Experimental Study and Molecular Simulation of Graphene Modification and Design and Preparation of SSBR Composites
Author:Luo Yan Long
Supervisor:wu si zhu
Because of its low rolling resistance and excellent wet skid resistance,solution-polymerized styrene butadiene rubber(SSBR)is widely used in tire industry and shoemaking industry,especially in high-performance tires,such as green tires and antiskid tires.In order to meet the requirements for higher performance of SSBR in production and life,it is of great practical significance to develop high-performance SSBR composites.For filled SSBR composites,filler-rubber interactions and filler dispersion are two key factors that affect the properties of composites.In addition,how to improve the compatibility between polar fillers,such as silica and graphene oxide(GO),and non-polar SSBR is the focus of research.In this work,from the point of view of SSBR macromolecular structure design and filler modification,we first investigate the effect of SSBR with various chemical structures on silica and graphene dispersion and fillers-rubber interactions by experiments and molecular dynamics(MD)simulation.The structures of SSBR studied are non-modified,star-shaped,in-chain modified and have different vinyl content.Then,it is studied that the solubility parameters change of graphene and its change mechanism,the compatibility mechanism between graphene and SSBR,and the effect of hydrophobically modified GO on the structures and properties of SSBR composites.The research of this paper is expected to provide the technical ideas and theoretical basis for the development of high-performance SSBR composites.The specific research contents are divided into four parts:(1)From the point of view of macromolecular structure design,the effect of non-modified,in-chain modified by 3-mercaptopropionic acid and star-shaped SSBR on dynamics properties,filler dispersion,and filler-rubber interactions was investigated by MD simulation.Besides,the effect of the content of 3-mercaptopropionic acid on the final results was also investigated.The parameters for binding energy,mean square displacement(MSD),glass transition temperature(Tg),and radial distribution function(RDF)were calculated.It was found that there was an optimum modifier content(14.2 wt%)at which the silica/SSBR composite had the lowest self-diffusion coefficient,the highest binding energy,and the best silica dispersion.The competing effects of hydrogen bonds,steric hindrance of 3-mercaptopropionic acid and rubber-rubber interactions led to the existence of this optimum modifier content.Furthermore,the star-shaped SSBR as well as in-chain modified SSBR had strong interactions with the silica dispersed uniformly in the rubber matrix.The star-shaped SSBR was also a considerable structure for silica,but was inferior to in-chain modified SSBR with modifier content of 14.2 wt%.The modeling results were in good agreement with our previous experimental results.(2)Three kinds of SSBRs with same styrene content and different vinyl content were used as the matrices to prepare the graphene/SSBR composites.The effect of vinyl content on the dynamic properties,interface bonding characteristics and fractional free volume(FFV)of composites was investigated by a combined experimental and MD simulation approach.We found that as the vinyl content increases in the SSBR matrix,the grapheme/SSBR interfacial interaction increases,the FFV decreases,and the graphene dispersion is improved.The interfacial interaction,which is derived from the introduction of graphene,can increase the activation energy and limit the mobility of SSBR chains.Additionally,MD simulations of the pullout of the graphene from SSBR matrix were carried out to explore the interfacial bonding characteristics at the molecular level.It is showed that the interaction energy,pullout energy,and shear stress between graphene and SSBR increase with the increase of the vinyl content.The interfacial bonding energy is constant during the pullout.This present study is expected to deepen the understanding of the basic physics for graphene reinforced rubber nanocomposites,especially the interfacial bonding characteristics at the molecular level.(3)The compatibility of graphene and SBR is the basic factor that affects the final properties of graphene/SBR composites.To predict the compatibility of different components,the most intuitive is to compare their solubility parameters.For the two component system,it is always hoped that their solubility parameters are as close as possible.Therefore,the effects of the number of layers,various defects and functional groups on solubility parameter of graphene were studied through MD simulation.We predigested three-component Hansen solubility parameters to two-component solubility parameters,and the two-component solubility parameters of graphene functionalized by different groups,such as hydroxyl,carboxyl,amino,methyl and epoxy with different grafting ratios were obtained.Except for the effect of single functional group,the common effect of multi-functional groups on solubility parameter was also investigated.Further the graphene/SBR composites were constructed to investigate the effect of functional groups and grafting ratios on components compatibility.It was found that the defects and functional groups had strong impact on solubility parameter of graphene,whereas the number of layers had a negligible effect.The combination of multi-functional groups with a proper content can obtain lower solubility parameter than a single group.Additionally,two-component solubility parameters were proved to be able to predict compatibility of graphene and SBR.(4)Based on the above research,we found that compared with the grafting of polar groups,the grafting of alkane can reduce the solubility parameter of graphene to a greater extent so that the solubility parameter of alkane-modified graphene is closer to that of SSBR.Therefore,alkanethiol-modified GOs containing alkanethiol(CxGO)molecules with varying chain lengths were synthesized through click chemistry.Then,CxGO/SSBR composites were prepared by a solution-mixing method.By combining experiments and MD simulation,we investigated the relationship between the microstructures and properties of the CxGO/SSBR composites.Results showed that the 1-heptanethiol-modified GO(C7GO)/SSBR composite had the smallest fractional free volume and the least mobility of the polymer chains.The 1-octadecanethiol-modified GO(C18GO)/SSBR composite displayed the largest binding energy.Thermal stability,gas barrier,dynamic,and static mechanical properties were improved by introducing CxGO.The long chain length of CxGO indicated that the composites had good performance.These results provide a basis for the design and fabrication of high-performance GO/SSBR composites.