Abstract
The stress at several finite drawing rates has been investigated from the point of plastic flow in the amorphous phase induced by deformation.
From the consideration of Bingham flow the stress was described as where σc, F: critical stress, η(T, R, Mf): viscosity as a function of temperature T, drawing rate R and molecular weight of amorphous chain derived from folded chain crystals, α: draw ratio during ultra draw, and αm: maximum draw ratio at completely extended state.
The stress-draw ratio relations of various polyethylene were determined at the temperature from 30 to 110°C and at the drawing rate from 1 to 1000mm/min. It was found for linear polyethylene that the stress increases with the drawing rate, being coincided with above equations in most drawing conditions. However, at high temperature and at low drawing rate, the stress-draw ratio relation did not agree these equations because the deformation is conducted not only by plastic flow but also by liquid flow. On the other hand the stressdraw ratio relation of crosslinked polyethylene conforms to the equation of FT type deformation in all drawing conditions. The law of time (drawing rate)-temperature reducibility is able to be applied to the stress increased by the friction of plastic flow, and the viscosity was revealed to follow the WLF equation.
