An Introduction and Glossary of Key Terms
Many of our clients have a specialized interest in the materials we use to manufacture our flexible packaging products. A good example of this is the film and tubing that we use for our roll stock and polyurethane bags. The Urethane Primer provided below explains our manufacturing processes and the properties that make polyurethane such an effective packaging material. For additional information about any of our other packaging products, from radioactive waste bags to polyurethane bags, please call us at 888-353-9732 or email us at firstname.lastname@example.org.
What is urethane?
Thermoplastic polyurethane (TPU) was discovered in the late 1930s as
part of Germany's World War II research. It is a thermoplastic elastomer
(TPE), which combines the mechanical and physical properties of rubber
with the advantages of thermoplasticity and processability. Other
examples of TPEs include polyethylene and polypropylene.
Noted for its high performance and general overall toughness,
urethane rapidly became the material of choice for a wide range of
critical and "can't fail" applications. Urethane's unique
characteristics make it an extremely versatile material that outperforms
many other thermoplastics. For example, it retains its flexibility even
at low temperatures, where polyvinyl chloride (PVC) becomes brittle.
On a molecular level, urethane is comprised of the four most common
elements in the world: carbon, hydrogen, nitrogen, and oxygen. To be a
urethane, it must contain the molecular urethane linkage (NHCO2). The
actual chemistry consists of a series of block copolymers with
alternating hard and soft phases. A block copolymer is a string of
chemically different molecules in repeated sequences. The ratio and
molecular structure of these segments determines the specific
characteristics of the resin, which can be varied by modifying its
Depending upon its chemical makeup, the urethane soft phase is
generally either Polyether or Polyester. These two categories are
further segmented into Aliphatic or Aromatic hard segments.
Polyether urethane provides a softer “feel” or drape
than polyester, with better moisture vapor transmission rates and
superior low temperature properties. It is also inherently stable when
exposed to high humidity, and polyethers are naturally more fungus
Polyester urethane offers greater toughness (i.e.
abrasion resistance, tensile/tear strength) at a given durometer than
polyether. It is more resistant to fuels, and offers better aging
(oxidation) resistance. However, polyester urethanes will eventually
break down when exposed to conditions of high humidity.
Aliphatic urethane is inherently light stable,
resistant to ultraviolet light degradation, and provides excellent
optical clarity. It is used as an optical interlayer, providing strength
as a lamination adhesive in encapsulated glass and security glazing, to
name a few applications. It is often a more expensive product.
Aromatic urethane is a strong, general-purpose resin originally
developed as synthetic rubber. It is generally less expensive than
aliphatic urethanes, but it is susceptible to UV light degradation,
which tends to yellow the polymer without affecting physical properties.
Our Urethane is manufactured by the extrusion process.
Tubing, cord and profile
Polyurethane combines the best properties of rubber and plastic,
without the weaknesses inherent in plasticized vinyl films. Because it
contains no plasticizers, it is not subject to the brittleness and other
problems caused when they leach to the surface. Urethane is easy to work
with, and is readily modified to suit a particular application through
the addition of fillers, colors, stabilizers, and lubricants, as well as
other additives. Urethane compounds possess a combination of properties
which are not available in any other thermoplastic material, offering
significant design flexibility.
Durometer (Hardness). Urethane film and sheet can be
produced in a range of durometers (Shore A 75 - Shore D 55) from a very
stiff material to a very thin film having an extremely soft, non-plastic
"feel" or "hand". The latter is ideal for use in products that come in
contact with the skin.
Low temperature flexibility. Urethanes feature
superior flexibility over a wide durometer range, even at temperatures
as low as -60°F.
Tensile strength. A tensile strength range from
4,000 to 10,000 psi assures reliability and durability over the lifespan
of the end product. Because urethanes are tough, they can be used in
thinner gauges when compared to vinyl.
Elongation. Urethane film and sheet can elongate as
much as 800% and return to its original dimension without significant
loss of "memory."
Abrasion resistance. Urethane provides excellent
abrasion resistance. For example, it is used in profile form as a
conveyor drive belt, and to protect elevator cables and pulleys from
excessive wear while cushioning the ride.
Chemical and environmental resistance. Excellent
resistance to hydrocarbons, chemicals, ozone, bacteria, fungus, and
moisture, as well as skin oils. Polyether or polyester urethanes offer
specific characteristics that provide durability and long life to
products that must survive and perform in harsh industrial environments.
The number of different ways in which urethane can be fabricated
enhances its design versatility. It can be cut, sewn, adhesive bonded
and laminated to a wide selection of substrates. It can be vacuum
formed, radio frequency (RF) sealed, and thermally bonded to itself or
other materials. Sheet can be fabricated with urethane tubing to provide
the benefits of urethane to an entire product system, such as in linked
bladder applications. Urethane may also be printed or silkscreened.
Urethane is more environmentally friendly than vinyl and other films.
Recently, manufacturers of disposable medical products have begun to use
urethane because of the toxic byproducts resulting from incinerating
contaminated medical disposables fabricated from PVC. Urethane is also
readily recycled, and trim, both from the manufacturing process as well
as from our converters and fabricators, can be reground and reused if
kept free from contamination.
Because of its toughness and versatility, as well as a generally
higher price tag than other TPEs, urethane is typically used for parts
requiring a high level of performance. These applications frequently
demand a flexible material with a high degree of flex resistance,
wearability, and durability. Particularly at lower temperatures, other
materials do not provide this combination of properties.
Some typical applications include:
- Medical: compression dressings, pressure
infuser bags, ergonomic cold packs, transdermal patches, orthodontic
bands, shoe insoles, flotation mattresses, tubing
- Industrial: drive belts, hoses, bellows
- Other: keyboard covers, flotation devices,
headphone ear cushions, buoyancy compensators, packaging of delicate