| Due to its unique viscoelasticity,light weight and ease of processing,rubber damping materials are widely used in aerospace,rail transit and other fields.But there are lots of shortcomings in pure rubber which could not meet the high application requirements.In these years,adding small polar molecules to the rubber matrix has become a new method for preparing high-damping materials.It is found that the rubber matrix will constitute hydrogen bond(H-bond)with small polar molecules,and the H-bond will consume mechanical energy persistently in the process of fracture and formation which has the effect on weakening useless noise and preventing vibration fatigue failure.In this article,three kinds of hindered phenol/nitrile-butadiene rubber systems were studied by means of molecular dynamics(MD)simulations and experimental tests,and the mechanism of different types of H-bond were analyzed in detail.According to the results between thermal and dynamic mechanics tests,the quantitative relationship between microscopic H-bond and damping performance were found.(1)Firstly,the repeating units of three systems of hindered phenol/acrylonitrile-butadiene rubber(AO-60/NBR,AO-70/NBR and AO-80/NBR)were constructed by using the MD simulations,and the related parameters were calculated.The solubility parameter simulation results demonstrated that the solubility parameters of hindered phenol AO-70 and AO-80 were closer to NBR molecular chains than AO-60.The statistical showed that the H-bonds in the three systems were mainly divided into the intermolecular H-bond(which formed between the H atom of the hindered phenolic hydroxyl group(-OH)and the N atom of the cyano group(-CN)in the NBR molecular chain),and the intramolecular H-bond(which formed between the H atom of the hindered hydroxyl group(-OH)oxygen atoms).The intermolecular H-bond was the main type which had the large number.According to the results of radial distribution function,it was deduced that the stability of intermolecular H-bond was stronger in high temperature conditions;and the sequence of intermolecular H-bond strength was AO-80/NBR>AO-70/NBR>AO-60/NBR in three systems.Furthermore,with the increase of the intermolecular H-bond,the free volume fraction started to decrease.The tightness of the binding between the hindered phenol and rubber matrix increased,which leaded to an increase in binding energy(Ebinding).The size of the Ebinding was linearly related to the number of intermolecular H-bond,and the correlation coefficient R2 was about to 0.94.(2)Three kinds of pure mixing rubber were prepared according to the component ratio of molecular simulations,and they were analyzed through the experimental methods.Scanning electron microscopy(SEM)showed that AO-70 and AO-80 could be evenly dispersed in NBR matrix,but AO-60 was agglomerated in it.According to the results of Fourier transform infrared spectroscopy(FTIR),the red shift of the hydroxyl absorption peak and the weak blue shift of the cyanogens absorption peak were both observed in three systems,demonstrating the existence of the intermolecular H-bond.The results of the temperature-dependent FTIR indicated that the sequence of the intermolecular H-bond intensity of three system was AO-80/NBR>AO-70/NBR>AO-60/NBR,which was consistent with the results of MD simulations.Furthermore,thermal and dynamic mechanical analysis results showed that the damping performance of three systems increased with the addition of hindered phenols.When the content of AO-60 exceeds 56phr,the AO-60/NBR system began to phase out.(3)The Ebinding in the three systems were linearly correlated with the effective damping peak area(TA)(R2 = 0.95),and the major contribution of the Ebinding got rise from the intermolecular hydrogen bonding,demonstrating that the intermolecular H-bond was the main factors of improving the damping performance in hindered phenol/nitrile-butadiene rubber systems. |
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