Silicone curing & vulcanisation — What’s the difference?

We are often asked, what’s the difference between silicone curing and vulcanisation?

We are often asked, what’s the difference between silicone curing and vulcanisation? In truth both terms describe essentially the same process — the transformation of the polymer into a cross-linked rubber.

But of course there are shades of difference. No two words mean precisely the same thing. And so in this article we are going to delve deeper into just what distinguishes both the curing and vulcanisation process, and explore a little bit more about the properties and applications of both types of silicone rubber in the world today.

What is the difference between the curing and vulcanisation of silicone?

The rubber curing and vulcanisation process is identical, but it’s the way that this process is carried out that distinguishes the two from each other. 

Vulcanisation is the name we give to curing when sulphur is used in the process. Mineral sulphur is commonly used to help form cross-links between the rubber chains because it helps to elongate the properties of the rubber — making it more elastic in the process while at the same time making it more stable and rigid (source). 

There are many other ways to cure silicone rubber without sulphur. Including:

  • Peroxide-cure
  • Platinum-cure (addition cure) 

These different curing mechanisms all result in the silicone having slightly different properties suitable for different applications. 

Did you know?
The word ‘vulcanisation’ is derived from the Roman god Vulcan, the god of fire and forge.

The different types of vulcanised silicone rubber and processing methods. 

Silicone rubber is available in both solid and liquid forms. Both have similar structures, but require different methods of curing and processing.

Solid silicone is also sometimes known as high consistency rubber (HCR). It is manufactured in large batches, and the components are mixed at high temperatures following the injection of a peroxide catalyst. The cross-linking following the chemical reaction is only allowed to partially vulcanise. The end result is large sheets of partially cross-linked silicone ready for shipping. 

Liquid silicone rubber (LSR) is a system featuring two components that also includes a platinum catalyst, a cross-linking agent, methylhydrogensiloxane and an alcohol inhibitor. It is normally processed using cold runner injecting moulding equipment, during which exothermic chemical reactions create long, stable chains of chemical bonds — resulting in a three-dimensional matrix. This method also serves to enhance the mechanical properties of the silicone (source).

Benefits and applications of cured and vulcanised rubber.

When silicone rubber is cured or vulcanised, it tends to shrink but still keep its shape. It also hardens, meaning it is less likely to deform under stress. Furthermore, this hardening increases the tensile strength of the silicone. 

Other great benefits of rubber curing or vulcanised silicone rubber includes:

  • Improved resilience 
  • Resistant to water absorption
  • Highly resistant to abrasion and oxidation
  • Improved electrical insulation properties
  • Resistant to organic solvents
  • Will return to its original shape

Because of all these handy features, cured and vulcanised silicone can be found anywhere and everywhere, in applications all around us. Examples include:

  • Car tyres
  • Shoe soles
  • Insulation
  • Conveyor belts
  • Toys
  • The rubber in pencils

And that’s just the tip of the iceberg. You will find cured and vulcanised silicone rubber is extremely popular across all major industries in production. 

Types of cured and vulcanised rubber 

Across the extrusions industry, there are different types of cured and vulcanised rubber and silicone such as peroxide and platinum cure.

At Viking Extrusions, we specialise in two types of cured silicone rubber: platinum cured and peroxide cured

We find there are numerous benefits to focusing on these two types. 

Benefits of platinum cured silicone

For example, platinum cured silicone has excellent biocompatibility, and is FDA and USP Class VI approved — making it very suitable for medical and pharmaceutical applications. It also has a high tear-strength and is naturally transparent. This makes it highly suitable for food processing, peristaltic pumps and many other applications. 

Benefits of peroxide cured silicone

With peroxide cured silicone, peroxide is broken down by high temperatures which cross-link the polymers in the chain.

Peroxide silicone products have a long shelf life, an improved compression set performance, and are cheaper to produce than platinum silicone. The process of curing is also easier, and can be done at lower temperatures. The result is that peroxide cured silicone can be produced at very competitive prices. 

Of course, each type has its own pros and cons. Find out more in our blog post ‘What are the Differences Between Platinum and Peroxide Cured Silicone?’ here. 

Why don’t we specialise in other types of cured and vulcanised silicone?

The reason we stick solely with platinum and peroxide-cured silicone is because we find that it boasts a longer shelf life over the other types available, and is often cheaper to produce than platinum silicone.

Over the last 30 years, Viking Extrusions are proud to have built a reputation based on exceptional customer service, flexibility and the ability to deliver challenging and innovative silicone products. We offer fast lead times, exceptional customer service, and complex extrusions.

Interested in cured and vulcanised silicone rubber extrusions? Then we can help. 

We have been serving worldwide customers for over 30 years now with profiles and components that are both complex and diverse. We pride ourselves on the knowledge and expertise that is available in-house, accumulated through years of prototyping and development work.

Years of continued investment have resulted in the company owning an impressive range of plant and equipment that is both high tech and ultra-reliable. Now we have over 8000 stock dies for profiles, cords and tubes — ensuring that most requirements can be catered for without a tooling charge.

If you’re interested or just have a question about our services, contact us today. You can email us or telephone — we’re always happy to help. 

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