Synthetic polymers are common materials used to manufacture components and equipment in many industries. These materials are popular for their tolerance to environmental stressors known to degrade natural substances. In this article, we explore thermoplastic polyurethane and silicone as examples of two of these synthetic materials.
TPU and Silicone as Synthetic Polymers
extracted from petrochemicals. In some cases, these molecules are derived from renewable sources.
Synthetic polymers can either be thermoplastics or thermosetting plastics. Thermoplastics are easily deformed multiple times but thermosets can only be molded once. In this case, TPU is a thermoplastic, while silicone is an elastomer. Further, elastomers are broadly regarded as thermosetting polymers.
What is TPU (Thermoplastic Polyurethane)?
Thermoplastic polyurethane is both an elastomer and a thermoplastic. This means it has both properties of rubber and plastic. These properties make TPU reliable in applications where elasticity and durability are needed. This explains why the material is always in demand by several manufacturers.
TPU is either amorphous or semi-crystalline.
- Amorphous TPU
The amorphous type of TPU has features such as softness, flexibility, and elasticity. Its polymer structure is characterized by the randomness of the molecules. This random configuration is what provides the amorphous structure of the material.
The random arrangement of amorphous TPU makes the material soft and elastic. This facilitates molding processes, which means that it is easy to mold it into many parts. This material is one of the most elastic when compared to other types of TPU.
Due to the soft nature of the material, it becomes useful in the production of shoes and athletic gear. The softness is important in this application since it ensures that the athletes have a soft material that is comfortable and safe. This means textile industries can highly benefit from this material.
- Semi-crystalline TPU
When compared to amorphous TPU, semi-crystalline is much more durable and stiff. This means that it has better physical endurance. These characteristics are supported by the arrangement of molecules in a crystalline structure.
Due to properties like stiffness and durability, this material is used in applications where endurance is a priority. This includes in automotive industries. Also, it can be used to make external components for large machinery.
What is silicone?
The scientific name for silicone is polysiloxane. This implies that the material is a substance and is a polymer of siloxane monomers. Siloxanes are compounds made of silicon and oxygen atoms in their molecular structure.
One of the key features of silicone is that it is an inorganic compound. This means that its polymer structure is made from substances that do not exist in nature. Inorganic elements are known to have high durability, and this explains why silicone is among the most durable rubbers.
Silicone can exist as a liquid, gel, paste, or elastomer (rubber). Each of these types of silicone has a specific use case. In other cases, they also have different compositions in the molecular structure of the polymer. This is important since it helps in the grading process of the compound. This is why you find different types of silicone such as adhesive, LSR, and so on.
TPU vs Silicone: Chemical composition
It would not be a detailed article if it lacked the chemical composition of these two synthetic polymers. Chemical composition is indicated by the monomers that make up the material. This also entails the synthesis process of the polymers.
The Chemistry of TPU (Thermoplastic Polyurethane)
The most basic form of TPU contains soft and hard segments in the molecular structure. Each segment has a particular element or compound that makes it up. In this case, the soft segment is made of polyether or polyamide while the hard one is made of polybutadiene or polyester.
Both segments play a crucial role in the properties of TPU. While the hard segment gives TPU resilience and rigidity, the soft segment controls the elasticity modulus of the material.
To balance these two characteristics of the material — hardness and elasticity — the ratios of the compounds must be in check. Also, the ratios can be adjusted accordingly to control one aspect. For instance, manufacturers can increase the ratio of polybutadiene or polyester to make TPU much harder and less elastic. This all depends on the use case of the material.
How is Thermoplastic Polyurethane synthesized?
The synthesis of TPU takes place in two steps. Step one is known as polycondensation, which is then followed by chain extension.
In the first step, polycondensation, monomers are reacted together to form a prepolymer. The monomers used for TPU are typically diols and diisocyanates. The diols are long-chain molecules with two hydroxyl groups, and the diisocyanates are long-chain molecules with two isocyanate groups.
Step one involves the formation of a prepolymer. This entails the reaction of monomers in specific conditions. The common monomers used in this reaction are diols and diisocyanates.
Diols contain hydroxyl groups and they are long-chain molecules. This is important since it means that they are easy to form polymers from. On the other hand, diisocyanates contain isocyanate groups, which are also long-chain. These two compounds have to be of high quality without impurities for a quality prepolymer.
In the second step, the prepolymer formed is then reacted with a chain extender. The purpose of the chain extender, as the name implies, is to extend the chains of the prepolymers. This is because polymers are typically long-chain compounds. This results in the formation of a long-chain polymer that is commercially known as TPU.
The Chemistry of Silicone
The polymerization of siloxane compounds is quite straightforward. What you need to keep in mind is that the type of polymerization technique is known as Ring-opening polymerization (ROP). This type of reaction transforms cyclosiloxane into linear siloxane polymers.
The magic of silicone is however influenced during the curing process. There are catalysts, enhancers, and other substances that are mixed with the latex to bring out the properties of the material. This is quite essential, and it’s what makes the material so durable.
Manufacturing silicone elastomer
To make the rubber, a process called hydrosilylation is used. This process involves the reaction of silicon and a hydrohalide. It is sort of a more advanced hydrosis. The most common hydrohalides used in this process are hydrogen chloride or hydrogen bromide.
This hydrosilylation reaction leads to the formation of silanol. Subsequently, silanol is reacted with an alcohol to form a siloxane, a monomer that is then polymerized as we have seen to produce a polymer compound known as polysiloxane or silicone.
TPU vs Silicone: Properties and characteristics
Comparing TPU and silicone as polymers helps us understand these materials at the molecular level. It is quite essential to do this since you will get insight into how these materials work. One of the best ways to study these comparisons is by looking at the properties of these substances.
Properties of TPU
TPU is a versatile material with a wide range of properties, including:
High Abrasion Resistance
The molecular structure of TPU makes the material durable. This is a required physical property for materials that are supposed to have high abrasion resistance. Abrasion resistance is the ability to withstand wear and tear that occurs due to repeated abrasion. This is mostly experienced by components that are used in shielding or sealing applications.
The strength and rigidity of the material are also influential in abrasion resistance. Urethane molecules that are found in the base monomers enhance this property. Therefore, TPU can withstand applications where friction is expected.
Materials that can maintain form and structure in cold environments are said to have low-temperature tolerance. That means that they can mostly remain rigid and flexible in these conditions. Like most elastomers, TPU has this ability.
Most rubbers lost their rigidity in low-temperature conditions. They become brittle and stiff, which is not expected for rubber at room temperature. This is different for most types of plastics. However, this can be changed during the manufacturing process of the compound.
High Shear Strength
Impact resistance is a product of stress management. Stress is everything from tension, friction, pull, and other elements. Materials that can remain undeformed under these conditions are said to have a high shear strength.
A high shear strength helps in applications where there is a lot of movement. This is because the material can remain unchanged and provide a long service life. This coupled with the fact that TPU has a high friction resistance makes the material quite ideal for many applications.
Like most elastomers, TPU is also elastic. Elasticity is defined as the ability to stretch and return to its original form without getting deformed. Most plastics tear apart when pulled. This is what differentiates TPU from other classes of plastics.
The elasticity of TPU is mostly influenced by the molecular structure of the compound. Also, the crosslinks of the molecules play a major role in the elastic modulus of the material. As such, TPU is quite useful in applications where elasticity is desired.
If you have ever come across something made from TPU, you might have noted the transparent nature of the material. Some variations of TPU are transparent by design. This happens when air bubbles are added during the manufacturing process of the compound. In most cases, the material is usually translucent, meaning some light can pass through.
Oil and Grease Resistance
Oil and grease are culprits that destroy many substances. However, TPU is engineered to handle the damaging effects of these compounds.
The most damaging aspect of oil and grease is surface tension reduction. These compounds eat up the surface by breaking down the polymer chains of TPU. This can end up causing many accidents in various applications.
Additionally, the oil and gas resistance properties are because the compound has hydrophobic properties. The urethane backbone is responsible for this. As you already know, oils and water do not mix. Therefore, oils would not be able to damage TPU since it shields itself by being a water-repellant.
Properties of Silicone
Let us now look at the common mechanical and chemical properties of silicone. Try to compare them to those of TPU and see whether there are any similarities or differences.
Like all rubbers, silicone is quite elastic. Besides, it is among the most elastic rubbers out there. This is because it has an elastic modulus of 0.0167 GPa. To get a sense of how massive this is, GPA stands for gigapascals, meaning in billions.
A high elastic modulus makes silicone quite reliable in applications such as the making of gaskets and seals. These applications require elasticity as a property to make sure the components can withstand stress. You can think of all applications where this would apply.
High Mechanical Resistance
When a substance can resist deformity, compression set, and other external forces, it is said to have a high mechanical resistance. This is seen in most types of silicone, and it would explain why silicone is used in rough environments. For instance, silicone O-rings require mechanical resistance for them to be strong enough to handle resistance.
Excellent Chemical Resistance
The military is one of the major consumers of silicone material. Specifically, the Navy branch uses silicone-based o-rings and seals for their equipment. This is because the material cannot be damaged by chemicals found in the water. The same applies to chemical plants where durable components are required.
Low Thermal Conductivity
For thermal conductivity, silicone is also a major material used. Low thermal conductivity means that the material cannot transfer heat from one region to another. In other words, it cannot allow heat to escape. This explains why silicone is used to make kitchenware. It is the insulation properties of the compound.
There are many toxic synthetic polymers, but silicone is not one of them. Toxic means the presence of foreign substances that are a threat to human life and the environment in general. If it was toxic, silicone would never be so reliable in the medical industry.
Excellent Thermal Stability
Do not confuse thermal stability and thermal conductivity. These are different properties with each having a particular meaning. Thermal stability is the ability to remain unchanged regardless of the level of heat. This means silicone maintains its chemical and physical properties in both low and high heat conditions.
TPU vs Silicone: Classification and grades
Both TPU and silicone can be classified into various categories based on several factors. In most cases, the polymer structure is used. In other cases, the categories are influenced by external factors such as curing and vulcanizing methods. Let us learn these common grades and types.
Classification of TPU
There are two main types of TPU. On one hand, we have those that are polyester-based while the other ones are polyether-based. Let us learn the differences.
As you can tell from the name, polyester-based TPUs contain a polyester backbone in their molecular structure. The other elements in the compound come from the chain extender used in the manufacturing process.
One of the tell-tale signs of a polyester-based TPU is its overall mechanical properties. These substances are quite rigid, which makes them desirable in many applications. These include the automotive and aerospace industries.
Ethers are compounds that have oxygen attached to an alkyl or aryl group. The backbone of polyether TPUs is made of polyethers and polyol chain extenders. This makes the material quite durable in many ways.
When you study them closely, you will realize that both polyether and polyester-based TPUs do not vary that much. They both share a similar structure, just that they differ from each other to a certain extent. This is important since it can help you choose by considering the two types of TPUs.
Types of Silicone Elastomers
Silicone can also be classified according to certain parameters. This will depend on the manufacturer or customer’s specifications. Also, there are specialty grades that are proprietary and only the manufacturer knows their composition.
- Methyl silicones (polydimethylsiloxane): Methyl silicones are quite common in many areas. One of the key indicators of these materials is the high degree of hydrophobicity, in other words, water repulsion. Still, they can withstand high temperatures. This type of silicone can be considered basic.
- Vinyl silicones: Vinyl groups are considered functional groups in most compounds. In this type of silicone, these vinyl groups enhance the resistance to hydrolysis of the material. As a result, vinyl silicones are much more tolerant to humidity and high heat compared to methyl silicone.
- Fluorosilicones: Have you ever heard of fluoroelastomers? These are synthetic elastomers that have a fluorinated backbone. Fluorine is known to thrive in many chemicals, and that is why it is an ideal element for manufacturing high-performance elastomers. Therefore, this type of silicone has excellent chemical and physical properties.
- Amino silicones: One of the characteristics of amino silicones is the touch feel one gets when they touch the material. It usually feels soft to the touch, but that does not mean it lacks rigidity. For this reason, they are used in the textile industry to produce high-performance garments.
- Phenyl silicones: The main characteristic of phenyl silicone is the ring-like structure that its molecules form in the curing process. It looks more like the benzene rings. Of course, this is facilitated by the phenyl group in the molecular backbone.
All the above types of silicone can be readily sourced from your trusted silicone manufacturer. The thing to keep in mind is that each of the types has slightly different properties from its counterpart. If anything, they are made to have particular properties to help you choose based on the intended use case.
TPU vs Silicone: Comparing similarities and differences
Another point of comparison for TPU and silicone is the similarities and differences. In other words, how similar or different are these materials? To do this, we mostly rely on the mechanical and chemical properties of these materials.
Similarities between TPU and Silicone
Let us start with the similarities. As you will see, the two compounds have a great deal of similarities. Some of them include;
Versatility is the ability to adapt to different conditions. In most cases, this is essential since it means that the materials can have a wide range of applications, among other things. Versatile materials are also in high demand since they have more value in their recycled states.
Nature of Polymer
The nature of the polymer of these materials is somehow related. On one hand, they are both synthetic materials. Secondly, they are both inorganic. These characteristics prove to be essential in the production of several materials.
Both TPU and silicone have a high degree of wear resistance. The monomers making up these polymer compounds have special elements that improve this property. Wear resistance is an important feature since it widens the possible applications of these compounds.
The properties of silicone and TPU do not quite match. However, the similarity here occurs because both can be identified by their properties. Also, they both have chemical and physical properties like most polymers. This is essential in manufacturing since it helps you choose materials that can sustain stressors.
Differences between TPU and Silicone
The differences between TPU and silicone are like day and night. In other words, it is quite easy to identify them both physically and chemically. Some of these differences include;
Silicone is manufactured using quite specific methods. They include injection molding, compression molding, and others. To some extent, the same methods can be used to produce TPU components.
Processing TPU is more challenging than silicone. One of the reasons for this is the class of polymer of each material. Thermosets and thermoplastics have quite different properties and behavior in the presence of heat. While thermosets cannot melt, thermoplastics can easily disintegrate when exposed to heat.
Ease of Processing
We can also compare these two materials based on the ease of manufacturing them. TPU is known to be harder to process than silicone. This is the case because TPU is generally a thermoplastic, which means that technicians have to be careful not to destroy it with heat.
Additionally, TPU has a higher viscosity than silicone. For this reason, it has challenges flowing through the molds during the molding process. These challenges are the reason TPU is much more difficult to process than rubber.
Quality of Material
Material quality is of utmost importance to you. This means that you always consider the quality of the material when making most decisions.
Silicone and TPU have different qualities of materials when compared side by side. Rubber and plastic are not the same materials. However, when you compare them in their broader categories, you will find that there is not much of a difference.
Lifespan is the period taken by a material from its manufacture date to the time it loses all its properties. This is a definition used when referring to these compounds.
Silicone has a longer lifespan than TPU. The protection from UV weatherabilty of silicone makes it last longer in most environments. The same cannot be said for TPU which tends to disintegrate faster than silicone.
The choice of material in many applications is based on several factors. Silicone and TPU might tick many boxes, but the ultimate choice of the compound could depend on many external factors. For one, silicone is an elastomer, while TPU is a thermoset.
The applications of silicone are quite niche and particular. These are applications that have been carefully chosen after gathering a lot of information about the use cases. Some of them include;
- Medical devices: Silicone is used to make medical implants, lenses, catheters, and other biocompatible inserts.
- Household products: In our homes, there are many products made from silicone. They include; kitchenware, sealants for appliances, and toys for kids and adults. Most of these toys take advantage of the non-toxic nature of silicone.
- Automotive applications: The automotive industry would collapse were it not for strong rubbers such as silicone. It is used to manufacture gaskets, hoses, seals, and so on.
On the other hand, TPU has designated use cases based on a lot of factors. For instance, the durability of the material makes it ideal for footwear, sporting equipment, and to some extent automotive parts.
TPU vs Silicone: which one to consider?
When met with the dilemma of choosing between silicone and TPU, you need to have a guiding map to find the perfect material. Having read this article, you now have a better understanding of the two materials. However, the dilemma can still exist.
One of the key points to consider is the specifications of the intended use case. What sort of properties are they looking for? With the understanding that some of these properties are overlapping, you need to be rather careful here. Therefore, be guided by the niche requirements such as resistance to a specific chemical.
There would not be a direct answer to which one to consider. However, with the right considerations, you will be able to navigate the dilemma and make the right choice. This is important since there is a guarantee that you will find the right material for the job.
Thermoplastic Polyurethane and silicone have proven to be quite reliable synthetic polymers. As the demand for more polymers rises, these materials will keep getting manufactured to fulfill the demand. To your advantage, you now have a better understanding of them if you were planning to use them for your next project.