Depending on how the compound was made, the rubber will exhibit different material properties. This means that it is especially important to select rubber of a suitable composition. To account for the differences in behaviour of the same material but differing compounds, they are split into grades. The material grade indicates the compound composition and the overall quality of the rubber. There are many grades available of both synthetic and natural rubbers. The grade of a synthetic rubber will be dependent on types and quantities of raw materials used in the compound. In natural rubber, impurity levels, collection methods and the process techniques used can all affect the quality of the final rubber obtained. International standards and guidelines for natural rubber quality can be found in the “Green Book”, published by the Rubber Manufacturers Association in the USA.
There are commercial grades, food grades, medical and pharmaceutical grades of rubber which are approved to be used in specific situations.
Any rubber product which will have contact with food, foodstuff or food additives must be chosen carefully to ensure that no contaminants are passed to the food. Certain rubber compounds can contain polymerisation aids, catalysts, plasticisers, and additives which could potentially be transferred to the food on contact.
Food grade rubber is more controlled in the types and levels of the additives which are permitted to be used in the compounds. In America, the standards of food grade rubber are set by the Food and Drug Administration (FDA). There are no standardised EU regulations for food grade rubber, but there are national regulations set out by the government in France, the Netherlands, Italy, and Germany.
Food grade rubbers should be used in all products throughout the manufacturing of food and are typically used in belting or seals. Rubbers that are approved by the FDA for these purposes include grades of EPDM, Silicone, Nitrile, Neoprene and Natural Rubber.
Medical and Pharmaceutical Grades
FDA Standards also exist for products which will be used within the medical industry. In this case, the final product must receive FDA approval rather that the individual materials themselves. The FDA has produced a Whitelist of chemicals which have been approved for use with selective percentages present in the compound.
Rubber can be used for a variety of different purposes within the medical environment ranging from dust covers for surgical equipment to components of implanted medical devices such as pacemakers. Rubber is commonly used in medical device components such as seals in syringes and IV penetration tubes.
Medical grades of rubber must undergo more thorough testing than food grade rubber. The level of testing required depends on the intended use of the final product and the drugs that it will interact with. These compounds must be biocompatible and must not cause adverse reactions within the human body or prevent any medicines from working effectively. Rubbers used in this environment may have to be able to withstand potent active pharmaceutical ingredients and aggressive cleaning regimes. Silicone rubbers are often a good material choice for these applications and are commonly used in cannulas and surgical breast implants.
Water Regulations Advisory Scheme (WRAS)
Water Regulations Advisory Scheme (WRAS) approval is provided to materials and products which are safe for use within potable water applications for human consumption. WRAS approved rubbers must be specifically formulated and manufactured to ensure they will not contaminate water.
Materials can contaminate water through the migration of toxic chemicals or by creating conditions that encourage the growth of bacteria. Some materials may pass a taste or smell to the water as well as causing cloudiness or decolouration.
To ensure safe drinking water, WRAS grades of rubber should be used in any product used within in the water supply system, including the transportation and storage of water. Rubber is often used in water pumps or as seals and washers within pipework.
Guidelines for the materials used in water fittings and plumbing systems are outlined by the government in Water Supply (Water Fittings) Regulations 1999. Using WRAS approved materials is a simple way of ensuring that products will comply to the regulations and will not contaminate water.
Products with WRAS approval are issued with a WRAS certification mark. WRAS grades are available for Nitrile and EPDM rubbers.