Biaxial Elongational Viscosity Research Articles

Uniaxial and biaxial elongational flow of low density polyethylene/polystyrene blends

Uniaxial and biaxial elongational flow behavior of low density polyethylene (LDPE)/polystyrene (PS) blends (LDPE/PS=2/1) with and without 5 wt. % styrene‐ethylene‐propylene block copolymer (SEP) was studied. In these blends, LDPE was the matrix phase and PS was the dispersed phase. Measurements of the uniaxial elongational viscosity η+(t,ε̇) and the biaxial elongational viscosity ηβ+(t,ε̇) were made using a Meissner‐type uniaxial elongational rheometer and a lubricated‐squeezing‐type equibiaxial rheometer, respectively. In the linear region, the relation between the transient shear viscosity η+(t) and the transient elongational viscosity, which were predicted by three‐dimensional linear Maxwell model, i.e., EE+(t)=3η+(t) and ηB+(t)=6η+(t), did not hold well. This may be attributed to a volumetric resistance against the deformation perpendicular to the elongational direction because of the existence of PS particles. In the long‐time region, a difference of ηE+(t,ε̇) between blends with and without SEP was observed. In the case of uniaxial elongational flow, it may be presumed that a contribution of the deformation of PS domains to the elongational flow behavior has to be taken into account when the elongational strain is large.

Uniaxial and Biaxial Elongational Flow of Low Density Polyethylene/Polystyrene Blends

Uniaxial and biaxial elongational flow behavior of low density polyethylene (LDPE)/polystyrene (PS) blends (LDPE/PS=2/1) with and without 5 wt. % styrene‐ethylene‐propylene block copolymer (SEP) was studied. In these blends, LDPE was the matrix phase and PS was the dispersed phase. Measurements of the uniaxial elongational viscosity η+(t,e) and the biaxial elongational viscosity ηβ+(t,e) were made using a Meissner‐type uniaxial elongational rheometer and a lubricated‐squeezing‐type equibiaxial rheometer, respectively. In the linear region, the relation between the transient shear viscosity η+(t) and the transient elongational viscosity, which were predicted by three‐dimensional linear Maxwell model, i.e., EE+(t)=3η+(t) and ηB+(t)=6η+(t), did not hold well. This may be attributed to a volumetric resistance against the deformation perpendicular to the elongational direction because of the existence of PS particles. In the long‐time region, a difference of ηE+(t,e) between blends with and without SEP was ...

Measurement of the equibiaxial elongational viscosity of polystyrene using lubricated squeezing

AbstractThe equibiaxial elongational viscosity of polystyrene was determined using a lubricated squeezing technique. Constant strain rates up to Hencky strains of 4.5 could be maintained by a newly constructed instrument. Test results from controlled stress and controlled strain rate measurement were consistent and yielded well‐defined steady‐state viscosities. Measurements appeared to be unaffected by sample geometry, although proper lubrication is important in achieving steady state. The measured biaxial viscosity appeared to be strain rate thinning above a biaxial strain rate of ≈ 0.01 s−1 at 160°C. As anticipated in the Newtonian region, biaxial elongational viscosity was approximately six times the shear viscosity. Thinning indices of both shear and biaxial elongational viscosities were 0.75. Data obtained at various temperatures were shifted following the timetemperature superposition principle. The resulting master curve could be fitted by a Carreau model with n ≈ 0.3 and a time constant of 110 s.

Inflation Characteristics of Unvulcanized Gum and Compounded Rubber Sheets

Abstract The inflation of rubber compound membranes to fill molds has a long history in rubber processing. There have, however, been few basic experimental studies of this topic. This free inflation of vulcanized rubber sheets was studied by Treloar and Rivlin and Saunders during the 1940's and 50's where it was used to investigate the form of the stress-strain relationship. Rivlin and Saunders sought to fit nonlinear elastic constitutive equations to data obtained at small inflation levels. In the early 1970's Denson and his coworkers utilized the inflation of unvulcanized polyisobutylene membranes to apply this as a procedure to evaluate biaxial and planar extensional viscosities. Similar studies were made by Maerker and Schowalter. These studies all involve free inflation of membranes. These studies of inflation of raw gum polyisobutylene sheets only looked at relatively small deformation levels where a hemispherical shape or less was achieved. Failure mechanisms in similarly inflated vulcanized SBR 1502 rubber sheets were described by Dickie and Smith. These authors did not describe the shapes of the inflated sheets. There seem to be no studies of inflation of rubber membranes into molds or useful equivalent studies of molten plastics such as thermoforming. It is the purpose of this paper to present a basic study of the inflation of membranes of various gum and compounded elastomers. We observe the manner in which the membranes freely inflate into air and also the manner in which they fill molds of various shapes. We begin with qualitative considerations but will also present quantitative measurements. Biaxial elongational viscosities have been estimated.