Effects of temperature on nucleation and collapse of volatile bubbles in the high density polyethylene melt

Abstract

High density polyethylene/n-Hexane system was adopted to investigate the bubbles nucleation and collapse in polymer melt with a visualization apparatus at different temperatures. The results showed that the initial bubble number, initial total bubble volume and the mean bubble diameter all increased with the temperature increasing, and the bubble diameter distribution changed from single peak distribution to bimodal distribution. Moreover, the effect of temperature on the maximum bubble diameter was mainly reflected in the change of the pressure in bubbles due to the change of the volatile content in the polyethylene melt. For bubble collapse, the collapse time became longer but the bubble collapse rate became faster with the temperature increasing, and a fitting model was established in which the collapse coefficient n was used to describe the collapse rate. Through dimension analysis, the correlation between the collapse coefficient n and the melt surface tension σ, zero-shear melt viscosity η0, diffusion coefficient D, maximum bubble diameter dmax, melt density ρ, initial bubble number density Nini were established and the variation of D with temperature could be predicted as an exponential correlation.