If you take a look around your home or your local supermarket, chances are you will come into contact with products made out of thermoplastic elastomers. Ever held a hammer or screwdriver with a shock reducing soft-grip? Or a toothbrush or hairbrush for that matter?
What about the soft spoons you use for feeding your baby? Do you grind your teeth at night and have a dental guard? If you answered yes to any of these questions, you have definitely come across thermoplastic elastomers. But what are they?
Getting To Know Thermoplastic Elastomers
Thermoplastic elastomers or TPE were first introduced to the commercial market in the 1960’s. They are biphasic materials that possess the combined properties of semi-crystalline thermoplastics and soft elastomers and enable rubbery materials to be processed as thermoplastics.
In short, TPE is a polymer material that has the characteristics of thermoset vulcanized rubber and thermoplastic. If you didn’t know, a polymer is basically a material that is made up of small molecules arranged in a simple repetitive structure to form a larger molecule.
TPE has the high elasticity of thermoset vulcanized rubber at room temperature and good processability of thermoplastic at higher temperatures. To be called a thermoplastic elastomer, a material must possess the following characteristics:
- It must be able to be stretched to moderate elongations and then be able to return close to that of its original shape when relaxed again.
- Processable as a melt at high temperatures (a melt is when a material is able to become liquified by heat)
- Absence of creep (having a lower tendency to move slower or deform permanently under persistent mechanical stress)
In general, TPE is considered to be a good cost-effective alternative to latex, silicone rubber and polyvinyl chloride (PVC) compounds and its rubber-like properties have led to the replacement of rubber with TPE in many industries and applications.
Properties
Properties of TPE materials are decided by the chemistry and nature of its components and its morphology.
Mechanical Strength
The mechanical strength of TPE compounds varies and depends on the hardness of the individual thermoplastic elastomer type.
Flexibility
Softer phase TPE materials generate the rubber-like properties of elongation and dynamic properties and to some extent, tensile strength.
Electrical Insulation
Most TPE materials give a degree of electrical insulation, especially present in TPO and TPV materials (detail on these types of TPE materials are given in the next section.
Thermal Properties
It has good overall thermal performance at different temperatures and exhibits different characteristics at different temperatures. It also has ease of melt processing and shows good flow properties. When cooled, they solidify rapidly and this is why it is such a popularly used material.
Chemical Performance
Depending on the type of TPE material, the chemical resistance varies. Because of its low permeability, generally TPE exhibits robust resistance to chemicals.
UV Stability
Depending on the type of TPE, the UV stability will vary.
Processing Methods Of Thermoplastic Elastomers
Because they can be processed using conventional thermoplastic machinery, they are an attractive material to use across different industries. TPE is utilized in major fabrication processes like injection and blow molding, extrusion, film extrusion, thermoforming as well as candelaring.
Injection molding is the most used technique in TPE processing as it is a clean process that produces little to no waste formation. Injection molding can be used in applications ranging from foams to finished articles.
Extrusion is when the melted thermoplastic elastomer is pushed through a die of a specific shape to make a shaped product like foams or tubes.
Thermoplastic elastomers are used widely in 3D printing, specifically TPU or thermoplastic polyurethane, and is used to print stoppers, springs, phone cases, and more.
Types Of Thermoplastic Elastomers
TPEs contain more than one type of polymer. It contains an elastomer that gives it its elastic properties and another polymer that reinforces its strength.
You get styrenic block copolymer TPE compounds (TPE-S), Thermoplastic Olefin (TPE-O) compounds which are made with polyolefin (polypropylene), and an elastomer called EPDM. TPOs are used to make automotive parts and used as insulation for wires and cables.
Then you get thermoplastic elastomer vulcanizate or TPV compounds that are vulcanized or crosslinked giving them improved resistance to heat deformation and higher compressive strength. They are used in welding and in the automotive industry.
Lastly, there is thermoplastic elastomer urethane (TPU) based on urethane monomers which are used for outdoor footwear soles.
Benefits Of Thermoplastic Elastomers
Thermoplastic elastomers have many advantages over other materials and so it is no wonder that they are so widely used. TPEs are easy to manufacture and have low energy consumption rates which makes them cheaper as they can be manufactured within shorter time periods and cost less energy-wise.
As stated earlier they can be easily combined with olefin materials like polypropylene without the use of any additional adhesive materials. In general, TPE has excellent electrical insulation properties.
They are also heat and oil resistant to a large extent and have low permeability which means that they do not absorb moisture from the environment very easily. They can be manufactured in different degrees of hardness and can be colored to suit any application.
Although there are all those benefits to TPEs, they also are not without their disadvantages. Even though they are cheap to manufacture, they have a higher cost to most thermoset rubbers, comparatively.
They are also not suitable for some applications due to the fact that they start to melt at elevated temperatures.
Thermoplastic elastomers, however, are less susceptible to creep, are shear sensitive, meaning that they can tear easily and are less resistant to aromatics compared to other materials out there.
Applications For Thermoplastic Elastomers
Soft-Touch Applications
As mentioned above, TPEs can be molded onto a hard thermoplastic material using the same processing equipment and so can be used to create a soft-touch handle on many items such as tools and toothbrushes.
Food-Grade Materials Applications
Any material that comes into contact with food must be safe and non-toxic, which TPE materials are. The TPEs used in the food industry are used to make items such as baby cutlery and toddler cups.
Medical-Grade Materials Applications
Because TPEs can withstand the temperatures of autoclaves and the effects of gamma irradiation as well as resistance to ethylene oxide, they can be sterilized easily and are used to make breathing types, syringe seals, ventilation masks, catheters, valves, and bags commonly used in hospitals.
Automotive Applications
In the automotive industry, TPE materials are used for all kinds of parts that make up a car. Good examples are the materials that encapsulate glass in a car, weather seals, exterior and interior trims, and drive belts.
Construction Applications
In the construction industry, TPE materials are used as extruded seals for doors and windows and are used as seals for many different applications.
Footwear And Sporting Applications
TPE materials are used to create items used for diving such as flippers, snorkels, and masks as well as skiing equipment. TPE materials are also often used to make up the soles of shoes, specifically outdoor shoes.
Summary
Thermoplastic elastomers are a collection of rubber-like materials that combine the properties of rubber-like elasticity with the processing advantages and the other characteristics of plastics like polypropylene. They are versatile materials that are used in many industries and applications.
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