As the leaching of fillers from silicone rubber is closely related to
the swelling of the silicone rubber, the volume expansion properties
of silicone rubbers in different aqueous solutions were further
investigated. Fig 2a displays the volume expansion ratio, defined as
the ratio of volume change before and after exposure in solution to
the initial dry volume of tested samples, as a function of exposure
time in simulated solutions. Clearly, after 30 days of exposure to
simulated solution, all the tested silicone rubbers swelled, reaching
the volume expansion percentages of 18.3%, 17.7%, and 16.0% for
silicone rubbers with hardness of 30, 40, and 50, respectively. The
swelling of silicone rubbers indicates that the fillers in silicone
rubbers can leach out from the bulk materials, resulting in the
weight loss of tested materials. Although the swelling degree of
silicone rubber with hardness of 50 is the lowest one due to the
high density of cross-linking, the highest weight loss value for the
sample with hardness of 50, as described in the above paragraph,
was probably attributed to the largest amount of fillers impregnated
among the tested samples. Fig 2b showed the swelling of
silicone rubber with hardness of 40 in different aqueous solutions.
Since silicone rubbers can be dissolved in strong acid, the volume of
sample shrinks after exposure to strong acid aqueous solution. It is
also evident, that silicone rubber exhibits larger volume expansion
ratio in acetic acid solution than that in simulated solution
although the pH value of the used acetic acid solution (pH ~5.0) is
higher than that of simulated solution (pH ~3.35). This can be
attributed to the existence of HF molecules in simulated solution,
which can accelerate decomposition of SieO bonds in silicone
rubbers.
As the leaching of fillers from silicone rubber is closely related tothe swelling of the silicone rubber, the volume expansion propertiesof silicone rubbers in different aqueous solutions were furtherinvestigated. Fig 2a displays the volume expansion ratio, defined asthe ratio of volume change before and after exposure in solution tothe initial dry volume of tested samples, as a function of exposuretime in simulated solutions. Clearly, after 30 days of exposure tosimulated solution, all the tested silicone rubbers swelled, reachingthe volume expansion percentages of 18.3%, 17.7%, and 16.0% forsilicone rubbers with hardness of 30, 40, and 50, respectively. Theswelling of silicone rubbers indicates that the fillers in siliconerubbers can leach out from the bulk materials, resulting in theweight loss of tested materials. Although the swelling degree ofsilicone rubber with hardness of 50 is the lowest one due to thehigh density of cross-linking, the highest weight loss value for thesample with hardness of 50, as described in the above paragraph,was probably attributed to the largest amount of fillers impregnatedamong the tested samples. Fig 2b showed the swelling ofsilicone rubber with hardness of 40 in different aqueous solutions.Since silicone rubbers can be dissolved in strong acid, the volume ofsample shrinks after exposure to strong acid aqueous solution. It isalso evident, that silicone rubber exhibits larger volume expansionratio in acetic acid solution than that in simulated solutionalthough the pH value of the used acetic acid solution (pH ~5.0) ishigher than that of simulated solution (pH ~3.35). This can beattributed to the existence of HF molecules in simulated solution,which can accelerate decomposition of SieO bonds in siliconerubbers.
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