What do the Physical Properties of Single Use Tubing Mean?

July 31, 2014
Sani-Tech Ultra Silicone Tubing

Sani-Tech Ultra Silicone Tubing

One thing that is on the marketing literature for every bioprocessing tubing on the market are the typical physical properties of the product. These are things like durometer, tensile strength, ultimate elongation, tear resistance, specific gravity, and tensile modulus. While these properties fill space on a piece of literature, it’s important that we understand what they each mean. This blog post is the first in a series that will try to give a concise overview of the properties relevant properties for single use tubing and connectors.

To begin, let’s take a look at Saint Gobain’s latest generation of platinum cured silicone tubing- SaniTech Ultra. On Saint Gobain’s marketing brochure, they list the following properties:

  • Durometer Hardness Shore A, 15 Sec
  • Tensile Strength, psi
  • Ultimate Elongation
  • Tear Resistance (kN/m)
  • Specific Gravity
  • Tensile Modulus

Along with these properties, they also list sterilization methods, which have been a focus of previous posts and we will continue to address in the future. Let’s take a look at each of the aforementioned properties one by one:

The first property is durometer. Durometer is the measurement of the hardness of a material. This is usually tested via the standard defined in ASTM D2240. Durometer is based on the resistance to penetration of a specific indenter into the material under controlled conditions. It is reported on using the shore scale, with Shore A hardness typical for silicone and other thermoplastic elastomers. This property is tested on a lot release basis. Lot release is a representative sampling from a lot of tubing that is tested as a requirement for product release.

Tensile Strength
Tensile strength is the measure of the force (stress) required to stretch a material to its breaking point. Tensile strength is usually tested in accordance with ASTM Method D412 and a lot release basis. Tensile strength testing is performed by placing the tubing into a device known as a tensiometer and stretching to its breaking point. The load required to do this, measured in psi or MPa, is the tubing’s tensile strength.

Ultimate Elongation
Ultimate elongation is the elongation at the moment the tubing breaks during tensile strength testing. This indicates how far tubing can be stretched prior to breaking. Results are determined by comparing the distance tubing was stretched at the time of break to its original state and reported as a percentage.

Tear Resistance
Tear resistance, or tear strength, measures the resistance to propagation of a rip or tear once the rip has been initiated. Measure in accordance to ASTM D624, tear resistance testing is usually done on a qualification basis during design or process qualification. ASTM D624 outlines a procedure where a tear is made in the tubing and a controlled force is used to pull the tubing apart.

Specific Gravity
This one is pretty simple. Specific gravity is a products density relative to water. But while the concept is simple, you may be wondering why it’s important for silicone tubing. Well, changes in density can reflect absorption and other physical changes in the tubing after processing. This is important when considering extractables and leachables.

Tensile Modulus
Also known as Young’s modulus, the tensile modulus describes the tendency of an object to deform along an axis when opposing forces are applied. It is the ratio of tensile strength to tensile strain or the stress at a given strain. In more simplified terms, this is a measure of rigidity. Tensile modulus should not be confused with strength, stiffness, or hardness. Because the tensile modulus is a measure of force per unit area, it has pressure units, like PSI or MPa

So there you go- more excruciating details than you’d ever want to know about a piece of silicone. It’s probably not critical that everyone understands exactly how each of these are tested, but it is important that you have a general idea of what each means, especially when you are comparing two different materials. For more information about elastomeric properties, contact a Holland Sales Engineer today.