Featured Rubber Research – March 2024
Introduction
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 March, the featured papers include:
Carbon Black Effect on the Pyrolysis Behavior of Natural Rubber in Tire Wear Particles: Measuring the type and quantity of rubber in road dust samples using pyrolysis techniques to identify carbon black.
Low-Temperature Characteristics of Rubbers and Performance Tests of Type 120 Emergency Valve Diaphragms: Assessing the performance of rubber valves for safety objectives in low-temperature environments.
Eco-Friendly Natural Rubber–Jute Composites for the Footwear Industry: The incorporation of natural jute fibres into rubber blends to create EVA-type materials.
Application of Tamarind Shell as a Green Additive in Natural Rubber: The use and performance of tamarind shell powder as a sustainable bio-filler in rubber blends.
Read the full features below, complete with citations and links to read the original research online.
Featured Research Papers
Carbon Black Effect on the Pyrolysis Behavior of Natural Rubber in Tire Wear Particles
How much rubber is in a typical sample of road dust? This may appear a simple question, but identifying the sources and levels of rubber debris from car and truck tyres in roadside dust remains a challenge.
Despite being designated as microplastics, these tiny particles of rubber tyre tread are often excluded from traditional studies on environmental microplastics. Instead, these studies tend to focus on the concentrations of PE, PP, PET and PVC.
However, one promising method to identify the elastomer content of road dust is pyrolysis, the process of combustion in the absence of oxygen. By quantifying the composition of the end pyrolysis products using key differential markers, the makeup of the original sample can be deduced.
In this study, researchers investigated the pyrolysis behaviour of tyre-wear particles generated via abrasion testing under laboratory conditions.
Natural rubber compounds with carbon black loading levels of either 35, 55 or 75 phr were prepared. After abrasion, the simulated tyre-wear particles were divided by particle size using a fine mesh.
For each sample, pyrolysis was performed at 520°C for ten seconds under a nitrogen atmosphere. The elemental makeup of the pyrolysis products was then identified using gas chromatography techniques.
Typically speaking, isoprene and dipentene are employed as critical markers for quantifying the concentration of natural rubber. Here, these concentrations were compared depending on the size and weight of the simulated tyre-wear particles, and the carbon black content. The researchers also demonstrated that carbon black adsorption and sulphur-crosslinked regions contributed to the observed differences.
The researchers concluded that both the production rates and ratios of pyrolysis products could be used for quantifying the amount and type of tyre-wear particles in real-world environmental samples. This would make measuring the amount of rubber debris making its way into the environment easier, leading to a better understanding of how tyre-wear particles affect our ecosystem.
Citation: Jung, U., & Choi, S. S. (2023). Carbon black effect on the pyrolysis behavior of natural rubber in tire wear particles. Polymer Testing, 127, 108184.
Low-Temperature Characteristics of Rubbers and Performance Tests of Type 120 Emergency Valve Diaphragms
Why do trains stop running in cold weather? One of the reasons is that at lower temperatures, the dynamic properties of materials can change dramatically, leading to responses that could fall outside of safe working ranges.
Within railway carriages, air control valves are a crucial component of emergency braking systems. Only activated during hard braking, the control valves are responsible for the rapid exhaust of air, supporting the reliability and sensitivity of emergency braking.
Engineered from rubber diaphragms, these control valves must have good flexibility, temperature stability, strong mechanical properties and meet the sensitivity and service life requirements of cryogenic conditions.
One of the challenges in designing these parts is that good performance at low temperatures is often accompanied by a weakening in the general mechanical and fatigue properties, and vice versa.
In this study, researchers compared the braking performance of two rubber blends at room temperature and at -40°C, the minimum temperature specified in railway standards. The rubber compounds were identical aside from the base polymer – one with natural rubber, the other with chloroprene rubber.
The samples underwent a series of tests to determine their physical properties, low-temperature characteristics, thermal stability and simulated performance.
While both demonstrated excellent physical properties, the natural rubber sample had superior low-temperature resistance, while the chloroprene rubber had improved ageing resistance. Both samples passed the performance requirements for sensitivity and stability at room temperature. However, at -40°C the chloroprene rubber was deemed unsatisfactory.
This study highlights the difficulty in choosing materials for dynamic environments with high-performance, high-safety requirements. In this example, the rubber diaphragm in train brake systems must be specified to perform reliably in cold-temperature conditions.
Due to the inherent nature of compromise in material design, the material choice may compromise the long-term reliability of the same products, leading to further service and maintenance obligations.
Citation: Gao, M., Pan, A., Huang, Y., Wang, J., Zhang, Y., Xie, X., … & Jia, Y. (2024). Low-temperature characteristics of rubbers and performance tests of type 120 emergency valve diaphragms. Railway Sciences, 3(1), 47-58.
Eco-Friendly Natural Rubber–Jute Composites for the Footwear Industry
Natural fibres, such as jute, form part of a new generation of biocomposite materials that are rapidly rising in popularity. Cost-effective, low density and not derived from petroleum, these new materials provide alternatives to synthetic polymers with reduced environmental impact. Existing applications for biocomposites include conveyor belts, shoe soles and V-belts.
In this study, jute fibres were incorporated into natural rubber as a reinforcement filler, both in an untreated and alkaline-treated format. Mixed at various loading ratios, the biocomposites were mechanically tested to assess hardness, tensile strength and flexibility compared to an unfilled rubber sample.
The morphology, rheology, crosslink density and abrasion resistance were also investigated. Compared to other studies that used natural fibres at concentrations as high as 30 phr, this research centred on using lower levels of up to 10phr jute.
At these levels, the stress-strain properties of the composites did not vary much from the pure rubber sample. However, these lower proportions were fundamental to lowering the relative density of the material. This resulted in hardness measurement values less than Shore A.
Consequently, the exhibited Shore OO hardness values make the biocomposites comparable to ethylene-vinyl acetate (EVA). This is an important result, as EVA is a popular mainstream material used for shoe soles and protective elements in children’s playgrounds.
Therefore, this research paves the way for a better understanding of the use of natural fibres, such as jute, at lower concentrations for use in sustainable industrial applications.
Citation: Torres, G. B., Hiranobe, C. T., da Silva, E. A., Cardim, G. P., Cardim, H. P., Cabrera, F. C., … & Carvalho, J. A. J. (2023). Eco-Friendly Natural Rubber–Jute Composites for the Footwear Industry. Polymers 2023, 15, 4183.
Application of Tamarind Shell as a Green Additive in Natural Rubber
The tamarind plant, widely cultivated throughout tropical regions, is primarily grown for the consumption of the sweet and sour pulp of its edible fruit. Of this, the tamarind shell, accounting for up to 30% of the fruit pod’s weight, is considered agricultural waste.
This waste can be used as a biomass fuel source, with the subsequent ash used again in biodiesel production. Alternatively, in a powdered form, tamarind shell can also be used as a source of activated carbon.
In this study, researchers added tamarind shell powder to natural rubber to investigate its potential role as a filler in rubber compounding. The tamarind shell was initially ground into a fine powder and then sieved through various-sized meshes to form three samples of differing particle sizes.
Prior to compounding, the tamarind shell powder was first characterised using Fourier transform infrared spectroscopy (FTIR). Alongside elemental analysis, the samples were also tested for particle size, functional groups, thermal behaviour, intrinsic density and pH level.
Next, the three powders were incorporated into a standard rubber formula at loading levels ranging from 0 to 10 phr. Then the cure characteristics of the blends were determined using a Moving Die Rheometer (MDR), measuring the scorch time, cure time and difference in torque to evaluate the degree of crosslinking.
Once vulcanised, further physical testing included hardness, tensile strength, abrasion resistance and accelerated ageing.
Overall, the results showed that the protein and moisture in the tamarind shell powder led to a shorter scorch and cure time that decreased more as the powder became finer and more chemically reactive. While the powder was not shown to affect hardness, it negatively impacted the physical properties of the rubber even at small loading levels.
The researchers suggested that this was due to the poor interaction between the hydrophilic tamarind power and the hydrophobic natural rubber. However, despite these impairments, the researchers concluded that tamarind shell powder could be used in small quantities as an inert, eco-friendly bio-filler for applications of cost reduction or environmental protection.
Citation: Intiya, W., Hatthapanit, K., Thaptong, P., & Sae-oui, P. (2024). Application of Tamarind Shell as a Green Additive in Natural Rubber. Polymers, 16(4), 493.
Conclusion
This month, Prescott Instruments has featured four recent scientific research papers concerning the world of rubber. March’s research topics include identifying rubber content in road dust, the safety of emergency train brakes, jute composite shoe soles and tamarind shell powder as a green additive.
If you would like to see your research featured, or to suggest any further topics, contact us online.
Discover More Featured Rubber Research From Prescott Instruments:
September 2023 Featured Research
October 2023 Featured Research
November 2023 Featured Research
December 2023 Featured Research
2023 Featured Research Overview