In the plastic industry, materials are defined by their properties, mode of synthesis, and applicable use cases. As such, many distinct or similar characteristics are seen in the various thermoplastics and elastomers being manufactured today. Comparing these aspects of materials helps you learn more about the materials. This article compares silicone and acrylic as synthetic compounds.
What is Silicone?
Silicone is an elastomer, a synthetic compound that exhibits rubber-like properties. It is also known as a polysiloxane polymer compound.
This synthetic elastomer is among the most common rubber-like materials in the world. Its superior properties have positioned it at the helm of every manufacturing plant. From kitchenware to industrial equipment, silicone applications are countless.
Silicone is made from silicon, a compound that is found in several rocks. As such, its availability is sufficient for the foreseeable future. Its molecular structure is made up of silicon-oxygen compounds with repeating methyl groups. This molecular composition is quite essential since it determines the properties of the material.
What is Acrylic?
Acrylic is categorized as a thermoplastic. The term thermoplastic is used to describe polymers that have a specific set of characteristics related to their response to thermal changes. It is a synthetic polymer made from methyl methacrylate.
This synthetic compound has characteristics that resemble glass. First of all, it is overly transparent and sturdy, unlike silicone. If anything, this material is used in place of glass or transparent plastic. Talking of which, acrylic is technically considered plastic. It is unlike regular plastic, otherwise known as commodity plastic.
Acrylic resulted from the works of German scientists working with or for Otto Röhm. Since it was discovered, many manufacturers jumped on it and have to date made several iterations of the original product.
Silicone and Acrylic as Synthetic Polymers
Synthetic substances have one common attribute — they are manufactured in the lab. This means they do not occur naturally as some substances do. The perfect example is natural rubber.
As synthetic polymers, silicone, and acrylic have base monomers from which they are made. These monomers are subjected to the polymerization method of choice by the manufacturer and closely monitored and controlled to produce the polymer compound.
Polymethyl methacrylate (PMMA) (Acrylic polymer)
This is the chemical name of the acrylic polymer. In another section, we will delve deeper into the polymerization process of the monomer, methyl methacrylate. Polymethyl methacrylate exhibits many properties such as transparency, rigidity, and low weight per given sample size.
The derivative of the polymethyl methacrylate is methacrylic acid. The esters of this acid, methacrylic acid esters, are polymerized to produce the polymethyl methacrylate. This is achieved under controlled reactions with the addition of modifiers and other agents to catalyze the reactions.
Polysiloxane (Silicone polymer)
There is a high chance that you know more about silicone than acrylic. Silicone has been heavily marketed for niche and mass markets. Silicone polymer is derived from siloxane monomers. Siloxanes are essentially compounds whose molecules have repeating units of silicone and oxygen atoms.
Unlike most polymers, silicone does not have carbon atoms in its molecular structure. This is a characteristic of inorganic compounds. While this does not affect the performance of the material, it affects its chemical properties.
Silicone vs. Acrylic: Manufacturing Processes
The synthesis of plastics and elastomers is quite different. However, since both are polymer compounds, there are similarities in the processes. The similarities could include that both start from a monomer and undergo polymerization. Let us see how these polymerization processes happen for both.
Synthesis of silicone
The synthesis of silicone happens in the following steps.
- Step #1 – Monomer synthesis
Siloxane monomers are processed when silanes (silicon and hydrogen atom compounds) are put through hydrolysis to form silanol groups. Essentially, this involves passing the silane gas through water to form a liquid. This liquid is the starting point of the whole process. The resultant product silanol, then undergoes a condensation reaction to form siloxane and water.
During the hydrolysis and condensation process, they are catalysts used to speed up the rate of the reaction. Mostly, they are base or acid catalysts. Selection of the catalyst requires a lot of deliberation to ensure that the catalyst will not interfere with the properties of the final product.
- Step #2 – Crosslinking
In the synthesis of polymers, cross-linking is a process where the monomers are subjected to various agents to support the three-dimensional network bond formation. Crosslinking is also known as vulcanization or curing.
In this step, additives are added that are supposed to improve the properties of the material and speed up the reaction. The crosslinking process can result in a variety of silicone structures, including linear, branched, or cross-linked networks, depending on the specific synthesis conditions and the presence of cross-linking agents.
Synthesis of acrylic
Acrylic is also synthesized by polymerization of its base monomer. It happens under controlled conditions and it is conducted by skilled technicians. The steps in the process are;
- Step #1 – Synthesis of methyl methacrylate (MMA)
The monomer, methyl methacrylate, is derived from methacrylic acid. This acid is esterified in the presence of an alcohol (methanol) to produce esters. An ester is basically an acid derivative. A catalyst is used in the esterification process to speed up the reaction.
Methyl methacrylate is a clear and colorless liquid that is prepared for the polymerization process to produce polymethyl methacrylate. This is the next step in the synthesis of acrylic.
- Step #2 – Polymerization
Unlike silicone, acrylic is polymerized through a special process known as free-radical polymerization. In this approach, free radicals are added to the reactants successfully until the polymer is formed.
Still, acrylic monomers can be polymerized through other polymerization methods such as suspension, emulsion polymerization, solution, or bulk methods.
The polymerization of acrylic monomers requires the addition of initiators such as peroxides or azo compounds. These are the catalysts that kickstart the process and hold it steady. This is essential as the polymerization of acrylic is a complex process.
- Step #3 – Chain growth
Chain growth is the formation of polymethyl methacrylate bonds after the free-radical process has occurred.
This polymerization is faster, more efficient, and more reliable. It leads to the formation of compounds with a high molecular weight. On top of that, the polymerization reaction or polymer molecule yield increases with time. This is why the reaction archives a high molecular weight at the end of the reaction.
The Main Difference Between Silicone and Acrylic
While both acyclic and silicone are polymers, one of the major differences between them is that acrylic is a plastic and silicone is an elastomer.
There are other subtle differences such as the applications, molecular makeup, and so on. These two compounds are in the same category in terms of synthesis but they end up having very unique characteristics.
Some aspects of the two compounds cannot be compared properly. For instance, we cannot compare their durability or functionality. This is because the two serve different purposes. However, for some applications where both materials can be used to serve similar functions, these aspects can be compared. An example is roof coatings.
Silicone vs. Acrylic: Physical Properties
The physical or mechanical properties of a compound let us know how the material behaves when external force is applied to it. This information is essential since it will help you decide if the material is capable of withstanding certain conditions.
Physical Properties of Silicone
Silicone has excellent physical properties compared to other synthetic elastomers. Some of them are as follows;
Elasticity is a defining feature of silicone. It is defined as the ability of the material to stretch to its maximum without breaking into parts. This property is essential in its application. Also, it shows that the material can withstand tension forces without getting deformed.
The high elasticity of silicone is contributed to by its molecular structure. Particularly, the polymers form a helical shape during polymerization. The combination of the helical shape and low intermolecular forces leads to a highly elastic compound.
Low and high-temperature tolerance
Silicone is among the synthetic elastomers that have a wide temperature range tolerance. This means that the material can tolerate both low and high temperatures.
Regular rubbers lose their ductility at around -30 degrees Celsius why silicone starts at -70 degrees. The loss of ductility (embrittlement) makes the material brittle and it starts breaking apart.
On the other end, this material can still maintain its form and properties at 350 degrees Celsius for a continued period. All this goes to show you that silicone is capable in extreme temperature conditions. Its durability is not affected by temperature changes.
Exceptional weather ability
The damaging effects of ultraviolet rays are known as weather ability. While most materials are affected by this, silicone remains strong over long exposure.
Tests conducted have shown that silicone can withstand ozone, UV, and other atmospheric gasses without losing its properties. This is important since it makes silicone a reliable material to use in extreme outdoor conditions without having to worry about the damaging effects of weather.
Moisture resistance at certain conditions
Like most synthetic elastomers, silicone is highly hydrophobic. Its dense molecular structure and weight leave no pores for water molecules to pass through. The kicker is that it can sustain both low and high-temperature moisture.
The resistance to both low and high temperatures is a contributing factor here. However, the changes become noticeable as the pressure of the steam increases. At low pressure, the steam has no effect on the material. However, the siloxane polymer bonds start to break down when the material is subjected to high pressure at temperatures above 150 degrees Celsius.
Excellent resistance to oils
Oils have many elements that can damage the structure of the material. For silicone, it can resist the damaging effects of oils and fuels. Examples of oils include machine oils, gasoline, and fuel oils. Other materials such as acrylic would swell or soften when exposed to these conditions.
Resistance to oils is one of the main reasons silicone is so reliable in the automotive and aerospace industries. This material is used to make gaskets and other parts that come into contact with substantial amounts of oils at high temperatures. Silicone gaskets are capable of maintaining their form under these conditions.
High insulation resistance
Silicone has excellent insulation against heat and electricity. This is important since it extends the applications of the material. For instance, there are many electrical appliances that use silicone as the insulator for this property. Similarly, kitchen products such as oven mitts are made from silicone to help prevent getting burned.
Moderate flame retardancy
Flame retardancy is the ability of a material to prevent the spread of fire through it. Most carbon-based products lack this feature. Generally, anything organic will have a low chance of stopping the spread of fire.
As an inorganic substance, silicone has some degree of flame retardancy. However, this does not mean that it does not burn because it does. What it means is that it burns slowly and it does not promote combustion.
Physical Properties of Acrylic
As a plastic, acrylic demonstrates excellent properties that are not present in most commodity plastics. It shares some similarities with silicone properties as well. The common physical properties of acrylic are;
The main characteristic of acrylic is that it is a transparent substance. It resembles clear plastic or glass when you look at it. The reason for this transparency is the arrangement of the molecules in a regular pattern, thereby allowing light to pass through the material.
The transparent nature of acrylic opens up the material to a load of useful applications. For one, it can be used as a glass. This use case is contributed to by its strength and impact resistance that it boasts.
High Impact Resistance
Impact resistance is defined as the ability of the material to withstand impact force without getting damaged. Regular glass shatters when an impact force is applied to it. Comparatively, acrylic does not shatter. This cannot be said for silicone since it is not as stiff as acrylic. High-impact resistance is another physical property that makes acrylic reliable in many applications.
Acrylic is quite lightweight compared to materials like regular plastic or silicone. Its low molecular density is a contributing factor to this property. Additionally, the elements found in this material such as carbon and hydrogen have low molecular weight. The composition of these factors yields a lightweight compound.
Highly Resistant to High Temperatures
Unlike commodity plastic, acrylic is known to sustain high temperatures without losing any properties. In short, it does not melt as fast as other plastics.
Acrylic can sustain temperatures of up to 80°C without deforming. When temperatures go beyond this point, the material expands. Similarly, it contracts when it cools down. This change in thermal balance is a limiting factor in its application. In other words, it would be unsuitable in conditions where temperature changes are frequent.
Limitations of Silicone and Acrylic
The properties of silicone and acrylic paint a picture of two capable and reliable synthetic compounds. However, the two have several limitations that you should know about before deciding which material to use.
Here are some limitations of the two compounds;
Limitations of Silicone
- Expensive: Silicone is a costly material to use compared to other rubber and plastic, which can be an issue in cost-focused applications.
- Bad at resisting scratches: Compared to other materials, silicone does not fare well in resisting abrasion. This means that it won’t last long in situations where friction or wear is a concern.
- Not reliable for heavy-duty work: The lack of tensile strength is another burden silicone has. Even though it’s flexible, it’s weak. It would crumble under pressure that many other rubbers could handle with ease. This makes it unsuitable for high-stress applications.
- Poor compression set: A problem called compression set occurs when silicone gets squeezed for too long. It’s unable to fully recover which will affect its gasket performance and ability to seal things completely.
Limitations of acrylic
- Suitable for moderate temperatures only: Acrylic fails to hold up at elevated temperatures, which means it has a limited temperature range. Therefore, it’s not ideal for high-temperature applications.
- Acrylic surfaces can lose their visual clarity and appearance due to scratch sensitivity. Marred surfaces are frequent when exposed to abrasive materials.
- Carefully consider situations of chemical exposure as acrylic is prone to crazing or cracking when exposed to specific solvents and chemicals due to its sensitivity.
- Over time, acrylic’s optical clarity might decrease due to its ability to absorb moisture from the environment, causing changes in its dimensions due to its hygroscopic nature.
- Acrylic’s resistance to UV is generally good, but prolonged radiation can certainly have an impact on its color and appearance, ultimately causing it to degrade and yellow over time.
Silicone vs. Acrylic: Applications
The applications of silicone and acrylic are quite different. Silicone is mostly used in situations where rubber-like properties are needed, while acrylic is used as a plastic. These differences bring out the comparison of the two.
Uses of Silicone
Some of the common uses of silicone include;
- Medical devices. There are many medical devices made from silicone. The lack of toxins in this material makes it ideal for the medical field. Some of the common medical equipment made from silicone include dental grips, nursing pads, and menstrual cups.
- Sealants. Due to its tension and compression set, silicone can be useful in making sealant products.
- Gaskets. Gaskets are similar to sealants but they are mostly solid. They include gasket tapes and o-rings. On the other hand, sealants are usually liquid or paste.
- Kitchenware. The temperature resistance of silicone makes it a perfect material for use in the kitchen. It is used to make oven mitts, spatulas, and other products that come into direct contact with heat.
- Roof coatings. Silicone is among the most common elastomeric coating materials used for roofs and other surfaces. It is used for waterproofing since it has high water and moisture resistance.
Uses of Acrylic
As a plastic, the applications of acrylic are quite specific. Also, the properties of this material limit specific uses. Some of them are;
- Windows and displays. Acrylic can be used in place of glass window panes. The material is sturdy enough to hold. Also, its transparent nature makes it ideal for this application.
- Signage and lighting. Transparency also is applicable in signage and lighting fixtures. Acrylic has a nice finish that looks quite aesthetic.
- Art and design. Acrylic can also be for sculptures and art installations.
- Industrial and consumer products. For the mass market, this material is also quite useful. There is a wide range of products that can be made from acrylic instead of regular plastic or glass.
Silicone vs. Acrylic: Elastomeric Roof Coating
Roof coating is one of the shared use cases between silicone and acrylic. This is the use of melted acrylic or silicone for roofing purposes. It is generally known as elastomeric roof coating. In most cases, roof coating is used for preventing leaks, containing temperatures, and preserving the quality of the roofing material.
Silicone elastomeric roof coating
With its superior resistance to temperature, UV, and other outdoor environmental stressors, silicone is a very good roof coating material.
The application of a roof coat fills in cracks and crevices. Liquid silicone sealant is applied in the same fashion as paint. It is then left to cure naturally and once it does, it creates a strong bond in the surface of the roof.
Acrylic roof coatings
Acrylic roof coatings refer to a liquid-applied rigid, fully adhered, elastomeric membrane that cures on the spot. The coat formed is 10 times thicker than roof paint. Also, unlike paint, acrylic can be applied to any roofing material.
The advantage of a roof coat is that the acrylic or silicone has the same viscosity as regular paint. As such, it is easy to apply. Conversely, elastomeric coating creates a stronger and more durable coat than paint. This is because the curing process of these polymers is permanent.
Which one to consider
Both silicone and acrylic have desirable properties for their elastomeric coating. Therefore, it is easy to get overwhelmed when choosing between the two.
The choice of the elastomeric roof coat should depend on a few factors. To start with, how long would you like the coat to last? Silicone has a longer lifespan than acrylic. Therefore, if you want a longer lifespan, silicone would be more useful here.
On the other hand, silicone is more expensive than acrylic. This means that you will spend more on silicone elastomeric roofing than acrylic. If financial constraints are a factor, you would have to opt for the cheaper option. Luckily, the cheaper option, in this case, acrylic, is better than roof paint.
Another factor to consider would be the climatic conditions of the area. If the area is unpredictable in terms of weather, a more durable option, in this case silicone, would suffice.
Silicone and acrylic polymers have similarities and differences that define them as synthetic compounds. Their properties, mode of synthesis, and applications differ but still, there are subtle similarities. Comparing these aspects of the materials has led to the realization that synthetic compounds need to be studied closely for better understanding.