Chasing the Magic Triangle
By TA News Bureau:
A specialist in materials research and application development in tyre and rubber, Dr Ping Zhang’s area of interest covers a whole range of elastomers. As the Lead Scientist at the Boston-based Cabot Corporation, he has been an innovator in reinforcement rubber and is currently involved in research in improving wear resistance, enhanced traction and reduced rolling resistance/increased vehicle fuel efficiency technology. In this interview to Tyre Asia, he shares his research experience and explains his views on rolling resistance and other related issues to enhance fuel efficiency by developing reinforcement materials that Cabot has been developing
A perennial challenge before tyre engineers is to address the issue of ‘magic triangle’ and obtain optimum efficiency of the tyre. It is said that rolling resistance of truck tyres, for example, accounts for about one-third of the power required to move a heavy-duty truck. Lowering rolling resistance is one of the major objectives of tyre engineers.
Dr Ping Zhang, Lead Scientist at the Boston-based Cabot Corporation, has been working on this issue for several years. Currently he is researching the chemistry and engineering of materials that would enable tyre manufacturers to produce the most perfect product.
“As a reinforcement materials supplier, we at Cabot focus our efforts on exploring different approaches to developing particles and their composite materials that would lead to rubber compounds with reduced hysteresis loss while maintaining other key compound performances,” says Dr Ping.
“The challenge is finding the balance while improving hysteresis. We do so by understanding and addressing the factors that improve rubber performance and those that have a detrimental effect.”
Other than the contribution from the viscoelastic nature of polymers, it is generally believed that a balance of particle/particle and polymer/particle interactions is the origin of hysteresis loss in a rubber compound.
Says he: “We design and develop particles and their composite materials to minimize particle/particle interaction and to improve polymer/particle interaction.”
An author of several research publications in peer-reviewed journals, this material scientist is also trying to address the perennial issue of ‘magic triangle’ while working towards lowering of rolling resistance of tyres.
By ‘magic triangle’ one typically means the balance among treadwear, rolling resistance/heat buildup and wet traction for passenger tyres and among treadwear, rolling resistance/heat buildup and tear strength for truck tyres.
While silica brings special balance in wet grip and rolling resistance, tyre performance requirements go beyond the ‘magic triangle’ such as dry traction and dry handling performance that calls for the use of other reinforcing materials such as carbon black, Dr Ping says.
Through manipulation of the aggregate size distribution and the surface chemistry to reduce particle/particle interaction and to enhance polymer/particle interaction, Cabot has developed the PROPEL® carbon black series that delivers reduced rolling resistance/heat buildup without significantly affecting other performances of tyres.
“We leveraged our unique surface modification capability to change the surface chemistry of carbon black for improved polymer/particle interaction and developed the ECOBLACK TM carbon black series where enhanced polymer/particle interaction is achieved via silane chemistry for significantly reduced hysteresis of rubber compounds,” he elaborates.
He said at Cabot laboratory scientists have explored mixing technologies to significantly improve the dispersion of reinforcing particles in rubber compounds to realize the full reinforcement potential of carbon black and developed Cabot Elastomer Composites (CEC).
“Our unique CEC technology helps customers create rubber compounds with an expanded “magic triangle” to meet performance requirements for different truck tyre lines ranging from off-the-road (OTR) mining/earthmover to highway long haul tyres,” he explains.
Other than tread compounds, other tyre components also contribute to rolling resistance performance of tyres. New materials can be developed for reduced hysteresis for base, carcass and other component applications for reduced rolling resistance without compromising other key tyre performances.
When asked on ways to improve rolling resistance by developing key parameters of tread compounds while at the same time maintain tread wear and durability of truck tyres, Dr Ping spoke about the possibility of easily reducing rolling resistance of truck tyres if one could ignore other performance requirements.
“From a compound standpoint, one could use, for example, low surface area carbon black or low carbon black loading for very low hysteresis. From a design standpoint, for example, the tread depth could be reduced to enhance the rolling resistance of tyres.”
However, that is not the reality – both strategies have impact on tyre tread life, tear strength and traction. He has some suggestions to make in this context.
The balance can be sought by (1) use of more advanced materials under development that seek to balance this performance, and (2) combining material and tyre design strategies.
For example, use of a high-wearing compound that would give longer life, but reducing the amount that is used to give the same tread life but in turn gaining on rolling resistance.
For truck tread applications, both hysteresis loss and stiffness of the tread compound affect the rolling resistance/heat buildup performance of tyres.
The compound design (choice of reinforcing particles, loading, selection of elastomers, use of other ingredients and mixing) should be such that the reduction of hysteresis loss should not be at the expense of the stiffness, abrasion resistance and reinforcement characteristics of the rubber compound, hence without negatively impacting wear and durability of truck tyres.
Commenting on the recent developments in elastomers and reinforcing material that impact rolling resistance, Dr Ping said researchers have made some significant efforts in developing polymers with functionalized groups tailor-made for enhancing interaction with reinforcing particles. A compound designer could take advantage of such polymers, not only to reduce rolling resistance, but also to improve treadwear and enhance traction of tyres.
A variety of approaches have been developed to modify carbon black or silica to enhance the particle interaction with polymers hence reducing rolling resistance of tyres. As these approaches grow, new particle and polymer pairs might bring the desired performance the industry is looking for.
Nanoparticles, such as graphene and nanoclay, are being explored to take advantage of different aspect ratios, with the intent to enable breaking loading versus reinforcement trade-offs. If successful, their use at low loadings can benefit the rolling resistance contributions from tyre compounds, he said.
Liquid mixing technology is also being explored not just to improve the mixing efficiency in the tyre plant, but also to improve the rolling resistance and other performances of tyres.
The first decision in formulating tyre compounds is usually the choice of polymer. For heavy truck tyres, natural rubber has traditionally been the polymer of choice due to its outstanding tear strength. We know that blends of natural rubber with other elastomers, such as butadiene rubber and styrene-butadiene rubber, are also used in some truck tyre lines to enhance the treadwear or improve the traction performance of truck tyres.
“Once the polymer is chosen, the reinforcing particles need to be selected to achieve the desired compound performances, taking into consideration the need to disperse the particles and the need to process the compounds through the tyre plant.”
Ultimately, compounds developed with desirable properties need to be combined with tyre construction and pattern designs to produce tyres to meet consumer’s needs.