Isocyanate (MDI) diffuses into silicone rubber (cross-linked PDMS) and reacts inside the silicone matrix with residual moisture to form polyurea derivatives. This creates an interpenetrating polymer network. So far, the spatially resolved mass content of isocyanate / polyurea in silicone was measured by thermogravimetric analysis. For this purpose, the thermal decompositon of pure PDMS was compared with that of MDI-contaminated PDMS. However, this method is not only very time consuming, but has also proven to be very unreliable. Another method that has been tested is the CHNX analysis to calculate the MDI concentration via the nitrogen content. Also, this method has delivered no convincing results so far. Would anyone have a suggestion for an alternative measuring method? Is it possible, for example, to use an X-ray fluorescence analysis? I am grateful for all suggestions!
Hi Martin,
is it free or bound MDI? With free MDI you can use GC or Headspace-GC.
Regards
Markus
Markus Christ the MDI is bound inside crosslinked silicone rubber which is not soluble. I need, so to speak, the total amount of non-silicone (MDI+Urea) inside the silicone matrix.
Hi Martin,
unfortunately, X-ray fluorescence is also ruled out. Theoretically, all elements would be accessible from boron, but in practice this only works from sodium (atomic number 11).
Regards
Markus
Hi Martin,
maybe 15N-NMR is an alternative.
Look here:
http://www.chemgapedia.de/vsengine/vlu/vsc/de/ch/3/anc/nmr_spek/andere_kerne.vlu/Page/vsc/de/ch/3/anc/nmr_spek/m_46/nmr_8_2/n1415einl_m46te0203.vscml.html
Regards
Markus
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