A study of the interfacial chemistry between polymeric methylene diphenyl di‐isocyanate and a Fe–Cr alloy

Abstract

The interactions of polymeric methylene diphenyl di‐isocyanate (pMDI) and a model Fe–Cr alloy have been studied by X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS). Films of two different thicknesses have been investigated: one with an extremely thin pMDI layer in which the interfacial chemistry can be probed directly and a thicker one in which sputter profiling using cluster ions is necessary to expose the interface chemistry for direct analysis. Multivariate analysis (MVA), using principal component analysis (PCA) and nonnegative matrix factorisation (NMF), has been used to identify specific ions associated with the interfacial region of the ToF‐SIMS sputter depth profile and chemical species from the XPS sputter depth profile. As an unsupervised method, this avoids an unconscious bias on the part of the analyst. Specific ions associated with pMDI interactions with both Fe and Cr allow the proposal of two complementary reaction mechanisms, supported by the XPS data. A range of cluster ions is used in this investigation, but the bulk of the work used argon clusters for the XPS depth profiles and Buckminster Fullerene projectiles for the ToF‐SIMS analyses. To ensure that such data were directly comparable, the ToF‐SIMS sputter profiles were repeated in a different system of the same type using argon cluster ions.

Interfacial Chemistry Investigation of Initial Fouling Conditions in Isocyanate Production: The Antifouling Performance of AISI 316L Stainless Steel

“…The work carried out by Bañuls-Ciscar et al built upon the above work by Tardio et al through an interfacial study of pMDI and an Fe–Cr alloy . Nitride-link bonds between iron and chromium in the metal and nitrogen from the pMDI were identified in their X-ray photoelectron spectroscopy (XPS) analysis.…”

“…It was concluded that a monolayer of MDI forms on the surface of the steel, bonding through a strong covalent bond between the isocyanate group of the MDI and the hydroxide group on the steel surface. 13 Cycloaddition reactions between FeO and −NCO were suggested based on time-of-flight secondary ion mass 14 Nitride-link bonds between iron and chromium in the metal and nitrogen from the pMDI were identified in their X-ray photoelectron spectroscopy (XPS) analysis. In addition to this, multiple interface-specific fragments were identified in non-negative matrix factorization analysis of a ToF-SIMS depth profile.…”

“…With the thicker layers formed on 316L-03 and 316L-04, this suggests that iron is migrating through the organic overlayer during its formation. Interactions between MDI and iron-containing metal surfaces have been observed previously. ,, It is proposed that these reacted iron species migrate through the organic material, depleting the metal surface of iron.…”

“…Peak fitting of high-resolution spectra was carried out using the Avantage v5.890 software package. Singlet peaks were added to C 1s, O 1s, and N 1s spectra based on the components present in previous studies of pMDI and related materials. − Component binding energies were maintained from previous studies ±0.1 eV to enable the best fit. The full width at half-maximum (FWHM) value was kept constant for C 1s (1.4 and 2.3 eV for C–C/H and shake-up satellite and 1.5 eV for all other components), O 1s (1.6 eV), and N 1s (1.5 eV).…”

“…In recent work from this laboratory by Bañuls-Ciscar et al., several organo-metallic fragment ions, in both the positive and negative SIMS spectra, were identified . These were ascribed to the interaction of pMDI with the alloy steel (Fe 0.8 Cr 0.2 ) substrate.…”