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Study on the Rubber Molecular Movement Ability under Static Pressure by Molecular Dynamics Simulation

Author: LiuHaiLu
Tutor: WuSiZhu
School: Beijing University of Chemical Technology
Course: Materials Science and Engineering
Keywords: pressure rubber molecular dynamics simulation glass transition temperature gas permeabilities free volume
CLC: TQ330.1
Type: Master's thesis
Year: 2009
Downloads: 164
Quote: 0
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Abstract


The aging research and prediction of sealing rubber on long time scales are very important in military and civil materials. Also the study on the storage aging is of great scientific value. However the wildly-used lifetime prediction methods are experimental formula model and half-experimental formula, such as Arrhenius and WLF equations. In this study, the modified Arrhenius equation was deduced as the prediction model to calculate the rubber lifetime of NR and EPDM.The parameters from the model were calculated by binary linear regression method.To study the basic theory of the damping properties of rubber, a modified Williams-Lendel-Ferry (WLF) equation which includes pressure parameters has been proposed. According to the loss factor tgδfrom DMTA experiments, the shift factors under different pressure can be calculated. Then, the mast curve of loss factor versus frequency could be plotted which the wide of frequency reached about ten orders of magnitude. The result showed that the peak of tgδhas been appeared after the reference temperature. With the increasing of the pressure, the glass transition temperature moved towards higher frequency of about 1.5 orders of magnitude. This method offered a theoretical method to quantitatively characterize the damping properties of rubber materials.Molecular simulation is widely used in polymer science field. In this paper, the effect of pressure on Tg of NBR was simulated. The influences of probe radius(Rp) and pressure on free volume was studied. The results indicated that Tg increased linearly with the pressure and the calculated (?)Tg/(?)P of NBR was about 2.09K/MPa. The free volume increased as the Rp and pressure decreased. Molecular dynamics simulation of gas permeabilities in SBR was also investigated through Einstein equation. It was concluded that the diffusion coefficient decrease as the styrene content in SBR increased. This can be explained that the increasing rigidity with the increasing styrene contents made the chain move difficultly, so the small gas is hard to transport. This method offers a quantitative way to study the relationship between the content of copolymer rubber with the gas peameability.

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CLC: > Industrial Technology > Chemical Industry > Rubber Industry > General issues > Basic theory
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