Fuel hoses have a layered construction. The cover is usually not the same material as the tube. A common cover rubber is a blend of nitrile rubber and polyvinyl chloride because the blend gains ozone and weather resistance compared with NBR alone while keeping some oil resistance.
Layers
Separate tube, reinforcement and cover. Cut the cover from the outside, discard any surface printing and sample the bulk.
The two key elements
- Nitrogen comes from the acrylonitrile in NBR.
- Chlorine comes from PVC (and from any chlorinated plasticiser).
Using elemental analysis for both, the NBR and PVC contents can be estimated: chlorine divided by about 56.7 % (the chlorine fraction of PVC) gives PVC, and nitrogen corrected for ACN content gives NBR. The ACN content of the NBR must be estimated by IR.
Other identification clues
- IR: nitrile band near 2237 cm⁻¹, with bands typical of PVC in the lower region.
- TGA: PVC loses hydrogen chloride at relatively low temperature (a step starting at about 250 to 300 °C), followed by polymer breakdown.
- DSC: two glass transitions in an immiscible blend, or a broadened one.
Plasticiser and stabiliser
PVC needs large amounts of plasticiser. GC-MS of the extract finds phthalate, trimellitate or polymeric plasticisers and the proportion in the extract. Metal soaps (barium, zinc, calcium, tin, lead in older products) show up in the ash.
Reconstruction
Take the NBR plus PVC as the rubber portion and then state the NBR/PVC ratio, as a range. Report plasticiser type and level separately because it is a large part of the total.
Testing target
Fuel resistance (volume swell in reference fuels), ozone resistance, low-temperature flexibility and heat ageing. A cover that is correct on chemistry but loses plasticiser in fuel will stiffen in service.
