Elastomer particle morphology in ternary blends of maleated and non-maleated ethylene-based elastomers with polyamides: Role of elastomer phase miscibility

The elastomer particle morphology in ternary blends of maleated and non-maleated ethylene-based elastomers with polyamides has been examined. The elastomers used include an ethylene/propylene copolymer, EPR, with a maleic anhydride (MA) grafted version, EPR-g-MA, and an ethylene/1-octene copolymer, EOR, with maleated versions EOR-g-MA-X% where X is 0.35, 1.6 or 2.5. The polyamides used were nylon 6 and an amorphous polyamide, Zytel 330 from DuPont. The morphology development was explored from both thermodynamic and kinetic points of view where the former refers to miscibility of the elastomers and the latter might include the ratio of the elastomers, the matrix type, the order of mixing, mixing intensity, i.e. the extruder type, and graft structure, etc. Both sources influence the morphology developed. For ternary blends with EPR-g-MA/EPR, the morphology (particle size and distribution) seems to be well controlled via the level of maleation in the rubber phase. The two polyamides generate comparable rubber particle sizes at the same of MA level. For ternary blends with EOR-g-MA/EOR, the morphology strongly depends on the level of MA; the rubber particle size, in general, is much smaller in nylon 6 blends than in Zytel 330 blends. Morphology of ternary blends with EOR-g-MA/EOR is much more complex than that of blends with EPR-g-MA/EPR due to the co-existence of miscibility limits and the kinetic factors. Miscibility of maleated EOR elastomers is examined via transmission electron microscopy (TEM) using a special staining technique; a miscibility boundary, as revealed by TEM, occurs around Δ(%MA)=0.9−1.25 MA%. If the two elastomers are miscible, a unimodal particle size distribution always appears in blends regardless of the kinetic factors; however, if immiscibility prevails, either a unimodal or bimodal particle size distribution may develop depending on the ratio of the elastomers and the matrix type. The order of mixing and the mixing intensity do not seem to change the modality of the size distribution.