Featured Rubber Research – April 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 April, the featured papers include:
Steady-State Temperature Field and Rolling Resistance Characteristics of Low-Speed and Low-Load Capacity Non-Pneumatic Tires: Modelling the thermo-mechanical properties of non-pneumatic tyres with complex patterns using direct experimental data.
Application of the Time–Temperature Superposition Principle to Predict Long-Term Behaviour of an Adhesive for Use in Shipbuilding: A study into the feasibility of adhesives in shipbuilding using Time-Temperature Superposition to model the long-term behaviour of dynamic and static loads.
Eco-friendly biocomposite foam from natural rubber latex and rice starch for sustainable packaging applications: A novel rubber-starch biocomposite foam is studied for use in extending the shelf-life of packaged bananas.
A new modelling approach for predicting process evolution of cork-rubber composites slabs vulcanization: Modelling the cure kinetics of a cork-rubber slab using rheological and thermodynamic experimental data.
Read the full features below, complete with citations and links to read the original research online.
Featured Research Papers
Steady-State Temperature Field and Rolling Resistance Characteristics of Low-Speed and Low-Load Capacity Non-Pneumatic Tires
The rolling resistance of a tyre, a measure of how much energy is lost during motion, is a key indicator of the overall fuel economy of any type of vehicle.
As a tyre rotates it distorts under pressure. Due to the viscoelastic nature of rubber, not all energy is conserved. As it deforms, some energy is lost through internal friction mechanisms that manifest as an increase in temperature.
By decreasing rolling resistance, the fuel economy of a vehicle increases, leading to reduced emissions. For electric vehicles, whose total weight is significantly greater, a decrease in rolling resistance is correlated with an increase in battery range.
While a huge amount of research exists on the rolling resistance of pneumatic tyres, there is much less knowledge on the performance of non-pneumatic tyres. Typically, these tyres are characterised by complex patterns that have a discontinuous structure in the circumferential direction.
In this study, researchers experimentally measured the steady-state temperature response of a non-pneumatic tyre using a suite of thermo-mechanical test methods. Then, they compared their results to a simulated model to assess the goodness-of-fit of their understanding.
Using a test rig to simulate various loads and velocities, the temperature of the outer ring, spokes and inner ring were recorded throughout the experiment. The tensile strength and viscoelastic properties of the rubber and PU were also measured. Then, these results were compared to the solution of a 3D finite element (FE) analysis model.
Overall, the results verified the solution to a good degree of accuracy. The highest temperature recorded was in the centre of the tread, with a secondary hotspot at the join of the spokes and the outer ring. The rolling resistance increased considerably with load, and less so with the velocity of the tyre. The spokes were shown to have the greatest impact on the overall rolling resistance.
This study is important for further research on non-pneumatic tyres, as it does not assume that the steady-state temperature of each cross-section of the tyre is the same. The researchers also noted that their proposed solution could also be applied to any object composed of viscoelastic materials, expanding the use of their solution outside of the automotive sector.
Citation: Liu, S., Liu, W., Zhou, S., Li, X., & Zhang, Q. (2023). Steady-State Temperature Field and Rolling Resistance Characteristics of Low-Speed and Low-Load Capacity Non-Pneumatic Tires. Lubricants, 11(9), 402.
Application of the Time–Temperature Superposition Principle to Predict Long-Term Behaviour of an Adhesive for Use in Shipbuilding
A new study has outlined the feasibility of adhesives in shipbuilding, as an alternative to traditional welding or riveting methods. While welding is widespread and considered the default bonding method, it uses high amounts of energy and can add up to 5% to the total weight of the ship.
As an alternative, adhesives have lower weight, improved corrosion resistance and can be used to join multiple materials. Sustainable material choices continue to play an important role in shipbuilding, especially in new technological developments for low-energy ships, Arctic ships and offshore wind power.
However, to be deemed suitable, an adhesive must be proven to hold for 25 years, the typical minimum service life of a ship. To do this, Time-Temperature Superposition (TTS) can be used to construct a master curve that can be used to assess the whole life cycle of the adhesive.
Experimentally, this involves using a Dynamic Mechanical Analyser (DMA) to perform a series of short tests at different temperatures and frequencies. This study also utilised both dynamic and static loading conditions to better reflect the types of stress experienced by naval steel.
Using prepared samples of methyl methacrylate (MMA) structural adhesive applied to a PTFE sheet, the specimens underwent a temperature sweep, frequency sweep and strain sweep on a DMA using a double cantilever fixing. Finally, a creep-temperature step test was performed.
By stitching the data together to form a master curve, predictions of the adhesive performance at 10,000Hz and after 25 years can be deduced.
Across this large range, two of the most important results are at low frequencies and long timescales. The TTS curve showed a decrease of 70-80% in modulus between 10,000 Hz and 0.01 Hz. Within this range, at less than 20Hz, resonant and dynamic effects are more apparent. Under a fixed load, the creep master curve showed a reduction in the flexural modulus of 97% over 3 months.
As all types of loads can occur on a ship, whether it be compressive, flexural, tensile or peeling, it is important to comprehensively characterise the long-term performance of adhesives in a number of environmental settings. With further investigation and optimisation, adhesives may begin to be used more widely in shipbuilding, as a lighter and lower-energy alternative to welding and riveting.
Citation: Souto-Silvar, D. A., Álvarez-García, A., Díaz-Díaz, A., Rodríguez-Dopico, F. J., & López-Beceiro, J. (2024). Application of the time–temperature superposition principle to predict long-term behaviour of an adhesive for use in shipbuilding. Arabian Journal for Science and Engineering, 49(2), 2345-2355.
Eco-Friendly Biocomposite Foam from Natural Rubber Latex and Rice Starch for Sustainable Packaging Applications
Packaging is a ubiquitous part of modern life, from bottles, wrappers, and bags to protective pellets and foams. At present, a large amount of packaging is manufactured from non-biodegradable synthetic polymers derived from petroleum.
Unfortunately, much of this everyday packaging ends up in landfills, contributing to a growing waste management problem with serious environmental consequences. Therefore, there has been growing interest in using biopolymers in packaging as an alternative to petroleum-based polymers. As a group, biopolymers are derived from natural origins and have attracted attention for their reusability, eco-friendliness, accessibility and sustainability.
Extracted from the Hevea Brasiliensis tree as latex, natural rubber is the most widely used natural elastomer worldwide. Inexpensive, non-toxic and renewable, it is often used in products that come into contact with food and drink. However, the biodegradability of natural rubber is inherently poor due to its high molecular weight and the additional crosslinking created during the vulcanisation process. To combat this, previous studies have demonstrated that by incorporating various forms of starch into rubber, the biodegradability prospects are improved.
In this recent study, researchers evaluated the feasibility of bio-composite foam sheets manufactured from natural rubber and rice starch. Once prepared, the bio-composite foam was assessed on its morphological, physical, mechanical, thermal and biodegradation properties. Lastly, the foam was tested as a solution for packaging fresh bananas for transportation. Placed between the foam sheets for 12 days at 25 C ambient temperature, the freshness of the bananas was investigated in comparison to a control group.
Overall, the foam demonstrated good physical properties as a result of the natural rubber content and a significant improvement in biodegradability due to the addition of rice starch. It was also shown that the foam had reduced the accumulation of ethylene, resulting in a delay in the ripening of the bananas.
Therefore, the researchers concluded that their bio-composite foam could be used as a green packaging alternative. In particular, they highlighted its use in produce transportation due to its ability to extend shelf life, which would have the secondary benefit of also reducing food waste.
Citation: Chueangchayaphan, W., Nooun, P., Ummarat, N., & Chueangchayaphan, N. (2024). Eco-friendly biocomposite foam from natural rubber latex and rice starch for sustainable packaging applications. Express Polymer Letters, 18(1), 27-40.
A New Modelling Approach for Predicting Process Evolution of Cork-Rubber Composites Slabs Vulcanization
Cork is a natural material harvested from tree bark, primarily in Portugal, Spain and Northern Africa. Impermeable, elastic and buoyant, cork is prized for its unique properties and has been used by humans for over five thousand years.
Synonymous with wine and champagne bottle stoppers, cork can also be mixed into other materials to form a composite, combining attributes to optimise performance. Cork-rubber composites are made by incorporating cork granules into rubber during the mixing stage.
Once fully incorporated and milled, the composite slabs are vulcanised in a compression moulding press. As a finished product, these pads are used extensively in vibration or acoustic isolation applications, owing to the bubble-form structure of the cork granules.
In a recent study, researchers investigated the vulcanisation process of cork-rubber slabs to evaluate several predictive cure models. During vulcanisation, crosslinks between polymeric chains are created, accompanied by a release of energy, transforming a material’s properties.
In practice, controlling these cure reactions to achieve specific characteristics can be challenging. Variations in geometry, compound characteristics and manufacturing processes can greatly affect the outcome of the end product.
To assess the numerical models, samples of a cork-rubber composite were tested on a Moving Die Rheometer (MDR) to study the cure characteristics at three distinct test temperatures. Next, to evaluate the temperature profile in the centre during compression moulding, a thermocouple was inserted in the middle of the sample under compression.
Using the cure reaction and heat transfer experimental data, the researchers were able to construct a kinetic cure model that considered both sample thickness and curing temperature. Not surprisingly, their results showed that the thicker the sample and higher the test temperature, the greater the difference in degree of cure between the middle and edge of the composite slab.
The model aims to achieve the optimum cure conditions in the centre of the slab without causing degradation at the outer surfaces due to reversion. With errors of less than 10%, the model was proven to simulate the evolution of curing reactions throughout the cork-rubber slab at various locations under different processing conditions, including post-cure behaviour.
Citation: Lopes, H., Silva, S. P., Carvalho, J. P., & Machado, J. (2022). A new modelling approach for predicting process evolution of cork-rubber composites slabs vulcanization. Scientific Reports, 12(1), 8002.
Conclusion
This month, Prescott Instruments has featured [number] recent scientific research papers concerning the world of rubber. April’s research topics include rolling resistance, adhesives, biocomposite foams and cure kinetic modelling.
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:
November 2023 Featured Research
December 2023 Featured Research
2023 Featured Research Overview
January 2024 Featured Research