Abstract
The relation between the physical consistency and chemical composition of a series of blown asphalts from Alberta bitumen has been studied. The amounts of asphaltous acids and anhydrides decrease on blowing, with rise in fusing point of the bitumen. The amounts of oily constituents and resins also decrease but the asphaltene content increases. The molecular weights of the resins increase from 733 to 1012 during blowing. The asphaltenes also show a pronounced increase in molecular weight from 2219 to 4690 Only traces of oxygen are found in the products blown for 6 to 8. 5 hr. at 270 °C; the amount however increases in the later stages of blowing to a maximum of 1.88%. The oily constituents do not contain oxygen, which is distributed mainly in the resin fractions, with smaller amounts occurring in the asphaltene fractions. The sulphur and nitrogen in the bitumen are distributed principally among the resins and asphaltenes. The essential process in blowing bitumen with air is one of condensation by removal of some hydrogen to form water, followed by polymerization, assisted by the sulphur in the bitumen, to products of higher molecular weight. Products similar in composition and physical properties to commercial grades of mineral rubber have been prepared from Alberta bitumen by blowing.
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