Wednesday, 7 February 2018

Rubber Additives

Rubber is one of the most interesting commercial materials on the market. Its uses are as varied as the composition of the rubber itself. In order to attain particular properties, manufacturers may use a whole host of rubber additives during the process.

Depending on which type of rubber you desire, both natural and synthetic rubbers may have their formulations modified to create the perfect end product.

Mix formulations often begin with a defined amount of elastomer. This can be butadiene rubber, natural rubber or styrene-butadiene rubber. This quantity is measured as 100 parts/weight.

Once the manufacturer is happy with this, they will then begin to add another ingredient which is expressed in parts by weight added per 100 parts by weight of the elastomer. Staying with me?

If you should decide to use two or more elastomers in order to achieve particular properties, these will be shown as fractions of 100 parts within the recipe formula.

"The Cure Package"

When formulating the perfect rubber mix, you will need to take in to account which products you will be purchasing for your "cure package". The cure package is the ingredients which are used to cause interlinking reactions within the mix when it is cured. To ensure that you are not left with a premature cure, it's important to add these ingredients after the mix is cured.

The cure package tends to be comprised of rubber accelerators such as sulfur, thiurams, or thiazoles. Once these are added the sulphur interlinking reaction will happen at a speedier pace and in a more efficient manner; hence the name "rubber accelerators". Rubber accelerators and rubber additives can be purchased from Prisma Rubber Additives, visit their website for more info.

Efficient Vulcanization (EV)

To create EV products which are known for having an enhanced resilience/lower strength (due to shorter-lengthed sulphur interlinks); you must ensure that the proportions of your rubber mix are correct. In order to achieve this type of rubber you must ensure that the ratio of sulfur to the accelerator is less than one, once created you will be left with an efficient vulcanization system.


Vulcanization Activators

Activators such as stearic acid and zinc oxide can be used in order to create a reaction between each other and the accelerators in the mix. Once this reaction takes place, you will notice that a zinc sulfurating compound has been formed. This compound is the perfect properties to work as the intermediary in adding sulfur to a diene elastomer, this, in turn, will result in the creation of sulphur interlinks.

Sulfur Donors

Sulfur compounds such as tetramethylthiuram disulfide may be used to introduce monosulfide interlinks between polymer molecules and peroxides (in particular, dicumyl peroxide).

Peroxides are special because when heated, they decompose, causing radicals to arise. These radicals will then abstract hydrogen from groups on the polymer molecules. Carbon radicals which are formed in this way on different molecules then combine to create carbon-carbon interlinks, once again, changing the composition of your rubber mix.

C-C interlinks are special as they are more resistant to heat and oxidative attack, however, their strength is lower than products with sulphur interlinks. Monosulfide links create weaker products than polysulfide links.

This paradoxical result—that inherently strong C−C interlinks give the weakest products, whereas inherently weak polysulfide links give the strongest products—is attributed to the fact that weak interlinks will break under stress before the main chain does, so failure of the elastomer molecule itself is delayed. - (source: https://www.britannica.com/science/rubber-chemical-compound/Additives)

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