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 September, the featured papers include:
Safety Rubber Vulcanizates Containing Natural Product for Toys Industry: A look into the antimicrobial benefits of using turmeric in rubber blends for use in children’s toys.
The Quantification of Anisotropy in Graphene/Natural Rubber Nanocomposites: Evaluation of the Aspect Ratio, Concentration, and Crosslinking: An analysis of the anisotropic effects of using nanoscale fillers in rubber blends.
NBR/CR-Based High-Damping Rubber Composites Containing Multiscale Structures for Tailoring Sound Insulation: A study into the use of micro and nano fillers in rubber blends for frequency-dependent sound attenuation.
Genomic Insight into Domestication of Rubber Tree: A detailed look into the full genomic profile of the natural rubber tree.
Management of Ground Tire Rubber Waste by Incorporation into Polyurethane-Based Composite Foams: Managing the harmful VOC emissions from ground tyre rubber when compounded and extruded with a base polymer.
Read the full features below, complete with citations and links to read the original research online.
Featured Research Papers
Safety Rubber Vulcanizates Containing Natural Product for Toys Industry
Children’s toys and infant dummies are a well-known breeding ground for bacteria. A combination of frequent exposure to germs, insufficiency or difficulty in cleaning and curious children makes this hard to control, generating further anxiety for parents.
To combat this, materials can be formulated with antimicrobial agents to prevent the growth of bacteria and fungi. Anti-microbial rubbers are compounded with an active agent that repels harmful microbes. This is superior to finishes or layers of anti-microbial protection as it is within the material and cannot be worn away.
Nano curcumin, a substance found in turmeric, naturally possesses antimicrobial properties. By mixing a solution of nano curcumin into a natural rubber compound, researchers hoped to create a functional antimicrobial rubber that was sufficiently safe for use in toys for children.
Researchers tested the curcumin-NR blend for rheological and mechanical properties, cytotoxicity and antimicrobial activity. While the antimicrobial rubber showed good resistance against gram-positive and gram-negative bacteria, it did not affect resistance to fungi. However, the rubber showed promise for use as an antimicrobial material, particularly as curcumin is a natural, plant-derived substance.
Citation: El-Nashar, D. E., Helaly, F. M., Khalaf, A. I., Rozik, N. N., Kandil, H. S., Khater, A. K., … & Soliman, A. (2022). Safety rubber vulcanizates containing natural product for toys industry. Egyptian Journal of Chemistry, 65(13).
The Quantification of Anisotropy in Graphene/Natural Rubber Nanocomposites: Evaluation of the Aspect Ratio, Concentration, and Crosslinking
Graphene, a material made up of a single layer of carbon atoms, has been heralded as one of the most promising materials of the 21st century, due to its exceptional material properties and its breadth of potential applications. When graphene is mixed with a polymer, an elastomeric nanocomposite is made that is reinforced in one direction and soft and elastomeric in another.
This directionality is because two-dimensional nanoparticles, such as graphene or even nanoscaled carbon black, align or orient themselves because of the high pressures shear forces typically found in elastomer processing. To a lesser extent, it is also possible for polymer chains to also orient themselves during the vulcanisation process, leading to observable anisotropic effects. Together, these two phenomena can be manipulated so that materials exhibit specific properties in defined directions. For example, elastomers reinforced with nanoparticles can be hard, strong and conductive in one direction whilst soft, damping and insulating in another.
In a recent study, nanoscaled carbon black (nCB) and graphene (few-layered graphene, FLG) were incorporated into a natural rubber mix. Compared against an unfilled control sample, the reinforced elastomers were processed and tested for anisotropic effects using transmission electron microscopy, dynamic mechanical analysis and volume and dimensional swell testing.
While minor anisotropy was observed even in unfilled natural rubber, the graphene blend exhibited the most pronounced anisotropic effects. With 1 being a perfectly isotropic material, the FLG blend had an anisotropy factor of 2.2 (DMA) and 1.6 (swelling) at a filler content of 3 phr.
While there are instances in which anisotropy is not desirable, working with nanoscale fillers that can be orientated during processing creates opportunities for selectively reinforcing materials in preferential directions.
Citation: Strommer, B., Schulze, D., Schartel, B., & Böhning, M. (2023). The quantification of anisotropy in graphene/natural rubber nanocomposites: Evaluation of the aspect ratio, concentration, and crosslinking. Journal of Applied Polymer Science, 140(16), e53753.
NBR/CR-Based High-Damping Rubber Composites Containing Multiscale Structures for Tailoring Sound Insulation
High-molecular polymers like rubber are frequently used in sound engineering to dissipate noise and vibration. As the sound waves travel through the rubber, the material undergoes an elastic deformation that converts some kinetic energy into thermal energy via internal damping, thus reducing the volume of the sound. As a viscoelastic material, rubber is well suited to any sort of vibration control due to its inherent mix of elastic and viscous characteristics.
These base properties can be enhanced by the addition of various nano/micro fillers, which increase the attenuation or dissipation of sound waves throughout a material via internal reflection. Through compound formulation and choice of fillers, the molecular relaxation and viscous resistance mechanisms can be manipulated for effective noise and vibration control across a range of frequencies.
This study features a mix of nitrile butadiene rubber (NBR), chloroprene rubber (CR) and the following fillers: mica powder, hollow glass beads and montmorillonite. To investigate the effectiveness of sound insulation, a Dynamic Mechanical Analyser (DMA) was used to measure the maximum value of the damping factor and the glass transition temperature.
The researchers demonstrated that by blending nitrile butadiene rubber (NBR) and chloroprene rubber (CR) in various ratios, the damping performance changes as the glass transition temperature range widens. The addition of mica powder, hollow glass beads and montmorillonite provided both positive and negative effects on damping properties when used individually. When used together, it is possible to create favourable damping conditions across a wider range of frequencies.
Citation: Zeng, X., Li, G., Zhu, J., Sain, M., & Jian, R. (2023). NBR/CR‐Based High‐Damping Rubber Composites Containing Multiscale Structures for Tailoring Sound Insulation. Macromolecular Materials and Engineering, 308(2), 2200464.
Genomic Insight into Domestication of Rubber Tree
While there are over 2000 plant species that are capable of producing rubber, it is Hevea Brasiliensis that remains the dominant producer, being responsible for 98% of natural rubber production. The literal and figurative roots can be traced back to Henry Wickham, who was first to cultivate the natural rubber tree in Kew Gardens, before expanding into Southeast Asia, where the majority of natural rubber plantations remain to this day.
The downside of such a successful cultivation programme it is the increased susceptibility to disease. As a genetically uniform population, a single pathogen could harper, or even obliterate global natural rubber production on an unprecedented scale. Rubber is defined as a critical raw material and as such, any disruption to global supply chains could have a devastating knock-on effect on countless downstream industries.
In a recent study, researchers compiled a high-quality genome of a rubber tree with population genetic analysis and genome wide association study (GWAS). Their research provided an insight into which specific genes can be targeted to improve rubber tree yields and for the ongoing domestication of other rubber-producing plants, such as dandelion. Their research has also added to growing body of work on the study of domesticated perennials, such as the rubber tree, which is significantly smaller than that of domesticated annuals.
Citation: Chao, J., Wu, S., Shi, M., Xu, X., Gao, Q., Du, H., … & Tian, W. M. (2023). Genomic insight into domestication of rubber tree. Nature Communications, 14(1), 4651.
Management of Ground Tire Rubber Waste by Incorporation into Polyurethane-Based Composite Foams
It is estimated that over 1 billion tyres are withdrawn from use each year, creating a vast amount of waste with no clear end-of-life pathway. Waste tyres cannot be landfilled due to their high flammability and the emission of harmful chemical compounds. Currently, Ground Tyre Rubber (GTR) is the most successful and widely used method of recycling waste tyres, with popular applications in both concrete and asphalt. However, another promising avenue is the use of GTR as a filler in polymer composites.
To ensure proper compatibility with the polymer the GTR can be modified, either by increasing the specific surface area or by introducing reactive functional groups, to enhance the interfacial interactions with the polymer matrix. One novel method of modification is reactive extrusion, a continuous process that takes place in the absence of solvents alongside the presence of additional modifiers.
But the drawbacks of this process are that this same thermomechanical action causes the emission of harmful volatile organic compounds (VOCs). The VOCs arise because of the evaporation of additives used in the rubber manufacturing process and the decomposition of the macromolecular chains of natural and synthetic rubber.
In this study, researchers introduced zinc borate to the GTR to provide additional friction during the twin-screw extruder process, to enhance the specific surface area and reduce GTR particle size. These improvements are vital to ensure the performance of a polymer, in particular the thermal stability. Next, the GTR/zinc borate compositions were introduced into a foamed polyurethane matrix. Then, the VOC emission profiles of composites were analysed and used to evaluate the interfacial compatibility and its impact on the cellular structure, insulation, mechanical, and thermal performance.
Citation: Hejna, A., Kosmela, P., Olszewski, A., Zedler, Ł., Formela, K., Skórczewska, K., … & Barczewski, M. (2023). Management of ground tire rubber waste by incorporation into polyurethane-based composite foams. Environmental Science and Pollution Research, 1-26.
This month, Prescott Instruments has featured five recent scientific research papers concerning the world of rubber. September’s research topics include naturally antimicrobial rubbers, the anisotropic effects of nanoscale fillers, tailored sound insulation, the genome profile of the rubber tree and the incorporation of waste ground tyres into composite foams.
If you would like to see your research featured, or to suggest any further topics, contact us online.