Rheology of polyisobutylene. I. Theory and experimental procedures

Abstract

A formulation is given of the response of a body manifesting linear viscoelastic behavior in shear to arbitrary simple shear stress history. A description is given of procedures for the measurement of the retarded elasticity function and of the viscosity by means of experiments under constant shear stress and following removal of stress. The non‐Newtonian flow of polymers is considered. Existing information on the viscosity of polyisobutylene as a function of temperature and molecular weight is reviewed. The applicability of the kinetic theory of rubberlike elasticity to a system of linear molecules is discussed. The use is described of the concentric cylinder rotational viscometer for the measurement of non‐Newtonian flow and of linear viscoelastic behavior.

Correlation of large longitudinal deformations with different strain histories

“…This is done to e mphasize th e result s at earl y tim es after th e ste ps whi c h are th e more c riti cal d ata. The blac k point s re prese nt th e calculated valu es as obtained us in g e qs (7) and (5). Th e agreement is e xcell e nt.…”

“…In order to correc t for thi s temperature diffe re nce, we adjusted the stress · relaxation data using tim e·te mperature superpositio n a ppropriate to th e BKZ elas tic fluid [2]_ The H(A, t) s urfaces at absolute te mperatures To and TI are rela ted as follow s 4 where po and PI are the de nsiti es at To and T] , and bT is a tim e s hifting factor whic h can eith er be obtained experim entally or es timated from se mie mpiric al eq uations. From previously reported work on polyi sobutyle ne by Leaderman [5] th e shiftin g factor bT was evaluated to be 1.45 for a shift from 25°C to 21 °C .…”

Viscoelastometer for measurement of flow and elastic recovery.

“…This "endeffect" has been obtained experimentally for ranges of two of the three geometrical pm•ameters. Th e procedures for obtaining the elftstic part of the shear creep compli ance, J(t) -t/'1 , from elastic recover~' meas urements over a range of time in a rotation~tl v iscom eter have been given previously [8].…”

“…This instrumen t constant J{ may b e defined as the ratio of r/r) to effective torque (W -WI) for any given geometry, where 7) is the viscosity of tIl e liquid. The same instrument constant is applicable for a material manifesting linear viscoelastic behavior , provided that inertia effects can be ignored [8).…”

“…Then: From about the glass transition temperature to 100 00 above this temperature, the viscosity may b e represen ted by a modified form of the William s-La nd el-Ferry relation [13,14,15]: (8) where C2 is an adjustable parameter. For this case, (9) NolV let 1/a be Lhe apparent viscosity measured in the vi C'oclasLometer with the temperature gradient.…”