Featured Rubber Research – December 2023
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 December, the featured papers include:
Upcycling Green Carbon Black as a Reinforcing Agent for Styrene–Butadiene Rubber Materials: This study investigates the use of recycled carbon black as a filler and the role of additional crosslinkers (POSS) in place of traditional virgin carbon black.
Stabilization of Lateritic Soil with Rubber Wood Ash and Lime for Road Construction: Researchers investigated the use of rubber wood ash as a pozzolanic material to improve lateritic soil conditions for use in road construction in Nigeria.
Investigation of the Potential of Using Liquid Rubbers in Rubber Industry: An investigation into the use of liquid rubber as a replacement for process oils in motorcycle tyre compounds.
Quantification of Sulphur Distribution on Rubber Surfaces by Means of μ-X-Ray Fluorescence Analysis: A novel method to use µ-Xray fluorescence techniques to qualitatively and quantitatively measure the concentration and dispersion of sulphur in rubber compounds.
Investigations of Dynamic Mechanical Performance of Rubber Concrete under Freeze-Thaw Cycle Damage: A study into the thermomechanical effects of freeze-thaw conditions on the structural integrity of rubber concrete.
Read the full features below, complete with citations and links to read the original research online.
Featured Research Papers
Upcycling Green Carbon Black as a Reinforcing Agent for Styrene–Butadiene Rubber Materials
Recycled carbon black, or so-called green carbon back, is an environmentally friendly alternative to virgin carbon black. Produced from waste passenger tyres via pyrolysis, rather than petroleum product, it has a lower carbon footprint, ample input supply and is more economical to produce.
Upon properly refining or modifying recycled carbon black, it could meet the requirements of technical products in high value applications. This is because there are differences in the filler-rubber and filler-filler interactions within a rubber mix. These interactions determine the rigidity of the rubber material and subsequently the mechanical properties.
In this study, recycled carbon black was produced from passenger tyres that underwent anaerobic digestion and pyrolysis at relatively low temperature, followed by a controlled pulverization process. When compared to a reference sample using virgin carbon black, the recycled carbon black sample was coarser and less uniform, which could cause poorer dispersibility in the polymer that could deteriorate the mechanical properties.
Upon investigation with FTIR analysis, the researchers hypothesised that a reduction in key functional groups in recycled carbon black caused a reduced interaction with the rubber matrix and therefore lower mechanical properties.
However, with the addition of an additional crosslinker (POSS), the overall properties (mechanical properties, thermal stability, and anti-aging property) were appreciably improved by increasing the crosslinking density of the entire polymer network.
The study showed promising results overall, demonstrating that a small amount additional crosslinker had a positive influence when using environmentally friendly and relatively inexpensive recycled carbon black as a replacement for traditional carbon black filler.
Citation: So-Hyeon Lee, Jun-Hyun Kim and Hyun-Ho Park. (2023) Upcycling green carbon black as a reinforcing agent for styrene-butadiene rubber materials. RSC Advances. RSC Adv., 2022,12, 30480-30486
Stabilization of Lateritic Soil with Rubber Wood Ash and Lime for Road Construction
In a typical rubber plantation, the productive life of a rubber tree is 15 to 20 years. But what happens once the latex dries up? Rubber wood is currently used for wood, wood products and firewood. As a fuel, rubber wood generates large amounts of ash as a waste product. A recent study has shown that this ash can be incorporated into lateritic soil to improve its properties.
Lateritic soil is prolific across tropical regions but can become unstable under load in the presence of moisture. Once improved, lateritic soil can be used locally as a construction material for roads, with the added benefit of using local, inexpensive pozzolanic waste materials to improve its functional properties. Most pozzolanic materials are created from the combustion of industrial waste or other waste materials, including husks, shells, bones, leaves or wood.
A large amount of rubber wood ash is produced in Nigeria, which is also one of the biggest producers of natural rubber in Africa. In this study, researchers mixed lateritic soil with rubber wood ash and a small amount of lime to study the changes and stability of the mixed soil.
Specific tests for soil quality and performance (natural moisture content, particle size distribution, specific gravity, Atterberg limit tests, proctor compaction test, California bearing ratio test and loss of ignition tests) all showed significant improvements with the addition of rubber wood ash and lime.
This study is an example of a regional need for good-quality sustainable materials for the provision of durable road networks, particularly in areas that lack naturally suitable materials. By using waste rubber wood ash to positively influence local soil quality, this adds another layer of circularity to the natural rubber economy that could be replicated in other tropical regions.
Citation: KAYODE-OJO, N; OSEMWENGIE, F. (2023). Stabilization of Lateritic Soil with Rubber Wood Ash and Lime for Road Construction. J. Appl. Sci. Environ. Manage. 27 (7) 151-1556
Investigation of the Potential of Using Liquid Rubbers in Rubber Industry
In rubber formulation, process oils are used to lower the hardness of a rubber compound, reducing the friction and permitting mixing without overheating. They are often used as fillers or cheapeners but can also negatively affect material properties.
For high-specification applications, many rubber technologists are turning to liquid rubber to use instead of process oils. This is not only because of the potential positive effect on material properties, but also the potential to deposit fillers like carbon black inside liquid rubbers to improve dispersion.
As a group, liquid rubbers can be divided into three groups: natural, styrene butadiene (SB) and butadiene liquid rubbers. Existing studies already outline the improvements to dispersion, abrasion resistance and low temperature properties in using liquid rubbers in racing tyres.
This study, four different varieties of liquid rubber, each with a different viscosity, were blended into a typical motorcycle tyre rubber to compare against a reference sample mixed with a process oil. The five samples were mixed, cured and then tested for their rheological and mechanical properties.
Firstly, using a Mooney Viscometer, the results showed that the introduction of liquid rubbers reduced the viscosity of the blends, resulting in easier and lower-energy processing conditions. The results from the Moving Die Rheometer demonstrated that all the liquid rubber variations decreased the optimal cure time, further reducing energy expenditure and increasing productivity.
Overall, the liquid rubber tended to decrease the hardness compared to the reference blend, whilst the change in tensile strength and elongation was dependent on the variety of liquid rubber used.
The study proved the appropriate amount of liquid rubber to substitute for process oils and demonstrated their effectiveness at improving the basic rheological and mechanical properties of the mixtures, which could improve their future popularity in rubber formulation.
Citation: Demir, E. , Altundal, G. , Gerengi, H. and Yüksel, C. (2023) Investigation of the Potential of Using Liquid Rubbers in Rubber Industry. Journal of Materials Science and Chemical Engineering, 11, 21-30.
Quantification of Sulphur Distribution on Rubber Surfaces by Means of μ-X-Ray Fluorescence Analysis
One of the main aims of rubber mixing is the homogenous dispersion of sulphur within a rubber blend, ensuring uniform crosslinking throughout the compound.
A new method of µ-Xray fluorescence has been proposed to analytically evaluate the elemental surface distribution of a rubber sample. With a lower resolution than an electron beam, an X-ray beam can scan a larger surface area to generate a statistically relevant data set.
The working principle is that under exposure to X-rays, electrons are ejected from the surface of the sample. As an electron fills the vacant spot, energy is released in the form of fluorescent radiation. Depending on the element, the energy has specific energy signature. With this method, the sulphur signature of a rubber sample can easily be identified by a colour marker, amongst other elements of interest.
For tyres and blends, the sulphur content and dispersion can be visualised exceptionally well. Another promising avenue is the visualisation of sulphur migration in rubber blends containing ground rubber crumb.
While visual assessments are useful, further calibration steps are needed to make a quantitative assessment of the amount of sulphur present in a sample. An alternative method for measuring the amount of sulphur present involves the complete combustion of a rubber sample in a furnace flushed with oxygen.
Compared to bulk analysis, X-ray fluorescence has the advantage of being non-destructive with the capability to detect concentrations of multiple elements. This technique can be used to display the sulphur homogeneity and distribution for large areas of several centimetres squared, revealing concentration differences and non-uniformity.
By evaluating larger areas of rubber, the results become more statistically reliable, allowing conclusions to be drawn about compounding quality. Other avenues of exploration using X-ray fluorescence include blooming or diffusion of sulphur or other elements. This is of particular interest when different compounds accumulate together, such as in tyres of recycled materials.
Citation: Frosch, V. Herrmann, F. Grunert, A. Blume, Quantification of sulfur distribution on rubber surfaces by means of μ-X-ray fluorescence analysis, Polymer Testing, Volume 128, 2023, 108237,ISSN 0142-9418.
Investigations of Dynamic Mechanical Performance of Rubber Concrete under Freeze-Thaw Cycle Damage
Ground rubber crumb is produced from waste rubber products and can be incorporated into concrete. By adding rubber to concrete, its deformation and absorption energy increases and its curvature ductility increases by nearly 90%. The downside of this is the overall reduction in compressive strength and modulus of elasticity.
Buildings in climates that are within a free-thaw environment, such as the monsoon freeze zone of northeast and northwest China, are particularly vulnerable to damage. This is because the freeze-thaw cycling change the internal structure of the concrete, affecting its mechanical properties. Over time, this effect can compound, leading to rapid deterioration.
In this study, concrete sample with 10% rubber content underwent compression and impact testing in simulated free-thaw conditions, followed by ultrasonic inspection. The freeze-thaw cycles were repeated a set number of times, ranging from 0 to 125.
Compared against standard concrete, the rubber concrete sustained fatigue damage during a freeze-thaw cycle. This damage was shown to increase with frequency. The peak stress and absorbed energy both decreased with the number of cycles, while the ultimate strain increased.
This is because of the differences in the thermal expansion coefficients between the rubber, cement and aggregates. The change in temperature between the three interfaces causes stress differences that reduce the integrity of the test piece.
This research demonstrates that, material scientists and civil engineers ought to be aware of the potential pitfalls of using of rubber concrete in regions that regularly experience free-thaw cycles. As the world experiences changes in weather and climate, these regions will likely evolve and expand, increasing the need for further awareness.
Citation: Zhang, J. (2023). Investigations of Dynamic Mechanical Performance of Rubber Concrete under Freeze-Thaw Cycle Damage. Shock and Vibration, 2023.
Conclusion
This month, Prescott Instruments has featured five recent scientific research papers concerning the world of rubber. December’s research topics include recycled carbon black, the use of waste rubber wood ash, an overview of liquid rubbers, measuring sulphur distribution using x-ray fluorescence and the dynamical mechanical impact of freeze-thaw conditions on rubber concrete.
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