摘要:

A new universal extensional rheometer, which makes it possible to investigate the elongational properties of polymer melts, is described. Measurements under a wide variety of constant stretching rates and constant tensile stresses can be undertaken and recoil and relaxation experiments can be performed on a small amount of material. The operation modes of the apparatus are demonstrated on a polystyrene sample. For this polystyrene the viscosity and the recoverable strain in the steady state of elongation were measured over more than three decades of the tensile stress. At small stresses the recoverable strain is proportional to the stress, i.e., the compliance is constant and the viscosity gives a constant value which is three times the zero‐shear viscosity. At higher stresses the recoverable strain seems to level off and the viscosity runs through a maximum which lies 30% above the stress‐independent value.

ISSN:0148-6055    

DOI:10.1122/1.549544

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

Observation of defatted soy flakes contained in the screw channel of an extruder suggested that the soy flakes were being conveyed as a powder and that a plug flow model should describe the process. Flow rates from an extruder, operating at low temperature (30–50°C), were measured for different die sizes, screw speeds, and feed moistures. Dynamic coefficients of friction for different moisture soy flakes on stainless steel and hard chrome plate were determined. The Darnel and Mol model of plug flow in solids conveying was then used to calculate theoretical outputs, which were in good agreement with the experimental results. Output rates versus die pressure indicated extremely pseudoplastic flow approaching plug flow (slip) through the die.

ISSN:0148-6055    

DOI:10.1122/1.549527

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

In this work, a simple bead‐spring (dumbbell) model is employed together with the Langevin analysis to show that the master curves for stress must be made in terms of the groupS/ρT,andSis the stress tensor,Tthe absolute temperature, and ρ the density of the solvent. The time‐temperature shift factor is shown to beηs(T0)T/ηs(T)T0,whereηs(T)is the solvent viscosity at temperatureT.

ISSN:0148-6055    

DOI:10.1122/1.549528

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

An apparatus was developed for measurements of the flow birefringence of polymer solutions in time‐dependent flow, such as the start and the sudden cessation of steady shear flow. A linearly polarized light beam was led through the sample held in the gap between two coaxial cylinders in relative rotation, and then through an analyzer. The intensity of the transmitted light was measured as a function of time. The birefringenceΔnand the extinction angle χ were evaluated from light intensities for which the angles between the direction of flow and the direction of polarization of the incident beam were −22.5°, 0°, 22.5°, and 45°, respectively. Measurements were performed at 35°C on an 8% solution of polystyrene of weight average molecular weight3.0×106in chlorinated biphenyl. The stress‐optical law was applicable to the solution at the start and on the cessation of steady shear flow over the range of rate of shear, from6.6×10−3 sec−1to2.14×10−1 sec−1,studied. The stress‐optical coefficient obtained was5.9×10−9 Pa−1,in good agreement with literature values. The first normal stress difference was evaluated from the birefringence data with the use of the stress‐optical law. The normal stress in relatively short times after the start of shear flow was consistent with that predicted from the second‐order fluid theory.

ISSN:0148-6055    

DOI:10.1122/1.549553

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

A pair of empirical equations are proposed for the purpose of approximating the dynamic mechanical viscoelasticity functions, the storage compliance,J′(ω),and the nonviscous loss compliance,J″(ω)−1/ωη,from the value of the recoverable compliance,Jr(t),and its logarithmic slope,m(t)=d log Jr(t)/d log t.The angular frequency is ω and the shear viscosity is η. Three examples representing various kinds of polymeric, viscoelastic response are presented as tests of the effectiveness of the proposed expressions. Most of the calculated points are in error by less than 10%.

ISSN:0148-6055    

DOI:10.1122/1.549545

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

Tanner has suggested a constitutive equation for polymer melts and solutions based on a network rupture hypothesis: entanglements are lost irreversibly in the process of deformation as soon as a limiting strain magnitude is reached. Although this model shows serious defects in describing time‐dependent material properties it has the appealing feature of irreversibility. On the other hand the BKZ model (considered here in the simplified version of a separable memory function), being more useful in describing startup experiments, does not posses this feature of irreversibility, leading to largely erroneous results in recovery calculations. An improved version of a single integral constitutive equation is presented, where the irreversibility of the process of network disentanglement is incorporated. Predictions of elastic recoil behavior in elongation and shear are compared with experimental results for a well‐characterized LDPE melt.

ISSN:0148-6055    

DOI:10.1122/1.549529

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The steady state shear rheological properties of solutions of a rodlike polyamide, poly‐p‐phenyleneterephthalamide (PPT), in 100% sulfuric acid have been compared with those of solutions of a flexible chain polyamide, nylon 6,6 in the same solvent. For solutions of similar concentration (c) and molecular weight (M), it was found that the primary normal stress difference(N1)and the viscosity (η), compared at the same shear rate (γ̇), were an order of magnitude greater for solutions of PPT. It was believed that this behavior could be accounted for through the formation of an enhanced entanglement network in the PPT solutions. Plots of the zero shear viscosity(η0)versuscM̄w,whereM̄wis the weight average molecular weight, for both systems revealed that “bends” occurred in the data corresponding to a critical entanglement molecular weight(Mc)of 1180 for PPT (this corresponds to 30 main chain atoms (z)) and to 5260(z=330)for nylon 6,6. More significantly,η0was found to be proportional to(cM̄u)6.8for solutions of PPT and to(cM̄w)3.4for nylon 6,6 solutions. η versus γ̇ curves were similar in shape for both systems and could be reduced to the same master curve with the only difference being that the relaxation times or shifting factors were considerably greater for the PPT solutions. This suggested that the process of destroying entanglements may be similar for both polymers. The overlap parameterc[η],where [η] is the intrinsic viscosity, provided a much better correlation ofη0data from the two sets of solutions than did the segment contact parametercM̄w.This suggested that the structural variable controlling the onset of entanglements may be a parameter such as the radius of gyration. Because of the inability of rodlike molecules to coil around each other, further insight into the nature of entanglements is obtained.

ISSN:0148-6055    

DOI:10.1122/1.549530

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The meticulously reported results of Hedley et al. [J. Rheol.,22, 91 (1978)] show that the observed flow of gases through glass capillaries having diameters of the order of 1 μm is from 3 to 6 times greater than that calculated from Darcy's Law, when the mean pressure in the capillaries is of the order of 1000 Torr. It is argued here that flow in an adsorbed phase will account for the results and an equation derived by Jones [Trans. Faraday Soc.,47, 381 (1951)] 28 years ago can now be tested for the first time.

ISSN:0148-6055    

DOI:10.1122/1.549531

出版商:The Society of Rheology    

年代:1979

数据来源: AIP

摘要:

The time dependence of stress in simple extension of polyisobutylene (viscosity‐average molecular weight2.3×106) was measured for extension at various rates to a stretch ratioλ=1.5followed by relaxation at constant λ. The course of relaxation was independent of initial stretching rate after a time interval of approximately three times the time required to reachλ=1.5.In a series of partial relaxation experiments at stretch ratioλ0=2.0,the stress was allowed to relax for periods from 100 to1.3×105 secand the sample was then released by cutting; the recovery after a time interval δ of either 5 or 15 sec was measured. The stretch ratioλscorresponding to this point of initial recovery agreed closely with that calculated on the basis of a two‐network model in which an entanglement network with reference stateλ=1is gradually replaced by another with reference stateλ=λ0during relaxation, while the total concentration of entanglement strands remains constant. The old network (in extension atλs) is described by a Mooney‐Rivlin formulation and the new network (in compression atλs) is neo‐Hookean. The Mooney‐Rivlin CoefficientsC1(t)andC2(t)required for the calculation are obtained from parallel experiments of stress relaxation at various stretch ratios.

ISSN:0148-6055    

DOI:10.1122/1.549532

出版商:The Society of Rheology    

年代:1979

数据来源: AIP