Troubleshooting Adhesives & Sealants (Part 2)
In the adhesive and sealant business, one often deals with problems involving product performance and failures. Getting to the root cause of adhesive and sealant failures requires taking a closer look into the product's components and formulation.
CAS-MI Laboratories uses analytical chemistry to investigate common problems with adhesives and sealants. Part 1 of this article discusses six causes of adhesive failures, including case studies. Part 2 will introduce the art of deformulation and formulation of adhesive and sealant materials.
Deformulation
In the process of troubleshooting adhesive and sealant issues, many clients need to understand the composition of their product. CAS-MI Laboratories has years of experience providing deformulation (reverse engineering) of a wide variety of coatings and other products. These challenging projects yield valuable insight into adhesive and sealants problems.
The secret to a successful deformulation of adhesives and sealants is the separation of the ingredients. One approach is to use proprietary solvents to separate components. Non-polar solvents, such as pentane, are commonly used first to extract hydrocarbons. From there, increasingly aggressive and more polar solvents can be used to extract materials for further analysis.
Once materials have been isolated, several analytical techniques can be used for identification. Fourier Transform Infrared Spectroscopy (FTIR) provides a fingerprint of a material. Databases of FTIR spectra can be searched to get the best match for the sample spectrum. Gas Chromatography/Mass Spectrometry (GC/MS) can be used to identify and quantify volatile components such as solvents. The mass spectrum of the material can be searched in databases so as to provide the best match for an unknown substance. Liquid Chromatography/Mass Spectrometry (LC/MS) can be used to identify less volatile materials such as additives which are higher boiling than those materials that will pass through a GC/MS. Scanning Electron Microscopy/Energy Dispersive X-Ray Analysis (SEM/EDXA) can be used to determine elements present in a sample. These elements are commonly metals which can give insight into filler, pigment, and additives compositions.
Once materials have been separated and identified, there are several analytical methods that may help to quantify them. Thermogravimetric Analysis (TGA) is a common way to quantify resins, fillers and pigments, and Inductively Coupled Plasma (ICP) is used to quantify metals. Differential Scanning Calorimetry (DSC) can be used in some cases to determine the amount of a resin based on heat of fusion calculations. Of course, there are also wet methods such as titrations for acid, hydroxyl, and amine content which can be used to quantify ingredients.
Formulation
Solving difficult issues may require creating a new adhesive or sealant formulation. The formulation of any new adhesive should start with a discussion with the client as to the top few properties that the adhesive must possess. These criteria are used to screen out formulations that will not give the required properties.
Several other pertinent questions should be asked before beginning any formulation work: What are the two materials that the adhesive will be used to join? How will the adhesive be applied? What is the desirable cure time for the adhesive? What is the mechanism of cure? What is the service environment?
Once these questions have been answered, the approach should start with a literature search to see what is known. Raw material vendors are frequently good sources of starting point formulations. Design of Experiments (DOE's) can be used to screen formulations quickly. A successful formulation will meet at least 80% of the desired physical properties.
Adhesive and Sealant Troubleshooting
Manufacturers and raw material suppliers often need to consult with outside laboratories for answers to tough questions. CAS-MI Laboratories has seen many product failures and can recognize many of the typical reasons an adhesive or sealant product may have performance difficulties. In addition, CAS-MI's scientists have years of experience with deformulation and formulation of these materials, providing answers to manufacturing and application problems.
