Stretching the limits of rubber analysis

One of our customers is active in the automotive industry. After complaints from their customers, they noticed that a newly delivered rubber shock-absorber behaved differently in the field than previously delivered ones, while they should have been the same in terms of material composition and physical properties. They suspected their supplier may have changed the rubber composition of the newly delivered products.

In order for us to find out what caused the different behaviour and to check the rubber composition, they provided us with samples of a reference and a new rubber shock-absorber. We used a combination of techniques to analyse these rubber samples. By combining the results from the different techniques, we succeeded in explaining the behaviour difference of the rubber products.

The first technique we used was infrared spectroscopy (IR). This is a very powerful analysis technique, which gives information about the molecular structure of a rubber. Analysis, however, can be complicated due to the presence of carbon black. In this case we used that to our advantage. We found the baseline of one of the rubber samples was much more affected by the carbon black than the other one. This suggested there was a significant difference in carbon black content between the samples.

To quantify the carbon black amount present in both samples, Thermogravimetric analysis (TGA) was used. With TGA both samples were heated to 900 °C under nitrogen atmosphere, burning away the organic rubber part. By switching then the atmosphere to air, after reaching 900 °C, all carbon black was also burned away, leaving only inorganic fillers. During the whole analysis the sample weight was very accurately measured, to determine the weight percentages of the different rubber components. From the TGA analysis we also obtained information on the amount of oil present in the samples. Oils are often used in rubber to provide flexibility.

From the TGA analysis we concluded that the new rubber sample contained approximately 13% more carbon black compared to the reference sample. We also saw that in the reference sample a 10% higher oil content was present.

Both samples were also analysed using X-ray fluorescence (XRF) to compare the elemental composition. This analysis showed the reference sample contained much less sulphur compared to the new one. Since sulphur is known to be a crosslinker for rubber, this result suggested the new sample was more crosslinked, which increased its stiffness. This difference in stiffness was observed when comparing both reference and new samples.

By combining all results, we found the reference rubber sample had a lower carbon black content, a higher oil content and was less crosslinked. So we concluded that these differences in rubber composition made the newly delivered rubber shock-absorber more stiffer than the reference one. This explained the different behaviour in the field.

With the help of our independent report, our customer then could start discussions with their supplier about the quality of the delivered rubber shock absorbers.

While there are much more properties that can be of interest, many of which we can help you with, the aforementioned techniques have proven very useful to our customer. Because your product’s quality is our priority, contact us to find out how we can help you maintain it. If you are interested in our complete rubber analysis package, feel free to contact us!