Study On Thermal-Oxidative Aging And Moleculer Simulation Of Natural Rubber

There are many kinds of rubber material in the world, one of which is called unsaturated rubber. Nowadays, rubber is wildly used in chemical industry and our daily life due to its special high elasticity that other materials do not have. Natural rubber (NR) is one of the most commonly used unsaturated rubbers and is often the first choice for industry because of its excellent physical and mechanical performance and its large output. However, as one kind of unsaturated rubbers, the degree of unsaturation of NR, which represents the content of carbon-carbon double bond, is so high that it makes it easy for NR to react with oxygen, in which case irreversible changes would take place in the main molecules, which finally would lead to the loss of performance and material aging. In this paper, we studied the aging properties and mechanism of NR by combining molecular simulation and experiments. It is of great significance not only in understanding aging of unsaturated rubber, improving the aging-resistant performance, looking for universal methods for unsaturated rubber aging research but also in the design and use of unsaturated rubber.In the aspect of experiments, we studied the thermo-oxidative aging mechanism of NR by thermo-oxidative accelerated aging method. FTIR results showed that oxidation, crosslinking and fracture mainly occurred in NR aging process. The main aging products contained aliphatic ester, lactone, aliphatic acid, aliphatic ether, side-chain methyl and peroxide and relevant reaction mechanism was concluded referring to literature. According to the two-dimensional correlation analysis of the FTIR results, the formation rate of aging products was aliphatic ether< peroxide< aliphatic ester. The crosslinking density results, DSC results and DMTA results were of good consistency and indicated that crosslinking reaction dominated during the NR aging process. The results of compression stress relaxation experiments showed that both increasing the aging temperature and the aging time would promote the movement and rearrangement of molecular chain, which could be compared with molecular dynamic (MD) simulation results. A fixed standard linear solid model (SLS model) was introduced to analysis the chemical stress relaxation and it turned out that oxidation reaction and the crosslinking reaction dominated during the NR aging process under high temperature, which was in accordance with experimental results before. The NR oxidation induction period experiments were also carried out and two non-Arrhenius temperature equations were used to fit the experimental data, and the service lives predicted respectively under the normal temperature 25?.In the aspect of molecular simulation, we studied the motion law of NR under high temperature by the means of MD method. Through the simulation analysis, we found that FFV,<s2> and MSD got larger with the rising of temperature, which showed that high temperature would promote the movement of molecular chain, keeping free volume and motion space increasing constantly, resulting in the increasing of relaxation rate. All the conclusion we got by MD simulation was of good consistency with the compression stress relaxation experiments.