Featured Rubber Research – January 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 January, the featured papers include:
Cleaning Steel by Devulcanizing Rubber from Used Automotive Tires: A new method to improve the efficiency and reduce the cost of reclaiming steel from used tyres for recycling.
Silicone Rubber-Nanoceramic Composites for 5G Antenna Substrates: The use of hybrid nanopowders to improve the microwave dielectric properties of silicone rubber composites.
Recognition of Rubber Tree Powdery Mildew Based on UAV Remote Sensing with Different Spatial Resolutions: Using commercially available drones to map mildew infection rates in large area rubber plantations.
New Recyclable and Self-Healing Elastomer Composites Using Waste from Toner Cartridges: The use of scrap printer toner powder and plastic cartridges in self-healing rubber blends.
Read the full features below, complete with citations and links to read the original research online.
Featured Research Papers
Cleaning Steel by Devulcanizing Rubber from Used Automotive Tires
One of the main challenges in the recycling of automobile tyres is the complexity of the product. Constructed from more than one rubber compound, a typical tyre also has polyester or polyamide cords to reinforce the sidewall and steel cords to reinforce the tread.
While steel is fully recyclable, most of the steel within tyres is not presently recycled as it is contaminated by rubber. Often, this contaminated steel is sent directly to landfill. Therefore, there is need to develop efficient methods to clean the steel cords fully prior to reclamation.
Existing methods utilise mechanical and chemical techniques to strip the rubber from the steel via devulcanisation. This involves breaking the sulphur bonds that crosslink the rubber itself, as well as bonds between the rubber and the steel. To achieve complete devulcanisation, this process involves the use of an expensive catalyst in quantities of up to 10% by weight.
In this study, researchers used a multi-step procedure to reduce the cost and increase the efficiency of the devulcanisation process. Starting with a batch of shredded tyres, the steel wires were firstly magnetically separated from the rubber crumb. Then, toluene was used to swell the elastomer content enough to facilitate dehesion.
Afterwards, simple mechanical agitation using a pestle and mortar or small hammer was sufficient to remove any additional rubber. At this point, up to 90% of the rubber had already been removed from the steel.
Finally, the chemical devulcanisation process used a small fraction of the catalyst normally used. By removing a significant amount of rubber prior to this stage and by continuing to use magnetic separation during the devulcanisation process, only the steel-rubber bonds are targeted.
Using these preceding steps, not only is the amount of catalyst reduced by nearly 90%, but also the catalyst is able to be reused 3 – 5 before exhaustion, permitting a continuous batch operation. In this manner, the researchers hope that their method can be implemented on a larger scale to increase the amount of steel reclaimed from scrap tyres for recycling, whilst reducing the amount of costly chemical catalysts.
Citation: Chen, Y., Ibrahim, S., Zheng, S., Wittenberg, L., Chapple, S., LaChapelle, G., … & Brook, M. A. (2023). Cleaning steel by devulcanizing rubber from used automotive tires. RSC Sustainability, 1(8), 2006-2013.
Recognition of Rubber Tree Powdery Mildew Based on UAV Remote Sensing with Different Spatial Resolutions
Like all cultivated crops, rubber trees are susceptible to blights and diseases that can threaten the productivity and health of the crop. Of these, powdery mildew is one of most concern, as it can delay the harvesting period and reduce latex production by up to 45%.
Whilst traditional detection relies solely on visual detection, mapping infection rates effectively across large plantations remains challenging. While remote sensing technology, such as satellite imagery, can be used to map larger areas, this is both costly and weather dependent.
Instead, unmanned aerial vehicle (UAV) platforms are becoming increasingly common due to their lower cost and short revisit cycles. In this study, researchers used a commercially available drone fitted with a real-time kinetic module to perform a multispectral analysis of an area of nearly 2 hectares in just over 8 minutes.
After dividing the images into a training and validation set, they tested various models for feature recognition and classification at various resolutions. The highest accuracy was achieved at the highest resolution of 3.4 cm. As the resolution decreased, the background areas such as tree branches, shadows and canopy plants introduced incorrect classification.
However, as lower flight altitudes and increased images are required for higher-resolution datasets, there is a natural trade-off between accuracy and efficiency. Overall, for spatial resolutions higher than 14 cm, the classification accuracy was over 90%.
In the future, the researchers hope that repeated detection will lead to the development of temporal infection models. Furthermore, the integration of additional drone sensors, such as hyperspectral and thermal infrared, will aid crop disease monitoring systems.
Citation: Zeng, T., Fang, J., Yin, C., Li, Y., Fu, W., Zhang, H., … & Zhang, X. (2023). Recognition of rubber tree powdery mildew based on uav remote sensing with different spatial resolutions. Drones, 7(8), 533.
Silicone Rubber-Nanoceramic Composites for 5G Antenna Substrates
As the Fifth-Generation Mobile Communications System (5G) is being implemented throughout the UK, much of the existing 3G/4G infrastructure needs to be updated. The choice of 5G antenna material is crucial to maintaining a low level of latency, defined as the delay between sending and receiving a signal. To achieve a latency of less than one millisecond, a material must have an appropriate dielectric constant and low loss tangent. While elastomers are a natural choice to meet the soft and rubbery requirement of the electronics industry, specific materials still need to be optimised for usage in high-performance electronics.
Dielectric ceramic fillers can be added to a polymer to increase the dielectric constant; however, high volumes are required, causing issues including difficult processability and limited flexibility. Alternatively, conductive and semi-conductive fillers can be used at lower volume fractions, but these conductive networks can induce excessive energy loss and overheating. To address this, hybrid fillers can be used instead. Hybrid fillers have the economic benefit of delivering improvements to microwave dielectric properties at a relatively affordable price and can be used in comparatively low volumes.
In a recent study, researchers incorporated nanopowders into a silicone rubber substrate in both mono and hybrid formats. The effect of the volume fraction of filler on the microwave dielectric properties was investigated, and the efficacy of the material as an antenna was analysed. To be considered as a candidate for a 5G antenna substrate, the composite must achieve a high dielectric constant and low loss tangent at an affordable level of filler volume.
Next, the performance of the antenna is assessed in terms of return loss, voltage standing wave ratio, directivity, gain, and efficiency. Overall, the composite substrates showed good potential for use as 5G antennas, with excellent microwave dielectric properties, flexibility, low cost, and low weight.
Citation: Altalebi, H. B., Atiyah, A. A., & Farid, S. B. (2023). Silicone rubber‐nanoceramic composites for 5G antenna substrates. The Journal of Engineering, 2023(9), e12312.
New Recyclable and Self-Healing Elastomer Composites Using Waste from Toner Cartridges
Despite recycling options, only 20% of printer toner cartridges currently avoid landfill by being reused or recycled. With special designation as waste from electrical and electronic equipment (WEEE), manufacturers and consumers should have improved access to recovery, reusability, disassembly and recycling processes. However, sustainable options for both the scrap plastic cartridge and black toner powder remain limited.
The use of waste toner powder has already been promoted in a wide range of materials, such as asphalt, cement, carbon sources and carbon by-products, but its usage is scant in the context of polymers. While the use of the plastic cartridge case in rubber has not been investigated previously, there is already precedent for incorporating scrap computer plastics, such as monitors, keyboards and other hardware, into nitrile rubber blends.
In this study, researchers used scrap cartridges and spent powder to create a self-healing polymer product. Crushed cartridge cases formed a thermoplastic phase in carboxylated nitrile rubber (XNBR), while toner powder was added as a reinforcement filler. A two-step methodology was used to optimize the loading ratio and measure reinforcement efficacy.
Firstly, the chemical composition of the cartridge plastic was investigated. Then, the effect of the thermoplastic phase on the cure characteristics, dynamic properties, tensile strength and hardness of the rubber blends was analysed.
Secondly, the use of the toner-powder filler was measured using surface morphology techniques. Lastly, the researchers used chemical degradation and physical repair tests to measure the self-healing properties of the samples.
In this way, it was possible to optimise the formulation of a filled rubber blend to achieve both good mechanical properties and self-healing properties, which can often act against each other.
The optimal blend showed improved mechanical performance and 100% self-healing efficiency. Black toner powder was confirmed as a reinforcement filler, increasing tensile strength by 50% at 20 phr without affecting self-healing properties.
Overall, this study shows promise for the incorporation of whole waste products that are difficult to recycle, such as printer toner cartridges, into sustainable materials. Additionally, by leveraging the self-healing properties of some polymers, the end material aims to satisfy the recycling, reuse and repairability requirements of sustainable products.
Citation: Utrera-Barrios, S., Martínez, M. F., Mas-Giner, I., Verdejo, R., López-Manchado, M. A., & Santana, M. H. (2023). New recyclable and self-healing elastomer composites using waste from toner cartridges. Composites Science and Technology, 244, 110292.
Conclusion
This month, Prescott Instruments has featured [number] recent scientific research papers concerning the world of rubber. January’s research topics include techniques for the reclamation of steel from tyres, the mapping of mildew on rubber trees using drone photography, the use of silicone rubbers for 5G antenna substrates and the use of waste printer toner and cartridges in self-healing rubber blends.
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:
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October 2023 Featured Research
November 2023 Featured Research