Stoichiometric defect on a Base/Hardener epoxy bicomponent mixture

A large crack appeared on a parking surface. This coating, however recent, probably presents a major failure .
What if a stoichiometric problem was the cause of this disorder?

Two-component epoxy resins, or also called epoxy polymers and more commonly "epoxy", are formed by polymerization of epoxy monomers with a hardener (crosslinking agent) to form three-dimensional polymers.
After polymerization, as soon as the mixture is "dry"; the polymer becomes rigid and retains its shape to form a practically inert material.

Respecting the base and hardener stochiometry is essential for the good performance of the material. Indeed, the adhesion properties of such systems are directly proportional to the quality of compliance with this ratio.

For this study, our mission was to determine whether the proportion by crosslinking in a two-component epoxy adhesive consisting of an epoxy resin based on DGEBA and a hardener based on aliphatic polyamines had been respected.

• The first step consists in producing a series of “standard” mixes centered on the ideal Base / Hardener (B/D) ratio but also comprising values with excess of B and excess of D.
• These mixtures are crosslinked, then analyzed by Pyrolysis/GCMS. Each pyrogram of each standard makes it possible to view and count organic fragments relating to each part B or D. The “tracer” fragments of the Base are in this case there, compounds based on DGEBA and Bisphenol A, those of the Part D are light nitrogen compounds with "Alkyls Pyrrole" motifs.
• All the areas of the chromatographic peaks (reduced to the mass of sample analyzed) of these compounds from these two families are summed and will be used to plot the calibration line: Ratio [Base / Hardener] vs [Hardener Rate%] .
• Subsequently, the crosslinked glue sample which has an adhesion defect will be analyzed by Pyrolysis/GCMS and the [Base/Hardener] ratio will be compared with the calibration line so as to check the Ratio [B/D%] and compare it to the ideal ratio.

=> This technique can be transposed with all bicomponents, whether they are aromatic, siloxane, aliphatic… it even works with polyurethane systems (PUr) as long as we can identify and identify tracer fragments of one either of the two matrices.