International audienceNon-vulcanized styrene-butadiene rubber thin films were exposed to Radio-Frequency low-pressure air plasma. Two different configurations corresponding to direct and downstream RF plasmas were compared. Optical emission spectroscopy provided information about plasma composition and temperature. The plasma treated SBR surfaces were characterized by contact angles and XPS spectroscopy. Two different phenomenological mechanisms are proposed to describe the observed differences according to the plasma configuration used and account for the impact of the activated gas phase on the structure of plasma-treated non-vulcanized SBR surfac
We have found that silicone rubber compounds undergo a reduction in effective chain concentration when heated in an environment of high temperature silicone oil and that this rate of reduction is dependent upon the effective chain concentration to the 3/2 power. The 3/2 power relationship results from a slower than expected reaction rate due to the dilution influence of further reactions of already ineffective network chains. Based on our experimental findings, we believe that below 204°C, in a silicone oil environment, the predominate degradation of the siloxane network is due to the siloxane rearrangement reaction between silicone oil and the crosslinked network. The resultant bond breaking and reforming have an experimentally determined average activation energy of about 60 kJ/mole. In addition, based on our experiments, we have concluded that above 204°C, the higher activation energy of 105–125 kJ/mole observed for the two compounds containing little or no iron oxide is caused by a depolymerization mechanism which involves breaking of the network and formation of low molecular weight cyclic siloxane materials. With significantly more iron oxide present, as is evidenced in the RTV (Fe2O3 + Al2O3) material, the lower activation energy seen even above 204°C is believed to be caused by the continued catalysis of the siloxane rearrangment reaction by the iron oxide.
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