A study about the structure of vulcanized natural rubber/styrene butadiene rubber blends and the glass transition behavior

Abstract

A study of the thermal behavior of cured elastomeric blends of natural rubber (NR) and styrene butadiene rubber (SBR) prepared by solution blending in toluene is presented. Binary blends with different compositions of NR/SBR were produced using a conventional cure system based on sulfur and TBBS (n-t-butyl-2- benzothiazole sulfonamide as accelerator. The compounds were vulcanized at 433 K up to an optimum time of cure determined by rheometric tests. From swelling tests, the crosslink densities of the compounds were obtained and compared with those obtained in similar blends prepared by mechanical mixing. The results were analyzed in terms of the disentangling of the chain structures of the SBR and NR phases and the achieved cure state of the blend. Using differential scanning calorimetry, the glass transition temperature Tg of each blend was measured. In most compounds, the value of Tg corresponding to each phase of the blend was determined, but in some blends a single value of Tg was obtained. The variation of Tg with thecomposition and cure level in each phase was analyzed. On the other hand, a physical mixture of two equal parts of NR and SBR vulcanized was measured and the results were compared to those of the NR50/SBR50 cured blend. Besides, to analyze the influence of the network structure,pure NR and SBR unvulcanized samples were measured. On the basis of all the obtained results, the influence of the interphase formed in the blend between SBR and NR phases is discussed.