Study On Rheology And Stability Of Polyethylene Modified Asphalt Based On Network Structure Evolution

This paper takes the polyethylene(PE)modified bitumen as the research object,to improve the high temperature storage stability of polyethylene modified bitumen as the breakthrough point,and to improve the overall stability by adding polyethylene glycol(PEG)to stabilize the polyethylene network structure.By changing the molecular weight of polyethylene glycol,the content of polyethylene glycol,adding the reactive material diphenyl methane diisocyanate(MDI)and other experimental conditions to preparation of modified asphalt in different systems,we can obtain modified bitumen materials with high modulus,high elasticity and high temperature stability.To investigate the effect of different molecular weight PEG on the bitumen/PE system.The study found that the increase of composite modulus of modified bitumen did not show a monotone increasing relationship with the increase of PEG molecular weight,in which the molecular weight of the two PEG with better modification effect was8×10~2and8×10~6.Combined with DSC results,when the temperature is lower than 70°C(near the melting point of PEG8×10~6),the bitumen/PE/PEG system with the highest composite modulus is PEG8×10~6,and when the temperature is higher than 70°C,the bitumen/PE/PEG system with the highest composite modulus is PEG8×10~2.phase separation structure shows that the PE-rich phase forms a network structure in all the modified bitumen systems,which is helpful to improve the high temperature stability of the modified bitumen.the bitumen/PE/PEG system of PEG8×10~2 has a more stable network structure during 180°C constant temperature annealing,which improves the composite modulus of the modified bitumen and reflects its better deformation resistance and rutting resistance.Based on the results of the previous section,the bitumen/PE/PEG system with a PEG molecular weight of 8×10~2 has good rheological properties,and it is amorphous in the modified bitumen system.It can directly distinguish between crystalline and amorphous phases.Better observe the evolution of the PE-rich phase network structure.To investigate the effect of different content of PEG on bitumen/PE system.It is found that with the increase of PEG fraction,the complex modulus(G~*)of bitumen/PE/PEG is improved.The G~*decreases with temperature and then keeps almost invariable once the temperature exceeds a critical value.The presence of plateau on G~*~Tcurve indicates the rheological stability at high temperature,and it disappear until crystalline PE totally melts into amorphous state.The addition of PEG can effectively decrease the starting temperature for the plateau,which would accommodate the actual service high temperature.All the modified bitumen can form a network structure composed of PE-rich phase via viscoelastic phase separation.The network in the blend with high PEG fraction can exist much longer since the PEG-rich droplets can prevent the breakup of PE-rich phase network.Themaintenance of network crosslinks is the original reason for the enhancement of complex modulus and rutting resistance in bitumen/PE/PEG blends.Based on the above research,a PEG with a molecular weight of 8×10~2 was selected,it has higher hydroxyl value and higher chemical reaction activity,providing conditions for chemical reaction with MDI.The bitumen/PE/PEG system was used as the main body.A reactive substance MDI was added to the system to modify the bitumen.It is found that the addition of MDI does not affect the melt-crystallization behavior of the modifier,but can increase the composite modulus of the modified bitumen.The improvement of its rheological properties is related to the formation of new substances in the bitumen system.The phase separation structure shows that the modified asphalt system after adding MDI has better dispersion,interconnection and high temperature stability of the PE-enriched phase network structure,which helps to balance and stabilize the modified asphalt performance.