Study On Functionalized Polyethylene Modified Asphalt And Its Mechanism

The development and utilization of polymer modified asphalt is an important method to improve the performance of asphalt,however it suffers from high costs,high construction temperatures and poor compatibility.In response to the national policy of"carbon neutral and carbon peaking"and the demand for high-quality pavements,this paper takes low-cost polyethylene(PE)as an entry point.By designing and studying the molecular weight(M_w),molecular weight distribution,and end group polarity of PE,a low-cost,high-performance,and environmentally friendly PE modified asphalt was synthesized.The influence of changes in molecular weight,molecular weight distribution,and end group polarity of PE on the rheological properties,workability,and storage stability of modified asphalt was systematically studied.Based on experiments,molecular dynamics model of PE modified asphalt with different structures was constructed.The effect of PE on the structure and microscopic motion of asphalt colloids was analyzed to reveal the intrinsic mechanism of the performance change of PE modified asphalt.This study provides a theoretical basis for the application of PE and recycled plastics in asphalt.The main research contents and conclusions are as follows:Firstly,polyethylene with different molecular weights was prepared by combining polyolefin synthesis and solvent gradient grading(SGF)method.The study on the viscosity-temperature curve of PE modified asphalt with different M_w concluded that the high temperature viscosity of asphalt can only be reduced when the M_w of PE is less than the critical molecular weight(M_c)of molecular chain entanglement in the melt state,thereby achieving the goal of energy saving and emission reduction.Low molecular weight polyethylene PE-4 was prepared.The construction temperature of PE-4 modified asphalt was lower than that of the commercially available warm mix modifier-Sasobit,and it had excellent rheological,workability,mechanical properties,and dispersibility.The molecular dynamics model of PE modified asphalt with different carbon chain lengths and different branch chains was constructed to simulate the microscopic movements and interactions between PE and four components of asphalt at different temperatures.Combined with macroscopic performance research,the influence and mechanism of PE molecular weight and branched chain structure on asphalt have been explored.The lower the M_w or the longer the branch chain of PE,the more conducive to reducing the high temperature viscosity of asphalt and the formation of a stable modified asphalt system.However,the small M_w or the long-branched chains of PE increase the repulsion between PE and asphaltene,weakening the interaction between PE and saturate,thus negatively affecting the asphalt performance.Then,a wide molecular weight distribution of polyethylene(VPE0)with M_w less than M_cwas obtained by efficient catalytic ethylene polymerization with Fe-based-polyolefin catalyst,and its modification of asphalt was studied.The mixing and compaction temperature of VPE0modified asphalt decreased by about 4°C to 7°C.The penetration of VPE0 modified asphalt decreased,softening point and low temperature ductility increased,and showed good rheological properties and dispersibility.The effect of different molecular weight components of VPE0 on the viscosity of asphalt was investigated by SGF method,and the components were compounded to achieve the regulation of the rheological properties of the modified asphalt.The study showed that reducing the M_w of PE is beneficial to reducing the high-temperature viscosity of asphalt and achieving energy conservation and emission reduction,but low M_w of PE is not conducive to the rheological properties of asphalt.Based on molecular dynamics simulation,a model of PE modified asphalt with a wide and narrow molecular weight distribution was constructed.It was found that PE changed the colloidal structure of asphalt,forming a"polyethylene micelle"structure similar to the structure of“asphaltene micelles”.The“polyethylene micelle”is centered on polyethylene,surrounded by the lighter components of asphalt,and then outwardly by the resin of“asphaltene micelles”,and then the asphaltene component.The"polyethylene micelles"and"asphaltene micelles"have overlapping parts,and the two micelles form a new equilibrium in the modified asphalt system.By comparing the microscopic effects of wide and narrow molecular weight distribution PE on asphalt,it was found that the narrow-molecular weight distribution will enhance the repulsion between PE and asphaltene,weaken the adsorption between PE and saturate,and PE tends to aggregate.Combined with the macroscopic properties,it is concluded that PE with a wide-molecular weight distribution is more suitable for eco-friendly asphalt modification.Finally,in order to improve storage stability,end-group functionalized PE was synthesized by a simple and efficient click chemistry reaction that converts end-group double bonds into functionalized groups.The low molecular weight end epoxy-terminated-polyethylene(EPE)was synthesized first.The mixing and compaction temperature of EPE modified asphalt decreased by about 3°C to 5°C,and the difference in softening point between the top and bottom was as low as 0.7°C.EPE has excellent storage stability and energy saving properties.The mechanism was further revealed by molecular dynamics:EPE enhanced the binding energy with resin,saturated and aromatic,while weakening the repulsive interaction with asphaltene,thus improving the storage stability of modified asphalt.Subsequently,the effect of terminal group polarity changes on the macroscopic properties and microscopic motion of PE modified asphalt was studied,and amino-terminated-polyethylene(NPE)was synthesized.The difference in softening point between the top and bottom of NPE modified asphalt further decreased to 0.4°C,with only an increase in high-temperature viscosity.In summary,it is concluded that enhanced polarity of PE end groups can improve the storage stability of PE modified asphalt,but is not conducive to high temperature viscosity reduction.In addition,molecular dynamics simulations reveal the effect of end-group polarity enhancement on the microscopic motion of asphalt:NPE and asphaltene present mutual attraction,therefore,end-group polarity enhancement can change the interaction between polyethylene and asphaltene from mutual repulsion to mutual attraction,and improve the binding energy between polyethylene and resin,saturated fraction,thus improving storage stability of modified asphalt.