Product story

Using minerals to prevent contamination of medicines

Calcined clay and talc provide the properties essential for the manufacture of secure and reliable rubber medical stoppers.


Every day, millions of people with short-term illnesses and long-term conditions rely on a safe supply of medicine. They need to be confident that the treatment they are using is free from contamination or degradation.

When medicines degrade, they do not maintain the physical, chemical, therapeutic and microbial properties needed to effectively control or reduce symptoms. If medicines become infected with harmful bacteria, they can make sick people feel even more unwell.

Medical stoppers are vital for sealing and securing liquid or powdered drugs and antibiotics, including insulins, in their bottles.

The surface of these rubber stoppers must be of the highest quality so that the syringe removes the correct dosage of medicine and then reseals completely.

When produced using best-in-class ingredients, including minerals, rubber pharmaceutical stoppers safely mitigate the risk of contamination, which is especially critical for bottles that require repeated use. They give medicines a long shelf life, reassuring patients with long-term conditions that batches can be safely stored at home, making life a little easier for those who are not easily able to visit a doctor for repeat prescriptions.

Talc and calcined clay provide a safe barrier from contaminants

Imerys has supplied a range of engineered materials produced from talc and calcined clay (calcined kaolin) to manufacturers of medical stoppers for 40 years.

These products are functional additives for the preparation of rubber compounds and are engineered in numerous formulations to meet the specific requirements of the pharmaceutical industry.

These minerals reinforce the rubber and improve its thermal resistance while maintaining or enhancing key existing properties. Calcined clay is best for resealing, which is required for multi-dose rubber stoppers. Resealing means that, when the needle is removed from a medical stopper, the stopper is resealed instantaneously to guarantee sterility of the packaging, disabling any exchange between the exterior environment and the medicine inside the packaging.

Talc enhances the barrier performance, providing the impermeability requirements for single-use rubber stoppers and the long-term storage of medicines.

Each of our pharmaceutical customers has specific requirements to fulfil. We work closely with them to engineer the mineral so they have a product that best serves the patients they are providing for. The global demand for effective stoppers is increasing. The global population is growing and ageing. In many countries, millions of people relying on insulin or antibiotics are not getting the right drugs because of poor access to adequate medical stoppers. The properties in minerals have the power to make a huge difference to the world’s health needs.

Anaïs Berjeaud
Plastics & rubber EMEA S&T Scientist at Imerys
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