Platinum-Cured Silicone Tubing in High Demand Applications

Silicone tubing is perhaps the most widely used material in a variety of high purity, high demand applications across a number of industries. Medical device manufacturers, and companies in other industries, have increasingly turned to silicone tubing because it has proven to be the best choice in single use applications. Safety and reliability are the major reasons that silicone tubing has become so popular.

Platinum-cured silicone tubing contains no plasticizers or additives that can leach into products traveling through the tube. Silicone tubing is also highly flexible, and is incredibly resistant to kinking and tearing during use which has made it the first choice in peristaltic pumps. But what is it about this particular rubber tubing that makes it the first choice in a variety of critical applications.

Chemistry’s Role in Platinum-Cured Silicone Tubing

Platinum-cured silicone tubing is manufactured using complex chemical reactions to create tubing stock that will perform well in high pressure and high demand scenarios. The actual tubing stock is created by combining long chains of polydimethylsiloxane (typically methyl or hydrogen-substituted) and polydimethylsiloxane gums with a metal complex that acts as a curing agent.

In the case of platinum-cured silicone tubing, that curing agent is platinum (Pt). The process that results in platinum-cured tubing is often referred to as an addition cure. The addition of platinum to the other polymers provides a jump start to the chemical reaction that forms the rubber tubing. There are two common methods for conducting this process. In one method, an organometallic complex is used as the curing agent. In the other process, platinum salt is added as the curing agent. The use of organometallic complexes is more popular today, with fewer manufacturers using the older chemistries that involve platinum salts.

The cost of creating platinum-cured rubber tubing is higher than alternative methods such as peroxide (or free radical) curing. Although the platinum curing process requires a relatively miniscule amount of the curing agent, typically between 5 and 15 ppm of Pt to be effective as a catalyst, the final products (e.g. medical grade silicone tubing) often cost more because of the higher cost associated with Pt.

Technical Information

Platinum-cured silicone tubing used in the medical field is available in a variety of sizes and thicknesses. The diameter of the tubing dictates the rate of flow for liquids moving through the rubber tubing, while the thickness of the tubing’s outer walls has an impact on strength, flexibility, and durability.

Medical grade silicone tubing is available in sizes ranging from a diameter of .012 in. up to .625 in. On the narrowest of tubes the thickness of the outer wall can range from a scant .006 in. to a more robust .156 in. The diameter and thickness measurements for rubber tubing are locked to one another as the dimensions increase. Tubing with small diameters will also have the thinnest outer walls, while the larger tubes have thicker outer walls.

One of the greatest benefits of platinum-cured tubing is its strength under pressure. Compared to peroxide-cured tubing, platinum-cured silicone tubing has a higher tensile strength and greater tear resistance during use. The typical 50-Durometer Elastomer rubber tubing (produced by Dow Corning and sold by SPS Canada) can withstand greater pressure and tougher conditions than peroxide-cured tubing.

The average 50-Durometer Elastomer tubing has a tensile strength of 10.16 MPa (1473 psi), compared to a slightly lower 9.41 MPa (1364 psi) for the same rubber tubing created using a peroxide curing process. In this same section of tubing, the tear strength of the platinum-cured product has a tear strength of 45.9 kN/m (262 ppi), compared to 35.9 kN/m (205 ppi) for its peroxide-cured counterpart.

The story is much the same for comparable 35- and 65-Durometer Elastomer rubber tubing products. In each of these examples, the platinum-cured silicone tubing provides a greater resistance to tearing and possesses a higher tensile strength than comparable peroxide-cured tubing.

The Advantages of Platinum-Cured Rubber Tubing

When the healthcare industry needs medical grade silicone tubing, it often turns to platinum-cured tubing because of its strength and durability. Safety remains the primary reason behind the popularity of platinum-cured rubber tubing. The highly flexible nature of the tubing, and its resistance to tearing, makes it a safer choice for transporting fluids between tanks or as a hose in filling machines.

Safety is, however, not the only reason for choosing platinum-cured silicone tubing over its competitors. The platinum curing process allows the resulting rubber tubing to withstand much higher temperatures during use than peroxide-cured tubing, for example. The average, unreinforced platinum-cured rubber tubing can withstand temperatures ranging from -100 degrees up to 400 degrees. What this means during medical and pharmaceutical applications is that fluids can move through the tubing while resisting sticking and encrustations that disrupt the flow.