The answer is a little more complex than most people realize. In the world of adhesive bonding, most failures can be categorized into three distinct groups. They are:

• Substrate Failure: Substrate fails before the adhesive.
• Cohesive Failure: Adhesive fails down the middle, adhesive remains on both substrates.
• Adhesive Failure: Adhesive fails from one substrate. Usually a customer would say, "The adhesive failed from the cold rolled steel but remained on the glass."

  In many cases, however, customers experience a combination of all three types of failure.

  When asked what would be the preferable mode of failure, most customers will answer substrate failure. Is this an accurate answer?

   

  My response to this question is that while the mode of failure is important, what should drive the adhesive manufacturer and the customer’s selection is choosing the adhesive that will meet the customer’s specific requirements. For example, if a company wants their assembly to withstand rigorous environmental testing while being subjected to 2500 psi of pressure, then the adhesive also needs to meet this requirement. Whether the customer experiences cohesive, adhesive, or substrate failure, for the most part, is irrelevant if the adhesive does not meet their requirements.

   

  Is there any situation when the mode of failure is important? Yes, when everything is equal during the qualification process, it may be helpful to review the failure modes to narrow the field of adhesive candidates down. Also, in the case of failure analysis, the mode of failure is important to help determine the root cause. This information can be used to determine why a particular adhesive is or is not bonding to one or more of the substrates.

   

  Ultimately, identifying the mode of failure is only important once the customer’s requirements have been met. And even then, does it really matter that the adhesive failed from one of the substrates if the customer’s requirements have been exceeded?

  
  

  

  Adhesives adhesive failure, Adhesives, bond failure, Cohesive Failure, substrate failure

“What are the effects of E-Beam sterilization (54-75 kGys) and accelerated aging (1 year @ 55^°C) on medical device PVC tubing (IV Set)?”

This was a little outside of my area of expertise, but Saint-Gobain Performance Plastics was able to provide information to answer this question.  E-Beam sterilization, as well as other radiation sources like Gamma, are normally run at a level of 25-30 kGys.  Under this condition, the sterilization will have only a minor impact on the properties of the PVC.  At 2x (50 kGys) or 3x (75 kGys) the typical dose, you can expect to start seeing some breakdown of the PVC tubing.  This will be evident by a slight browning of the PVC, or perhaps a drop in tensile strength and elongation, as well as plasticizer exitation/migration to the surface of the PVC.  The variables that can affect the impact of sterilization would be the type and concentration of stabilizers in the PVC, as well as blue colorant levels which may mask the slight browning color.

The effects of accelerated aging, defined in this case as 1 year @ 55^°C, will also show a slight change in performance and characteristics of the PVC tubing.  The plasticizer may also come to the surface, migrating out of the PVC, to form droplets or even volatilize to a gaseous state.  This will leave the tubing harder, less flexible, or even brittle.  You may also experience some browning, depending on the formulation.  Typically, Saint-Gobain uses a standard of 53 days @ 55^°C, which approximates 1 year of actual shelf life, and does not normally recommend going beyond this temperature/time.

Medical E-Beam Sterilization, ebeam, Gamma, Medical Device, PVC Tubing