Featured Rubber Research – February 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 February, the featured papers include:
Eco-Friendly Degradation of Natural Rubber Powder Waste Using Some Microorganisms with Focus on Antioxidant and Antibacterial Activities of Biodegraded Rubber: An investigation into the use of common bacteria and fungi to break down waste natural rubber.
Neural Network Calculator of Rubber Characteristics with Improved Properties: A proof-of-concept study into the use of Artificial Neural Networks to optimise rubber formulation.
Effect of Waste Zinc Oxide Particles on Properties of Natural Rubber Vulcanizates: The incorporation of waste zinc oxide from the ceramics industry into rubber blends.
Raw and Pre-Treated Styrene Butadiene Rubber (SBR) Dust as a Partial Replacement for Natural Sand in Mortars: The incorporation of waste rubber powder in mortar for use in passive buildings.
Read the full features below, complete with citations and links to read the original research online.
Featured Research Papers
Eco-Friendly Degradation of Natural Rubber Powder Waste Using Some Microorganisms with Focus on Antioxidant and Antibacterial Activities of Biodegraded Rubber
Common bacteria and fungi, such as E.coli, have been shown to successfully degrade waste natural rubber. A team of researchers in Egypt, Saudi Arabia and the UAE have collaborated on a study outlining the eco-friendly method as an alternative to current rubber disposal methods.
In their study, the researchers collected wastewater from a range of industrial and agricultural sources, to create a diverse microbial array. From a total of 51 and 69 bacterial and fungal isolates, E. coli AY1 and A. oryzae were shown to be the most promising bacterium after an initial screening process.
Using either E. coli AY1, A. oryzae, or a combination of both, the microbial cultures were introduced to sources of powdered natural rubber in a sterile medium and incubated for between 30 and 210 days. Afterwards, the degradation was measured as the proportionate decrease in weight of the remaining natural rubber content. The best result showed a decrease of 69% after seven months of incubation.
The degradation occurs as isoprene, the base polymer of natural rubber, acts as carbon and energy source to feed the bacteria and fungi. This colonisation can also be used to change the chemical structure of rubber, as the enzymatic activity of microorganisms can modify the rubber molecules via oxidation processes.
The benefits of this method include gentle reaction conditions, minimum chemical and energy consumption and low discharge of secondary pollutants. Additionally, the remaining biodegraded natural rubber was shown to have antioxidant and antibacterial activity, with potential future usage in animal feed or pharmaceuticals.
Citation: EL-Wafai NA, Farrag AMI, Abdel-Basit HM, Hegazy MI, Al-Goul ST, Ashkan MF, Al-Quwaie DA, Alqahtani FS, Amin SA, Ismail MN, et al. Eco-Friendly Degradation of Natural Rubber Powder Waste Using Some Microorganisms with Focus on Antioxidant and Antibacterial Activities of Biodegraded Rubber. Processes. 2023; 11(8):2350.
Neural Network Calculator of Rubber Characteristics with Improved Properties
Can Artificial Neural Networks (ANNs) be used to optimise the properties of rubber compounds? Researchers have used a Neural Network calculator to match the material characteristics to an input variable based on a limited set of experimental data.
Neural Networks are machine learning models based on the structure of neurons within the brain. Consisting of an input layer, hidden layer and output layer, the model is usually trained on an extensive dataset to generate correct outputs with an ever-increasing level of accuracy. Current applications include predictive modelling, adaptive control and AI problem-solving.
In this study, the researchers aimed to use a Neural Network calculator to predict the material properties of a rubber compound based on the proportion of a single ingredient – basalt fibre, a filler used for its anti-vibration properties in rubber railway pads.
Six rubber blends with varying amounts of basalt fibre were physically and dynamically tested and the resultant dataset was fed into the Neural Network calculator. Using interpolation methods, the ANN was able to predict the outcome of twelve individual characteristics, including tensile strength, hardness, the effects of ageing, modulus of elasticity and tan delta.
Likewise, the calculator can also be used in reverse. With an input of desired values for tensile strength, hardness and tan delta, the calculator determined the level of basalt filler required.
Unlike other examples of neural networks trained on extensive datasets, this study proved the feasibility of using ANN to interpolate experimental results in the case of a small number of examples, opening the door for their future use in rubber formulation and compounding.
Citation: Abrukov VS, Konnova KA, Egorov EN, Anufrieva DA, Koltsov NI. Neural Network Calculator of Rubber Characteristics with Improved Properties. Ann Adv Chem. 2023; 7: 064-067.
Effect of Waste Zinc Oxide Particles on Properties of Natural Rubber Vulcanizates
Waste zinc oxide from the ceramics industry could be an attractive substitute for commercially available zinc oxide. A team of researchers in Thailand demonstrated how the ceramic waste product can be incorporated into natural rubber to act as an activator for sulphur vulcanisation.
The study involved comparing the synthesis, properties and compounding of commercial zinc oxide with that obtained from the ceramic glazing industry. The waste zinc oxide was divided into two and either left untreated or calcined at 800°C for six hours.
Chemical analysis showed that the waste zinc oxide already contained sulphur, while the calcined sample showed a 75% reduction in the sulphur content. As the effect of the sulphur compounds was unknown, it was necessary to test both a simple and adjusted blend, where the overall sulphur content of the individual natural rubber blends had been balanced.
However, this increase in sulphur content did not aid vulcanisation as there was no noticeable increase in crosslink density. Rather, the amount of zinc oxide was the major contributory factor. Furthermore, the different types of zinc did not greatly influence either the thermal stability or viscoelastic properties of the rubber blends.
Across all tests, the calcined zinc oxide stood out as the best alternative to commercial zinc oxide. The near-matching crosslink density, superior tensile and tear strength, hardness and storage modulus demonstrated the value of reducing the baseline sulphur content before compounding.
Proved to be an effective activator, zinc oxide from waste ceramics could also be combined with silica or carbon black reinforcement to be made suitable for commercial rubber products.
Citation: Tumnantong, D., Prasassarakich, P., & Poompradub, S. (2023). Effect of waste zinc oxide particles on properties of natural rubber vulcanizates. Express Polymer Letters, 17(3), 290-299.
Raw and Pre-Treated Styrene Butadiene Rubber (SBR) Dust as a Partial Replacement for Natural Sand in Mortars
The design of nearly energy-zero buildings (NZEBs) has been updated to include vibrational comfort as a key criterion necessary to achieve the environmental goals of a circular economy. More commonly known as passive buildings, NZEBs have a hermetic outer layer that has high heat resistance and low demand for useable energy.
They are characterised by their adherence to thermal comfort, air quality, acoustic comfort and visual comfort guidelines. To address the new vibration comfort requirement, a recent study has investigated the use of recycled rubber powder in place of sand in the construction of insulating flooring.
While rubber granulate is already used extensively in concrete, there is little use of rubber powder, a waste product of rubber recycling. The positive effects of rubber granulate in concrete are well understood but the significantly smaller particle size of rubber powder necessitates further investigation.
The main results of the study demonstrated that the brittleness of the cement mortar decreased with the addition of SBR powder, as the ratio of the tensile strength to compressive strength increased. However, without thermal treatment, the SBR powder overall decreased the strength of the mortar.
After thermal treatment at 275°C, the proportion of rubber could be increased to 60% and showed a positive effect on the mechanical properties of the mortar. The research also investigated the use of epoxy glue to improve the binding and strength of the mortar.
Overall, the research confirmed the limited applicability of SBR dust in concrete structural elements due to the decrease in strength. But, after thermal treatment, the researchers concluded that SBR powder could be incorporated up to a limit of 20%. At this level, the mortars could be used in non-structural elements, exhibiting decreased specific weight and enhanced thermal insulation.
Citation: Pikoń, K., Poranek, N., Marczak, M., Łaźniewska-Piekarczyk, B., & Ścierski, W. (2024). Raw and Pre-Treated Styrene Butadiene Rubber (SBR) Dust as a Partial Replacement for Natural Sand in Mortars. Materials, 17(2), 441.
Conclusion
This month, Prescott Instruments has featured four recent scientific research papers concerning the world of rubber. February’s research topics include the bacterial degradation of rubber, advanced neural network calculators, the recycling of ceramics zinc oxide, and the use of rubber powder in passive building design.
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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