Disclosed percolation phenomena and mechanism in reinforcement of elastomeric polymer by nano-filler

Disclosed percolation phenomena and mechanism in reinforcement of elastomeric polymer by nano-filler
Zhang Liqun^1,2, Yang Haibo¹, Wu Weidong¹, Zou Hua^1,2
1 Key Laboratory of Beijing City on Preparation and Processing of Novel Polymer Materials at Beijing University of Chemical Technology, Beijing, 100029, China
²  Key Laboratory of Ministry of Education on Preparation and Application of Nano materials at Beijing University of Chemical Technology, Beijing, 100029, China
Email:zhanglq@mail.buct.edu.cn
Nano-reinforcement by employing nanoparticles is necessary for high-efficiency reinforcement of elastomeric polymer materials, which was already proven by numerous researches and industrial applications. This report firstly disclosed the percolation phenomenon in the rubber nano-reinforcement, which is similar to the percolation behavior occurred in the rubber toughened plastics. That is, as the loading of nano-fillers (carbon black, nano sized zinc oxide) increases, the tensile strength of rubber (SBR, EPDM) first increases slowly and then increases rapidly, finally reaches the balance; meanwhile, the bigger the particle diameter is, the higher the volume fraction of reinforcement filler at the percolation point is, the lower the corresponding tensile strength of the composites is. This percolation phenomenon indicates that lower loading of nano-filler can’t reinforce the rubber effectively, and in a certain loading range, the smaller the particle diameter is, the more effective the reinforcement is. Further analyzing this percolation behavior, it is suggested that the rubber reinforcement through nanoparticle was corresponding to the formation of the stretched polymer chains between the neighbor particles induced by slippage of polymer chains on the filler surface during stretching. The concept of critical particle-particle distance (CPD) is hereby put forward for the first time in rubber reinforcement. The factors to govern this critical particle-particle distance are investigated. Moreover, the concept of critical particle diameter for reinforcement is also figured out. Based on the percolation theory, some new view points for reinforcement design of rubbery materials are brought forward, including that the interfacial interaction between the nanoparticles and the rubber couldn’t be the complete chemical bonding, and partial physical absorption of  macromolecular chains on the filler surface is necessary, otherwise the formation of stretched chains would be seriously hindered; there should existed a optimum crosslinking density for a filler reinforce rubber composites; there should be the smallest particle diameter for reinforcement. TEM, FTIR, FEA and MDS (Molecular Dynamic Simulation) are employed to demonstrate the relative mechanism of percolation behavior.
Keywords: rubber, nanometer, reinforcement, percolation, interface
Acknowledgement: supported by distinguished youth research foundation of NSF (50725310)