COARSENING IN POLYETHYLENE COPOLYMER BLENDS

Artificially mixed binary blends of polyethylene and hydrogenated poly butadiene are equilibrated as two liquid phases at aging temperatures T-a 140-160 degrees C. Phase separation occurs in similar to 30 s, fol lowed by gradual coarsening of dispersed droplets during which the ave rage particle size increases with time as (r(3)) over bar similar to K t. The coarsening constant K is varied from 5 x 10(-8) to 1.2 x 10(-5) mu m(3)/s by changing blend components and is compared to calculated rates based on coalescence and Ostwald ripening. Quantitative agreemen t is obtained for all conditions, even when the two coarsening mechani sms are operating in parallel with nearly equal rates. Coalescence is favored in blends with a low-viscosity matrix, while Ostwald ripening is dominant when both solubility and diffusivity of the minority compo nent in the matrix are large.