摘要:

Highly viscous, pseudoplastic, and viscoeleastic solutions can be made from low molecular weight polymers by designing polymers with high radii of gyration. Solutions of starch‐acrylamide, graft copolymers, one type of high radius, low molecular weight polymer, have relaxation times which increase with increasing copolymer concentration, increasing copolymer molecular weight, or, at constant molecular weight, decreasing number of grafts per starch molecule. Intrinsic viscosity, radius of gyration, and filtration data show the graft copolymers to be 1 to 6 times larger molecules than equal molecular weight polyacrylamide. None of these nonionic polymers form complexes with electrolytes or aggregate in water. Copolymer solutions lose up to 60% of their original viscosity when sheared 100 times at a shear rate of4,300 s−1.The amount of copolymer degraded by shear increases and, thus, the loss of solution viscosity increases when copolymer molecular weight increases or, at constant molecular weight, when the number of grafts per starch molecule decreases. Solution rheology changes slowly with time for two months after solution preparation. Viscosity loss, reduction in psuedoplasticity, and reduction in viscoelasticity are all due to disentangling of polymer chains. All copolymers were prepared by redox initiated, free radical polymerization of acrylamide on starch.

ISSN:0148-6055    

DOI:10.1122/1.549626

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

Stress relaxation in uniaxial extension has been studied in networks of dihydroxy‐terminated polybutadiene,cis:trans:vinyl=26:38:36,cross‐linked by triphenyl methane‐4,4′,4″‐triisocyanate and containing 9.3% by weight of unattached polybutadiene with similar microstructure, various molecular weights, and weight to number‐average molecular weight ratios of 1.15 to 1.50. Stress relaxation measurements were made also on networks containing no unattached species and on most of the various uncross‐linked linear polymers; for two of the latter, equivalent data were obtained by conversion of dynamic measurements of the complex shear modulus. The stretch ratio was usually 1.25 and the Young's relaxation modulus was calculated from the neo‐Hookean stress‐strain relaxation. For the uncross‐linked polymers, the relaxation modulusE11(t)corresponded to a rather narrow distribution of relaxation times whose magnitudes were approximately proportional to the 3.2 power of viscosity‐average molecular weight. The contribution of the unattached species in the networks,E1(t),was calculated by difference; after multiplication by(1−v22)−1,wherev2is the volume fraction of the network component, it was compared withE11(t).The relaxation in the network appeared to be slower and more gradual to an extent which was correlated with molecular weight distribution.

ISSN:0148-6055    

DOI:10.1122/1.549627

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

A method is derived for estimating the lifetime of engineering polymers and composites acted upon by steady loads. The method applies a recently developed theory of crack growth in polymers. The basic properties that enter the analysis are the viscoelastic creep function of the material and the energy content of the crack‐generated surface layer. In addition, the characteristic (failure) dimension of the body must be specified, together with the load (stress) level acting upon the body and a stress‐distribution parameter. The final result of the derivation is a single, simple formula that expresses time to failure as a function of the input parameters. The method has been compared with experimental data upon arimid composite‐material strands, with encouraging results. The resulting predictions are fundamentally different from those of the Zhurkov formula, which is based upon an activation‐energy characterization for molecular schism. The model has been cast into a statistical form to accommodate a realistic treatment of data having wide scatter.

ISSN:0148-6055    

DOI:10.1122/1.549630

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

Kinetic theory of crack growth is used to predict the residual strength of polymetric materials acted upon by a previous history. Specifically, the kinetic theory is used to characterize the state of growing damage that occurs under a constant‐stress (load) state. The load is removed before failure under creep‐rupture conditions, and the residual instantaneous strength is determined from the theory by taking account of the damage accumulation under the preceding constant‐load history. The rate of change of residual strength is found to be strongest when the duration of the preceding load history is near the ultimate lifetime under that condition. Physical explanations for this effect are given, as are numerical examples. Also, the theoretical prediction is compared with experimental data.

ISSN:0148-6055    

DOI:10.1122/1.549629

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

The effects of thermal properties of Newtonian liquids on die swell were studied numerically using the finite element method. In particular, Newtonian liquids with temperature‐dependent viscosity were studied under variable operating conditions. The viscosity was assumed to be a decreasing exponential of the temperature, with a proportionality constant β which was assumed to be a given material property. Temperature and pressure distribution in the liquid, as well as the swelling ratio (extrudate diameter/capillary diameter) were found as a function of the constant β, Peclet number (Pe), and Nusselt (Nu) number. Two‐dimensional and axisymmetrical geometries were examined. The results show that a change in value of either β,Pe, orNutends to alter the intensity of the stress singularity at the lip of the capillary as indicated by the swell. An increase in β has very little effect on the temperature distribution, but tends to decrease the amount of swell. An increase in Peclet results in a hotter jet while increasing Nusselt results in a colder extrudate; in both cases, however, the amount of swell increases.

ISSN:0148-6055    

DOI:10.1122/1.549628

出版商:The Society of Rheology    

年代:1981

数据来源: AIP

摘要:

The shear stress σ and normal stress differenceν3,the sum of the first and the second normal stress differences, were measured for a concentrated polystyrene solution in double‐step shear deformations: a shear strainγ1was applied at timet=−t1,another shear strainγ2was added att=0,and the stresses were measured fort>0.Whent1andtwere larger than a certain characteristic timeτk,the observed results for σ andν3were in accord with the prediction of the tube‐model theory of Doi and Edwards for various combinations ofγ1andγ2.Here the characteristic timeτk,previously determined from the strain‐dependent relaxation modulus, gives the measure of the equilibration time of the contour length of polymer chain. The results fort>τk≫t1were well described with the phenomenological BKZ model. The success of this model fort>τk≫t1can be accounted for with the concept of tube model.

ISSN:0148-6055    

DOI:10.1122/1.549650

出版商:The Society of Rheology    

年代:1981

数据来源: AIP