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Polyisobutylene (PIB) “Drip” and Insulated Glass Units

Since we have extensive experience analyzing Insulated Glass Units (IGUs), we have recently shared a series of informative blogs on this topic, such as, a look at commercial grade windows and IGUs as well as two common problems associated with IGUs. In this piece, we want to examine a third issue with IGUs that is pervasive.

This third type of IGU problem is related to the polyisobutylene (PIB) primary sealant.  Occasionally, PIB may be observed within the vision area of the IGU. The visible PIB may be referred to as a “drip” or as “PIB movement.”

To quickly recap, IGUs are made of multiple glass panes assembled with spacers and adhesive. The PIB is the adhesive used to join the spacer to the panes of glass.   Like a lot of polymer technology, when it works we don’t even notice it or consider it is there. However, in this instance, when there is a PIB problem, it may be quite noticeable.

At a Glance: Two PIB Movement Issues

At times, the PIB adhesive is formulated improperly and has too low of a molecular weight or lacks the proper additives package (not a proper amount of UV stabilizer). When this happens, the adhesive can begin to move down into the vision area of the IGU, which is supposed to be clear. Since it is contained between panes of glass, the PIB adhesive is not something that can be scraped, cleaned, or simply removed. To rectify the problem, the IGU–some of which often weigh hundreds of pounds–must be removed and replaced. That’s a major issue and expense a building owner will not want to deal with.

PIB, IGUs, and Molecular Weight

Let’s start by discussing the viscosity, or thickness, related to molecular weight issues. Low viscosity is more fluid, think of something like oil. High viscosity is not runny, think of shortening. Typically a mixture of high and low molecular weight PIB is used for IGU applications. If the blend is wrong– too much of low molecular weight– it can be prone to being more runny.

This begs the question: Why isn’t that characteristic immediately obvious upon assembly of the window?

The PIB movement may occur so slowly over time that the issue will not be apparent until the IGU has left production and been installed.

Additives Packages and Adhesives

Even if the molecular weight is properly formatted, there is a chance that the additives package is not, ultimately creating the same adverse effect of PIB movement. UV stabilizer is very important for adhesive used within window assemblies, as windows are designed to be exposed to sunlight. Without proper stabilization, the PIB can degrade and move into the vision area, causing undesirable and unsightly black streaks. Carbon black is a common UV stabilizer, so in sufficient quantities, it maintains the stability of the PIB. Gray PIB, as an alternative, requires additional stabilizer as the carbon black in this formulation is present at too low of a concentration to be an effective UV stabilizer  on its own.

Introducing a PIB Problem: Phthalates

It is possible the PIB is properly formatted in terms of the molecular weight and the stabilizer package, but a problem is created by the introduction of ancillary materials that have ingredients like a phthalate plasticizer that migrates into the PIB. That migration creates contamination and weakens the PIB, resulting in movement.

(If you’re curious about the impact of phthalates on polymers, we encourage you to view this time lapse video!)

Getting at the Root Case of PIB Movement

It is important to note that you cannot determine the cause of PIB movement visually. It requires analysis and expert interpretation of data sets to determine  the root cause. Since these types of window failures and defects cost a great deal of time, money, and resources to resolve, an expert analysis is absolutely necessary to eliminate the debate.

If needed, we will send a materials scientist on location to obtain photographic evidence of window/IGU defects and make recommendations for analysis. That is often a great starting point. Once the analytical needs are more clearly established, we can bring samples (of all sizes) to our state-of-the-art legal testing lab for inspection and analysis.

We have multiple analytical methodologies we employ in cases such as this. Two key analytical techniques we use are Gas Chromatography Mass Spectrometry (GC-MS) and Gel Permeation Chromatography (GPC) to determine if PIB is contaminated or is degraded.

We use careful photo documentation to show the condition of samples received, context, and scale. Testing procedures and results are carefully documented and we have the instrumentation necessary to provide the required data sets.

Experiencing PIB Movement?

If you are faced with PIB movement and aren’t sure where to go from there, we welcome you to start a conversation with us about the next best steps and how we can be of service. Our team of technical experts is ready and available to provide the answers you need.