Controllable Fabrication Of Polymer Modified Bitumen Emulsion With Hierarchical Structures

Bitumen emulsions are by far the most widely used binder in cold paving and waterproof technologies.However,its engineering performance at high temperature are too low to meet the demands in the various applications.Styrene-b-butadiene-b-styrene triblock copolymer(SBS),being a kind of thermal plastic elastomers(TPEs),is the most effective modifier for bitumen as a small dosage of SBS can significantly improve the engineering performance of bitumen at both high/low temperatures.Unfortunately,the employment of SBS-like block copolymer from solution anionic polymerization is difficult in the modification of bitumen emulsions.In this thesis,styrene-b-isoprene-b-styrene triblock copolymer(SIS)latex was synthesized directly from RAFT emulsion polymerization.The SIS latex was then applied to modify the bitumen emulsions to develop a new energy-saving and low VOC emission technique to modify bitumen and to expand the application of the bitumen emulsions.To this end,new techniques were proposed and investigated to achieve hierarchical structures desirable for high performance the modified bitumen.It was turned out SIS latex could be very effective in improving the engineering performance of bitumen emulsions.The main research contents and new results achieved are as follows:(1)On the control over chain microstructures of a modifier,the stable latex of SIS triblock copolymer with different chain structures was synthesized by RAFT emulsion polymerization mediated by poly(acrylic acid)20-b-poly(styrene)5 trithiocarbonate,which also acted as a surfactant.The chain microstructures were found to play a significant influence on the engineering performance of the modified bitumen.Among SISs we synthesized,the bitumen modified by SIS with theoretical molecular weights for each block being 15,55,and 9 kg/mol exhibited the best engineering performance.(2)To control over the morphology of the modified bitumen,two novel mixing approaches,a heterocoagulation process and a Pickering emulsion technique,were proposed and developed to make SIS particles adsorbed on the interface of bitumen droplets to form core-shell composite droplets with SIS as shells,leading to the stable cationic and anionic SIS-modified bitumen emulsions.The construction of the core-shell morphology not only to address the problem of colloidal instability from depletion effect in the mixture of SIS latex and bitumen emulsions but also to facilitate the formation of the continuous polymeric phase in the modified bitumen evaporated off water.The later is key for improving the engineering performance of the modified bitumen.(3)In a heterocoagulation process,betaine-modified anionic SIS latex particles adsorbed on the cationic bitumen droplets when mixing the SIS latex with bitumen emulsions,leading to a stable cationic SIS-modified bitumen emulsion.When SIS(theoretical molecular weights for each block:15,55,and 9 kg/mol)dosage increased up to 5 wt%,a continuous polymeric phase formed in the SIS-modified bitumen evaporated off water,significantly improving the elasticity and engineering performance of bitumen at high and low temperatures.Compared with the original bitumen,the 5 wt%SIS-modified AH-70 bitumen showed a significant increase in the complex modulus at high temperature(from 5 kPa up to 14 kPa at 60?),and a significant decrease in loss tangent(from 10.7 down to 2.4 at 60?),suggesting excellent resistance to rutting at high temperature,which was consistent with significant increase in softening point up to 64 ?(compared with 48 ? of the base bitumen).In the meanwhile,the ductility at 5? of the modified bitumen was also dramatically increased to 36 cm,indicating that the low-temperature cracking resistance also be much enhanced.(4)A Pickering emulsification process using as-prepared SIS latex particles as Pickering stabilizing particles was investigated and developed.It was found that a stable emulsion could be formed at pH 8?12.Stable SIS-modified(theoretical molecular weights for each block:15,55,and 9 kg/mol)bitumen emulsion was made by using SIS latex particles as Pickering stabilizing particles with the aid of a small fraction of surfactant AM90.When evaporated off water in the 5 wt%SIS modified AH-70 bitumen emulsion,a continuous polymeric phase was observed.The ductility at 5? of the modified bitumen increased up to 31 cm and the softening point increased up to 67?,which was 3? higher than that from the hetercoagulation process.(5)The interactions between SIS and bitumen were investigated via thermal analysis together with Fox equation.It was found that polyisoprene phase in SIS(theoretical molecular weights for each block:15,55,and 9 kg/mol)was swollen by the oil fractions.The swollen degree was dependent on the bitumen grades.In 5%SIS modified AH-70 and AH-90 bitumen,polyisoprene was swollen respectively by 20 wt%and 38 wt%oil fraction based on polyisoprene.It was indicated that SIS should be more miscible with AH-90 bitumen than AH-70.This was consistent with the higher efficiency in the modification of AH-90.The continuous polymeric phase appeared at 5 wt%SIS in the case of AH-70 but at 3 wt%SIS in the case of AH-90.As a result,the modified AH-90 showed higher complex modulus,lower loss tangent value,higher softening point and higher ductility.