The overall objective of this research is to develop natural rubber/acrylonitilebutadiene
rubber (NRlNBR) blends having physical properties superior to NBR
compounds and a tolerable resistance to swelling in oils and fuels. This would
increase consumption of NR by replacing NBR used in various engineering
applications with less costly NRlNBR blends.
The rheology of blend components was studied in detail in order to choose mixing
conditions and interpret the morphology of NRlNBR blends filled with 20 phr N660
carbon black. It was found that a high shear rate/high temperature combination results
in similar apparent viscosities for the two elastomers.
Blends were prepared according to single-stage and masterbatch mixing techniques
with an intermeshing rotor internal mixer. Rheological, cure and physical properties
of the blends were measured and related to mixing conditions, morphology and
carbon black distribution.
The filled 40/60 NRlNBR single-stage blends prepared at a high rotor speed had a
finer morphology than the blends prepared at a low rotor speed. The fine textured
blends showed higher tensile strength, lower abrasion resistance and improved
compression set at elevated temperatures over those of coarse textured blends. Also,
the fine textured blends showed a positive synergism of tensile strength. Modulus and
tear strength were highest with most of the carbon black in the NBR phase, whereas
ASTM oil and toluene uptake were lowest with most of the carbon black in the NR
phase. However, percentage compression set was lowest with carbon black equally
distributed between the phases.
It was concluded that an NBR (26.6% acrylonitrile) compound could be replaced by
the single-stage blends, particularly the fine textured ones, with regard to physical
properties such as moduli, hardness, tear strength and compression set in engineering
applications, where 2-4 % (by mass) oil swell is tolerable. Oil swell of the NRlNBR
single-stage blends is about 5 % (by mass) lower than the predicted.
A Master's Thesis submitted in partial fulfilment of the requirements for the award of Master of Philosophy of Loughborough University.