Bitumens from six diverse tar sand deposits were obtained by toluene e
xtraction. The viscosities of each of the bitumens were determined in
the temperature range 60 to 90 degrees C and were found to be Newtonia
n in character. All bitumen samples were fractionated using a modified
SARA (saturates, aromatics, resins and asphaltenes) type analysis. Th
e separated fractions were examined by transmission and specular refle
ctance FT-i.r. spectrsocopy (SR-FT-i.r.). The FT-i.r. analysis indicat
ed that carboxylic acid present in the bitumen accumulated in the pola
r fractions, particularly in the resin fraction. The carboxylic acid c
oncentration was estimated from its characteristic FT-i.r. absorbance
band by the band-fit method. The carboxylic acid in the resin fraction
s was also estimated by a potentiometric titration method using a mixe
d solvent. Although it was clearly indicated from the infrared analysi
s of the bitumen fractions that bitumens with higher viscosity general
ly contained larger amounts of carboxylic acid, a simple quantitative
relationship between these two variables to the exclusion of others in
a complex material such as bitumen was found to be difficult. The vis
cous nature of the bitumen is principally attributed to the internally
suspended asphaltene particles. The fractional compositions of the va
rious bitumens clearly indicated that the viscosity of a given bitumen
cannot always be correlated with its asphaltene content alone. Howeve
r, the introduction of another variable, namely the carboxylic acid co
ntent of the bitumen, together with asphaltene content can better acco
unt for the property of viscosity. The Athabasca sample was the least
viscous of all the bitumens under study, although it contained an inte
rmediate amount of asphaltenes. FT-i.r. analysis indicated that the At
habasca resin fraction contained only a small amount of acid and was e
xplained to be inadequate to optimally engage the asphaltenes in suspe
nsion through hydrogen bonding. In addition, it was shown that the maj
or oxygen functional group in Athabasca bitumen is an ester which was
believed to be not as efficient as an acid in the hydrogen bond format
ion. The presence of esters in the Athabasca resin fraction was confir
med by the hydrolysis of the resin fraction and analysis of the hydrol
ysis products by SR-FT-i.r.. The influence of carboxylic acid and asph
altene contents on bitumen viscosity is discussed with reference to th
e structural model developed by Nellensteyn.