Featured Rubber Research – August 2023


Every month, Prescott Instruments features several recent scientific papers covering the world of rubber – from cultivation, production, processing, and testing to real-world applications, sustainability and novel concepts.

This August, the featured papers include:

Study of Non-Negligible Chemical Reduction of ZnO in the Rubber Industry: Measuring the environmental exposure to zinc due to tyre particle debris at the roadside.

Some Metal Oxide-Natural Rubber Composites for Gamma- and Low-Energy X-Ray Radiation Shielding: The use of heavy metals in rubber as an effective shield from sources of ionising radiation.

Temperature and Frequency Dependence of the Dynamic Viscoelastic Properties of Silicone Rubber: An overview of the viscoelastic properties of silicone rubber using Time-Temperature Superposition (TTPS).

Preparation of Skim Natural Rubber and Polypropylene Blends via Melt Blending: A study on Processability: A commercial feasibility study into the use of skim natural rubber in thermoplastic natural rubber blends.

Read the full features below, complete with citations and links to read the original research online.

Featured Research Papers

Study of Non-Negligible Chemical Reduction of ZnO in the Rubber Industry

Zinc Oxide and stearic acid are frequently used together in rubber compounding to reduce vulcanisation time and improve rubber properties. While effective, there is growing concern about the environmental cost of using zinc oxide as an activator due to its prevalence in tyre particle debris.

By measuring the chemical level of the soil at the roadside, researchers found non-negligible concentrations of zinc up to distances of 150m. This chemical loading occurs from a continuous build-up of road dust that only increases with time and traffic intensity. At high levels, the zinc that settles on snow or arable soil can cause chronic or acute toxicity.

As a result, there is momentum to reduce zinc oxide without compromising material properties. In this study, researchers conducted a simple experiment to compare the material properties of two rubber formulations: one with typical levels of zinc oxide and stearic acid, the second with 20% less. The two compounds were tested for viscosity, curing time and mechanical strength.

While the reduced formula was less efficient, it demonstrated a promising working range that was not too dissimilar to the control compound.

Citation: Wilaiwong, W., & Smitthipong, W. (2022, March). Study of non-negligible chemical reduction of ZnO in the rubber industry. In IOP Conference Series: Materials Science and Engineering (Vol. 1234, No. 1, p. 012014). IOP Publishing.

DOI: https://doi.org/10.1088/1757-899X/1234/1/012014

Some Metal Oxide-Natural Rubber Composites for Gamma- and Low-Energy X-Ray Radiation Shielding

Gamma rays and X-rays are two types of ionising radiation that are powerful enough to penetrate the human body. This ionisation can cause damage to tissue and DNA that has been linked to an increased risk of cancer. Therefore, it is important to shield workers who are regularly exposed to ionising radiation via protective shielding.

Researchers have recently investigated polymer-composite-based radiation shielding that incorporates heavy metals into a polymer blend. This type of material is used in wearable shielding products such as gloves, aprons and rubber underwear. The mix of heavy metal oxides (tungsten, bismuth and lead) with natural rubber causes an increase in density that improves the attenuation of X-rays and gamma rays directed at the material. As such, the thickness of protective materials can be reduced whilst maintaining the same level of radiation protection.

In addition, researchers found that adding metal oxides to natural rubber increased the maximum torque during the vulcanisation process. This implies that a metal oxide can act as a co-activator in the vulcanisation process, increasing the crosslink density and enhancing physical properties, such as tensile strength and elongation at break.

Citation: Fisli, A., Yulianti, E., Hanurajie, B., Sukaryo, S. G., Mashadi, M., Rivai, A. K., … & Fathurrahman, M. I. (2023). Some metal oxide-natural rubber composites for gamma-and low-energy X-ray radiation shielding. Atom Indonesia, 1(1).

DOI: https://doi.org/10.55981/aij.2023.1213

Temperature and Frequency Dependence of the Dynamic Viscoelastic Properties of Silicone Rubber

Silicone rubber has a unique set of physical properties that differentiate it from other common types of rubber, such as ethylene propylene diene monomer (EDPM) and polymerized styrene butadiene rubber (SBR). Widely used in the aerospace, medical, electronics and consumer goods industries, silicone rubbers are stable, non-reactive and resistant to extreme temperatures and environments.

Like all rubbers, silicone rubber is a viscoelastic material, meaning that it exhibits both elastic and viscous properties. These properties are heavily influenced by two factors – temperature and time. The Time-Temperature Superposition Principle (TTPS) is a method that uses the measured temperature-frequency effects of a viscoelastic material construct a master curve that extends beyond experimental capabilities.

Using a Dynamic Mechanical Analyser (DMA) to measure the response of silicone rubber across a range of frequencies and temperatures, researchers applied TTPS to the results to obtain a master curve covering 10 frequency decades. They then assessed various viscoelastic models to ascertain which provided the best fit against their experimental data.

Citation: Liu, X., Zhu, D., Lin, J., & Zhang, Y. (2023). Temperature and frequency dependence of the dynamic viscoelastic properties of silicone rubber. Polymers, 15(14), 3005.

DOI: https://doi.org/10.3390/polym15143005

Preparation of Skim Natural Rubber and Polypropylene Blends via Melt Blending: A study on Processability

Skim Natural Rubber (SNR) is generally considered a low-cost lower-quality alternative to natural rubber. Produced as a by-product of field latex during the centrifugation process, SNR contains a mix of rubber, proteins, fatty acids and some metal ions. At present, the presence of these non-rubber substances can lead to some undesirable qualities that limit the commercial viability of SNR despite its natural rubber content.

Inspired by the downstream use of other inferior-quality rubber materials, such as reclaimed rubbers, ground rubber tyres and rubber glove waste, researchers recently conducted a pilot study into the processability of thermoplastic natural rubber blends produced using a mix of SNR and Polypropylene.

The SNR/PP blends were prepared in a variety of ratios via melt mixing and tested to assess mixing, long-term processability, cure dynamics, melt flow index and morphology. The blends were tested against a series of control blends prepared using conventional natural rubber.

The researchers found that the non-rubber content in Skim Natural Rubber provided a positive impact on the processability of the blends, and that these blends required less energy to mix. Furthermore, their research demonstrated promise in using SNR/PP blends for compression moulding instead of conventional thermoplastic elastomers.

Citation: Wijewardane, D. S., Senevirathna, M. A. S. R., Siriwardena, S., Edirisinghe, D. G., & Sudusingha, Y. C. Y. (2022). Preparation of skim natural rubber and polypropylene blends via melt blending: A study on processability. Progress in Rubber, Plastics and Recycling Technology, 38(3), 207-226.

DOI: https://doi.org/10.1177/14777606221105293


This month, Prescott Instruments has featured four recent scientific research papers concerning the world of rubber. August’s research topics includes reducing zinc oxide in rubber formulation, the use of heavy metals in rubber fabrics for radiation shielding, the frequency dependence of silicone rubber and the improved use of skim natural rubber.

If you would like to see your research featured, or to suggest any further topics, contact us online.