Finding the Right Compound
By TA News Bureau:
As rubber and tyre technologists race to discover the perfect rubber compound to make fuel-saving green tyre formulations, Dr Siti Salina Sarkawi is quietly working in her lab to find the most eco-friendly substance to achieve this goal. She is presently the programme head of ‘Silica Dispersion Technology for Green Tyres’ under Technology & Engineering Division of the Malaysian Rubber Board. Her current projects are Application of Ekoprena for Environmentally Friendly Retreaded Tyres and Passenger Car Tyres. In an interview to Tyre Asia, the research scientist whose expertise includes silica technology, green tyre, epoxidized natural rubber, deproteinized natural rubber and nano-fillers, she speaks of her work and the current research trends in this area. She is also involved in various aspects of rubber technology, particularly in areas of mixing and compounding, compound design, rubber analysis and processing technologies. Her R&D projects include silica reinforced deproteinized natural rubber, graphene nano composite, rubber coated carbon black, kenaf fibre, rice husk as bio-filler, reduction of zinc oxide level, epoxidised palm oil and latex stimulant (Excerpts from the interview)
Please explain your major research findings in the use of compound made from epoxidized natural rubber reinforced with silica in truck tyre tread compound?
Epoxidized natural rubber (ENR) is a modified natural rubber that transforms natural rubber (NR) into polar elastomer which is more compatible with polar fillers such as silica. The epoxidation process increases the polarity of natural rubber, and hence improves the properties of NR to be comparable to synthetic rubber. The commercial grade of ENR is ENR-25 with 25% epoxidation level and ENR-50 with 50% epoxidation level. ENR-25 has been proven to be suitable for tyre application. Our study shows that ENR-silica compound has high chemically bound rubber which indicates enhanced interaction and bonding between filler and rubber matrix. This is particularly important for reinforcement of rubber compound. The reinforcement effect of the silica fillers is further translated in dynamic test where the ENR-25-silica compound exhibits higher tan delta at 0°C and lower tan delta at 60°C as compared to control conventional natural rubber compound, which indicates higher wet grip and lower rolling resistance of the tyres made out of it. Thus, ENR-25 compounded with silica is a unique combination that improves the tread compound properties in terms of wet grip and rolling resistance.
Is such special compound better than what is made from carbon black and butadiene (BE) compound used in tyre truck treads?
We have conducted a series of studies with ENR in tread compound for truck and buses as well as passenger car tyres. Our laboratory data give good indication that the ENR compound is giving better properties than the control compound. We have successfully reported progress in large scale trial of Ekoprena retreads with trucks and buses in collaboration with public transport and logistic providers in Malaysia. The results from the trials show improvements in the mileage and cost per distance travelled compared to the commercial tyre used. In addition, the wet grip of the Ekoprena tyres is excellent and it correlates well with our laboratory data.
Besides this, are there any other rubber compounds that could be used in truck tyre tread to get better wet grip and lower rolling resistance?
To get a balance in the magic triangle of a tyre is quite difficult. Once, one property is improved, then it will reduce the other property. A carefully chosen elastomer used in the compound is important to obtain this balance. Other rubber compounds normally will use blend of natural rubber with synthetic rubber to increase the properties. The advantages of using ENR are it is a renewable resource material and gives positive impact to the environment. ENR negative carbon footprint and its use in tyre compound provide a path to greener tyres.
Can you elaborate on your observation that silica-filled ENR-25 compound in tread application is the best for green tyre application?
Our research has shown that tread compound from silica-filled ENR-25 gives higher tan delta at 0°C and lower tan delta at 60°C which indicates better performance in the wet grip for safety of the users and improvement in the rolling resistance of the resultant tyre. This makes it a good candidate for the green tyre application. We have sent the Ekoprena tyres for performance testings at IDIADA testing facilities in Spain for rolling resistance, wet grip and rolling noise. The test results are quite encouraging and it correlates well with our laboratory data. Ekoprena retreaded truck tyre gives A rating in wet grip, D class for fuel efficiency and 72 dB for rolling noise. In addition, for Ekoprena PCR tyre, the performance is super as the tyre has A rating for wet grip, E class for fuel efficiency and 70 dB for rolling noise. In addition, as mentioned before, Ekoprena has negative carbon footprint and this can reduce the carbon footprint of the resultant tyres made from Ekoprena.
Is such formulation of ENR-25 compound suitable for application in speciality tyres for electric vehicles that call for low weight, low rolling resistance and better wet grip?
Based on the results of our study, we are very positive that it is the future direction for the ENR-25 tyre compound to be used for specialty tyres in energy efficient vehicles (EEV) application such as electric vehicles. Our study also has shown that nano-filler such as graphene can be used as hybrid filler with nano-silica in ENR compound. Graphene has better interaction in ENR matrix and improves the properties of the compound. This is particularly useful for intelligent tyres that need to be incorporated with sensors etc.