Dynamic mechanical and impact properties of polypropylene/EPDM blends

It was established by instrumented impact testing on notched Charpy specimens (DIN 53453 standard, No. 2 bar) that PP homopolymers impact modified by EPDM sorts of different melt viscosities at a rate lower than 10% were subject to brittle fracture in a wide temperature range. The most efficient of the EPDM impact modifiers had melt viscosities similar to that of the starting PP under the conditions of mixing. The course of maximum load at rupture (F_max) and notched impact strength as functions of temperature showed some analogies with one another as well as with the dynamic mechanical storage (E′) and with the mechanical loss factor (tan δ). Thus, linear regression analysis was applied to the following relations: F_max vs. (E′; tan δ; impact strength), F²_max vs. (tan δ, impact strength) and impact strength vs. tan δ. The optimum correlation coefficients were obtained for F_max vs. E′ and impact strength vs. tan δ. The supposed linearity of the former relation suggested that notched small Charpy specimens behaved as linear elastic bodies at high-rate three-point bending while the latter function referred to the significant role of relaxation of the EPDM impact modifier in the dissipation of impact energy during brittle or semi-brittle fracture of the two-phase PP/EPDM blends. The above relations are rendered probable by the fact that frequency of impact load is 10² to 10³ Hz while that of the dynamic mechanical measurements is about 10¹ Hz.