Ozone resistance of crosslinked blends of butadiene-acrylonitrile and ethylene-propylene-diene elastomers and interphase interaction in these blends

Structure of the interfacial layer in blends of elastomers with different polarities and ozone resistance

“…Formation of a strong interfacial layer is the key factor of the mechanism describing retardation of ozone degradation of a diene rubber by elastomer additives with a low degree of unsaturation [1][2][3]. The effect of comonomer ratio in ethylene-propylene-diene terpolymers (EPDMs) and stereoregularity of propylene units on the interfacial interaction and the amount of crosslinks in the interfacial layer was considered for heterophase crosslinked blends with butadiene-acrylonitrile rubbers (BNRs) of different polarities.…”

“…The largest amount of crosslinks in the interfacial layer forms when EPDM with a high content of ethylene units is used despite the moderate amount of diene contained in it. The ozone resistance of the blends was studied via the method of stress relaxation at an ozone concentration of 8.5×10 -5 mol/l, 30°C and at a tensile strain of 30-150% on an IKhF-2 relaxometer [2]. Relaxation rate v r in the ozone-containing medium in the steady-state region next to the region of the fast physical relaxation reflects the kinetics of accumulation of chain ruptures in the diene matrix.…”

“…Relaxation rate v r in the ozone-containing medium in the steady-state region next to the region of the fast physical relaxation reflects the kinetics of accumulation of chain ruptures in the diene matrix. The efficacy of retardation of degradation during the introduction of EPDM, v r rel , corresponds to the intensity of the decrease in the rate in the presence of the ozone-resistant component relative to that in the presence of the BNR vulcanizate [2]. The region of a low relaxation rate with quasiequilibrium stress σ* reflects the strength of the EPDM network because it represents the superposition of stresses in the network and in the matrix connected through interfacial layers [2.…”

“…Data on the efficiency of retardation of the ozone induced degradation of diene rubber in the absence (85:15 blend) and presence of the EPDM network (70:30 blend) at different strains are given in Table 3. In the case of the continuous EPDM network, the degradation rate for the BNKS-18 or BKNS-28 matrix reaches a minimum (value v d rel is maximum) [2,3]. The efficiency of retardation of the ozone degradation of BNKS-18 in the presence of the Royalen EPDMs (except R 505), which have a high stereoregularity of propylene units, is much higher than that in the case of DSM EPDMs of the same composition In blends of highly polar NBRs, v d rel sharply decreases and the differences between the blends level out.…”

“…The density of the interlayer and the amount of crosslinks in this layer, as determined from the deviation of the equilibrium swelling ratio from the values predicted in terms of the additivity rule of -α (Table 3), are maximal with EPDMs of both brands having a high content of ethylene units. However, the volume of the region of interpenetrating copolymer chain segments in the case of EPDM with a low stereoregularity of propylene units (DSM) is smaller than that in the case of Uniroyal EPDM [1,2]. The amount of crosslinks between the phases in the blend of EPDM R521 is considerably greater, unlike the case of EPDM 712 of the same monomer composition with a low microtacticity of propylene units [1.…”