Uncured Rubber Material Properties and Rheology Testing

Long chain branching, molecular weight, and molecular weight distribution of uncured rubber compounds are key characteristics to predict the curing process and final material properties of cured rubber.

This article discusses the measurement of tan delta and dynamic shear moduli of four uncured rubber compounds of butyl rubber and carbon black using the ElectroForce 3200 test instrument (Figure 1) from Bose Corporation. These analyses clearly demonstrate the amount of branching of each compound.

Figure 1. The ElectroForce 3200 test instrument

Experimental Procedure and Results

The sample analyzed was a double lap shear specimen with an area of 800mm² and a thickness of 4mm. It was subjected to a sinusoidal strain at 5% amplitude (0.2mm peak to peak displacement) between 0.001 and 16Hz (0.006 to 100rad/s). Temperature was maintained at 125°C. A strain gauge load cell was used to measure the transmitted force, and an FFT was used to analyze the timed data for determining the fundamental frequency’s amplitude and phase relation at each test condition.

Figure 2. The compound with little or no branching shows a crossover of G' and G" when graphed as a function of frequency

Figure 3. There is no crossover in the data from the highly branched material

The compound with little or no branching shows a crossover of G' and G" when graphed as a function of frequency (Figure 2.). However, crossover is not observed in the data acquired for the highly branched material (Figure 3). Moreover, branched materials exhibit low tan delta values at lower frequencies, as depicted in Figure 4.

Figure 4. Comparison of tan delta vs. frequency

Conclusion

The results clearly demonstrate the ability of the ElectroForce 3200 instrument to measure the properties of uncured rubber compounds. The instrument is also able to provide accurate measurements of the properties of fully cured rubbers. Hence, it is recognized as one of the most versatile material test solutions in the industry.

This information has been sourced, reviewed and adapted from materials provided by TA Instruments.

For more information on this source, please visit TA Instruments.