There are two basic types of acetal resins: homopolymer and copolymer. The homopolymer is
a POM chain capped at both ends with an ester of an organic acid. Copolymers are made by
reacting trioxane (a trimmer of formaldehyde) with a copolymer.
The homopolymers strength properties tend to be slightly higher than those of the copolymers.
They also have higher short-term heat deflection temperatures than copolymers, but their
continuous use temperature is 85oC/185oF versus 100oC/212oF for copolymers.
The homopolymers also tend to have somewhat greater surface hardness, and a slightly lower
coefficient of friction.
The copolymers, compared to homopolymers, tend to absorb less water, are more resistant to
hydrolysis, and have superior processing characteristics, including reduced odor, gassing
and mold deposit. They offer faster cycling, better regrind utilization, and exhibit better
long-term stability and retention of properties in elevated temperatures.
Delrin is a trade name for acetal.
The IAPD Plastics Primer, Module 4

20. Acetal (POM) Applications
Bearings
Bushings
Valve seats
Washers
Nozzles
Spools
Cams
Other general uses for acetal are guides, gears, electrical components, slides and
packaging equipment.
Next we will look at thermoplastic polyesters in more detail.
The IAPD Plastics Primer, Module 4

21. Thermoplastic Polyesters Key Characteristics
Good range of mechanical properties
Good dimensional stability
Superior chemical resistance
Good electrical properties
Like other semi-crystalline engineered plastics, polyesters offer a good
range of mechanical properties. However, they excel in applications requiring
good dimensional stability, superior chemical resistance and/or electrical
properties.
The IAPD Plastics Primer, Module 4

22. Thermoplastic Polyesters Materials
Polyethylene terephthalate (PET)
Polybutylene terephthalate (PBT)
These two resins are part of the thermoplastic polyester family. We will discuss
each of these materials in more detail.
Methods of manufacture include extrusion, compression molding and injection molding.
Like the other materials in this section, consideration should be given to finished part
size, part configuration and quantity, all of which impact the cost depending on method
of manufacture.
The IAPD Plastics Primer, Module 4

23. Polyethylene Terephthalate (PET) Polybutylene Terephthalate (PBT) Key Characteristics
High dimensional stability under heat
High stiffness and hardness
Good bearing strength
Good electrical properties
Good resistance to chemicals
Good stress-cracking resistance
Excellent flow characteristics
Commercial production of polyester bottle polymer began in There are tremendous commercial
applications for PET — as an injection-molding grade material, for blow-molded bottles and for oriented films.
PET does not require the use of plasticizers or other processing additives and is shatter resistant and has excellent
clarity and gloss. PET is lightweight and resistant to abrasion and stress cracking and has excellent stability and
provides a very good barrier for water vapor, oxygen and carbon dioxide.
Semi-crystalline PET has a sharp melting point, which varies depending on its composition and the conditions of
crystallization. Depending on the end use, PET can be processed using a variety of processes, such as stretch blow
molding and extruding.
Polybutylene terephthalate (PBT) is another member of the thermoplastic polyester family. Blending polycarbonate
(PC) with a thermoplastic polyester like PBT improves flowability, low temperature ductility, notch sensitivity,
weatherability and chemical resistance.
The only structural difference between PBT and PET is the substitution in PBT of four methylene repeat units rather
than the two present in PET. This feature imparts additional flexibility to the backbone and reduces the polarity of
the molecule, resulting in similar mechanical properties to PET — high strength, stiffness and hardness.
The IAPD Plastics Primer, Module 4

24. Thermoplastic Polyesters Applications
Pump components
Automotive components
Food packaging components
Insulators
PBT has grown 10 percent annually due to automotive exterior and under the hood applications,
such as electronic stability control and housing which are made out of a PBT/ASA blend.
Another development involving the use of PBT is coextrusion of PBT and a copolyester
thermoplastic elastomer. This can then be blow molded into under the hood applications
which minimize noise vibration. Highly filled PBTs are also making their way into the kitchen
and bathroom tile industries. As with PET, PBT is also often glass fiber filled in order to
increase its flexural modulus, creep resistance and impact strength. PBT is suitable for applications
requiring dimensional stability, particularly in water, and resistance to hydrocarbon oils
without stress cracking. Because of this, PBT is used in pump housings, distributors, impellers,
bearing bushings and gear wheels.
PET is primarily used in food packaging, such items as two liter soda bottles and dual
microwaveable trays for frozen dinners.
PBT is extensively used in automotive components (body panels, grilles, wheel covers, fenders),
electrical components (keyboards, switches and relays), and in household appliances (iron handles,
coffee makers, hair dryers).
These materials do find there way into mechanical applications as well, such as guides, bearings,
bushings and gears.
The IAPD Plastics Primer, Module 4

25. Thermoplastic Polyesters Caution!
Watch high temperature environments!
Use caution when recommending thermoplastic polyesters in applications requiring high temperature resistance, above oC/ oF.
Use caution with thermoplastic polyesters because they are prone to cracking and breaking in
applications requiring high temperature resistance.
The behavior under temperature stress of PBT and PET is determined by their
semi-crystallinity. Because of the high degree of crystallinity, molded parts can be heated
briefly close to the melting temperature without significant damage or deformation.
Therefore, the temperature for practical use for PET is between oC/ oF and up to
129°C/265°F for PBT, depending on the degree of reinforcement needed to accommodate
short-term stress.
The temperature for long-term use is 110oC/230oF for PET in non-reinforced and reinforced
standard products, 129oC/265oF for PBT. Depending on the degree of crystallinity, short
term exposures can be as much as 38°C/100°F higher than the continuous use temperature.
Since at low temperatures an extremely long time is necessary to produce property changes,
the application possibilities for thermoplastic polyesters are limited only by the highest use
temperatures of the materials.
Next, we’ll discuss UHMW-PE.
The IAPD Plastics Primer, Module 4

26. Ultra High Molecular Weight PE (UHMW-PE) Strengths
Highest abrasion resistance and impact strength of any plastic
Very low COF
Excellent cryogenic (low temperature) material
Self-lubricating
FDA/USDA compliant
UHMW-PE has been produced commercially since It is a linear, high density polyethylene. Its average molecular weight is approximately ten times that of high molecular weight HDPE. The extremely high molecular weight of this material yields several unique properties. UHMW-PE has both the highest abrasion resistance and highest impact strength of any plastic. In fact, a one-inch thick slab can stop a 0.38 caliber pistol slug at a distance of six feet. Combined with abrasion resistance and toughness, the low coefficient of friction of UHMW-PE yields a self-lubricating, non-stick surface. Static and dynamic coefficients of friction are significantly lower than steel and most other plastics. UHMW-PE also has good chemical resistance, negligible water absorption and excellent insulating and dielectric properties.
The absorption capacity of UHMW-PE for shock stress is extraordinary, even at temperatures approaching absolute zero. Seals, pistons and pumps made from UHMW-PE and exposed to liquid hydrogen at -253°C /-423°F perform satisfactorily.
The most common processing of UHMW-PE resin involves ram extrusion and compression molding. The extremely high processing viscosities resulting from the high molecular weight of UHMW-PE require the special procedures offered from these methods. This is because the resin does not exhibit a measurable melt index and, therefore, processes more like an amorphous solid. In ram extrusion and compression molding, the UHMW-PE particles are fused into an apparent solid, but microscopically they remain as distinct particles. Both of these processing techniques combine heat and pressure.
In general, as density increases, hardness, heat resistance, stiffness and resistance to permeability increase. Density is measured in grams per cubic centimeter and ranges from 0.88 to and is typically referred to as low, medium and high. Ultra high molecular weight polyethylene can fall within both the medium and high density ranges and thus is more commonly thought of in terms of its molecular weight.
The IAPD Plastics Primer, Module 4

27. Ultra High Molecular Weight PE (UHMW-PE) Limitations
Only good until 82oC/180oF
Not a self-supporting material
High cost for tooling for custom extrusion and custom parts
The IAPD Plastics Primer, Module 4

28. Ultra High Molecular Weight PE (UHMW-PE) Applications
Guides
Wear strips
Liners
UHMW-PE is a versatile, high performing material that stands up to demanding applications
in many industries. It is often chosen for wear and sliding surfaces for bulk materials and ores,
where it provides a low-friction surface that resists wear and chemicals. These properties are also
important on equipment for paper making, chemical, textile and water and wastewater treatment
facilities.
Because of its self-lubricating, non-stick, lightweight and wear resistant characteristics,
UHMW-PE has been used for many years in the bulk material handling industry for enhanced
product flow (grain, cement, gravel among other bulk solids). Other applications include
liners for silos, hoppers, dump trucks, railcars and chutes, conveyor troughs and flights,
wear strips, slide plates and unlubricated bearings, bushings and guides. Other
benefits for some usages include noise abatement and reduced energy consumption.
The food, beverage and pharmaceutical industries use UHMW-PE extensively because
oil and grease can be eliminated from most bearing applications. Furthermore, the
growth of fungus and bacteria is discouraged because the material, as normally produced,
is nonporous. Common applications include bottling plant star wheels and guide rails.
Virgin grades are in compliance with U.S. Department of Agriculture and U.S. FDA
regulations.
Other applications include pump impellers, pump housings, valve seats and valve gaskets
for the chemical industry, doctor blades, suction box covers and foils for the paper
industry, ski bottom surfaces, snowmobile drive sprockets, golf ball cores, ice skating
rink surfaces and dock fender facing for the marine industry.
The IAPD Plastics Primer, Module 4

29. The IAPD Plastics Primer, Module 4
In our next module, we will discuss high performance thermoplastics.
The IAPD Plastics Primer, Module 4