AbstractExisting viscosity data on polyethylenes were studied as a function of temperature and molecular weight. New measurements were made on low density polyethylenes which had molecular weights useful for the test of theory. Viscosities of normal alkanes, considered as a lower extension of polyethylenes, were also correlated. The equation, log η =Alog (M) −B(where η is absolute viscosity,Mis molecular weight, andAandBare constants), is applicable over a wide range of Newtonian viscosities. Bueche's theory postulates thatAapproaches unity for chain lengths up to a critical molecular weight,Mc, where molecular entanglement abruptly becomes important. AboveMc, the theory requiresAto be 3.4. Values ofAfor normal alkanes are shown to approach unity belowMc. The entanglement point,Mc, is temperature dependent and occurs at relatively low molecular weights. AboveMc,Afor linear polyethylenes is near 3.4. However, certain polyethylene data give higher values forA. Activation energies for viscous flow, ΔE*, were obtained for polyethylenes and normal alkanes. They were found to be internally consistent and to vary as a linear function of the log of molecular weight. The change of ΔE*with less general functions of molecular weights shows a maximum curvature nearMc. Results are considered in terms of flow t
展开▼
