Choosing the best thermoplastic elastomers can be a challenge without the right information – a reason we have this guide for you.
Whether you want to learn about the properties, features, applications or classification criteria – everything you want to know about thermoplastic elastomer is right here.
Let’s dive right in
What Are Thermoplastic Elastomers
TPE is a term we commonly use to describer blended polymers. Depending on the specific composition, it may have elastomery and thermoplasticity.
We sometimes refer to TPE’s as Thermoplastic Rubbers. Due to their high resilience and ability to stretch, we can easily apply them in manufacturing processes such as injection molding.
Thermoplastic Elastomers Advantages
- They have limited or totally lack compounding. This means that many Thermoplastic Rubbers come when they are fabrication-ready and completely formulated.
- We have a very simple processing routine with brief molding phases. This ensures that the energy consumed is at its lowest.
- Processing TPEs is much cheaper compared to other rubber materials. We use less and simpler processing stages making it efficient and costing less.
- Thermoplastic Rubbers have a lower cost per volume. This is because compared to standard rubbers, their density is much lower.
- We can easily reuse scrap coming from TPEs. The material can be reground to produce products with similar properties as the original.
- Since they are extremely versatile, we can easily custom shape any product. This also means we can custom size a variety of those products.
- Due to their stability and impeccable chemical properties, they are resistant to flames and chemicals. Consequently, it ensures that all thermoplastic rubber products exhibit unmatched durability.
Disadvantages of TPEs
Although thermoplastic elastomers are popular in modern manufacturing industry, they have some limitations such as:
- Few Low-Hardness Thermoplastic Rubber
It is an open fact that most TPEs we manufacture have a hardness of approximately 80 Durometer A.
In retrospect, we have more materials that have emerged with softness’s that go below 50 Durometers A.
- Melts At Extreme Temperatures
As a result of this characteristic, we tend to limit the use of Thermoplastic Rubber parts to conditions below their melting point. This aside, we have modern improvements that increased the number of component materials in TPEs.
The reason behind this is simply logical – to enable them to operate at temperatures above 150°C.
- Pre-process Drying
It should be noted that many we need to carry out drying of most TPEs prior to processing them. This is contrary to other standard rubber materials which we directly process.
How Thermoplastic Elastomers are Made
To produce TPEs, we can either use two methods to blend them. They are Dynamic Vulcanizes Blending or Mechanical Blending.
Dynamically Vulcanized Blending
We use a disjointed elastomeric phase in this type of TPE production. We initially apply a shear rate to vulcanize the lax elastomer stage.
For the vulcanization to be activated, we have to apply extreme temperatures beyond the TPEs melting point. For efficient properties to be realized, we consider the rate of cure and size of the particles as vital parameters.
Mechanical Blending
As the name suggests, we prepare the TPE by mixing it mechanically. We use a continuous mixer to blend the elastomer to a hard polymer.
To ensure quality TPE, we must ensure that the two viscosities are the same at a given temperature. We also have to confirm that the ratios of the two are the same besides checking on other parameters such as solubility.
Types Of Thermoplastic Elastomers
There are many grades or classes of Thermoplastic rubber formulated for unique applications. As a result, these rubbers exhibit numerous properties for versatile application requirements.
1. Styrenic Block Copolymers
Also known as TPE-S, we manufacture it using two different methods. It can be either using Styrene Ethylene Butylene Styrene (SEBS) or Styrene Butadiene Styrene (SBS).
In SBS, we have TPE molecular composition of styrene in hard blocks and butadiene in soft blocks repeatedly. The end caps in these compositions is usually styrene.
SEBS involves a process where we add hydrogen to SBS. The main purpose for this is to acquire ethylene butadiene by disintegrating the butane mid-block.
Some of the properties of this TPE include an extensive range of hardness, resistance to abrasion and electrical insulation. We use it to make footwear, adhesives and agents that modify asphalt.
2. Thermoplastic Polyurethanes (TPE-U)
We form this type of Thermoplastic Rubber through chemical reaction of polyester and diisocyanates. The result is a TPE with soft parts made of polyesters and hard diisocyanate segments.
While processing TPEs, we use various methods such as blow and injection molding. We might as well alter it by varying the diisocyanate and polyol composite.
Besides its exceptional tear strength, TPU resistant to abrasion with a high tear and tensile strength. That makes it perfect for the manufacture of drive belts and grips for power tools and caster wheels.
We also call them Thermoplastic Olefins because we it is a composite of an elastomer and a polyethylene. Furthermore, for meet the diverse application requirements and needs mechanical blending is an option with EB or EPR.
In the event that polypropylene is not rigid enough, we recommend the use of TPE-O. This is because of its extreme high hardness of 80 on the A.
Some of the notable applications of TPE we have include manufacture of airbag covers together with mudguards and dashboards. With its good resistance to chemicals and weather, we can safely conclude that its stronger compared to copolymers of polypropylene.
3. Melt Processable Rubber (MPR)
In most cases, the MPR has proved to be a perfect choice especially for vulcanized rubber processes. You will be amazed how a halogenated polyolefin that has been cross-linked blends well with stabilizers and plasticizers.
MPR literally does wonders on any condition above 120°C compared to other conventional rubbers. That’s why we prefer making processing equipment using MPR largely.
Based on the fact that it is UV resistant, goggles and weather strips are some of its perfect applications. In addition to that, its high friction coefficient makes it suitable for seals and hand grips.
4. Thermoplastic Vulcanisates (TPV)
When you mix polypropylene with EDPM, you get vulcanized TPVs. The process nearly resembles that in the manufacturing polyoefins.
They exhibit a high resistance to temperature and can operate above 120°C. It is for this reason that we prefer making engine compartments using TPV.
Thermoplastic Elastomers Stretching Properties
- Tear Strength
This term dictates the ability of TPE to resist tear. We can measure it stretching the material using a certain force.
We term the force at which the part tears as its tear strength. We describe the tear strength using units called kiloNewtons per meter (kN/m) or alternatively in psi.
- Elongation At Break
We use elongation to basically see how far the TPEs can stretch just before the snap. We describe it as a fraction of the initial part length.
Usually, the stretching property will depending on the softness of elastomer. For instance, very soft rubbers may stretch more than 900 times compared to their initial length. This is in contrast to hard TPEs which have minimal elongation capabilities.
- Tensile Properties
Elastomers behave differently when subjected to any form of stretching force. Of course, you must establish a viable testing procedure for all your TPE.
- Tensile Modulus
In this type of test, we use two elongation points to stretch an elastomer. We then measure its resistance in response to the stretching force applied.
We have a tendency in elastomers of responding extremely well to a stretching force. Remember, whenever there is a point of weakness, a phenomenon called necking will begin to occur.
- Tensile At Break/Ultimate Tensile
When we carry out this test on an Elastomer, we stretch till its breaking point. We measure and record the force required for the material to break in psi.
Compression Set in Thermoplastic Elastomers
We can define compression set as the extent of deformation on a material that undergoes compression. We measure this at a certain temperature for a given period of time.
We regularly confuse TPE compression set with creep. The difference is that compression set normally occurs under a continuous strain.
Contrary to that, creep is the level of deformation on a Rubber Elastomer having a continuous strain applied. While testing for compression set, we utilize a testing process called ASTM D395.
It requires that the rubber elastomer to undergo a 25% compression for a set time. We can then measure the TPE after it has recovered for at least 30 minutes.
Service Temperature For Thermoplastic Elastomers
We can basically define the service temperature for TPEs as the most extreme temperature that it can function in. For this, we have several factors that come into play to influence this temperature.
The design of the part together with the available load influence the temperature. Additionally, the time taken we require to expose the TPE and the performance parameters also play a role in determining temperature.
Instances where we require extreme service temperatures include automotive engine parts. On the other hand, we only need minimal service temperatures for basically indoor parts like toys.
Thermoplastic Vs Thermoset Elastomer
In today’s industry, there are two main Elastomers:
The difference between these two is the tendency of Thermoplastics to melt and harden when heated or cooled respectively.
Thermoplastics are extremely sensitive to heat. This makes them easily degrade if we handle them without care. In contrast, we can the chemical structure of Thermoset Elastomers to make them insoluble when processing.
This chemical alteration is what differentiates the two. Additionally, we can process TPEs over and over again thus giving them an edge over Thermoset Rubbers.
Thermoplastic Elastomers Features
There are 3 critical features you must consider when evaluating elastomers:
- They contain little or no amount of creep
- We can use extreme temperatures to process them without damaging their structure.
- They can regain their original form when we remove any force stretching them.
Thermoplastic Elastomer Polyefins Vs. Bio based Thermoplastic Elastomers
At times, TPE may require mixing with other materials for better performance properties. For instance, a mixture of ERDM rubber and polypropylene results into a cross-linked structure making TPE heat resistant.
We mostly utilize them in environments requiring rigid parts. These include parts such as car dashboards and automotive bumpers.
Bio based Thermoplastic Elastomers are new in the industry. In fact, they are becoming popular in modern manufacturing industries. The whole point behind it is to wear down over-reliance on non-n renewable resources.
We create this type of Elastomer by using monomers prepared from biomass. The advantage is that since we get them from nature, its sustainability is greatly improved.
Shrinkage in Thermoplastic Elastomer
After molding TPE, there may exist some significant degree of shrinkage, which is a common scenario in plastics. Therefore, during molding process, it is vital to increase the dimensions of your mold.
Usually, there are numerous measures to counter this phenomenon. For instance, a mold test may act as a viable solution. At the same time, dealing with under sized mold as opposed to filling up a mold which is too big.
Effects Of Shrinkage On Thermoplastic Elastomers
Shrinkage occurs in TPEs after we heat them. The reason behind this is the orientation of the part molecules which lead to decreased size.
Some of the effects we have of shrinkage include difficulty in removing the molded part from the mold. Additionally, it can also significantly alter the final look of the molded part.
We also have parts that warp after shrinkage hence they appear bent instead of flat. Where tight tolerance is a requirement, such shrinkages may end up distorting how the part fits.
This requires us to critically factor in shrinkage when doing production of TPEs. Perfection is always a necessity for us.
Applications Of Thermoplastic Elastomers
Now let’s have a look at the daily applications of the Thermoplastic Rubber.
· Construction
We have a very wide application scope when it comes to Thermoplastic Rubber and construction. When roads are being asphalted, we use TPEs as an additive substance to reinforce it.
Coatings used on walls together with sealants are also other applications we use in construction. Besides that, we have electrical wirings that are insulated using thermoplastic rubber.
· Automotive
Being the largest industry, we have the automotive industry making the most use of TPEs. This is due to their excellent properties like resistance to extreme temperatures and abrasion.
We can have parts that absorb impact like shock absorbers and vibration dampeners. Other than that, weather stripping parts and bumper stops are also made of TPE.
· Medical
We have a bunch of patients who are allergic to Latex. TPE is generally latex-free hence perfect for healthcare material.
They are physically soft hence they can be easily used for direct body contact medical applications. It should be noted that we can also sterilize TPEs very easily making them most suitable for the healthcare environment.
Conclusion
The unique features of thermoplastic elastomers makes them perfect for many applications in today’s industries. You can choose any depending on your unique requirements and specifications.
At LegenDay, we offer man rubber fabrication technologies for your unique requirements.
Contact us today for all your silicone products.
More Resources:
Thermoplastic Rubbers – Source: Wikipedia
Advantages and Disadvantages of TPE – Source: Science Direct
Thermoplastic Rubbers (TPE – Source: Science Direct
What is TPE – Source: Kuraray
What is Silicone Made of – Source: LegenDay