What is SBS modified bitumen?
PMB polymer modified bitumen is blend of bitumen 60/70 with specific grade of SBS Styrene butadiene styrene in very special temperature and pressure. Polymer modified bitumen has less sensitive to temperature it means in high temperature of summer will not get flow and in cold temperature of winter will not break since in low temperature there is still flexibility. PMB polymer modified bitumen has high straight on fatigue and also high viscosity so will stick to aggregate and it will not segregate.
Specification of the SBS modified bitumen
|Grades & Requirements
|Penetration at 25 °C
|Softening point, ( R & B ), C Min.
Elastic recovery of half thread in
Ductilometer at 15 °C, % Min.
|Flash point °C Min.
|Separation difference in softening
point, ( R & B ) °C Max.
|Thin Film Oven Test (TFOT) on residue
|a). Reduction in Penetration of residue at 25 °C, Min. % of original
|IS 1203 – 1978
|b). Increase in softening point, °C Max.
|IS 1205 – 1978
|c). Elastic recovery of half thread in Ductilometer at 25 °C, % Min.
|IS 15462 -2004
Composition of PMB polymer modified bitumen
Composition of polymer modified bitumen is bitumen plus polymer and a compatibilizing agent prepared by reacting one or more unsaturated monomers with a bituminous composition comprising asphaltenes or resins.
Asphaltenes and resins are two of four broad component groups found in bitumen (the others are aromatics and saturates; resins, aromatics and saturates are collectively known as maltenes) . Asphaltenes are n- heptane insoluble black or brown amorphous solids, and are generally considered to be highly polar and complex aromatic materials of fairly high molecular weight. Resins are soluble in n-heptane and are typically dark brown in colour, solid or semi-solid and polar. In one embodiment of the invention, the bituminous composition comprising asphaltenes and/or resins is a bituminous composition comprising all four components, i.e. resins, aromatics, saturates and asphaltenes.
Composition of PMB
In another embodiment of the invention, the bituminous composition comprising asphaltenes and/or resins is a composition consisting solely of asphaltenes, a composition consisting of solely of asphaltenes and resins, or a composition consisting solely of resins. It is believed that the reaction provides \”surfactant\” type structures wherein a short polymer chain is chemically bonded to an asphaltene or a resin.
It is thought that the surfactant structure consists of a bitumen-like moiety and a polymer-like moiety, and can therefore improve the interaction between the bitumen and the polymer in the polymer-modified bitumen. The polymer-modified bitumen compositions of the invention are essentially physical blends of bitumen, polymer and compatibilising agent wherein the compatibilising agent improves the interaction between the bitumen and the polymer.
The compatibilising agent helps to avoid phase separation in the bitumen composition, and allows the use of smaller quantities of polymer to achieve desirable physical properties. Additionally the compatibilising agent may improve the rheological properties of the bitumen composition.
Process for preparing of PMB polymer modified bitumen
Process for preparing a PMB polymer modified bitumen binder composition in the substantial absence of cross linking agents by heating a bitumen component in a stirred tank to a temperature from 185° C. to 221° C.; adding a block copolymer composition to the bitumen component while the bitumen component is being stirred to form a homogeneous mixture of the bitumen component and the block copolymer composition; and continuing to stir the homogeneous mixture while maintaining the temperature from 185° C. to 221° C. for a period of time from 4 hours to 30 hours thereby forming a cured polymer modified bitumen binder composition.
Polymers in PMB modified bitumen
The block copolymer composition utilized in the process comprises a diblock copolymer comprising one block of a Monovinyl aromatic hydrocarbon and one block of a conjugated diene having a peak molecular weight from 30,000 to 78,000 and a vinyl content from 35 to 80 mol percent based on the number of repeat monomer units in the conjugated diene block, and optionally one or more block copolymers comprising at least two blocks of monovinyl aromatic hydrocarbon and at least one block of conjugated diene, the block copolymer selected from linear triblock copolymers having a peak molecular weight that is 1.5 to 3.0 times the peak molecular weight of the diblock copolymer, multiarm coupled block copolymers having a peak molecular weight that is 1.5 to 9.0 times the peak molecular weight of the diblock copolymer, and mixtures thereof, wherein each block copolymer has a vinyl content from 35 to 80 mol percent based on the number of repeat monomer units in the conjugated diene block, wherein when both (i) and (ii) are present in the block copolymer composition, the ratio of (i) to (ii) is greater than 1:1.