Industrial Rubber Ltd | Basic Rubber for Engineers Part 2 0

Basic Rubber for Engineers Part 2

Basic Rubber for Engineers Part 2

Published - 24th Jun 2019

Part 2 – Rubber Compounding / Mixing

Most Thermoplastic and Thermoset Elastomers need to be mixed with other ingredients to modify their properties and to make them easier to process and made into the material we recognise as rubber. The raw rubber that has ingredients mixed into it is called a Rubber Compound.

For Thermoset Rubbers the most important additives are those chemicals that ” vulcanise” or ”cross link” the polymer chains. Why do we need to do this? This process converts the very plastic easily deformed material that is useless for most applications into the Elastic, resilient material that we recognise as Rubber. This process is called vulcanisation or sometimes referred to as curing. Vulcanisation involves heating a rubber compound containing materials such as sulphur or organic peroxides. These chemicals can form chemical links or bonds between the polymer chains.

The polymer chains are arranged in a random matrix that can be relatively easily deformed,i.e it is very plastic and the formation of these chemical links between the main polymer chain binds it all together to form a 3 dimensional lattice that now has some memory and wants to return to its original position after being deformed- it has become elastic.

Other materials will be added to the raw polymer to change such physical propertires as Hardness, Tensile Strength, Compression Set, Weathering/Ageing. Materials will also be added to speed up the process of vulcanisation and improve the cross link density.

The list of ingredients a Rubber Technologist has at their dispoal is very large they include;

Fillers/Extenders such as Carbon Black, Clays, Calcium Carbonate and Silica. These will re-enforce and/or change the hardness ior extend (cheapen) the compound.

Oils/Process Aids. These can change the hardness, improve low temperature performance and make the compound process more easily.

Accelerators- These speed up the vulcanisation process

Acclerator activators- these assist in the vulcanisation process

Antioxidants and anti-ozonants to improve the long term ageing of the rubber

Pigments- These can be added to make coloured compounds

Blowing agents can also be added to the compound to make sponge rubber. Blowing agents are materials that, when heated, give off a gas- usually Nitrogen or Carbon Dioxide. As the gas is generated it causes the uncured rubber to expand forming cells. It then vulcanises to set it in shape, This is a specialised process for Industrial Rubber

The final compound is like a cake recipe and it will usuall be based on a 100 parts of raw polymer. A very basic Natural Rubber compound may be something like this:

Natural Rubber   100 parts  Base Polymer

Carbon Black    50 parts for re enforcement

Clay                    30 parts     to extend- cheapen the mix

Oil                       25 parts     to reduce the hardness

Zinc Oxide         5.0 parts     to activate the cure system

Stearic Acid       2.0 parts     to activate the cure system

Sulphur              1.5 parts     to form the cross links (vulcanise) in the polymer

Accelerators     1.5 parts     to speed up vulcanisation

Antioxidant        1.0 part      to improve ageing

Anti-ozanant wax  2.0 parts to improve ozone resistance (ozone will attack the polymer chain and break them this can often be seen as cracks when the material is strectched- in everydat terms the rubber has ”perished”

Latest News

BS 1154:2003 Natural rubber compounds

01st Aug 2023
BS 1154:2003 is a British Standard specification that outlines the requirements for natural rubber compounds used in various industrial applications. Natural rubber is a highly elastic and durable material made from the sap of the Hevea brasiliensis tree.

BS 2752:2003 Chloroprene rubber compounds

01st Jul 2023
BS 2752 is a British standard that specifies the requirements for chloroprene rubber compounds. Chloroprene rubber, also known as neoprene, is a synthetic rubber that is widely used in various industrial and commercial applications.

BS 2751:2001 General Purpose Acrylonitrile-Butadiene Rubber Compounds

01st Jun 2023
BS 2751 is a British Standard that specifies the requirements for general purpose acrylonitrile-butadiene rubber (NBR) compounds.

What is Nitrile Rubber/ Buna-N?

15th May 2023
Nitrile rubber, also known as Buna-N or NBR, is a popular elastomer that is widely used in various applications because of its oil and fuel resistance properties, as well as its high tensile strength. Nitrile rubber is a synthetic rubber copolymer made of acrylonitrile (ACN) and butadiene.

Viton® – What is it?

03rd May 2023
Viton® may not be a name that’s familiar to you, but it’s a material that you’ve probably come into contact with many times before. Viton® is a synthetic rubber and fluoropolymer elastomer, commonly used in O-rings, gaskets and seals, and is renowned for its ability to withstand even the harshest environments, temperature extremes and harsh chemicals.

ISO 3302-1:2014 Rubber Tolerances for products Part 1: Dimensional tolerances

01st May 2023
ISO 3302-1:2014 is a standard that sets out guidelines for dimensional tolerances for rubber products. This standard is the first in a series of standards for rubber tolerances and is intended to provide a consistent approach to the measurement and acceptance of rubber products.

ASTM D 1056 Standard Specification for Flexible Cellular Materials — Sponge or Expanded Rubber

01st Apr 2023
ASTM D 1056 is a standard specification that outlines the requirements for flexible cellular materials, also known as sponge or expanded rubber.

ISO 2230:2002 Rubber products — Guidelines for storage

01st Mar 2023
ISO 2230:2002 Rubber products – Guidelines for storage is an international standard that provides guidelines for the proper storage of rubber products.