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Reactive blending, reinforcement and curing of NR/BR/EPDM compounds for tyre sidewall applications
von Kannika Sahakaro, Pattani Campus, Nityananda Naskar, Jadavpur, Calcutta, Dr. Rabin N. Datta †, Teijin Aramid B. V., Prof. Jacques W. M. Noordermeer
Tyre sidewall compounds are generally formulated using NR and BR to achieve
the required dynamical properties. The most widely used antiozonant, N-(1,3-
dimethylbutyl)-N’-phenyl-p-phenylenediamine (6PPD), is a staining, toxic and environmentally unfriendly substance.
Incorporation of EPDM into NR/BR blends improves ozone resistance, but leads to poor properties because of differences in filler affinity and cure incompatibility of the rubber components. In this work, the cure incompatibility is overcome by utilising a reactive processing technique, making use of the most commonly used accelerator CBS and sulphur.
The entire amount of curatives is first added into the EPDM. After a thermal pretreatment step related to the scorch time of the EPDM, the modified EPDM is mixed with pre-blended NR/BR. The reactive blends show significant improvements of physical properties in comparison with those of conventional straight mixes, due to improvement of the crosslink and carbon black distributions, confirmed by AFM and TEM images.
The physical properties of the reactive mixed NR/BR/EPDM blends are equivalent or even superior to regular filled NR/ BR blends for tyre sidewall applications. The blend with 30 phr of EPDM has excellent ozone resistance while 6PPD can be totally omitted from the formulation.