Monitoring of Homogenization and Analysis of Nanoscale Structure in a Butadiene−Acrylonitrile Copolymer/Poly(vinyl chloride) Blend

The progress of homogenization in the mechanical blending of a butadiene−acrylonitrile copolymer (NBR) and a poly(vinyl chloride) (PVC) was observed with scanning and transmission electron microscopes. The significant events of the microscopic examinations were as follows: (i) NBR formed a continuous and PVC a dispersed phase. (ii) The skins of PVC grains (100−150 μm) were removed first, and the grains were broken into agglomerates (∼10 μm). (iii) The agglomerates were disintegrated stepwise into primary particles (∼1 μm), domains (∼0.1 μm), and eventually the nodular particles of the size between domains and microdomains (∼10 nm). The electron microscopic visualizations, together with the material behavior expressed in terms of the internal mixer geometry and the viscoelastic properties during mixing action, suggest a schematic model for the homogenization mechanism. The microphase structure of the finished blend was characterized by cross-polarization/magic angle spinning (CP/MAS) 13 C NMR spectroscopy. Analyses of T 1 ρ spin−lattice relaxation for specific carbons permitted a precise identification of the microstructures. Double-component resolution of the magnetization decay confirmed a coexistence of a mixed phase and two microseparated phases, the latter corresponding to an unmixed NBR phase and PVC microcrystallites. From the T 1 ρ relaxation times, the sizes of the microphases were estimated to be in the nanoscale.