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Silicone vs Neoprene
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Choosing an elastomer for a new design or application can be overwhelming due to the wide range of materials available on the market today. We at Jehbco are often asked to help consult our customers on what elastomer is the right choice for their application.  Are our 100% silicone products the right choice for you? Or would a different material be more appropriate?

In this article, we’ll explore the different properties of silicone and neoprene, and what applications each material would be best suited for. Silicone and neoprene are both commonly used materials for o-rings, gaskets, seals, tubing and membranes. While both elastomers may be used to create similar products, the specific application and environment will ultimately determine whether neoprene or silicone will be the better choice for you. The table below summarises some of the key differences between the two materials.

 

Neoprene Silicone
-40 °C to 110 °C -50 °C to 230 °C
Good compression set Excellent compression set
Great weather resistance Excellent weather resistance
Approx. tensile strength 12 MPa Approx. tensile strength 5 MPa
Excellent abrasion resistance Poor abrasion resistance
Not compatible with: concentrated acids, hydrocarbon fuels, aromatic hydrocarbons, oxygenated solvents. Not compatible with: hydrocarbon fuels, alkalis and acids, steam over 121 °C, trichloroethylene, aromatic hydrocarbons.
Compatible with: hot and cold water, alkalis, dilute acids, steam, refrigerants, some oils and greases Compatible with: oils, brake fluids, hot and cold water, salt water, high molecular weight chlorinated hydrocarbons, fire resistant hydraulic fluid, ozone.

 

Both neoprene and silicone can operate at extremely low temperatures, although silicone is the far better option in high temperature environments. Silicone can resist intermittent temperatures of up to 230°C, or up to 280°C if a heat stabiliser is added into the raw material.

 

Silicone vs Neoprene

Silicone vs Neoprene

 

Neoprene has high tensile strength and excellent abrasion resistance, whereas silicone has good tensile strength, but poor abrasion resistance. For dynamic applications with friction, neoprene would most likely be a better option.  With this being said, silicone can be formulated to have improved tear strength, making it an ideal choice for applications such as vacuum sheeting and peristaltic pumps. Silicone also has the superior compression set, which makes it a better choice for applications requiring a long lasting, reusable seal, especially in high temperature environments.

While silicone has an excellent resistance to ozone and UV, neoprene can also resist ozone and UV to a degree, making both options viable for most outdoor applications. Neoprene is more suited for any applications that require contact with alkali compounds or dilute acids, while silicone is more suitable for applications that require contact with high temperature oils. Neither material is compatible with hydrocarbon fuel, but silicone is resistant to automotive brake fluids.

It is clear to see that there is merit in using either neoprene and silicone, depending on what physical properties you require and the operational environment.  For help selecting a material for your application, consult our applications page and contact us with any questions.

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Mechanical Testing & Simulation

Mechanical Testing & Simulation
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At Jehbco, research is constantly carried out to understand the behaviour of silicone rubber and its properties under various conditions to achieve control over the entire product lifecycle. Silicone rubber is a viscoelastic amorphous polymer which simultaneously exhibits internal resistance to flow as well as molecular positional memory under deformation over a temperature range specific to the material. Thanks to these properties silicone rubber can be extensively used in sealing applications.

Mechanical sealing is important in equipment with movable parts. The compartmentalisation between sections of machinery or equipment is achieved using rubber gaskets and seals.

For the manufactured silicone rubber product to perform the functions it is designed for, it should retain the design properties under operating conditions. The form or shape of the seal or gaskets, deformation behaviour, hardness, coefficient of friction, and compression set define the final properties of the product.

 

Tensile testing machine

Tensile testing machine

In comparison to materials that behave linearly under load, understanding viscoelastic materials is challenging. Below are the differences between stiffness, strength and hardness and their corresponding indicating parameters which are generally used to describe the property of the rubber product.

  • Stiffness is an indicator of the tendency for an element to return to its original form after being subjected to a force. (Compression set)
  • Strength measures how much stress can be applied to an element before it deforms permanently or fractures. (Tensile strength)
  • Hardness measures a material’s resistance to surface deformation. (Shore hardness)

Hyperelastic numerical models are used to represent various non-linear material behaviour under different conditions. Hyperelastic models for expressing the behaviour of elastomers are modelled as incompressible (i.e. changes in shape but the overall volume remains same), isotropic (i.e. internal properties such as stress are uniform in all directions) and homogeneous. The model is validated against the customer’s specimen or initial test piece developed at our facility. Finite element analysis is carried out using SolidWorks using which the developed Hyperelastic model is computationally tested. The results are then indicative of the stiffness, strength and hardness characteristics which is used in product development.

Our understanding of non-linear behaviour of the material is key to our product development capabilities. Developments are constantly being made to pour in-house testing facility improving both simulation and physical testing capabilities.

We have developed a software to calculate custom size of O-rings and butt-joined chord type gaskets, adding to Jehbco’s expertise in providing solutions for non-standard applications. The software is a result of comprehensive design-engineering and experimental testing carried out by our research and development team.

The mechanical testing and research facility at Jehbco is equipped to meet industrial product testing standards for variety of applications, making sure the customer gets the best engineered product.

For further information or advice about our product testing and development, please review Jehbco’s articles and contact us with any questions.

 

References

  1. Villasenor-Ochoa, H. (2017). Engineering Fundamentals Refresh: Strength vs Stiffness vs Hardness | Fictiv – Hardware Guide. [online] Fictiv.com. Available at: https://www.fictiv.com/hwg/design/engineering-fundamentals-refresh-strength-vs-stiffness-vs-hardness [Accessed 25 Jul. 2018].
  2. Dickey, R. (1973). Nonlinear elasticity. New York [etc.]: Academic Press.
  3. A.N., G. (1994). Science and Technology of Rubber. 2nd ed. ACADEMIC PRESS. Published by Elsevier Inc., pp.1-22.
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Replacing Toxic Silicone Sealants with Solid Silicone Seals
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Room temperature vulcanising (RTV) silicone sealants are a popular and versatile joining material frequently used in the construction industry.  These ready-to-use silicones cure at room temperature by reacting with moisture in the atmosphere, forming a strong and stable join. However, this curing process produces unwanted, toxic by-products which are released into the immediate surroundings. Excessive short term and long term exposure to these by-products have significant associated health risks, including suspected carcinogenicity and damage to the eyes, skin and respiratory system.

The most common kind of RTV silicone sealants are acetoxy and neutral curing silicones. Acetoxy curing silicone sealants produce acetic acid upon curing, emitting a pungent, sour odour resembling vinegar. While these sealants are commonly used for domestic applications and glass or ceramic substrates, the corrosiveness of acetic acid makes acetoxy curing RTV silicone unsuitable for many substrates used in construction applications. Neutral-curing silicones do not form corrosive by-products, allowing them to be used with a wide range of substrates. Oxime curing silicones are a commonly used weather resistant neutral curing sealant, producing methyl ethyl ketoxime (MEKO), also known as butan-2-one oxime, as a by-product upon curing. While MEKO is non-corrosive, it is important to understand the significant health risks that are associated with exposure to this substance.

 

 

Hazardous chemicals associated with silicone wet seals

Hazardous chemicals associated with silicone wet seals

 

The short-term MEKO exposure risks from using oxime silicone sealants are associated with its acute toxicity upon skin contact, eye contact or inhalation [1, 2]. At low concentrations generated from oxime cure, skin contact may cause some skin irritation or facilitate an allergic dermal reaction. Eye contact is severe, causing serious eye irritation upon contact with fumes and irreversible eye damage upon concentrated contact [3]. While the acute toxicity through inhalation is classified as low, respiratory irritation may occur along with significant long exposure risks. Acute oral toxicity is low, but is not as relevant for sealant applications.

 

Even more concerning is the carcinogenicity of MEKO over a long exposure period. MEKO is classified as a Category 3 carcinogen by Safe Work Australia [1, 2]. Substances with this classification usually carry an associated ‘suspected of causing cancer’ warning in accordance with Australian Work Health and Safety (WHS) legislation. The carcinogenicity study exposed rats to 374 ppm doses via inhalation over 18 months [3]. Upon the closing of the study, degeneration of the respiratory system was observed as well as significant increased incidence of hepatocellular carcinomas, the most common kind of liver tumour [3]. These results, along with other studies of MEKO, are strong indications of the carcinogenicity and long term exposure risks of MEKO.

It is important to understand the risks associated with using wet silicone sealants such that they can be minimised and effectively controlled. The maximum MEKO exposure limit recommended by the American Industrial Hygiene Association is 36 mg/m3 (10ppm) [2]. Workspaces must be well ventilated to keep the concentration of MEKO below this level, along with all other personal protective equipment recommended by the sealant manufacturer, in order to use oxime based sealants in a safe manner. While there are other neutral curing silicones being developed that have lower carcinogenic risk, including alkoxy and amine curing sealants, each continue to produce by-products that are harmful to human health. Inherently, the use of any wet sealant constitutes some form of exposure risk to human health and safety.

While exposure limits and personal protective equipment provide a basic level of risk reduction, those familiar with the Hierarchy of Hazard Controls will know that elimination and substitution are more favourable and effective methods of risk reduction. Reducing the quantity of wet sealant used can substantially reduce workplace risk by reducing the amount of toxic by-products released into the surroundings. A suitable replacement for wet silicone seals are dry gap sealing with a solid silicone join.

Jehbco’s Quick Joint Extrusion is a solid silicone dry seal that does not produce any vapours and has excellent binding strength and better durability than wet seals. As a wet seal replacement, quick joint silicone also minimises installation time significantly and provides a polished, more visually appealing finish to the join. Because the installation time is reduced, the workplace exposure to wet sealant by-products is also reduced significantly. A lower exposure time further minimises health risk and promotes a safer, more productive working environment.

 

REFERENCES

  1. Safe Work Australia. Hazardous Substances Information System (HSIS).  [cited 16 April 2018]; Available from: http://hsis.safeworkaustralia.gov.au/HazardousSubstance.
  2. National Industrial Chemicals Notification and Assessment Scheme. HUMAN HEALTH TIER II ASSESSMENT FOR 2-Butanone, oxime CAS Number: 96-29-7.  [cited 16 April 2018]; Available from: https://www.nicnas.gov.au/chemical-information/imap-assessments/imap-assessment-details?assessment_id=103#cas-A_96-29-7.
  3. REACH Dossier. Butanone Oxime (96-29-7).  [cited 16 April 2018]; Available from: http://echa.europa.eu/web/guest/information-on-chemicals/registered-substances.
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Silicone Mixing Quality
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At Jehbco, we ensure that every product is of the highest quality before being sent to our customers. Raw silicone must be fed through a roller mill to mix in any extra additives or colouring, but insufficient mixing can lead to a poor-quality product. For example, if an additive to improve fire resistance is not properly mixed into the raw silicone, there may be portions of the final product that may not be fire resistant. Hence, it is crucial that the quality of mixing during the milling stage of silicone rubber production is constantly monitored, to ensure a homogenous product.

 

 

Figure 1: Raw silicone being passed through a roller mill for mixing [1]

Figure 1: Raw silicone being passed through a roller mill for mixing [1]

One method of measuring the mixing quality during the milling stage is to calculate the coefficient of variation of additive particles in samples of the mixed silicone material. The coefficient of variation is a percentage that represents how similar each sample is to one another. Samples of the mixed silicone product are taken and analysed under a scanning-electron microscope (SEM). The high magnification of the SEM will allow the user to determine the approximate concentration of additive particles in each sample, which can be used to determine the coefficient of variation, as shown in figure 2 below.

 

Figure 2: Coefficient of Variation Equation

Figure 2: Coefficient of Variation Equation

 

 

A low coefficient of variation means that the amount of additive in each sample is similar, which suggests a well-mixed product. Thus, the quality of mixing can be determined using the coefficient of variation. Table 1 below correlates the calculated coefficient of variation of the samples, to the quality of mixing in the mixed silicone product. For example, if the coefficient of variation of the samples is between 10-15%, the quality of mixing in the mixed product is good, but can be improved by increasing the number of passes through the roller mill.

 

Table 1: Correlation between correlation of variation and quality of mixing

Coefficient of Variation (%) Quality of Mixing Corrective Actions
<10 Excellent –
10-15 Good Increase number of roller mill passes
15-20 Fair Increase number of roller mill passes

Inspect roller mills for wear

Alter sequencing of additives
>20 Poor Consult raw material supplier or mill manufacturer for professional advice

 

By calculating the coefficient of variation, and hence, the quality of mixing in the mixed product, a high quality of silicone rubber product can be consistently maintained. At Jehbco, we strive to provide only the highest quality of silicone products for your needs.

For further information or advice about which silicone rubber best suits your application, please review the Jehbco website www.jehbco.com.au, and contact us with any questions.

 

References:

[1] Medical Design. (2013, April 3). [Roller Mill with Raw Silicone]. Retrieved November 14, 2017, from http://medicaldesign.com/silicone/new-silicone-elastomer-offers-wider-processing-flexibility

 

 

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Silicone Tubing for Peristaltic Pumps
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Jehbco’s Silicone has a number of excellent properties, making it a good choice for many applications.  Jehbco has many years of experience designing and manufacturing parts for a wide range of applications, from aircraft parts to food and medical tubing.  One area where we have expertise is peristaltic pump tubing.

Peristaltic pumps are used in sensitive applications where fluid cannot be exposed to pump components.  They are often used when the fluid must remain sterile (such as in medical applications), and when the fluid is very aggressive or corrosive.  A peristaltic pump works by squeezing fluid through a flexible tube.  The tubing must be able to withstand thousands of squeeze repetitions and also not react with or absorb the fluid being pumped.  Jehbco’s medical grade silicone is an ideal material for peristaltic pump tubing.

 

Peristaltic pump

Peristaltic pump

 

Jehbco manufactures medical grade tubing from pure silicone.  Our silicone is inert and non-absorbent, making it suitable for most medical fluids, acids, bases and many other chemicals.  Furthermore, our silicone tubing can withstand the repeated squeezing that occurs in peristaltic pumps with minimum fatigue.  Jehbco’s tubing meets pharmaceutical industry standards and is ready to install in pharmaceutical pumping applications.

Peristaltic pumps are just one of the many applications of Jehbco’s high-quality silicone products.  For help with the design of your own application, review our website at www.Jehbco.com.au and contact our sales team with any questions.

Image Credit & Thanks: Wikipedia

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O-Ring Design with Jehbco: Sneak Peek

O-Ring Design with Jehbco: Sneak Peek
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O-Rings are an extremely common and effective seal, consisting of a rubber ring with a circular profile, which is pressed into a rectangular groove or gland.  Most applications can use a standard, off-the-shelf o-ring, but for those special applications that need a non-standard o-ring, here at Jehbco we can manufacture a custom o-ring perfect for the task.

Several standards exist for o-ring design, the most common being AS5857.  These standards simplify design of o-ring seals, giving dimensions for both the rectangular gland and the o-ring itself.  But some applications require a non-standard o-ring – very large seals, seals for existing non-standard glands and seals for non-rectangular glands, for example.  When the seal is non-standard, the design is a nightmare – working out the gland size, the seal size, checking the seal squeeze and fit all require many design iterations and physical tests.  Here at Jehbco, we’re working to simplify the design process with our in-house o-ring design software.

 

Figure-1 Testing our face seal designs with Jehbco Silicones

Figure-1 Testing our face seal designs with Jehbco Silicones

 

We are conducting physical tests of our automated o-ring designs, to ensure that the values our software gives work in the real world.  Of course, new designs will still require physical testing, but we aim to reduce the number of test iterations required to produce the final design, and eliminate all the tedious hand calculations required for non-standard o-ring designs.

 

Figure-2 A sneak peek of our o-ring design software with Jehbco Silicones

Figure-2 A sneak peek of our o-ring design software with Jehbco Silicones

 


Our software is still under development, but stay tuned for more news as we put our design software into service.  For more information on our products and services, review our website www.jehbco.com.au and contact us with any questions.

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Improving Extreme Temperature Degradation of Silicone Rubber Using Flame Retardant Additives
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Silicone rubber is well known for its durability at high temperatures. While other polymers such as nitrile, polyacrylate, and polyurethane have maximum service temperatures of around 70-150oC, silicone can withstand operating environments around 200-250oC. However, exposure to extreme temperatures will cause the silicone to combust. A common way to improve the resistance to extreme temperatures and fire is to include flame retardant additives in the manufacturing process. Not only does this increase the ignition temperature of silicone, but it also increases the durability of silicone at high temperatures and changes the way it combusts. Jehbco’s flame retardant silicones have been tested under AS1530.3, EN45545 and other standards to guarantee your peace of mind for high-temperature applications.

Silicone rubber has exhibits unique behavior at elevated temperatures. While most plastics will begin to melt at high temperatures, silicone does not have a melting point and remains solid until combustion occurs. At high temperatures (200-450oC), silicone rubber will slowly lose its mechanical properties over time, becoming brittle. The exact autoignition temperature of silicone depends on many factors such as the hardness of silicone, curing catalyst and any additives used. The standard autoignition temperature is around 450oC.

Silicone also exhibits unique behaviour during the combustion process. As the autoignition temperature is reached, the sample will smoke briefly before it begins to crack and combust. The silicone will expand in volume as volatiles are released, before the brittle combusted silicone breaks away from the sample, and will disintegrate into a fine powder upon any application of pressure. Silicone rubber primarily consists of a silicon-oxygen-silicon backbone with various carbon-containing methyl and vinyl groups. Upon combustion, silicon dioxide and carbon oxides are produced. The carbon monoxide and dioxide gasses are released into the atmosphere, while the silicon dioxide, as shown in Figure 1, creates a layer of white powder on the surface of the sample. This layer of silicon dioxide cannot be combusted further and acts as an insulating layer to help slow down and prevent further combustion of silicone.

 

Figure 1: Insulating silicon dioxide powder forming on a combusted silicone rubber sample

Figure 1: Insulating silicon dioxide powder forming on a combusted silicone rubber sample

 

At Jehbco, we have been researching and developing new silicone rubber for over 40 years. Our flame retardant silicones have had extraordinary success in improving the flame retardant properties of silicone rubber. As shown in Figure 2, two different levels of flame retardant silicone were combusted along with a standard silicone rubber sample. The flame retardant silicone both ignited at higher temperatures than silicone rubber, and the extent of damage in the samples after combustion is much lower than the standard silicone rubber.

 

Figure 2: Combustion of standard silicone rubber (left) compared to various flame retardant silicone (right)

Figure 2: Combustion of standard silicone rubber (left) compared to various flame retardant silicone (right)

 

Ultimately, if you are looking for a reliable construction material for high-temperature applications, Jehbco’s flame retardant silicones are among the most durable and reliable materials available on the market.  For further information or advice about which flame retardant silicone best suits your application, please review the Jehbco website www.jehbco.com.au, and contact us with any questions.

 

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Silicone vs Natural Rubber
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At Jehbco, we manufacture our products exclusively from pure silicone. Silicone is a type of polymer known as an “elastomer” – these polymers are stretchy or elastic. For many applications, it is not quite clear which elastomer is the best to use. Probably the most well known elastomer is natural rubber, commonly known as latex.  In this article, we’ll look at the properties of silicone and natural rubber and discover when you might choose one or the other.

Natural rubber, with the chemical name polyisopropene, is produced naturally from the sap of the rubber tree.  Silicone, on the other hand, is a synthetic material.  While both materials are elastomers, they differ in many of their properties.  Some of these properties are summarised in the table below.

 

Natural Rubber Silicone
-50 °C to 80 °C -50 °C to 230 °C
Excellent compression set Excellent compression set
Poor weather resistance Excellent weather resistance
Approx. tensile strength 25 MPa Approx. tensile strength 5 MPa
Excellent abrasion resistance Poor abrasion resistance
Not compatible with: ozone, strong acids, fats, oils, greases, hydrocarbons. Not compatible with: hydrocarbon fuels, alkalis and acids, steam over 121 °C, trichloroethylene, aromatic hydrocarbons.
Compatible with: hot and cold water, weak acids, alcohols, ketones, aldehydes. Compatible with: ozone, oils, brake fluids, hot and cold water, salt water, high molecular weight chlorinated hydrocarbons, fire resistant hydraulic fluid.

 

Both natural rubber and silicone are able to operate at very low temperatures – down to -50 °C.  However, silicone is able to operate at much higher temperatures than natural rubber.  Natural rubber starts deteriorating at 80 °C and melts at 120 °C.  Silicone is able to be formulated to operate up to 230 °C.  Silicone also has significantly better flame resistance than natural rubber.  For high temperature applications, silicone is certainly the better choice.

Neither silicone nor natural rubber have good resistance to hydrocarbon fuels and lubricants.  However, silicone exhibits a wider chemical resistance than natural rubber, often making it the better choice for chemical sealing applications.  The choice of material in chemical applications will depend however on the exact chemicals that the material will come into contact with.  Both materials are used in applications such as piping and tank lining.

 

A discussion on Silicone Vs Rubber with Jehbco Silicone Specialists

A discussion on Silicone Vs Rubber with Jehbco Silicone Specialists

 

Natural rubber exhibits much higher tensile strength, tear strength and abrasion resistance than silicone.  It is used in high wear applications such as tyre treads and conveyor belts.  Silicone has relatively low abrasion resistance, and in applications where a part will be subjected to abrasion and wear, natural rubber is a better choice.

Silicone has excellent resistance to weathering and UV, and is often found in outdoor applications such as door and window seals.  In contrast, natural rubber weathers very quickly and is not suited to outdoor applications.  If your application involves exposure to the elements, silicone is the better choice.

For help selecting a material for your application, please contact us with any questions.

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Parylene-C Coatings on Silicone
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In the silicone industry, a wide variety of coatings are implemented to enhance the physical properties of silicone products. There are many benefits of using chemical coatings, which include, but are not limited to: increased chemical resistance, decreased coefficient of friction, and decreased permeability to moisture.

Amongst the many types of chemical coatings available for silicone products, Parylene coatings are one of the most commonly used materials for silicone products in the food and medical sectors. Parylene is the colloquial name for a series of vapour-deposited coatings that provide chemical and moisture resistance to a range of different products. Parylene-C is the most popular type of Parylene coating used in the silicone industry, due to its ease of application, low cost, and the significant barrier properties it provides. Below is the chemical structure of a Parylene-C monomer, as well as its raw dimer form, known as diparaxylene.

 

 

Currently, Parylene-C coatings are used in the silicone industry to provide a low-friction, almost impervious barrier that can resist chemical attack and high electric currents. The inert, non-toxic properties of Parylene-C make it an ideal coating for silicone materials in the medical industry. Additionally, Parylene-C coatings are FDA approved, which make it an ideal coating for silicone products in the food industry.  Furthermore, the high level of coating thickness control during the vapour deposition process can allow Parylene-C coated products to be used in high-precision instruments, such as seals in medical sterilisers.

Parylene-C is a thin conformal coating, meaning that it conforms to the topography of the material it is applied to.  This is very beneficial for products such as oddly-shaped silicone extrusions, that may not be compatible with other forms of coatings. The ability of Parylene-C to conform to the topography of the given product is due to its unique vapour-deposition application process. Additionally, the vapour-deposition of the Parylene-C coating is normally conducted at room temperature, with no additional catalysts or solvents needed, which allows for the coating of thermo-sensitive or delicate products.

The application process of Parylene-C, while relatively simple, is an integral factor of the effectiveness of Parylene-C coatings. Raw, solid Parylene-C dimer is vapourised into a gas at 100-150°C and is split into individual Parylene-C monomers following exposure to temperatures >500°C. Under vacuum, the monomer gas is pulled into a deposition chamber, in which the desired product is coated at room temperature as the monomer gas polymerises into a solid, uniform coating. The product is removed to storage, and a cold trap at -100°C following the deposition chamber is used to remove residual Parylene-C.

At Jehbco, we strive to provide the perfect silicone product for your needs. For further information or advice about which silicone rubber and coating best suits your application, please review the Jehbco website www.jehbco.com.au, and contact us with any questions

 

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