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BOOST TO CURE EFFICIENCY

By TA News Bureau:

Dr Ali Ansarifar

Top elastomer scientist Dr Ali Ansarifar’s research interests include elastomer-to-elastomer adhesion failure and adhesion enhancement, reinforcement of rubbers with nanofillers, and development of novel sulphur cure systems for rubber compounds, among others. His work has won international recognition, one of which was an award for the best research paper by the Malaysian Rubber Board in 2014. He is on the editorial board of Journal of Rubber Chemistry and Technology, US and Journal of Adhesion and Adhesives. In an interview to Tyre Asia, Dr Ansarifar, who is teaching in the Department of Materials at Loughborough University, speaks about the relevance of his research for the tyre industry

Can you please tell us the relevance of your research on kaolin to the tyre industry?

Solid carbon black and silica/silane systems are used extensively to reinforce the mechanical and dynamic properties of tyre compounds. However, petroleum-based carbon blacks (CB) are toxic and synthetic silica and silane systems are often too expensive. Furthermore, silanisation of silica particles with liquid silane during mixing can be problematic. Mineral fillers such as kaolin offer a viable alternative to carbon black and silica. Kaolin is abundant in nature and is much less harmful to humans and animals than carbon black and silica are. Recent work has shown promising potential for kaolin as reinforcing filler in tyre compounds. Using kaolin in tyre compounds in place of more traditional solid fillers such as CB and silica offers major cost benefits as well as significant improvement in health, safety and the environment.

Can you please explain the curing process of natural rubber when kaolin is used as a composite material?

Selecting suitable sulphur cure systems (sulphur, accelerators and activators) for natural rubber (NR) compounds to achieve optimum properties is very challenging and dictated by many factors. The task is even much harder when the filler system is switched to kaolin which is fundamentally different in composition and physical properties. Thus, before kaolin is used in NR, the chemical curatives in the sulphur cure system must be measured accurately to ensure optimum effect on the final properties of the rubber vulcanisate. A new study uses experimental results from cure tests to provide a highly efficient method for selecting sulphur cure systems for NR.
In this study, NR containing different amounts of sulphur is cured in a cure meter to produce a trace  from which Dtorque, which is the difference between the maximum and minimum torque values on the cure trace, is measured. The loading of accelerator in the rubber with sulphur is increased progressively until Dtorque reaches its optimum value . To improve the efficiency of the accelerator, zinc oxide (activator) is added to the rubber with sulphur and optimum loading of the accelerator, and then the loading of zinc oxide is raised progressively until an optimum value for Dtorque is determined . Therefore, the cure system for the rubber consists of the optimum loading of the accelerator and activator at a given loading of sulphur. This method provides a highly efficient cure system for the rubber by eliminating secondary accelerators and activators.

Curing with NR

You have tried your experiment with curing with various kinds of rubber including natural rubber, polybutadiene etc. Have you found anything special while curing with natural rubber?

Yes. I found that the requirement for the chemical curatives depends on the loading of kaolin and composition of the rubber. For example, when the loading of kaolin in NR is raised from 0 to 140 parts per hundred rubber (phr) by weight, there is a significant increase in the crosslink density as indicated by a rise in torque. Other benefits include reduction in scorch and optimum cure times as well as a major increase in the rate of cure which helps to shorten the cure cycle of the rubber compound.
It is encouraging that kaolin is so beneficial to the curing process of the rubber. However, this is not the case for polybutadiene (BR) and ethylene-propylene-diene (EPDM) rubbers. The amount of the chemical curatives required for the optimum cure of BR and EPDM rubbers are very different to that of NR. This indicates that the requirement for curatives to fully cure the rubber depends on the rubber composition.

What are the implications of your research for the tyre industry?

It has long been acknowledged that excessive use of chemical curatives in industrial rubber articles such as tyres is harmful to health, safety and the environment. Use of these chemicals is restricted by the new European chemicals policy, Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) and various legislations for environment and safety.
The tyre industry faces major challenges to develop more efficient and refined cure systems and curing processes for tyre compounds. My research has shown that the use of chemical curatives in sulphur cure system can be measured more accurately than before and as a result, there can be a substantial reduction in their use in tyre compounds without compromising the properties of the final product.
Furthermore, the exact amount of the chemical curatives for sulphur vulcanisation depends, to a large extent, on the rubber composition. Therefore, traditional conventional, EV and semi-EV cure systems may no longer be the best choice for curing tyre compounds. There is significant scope to improve cure efficiency and reduce cost. My research is addressing some of these important issues.

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