Bituminous polyurethane network: Preparation, properties, and end use



Industrial-grade bitumen (85:25) was treated with 4,4′-diphenyl methane diisocyanate as a blocking agent to make it compatible with polyurethane resin. Optimization of treatment conditions for the bitumen such as isocyanate dose (∼3 wt % of bitumen), reaction temperature (180°C), and treatment time (120 min) was done on the basis of estimating its residual acid value and unreacted [BOND]NCO groups. Formation of the urethanized bituminous species after treatment resulted in a reduction in the glass-transition temperature of the base bitumen from −9.63°C to −17.09°C and in moisture vapor transmission from 16.95 to 12.21 g 24 h−1 m−2. The bituminous networks were prepared from these treated/SBS-modified treated bitumen and polyurethane prepolymers by in situ and conventional liquid blending methods. Lack of low-temperature flexibility in the bituminous network made from the blending method restricted its use for waterproofing/sealing purposes. Modulated differential scanning calorimetry showed the presence of two overlapping glass-transition temperatures and an endothermic peak in the in situ prepared networks similar to the base bitumen, evidence of a close intermixing of the bitumen constituents with the polyurethane phases. Rheological studies revealed that the SBS-modified bituminous polyurethane network exhibited superior behavior than that of other systems in terms of stiffness and elasticity over a wide range of frequencies. The compounded bituminous networks satisfied the requirements of standard specifications and can be suitably used for waterproofing purpose and sealing of concrete joints. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 217–226, 2006