摘要:

An investigation has been made of the degradation of Vistanex polyisobutenes having viscosity‐average molecular weights from about 500 000 to 2 500 000 by shearing in solution in cetane at polymer concentrations from 5 to 20 weight percent, at nominal rates of shear from 9000 to 66 000 sec−1, and at temperatures from 20° to 80°C. The initial apparent shearing loads, observed at the beginning of the degradation process, vary in unexpected ways with variations in nominal rate of shear, temperature, concentration, and initial molecular weight of the polymer. In some cases the observed variations are opposite to those which would be expected on the basis of viscoelastic resistance to shearing. These results can be explained on the basis of the hypothesis that the observed apparent shearing forces include some contribution associated with the energy used up in breaking chemical bonds in the polymer molecules during the degradation process. If this hypothesis is correct, valid viscosity values cannot be obtained directly from observed apparent shearing forces in viscometry measurements under conditions where shear degradation occurs.

ISSN:0021-8979    

DOI:10.1063/1.1721816

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

The effect of temperature, rest period, and water content on stress relaxation in doughs held at constant extension has been studied with a relaxometer previously described. Temperature was varied from 13 to 35°C, rest period from 2 to 120 min, and water content from 74.4 percent to 86.0 percent dry basis. It is found that the shape of the relaxation curves on a log time plot does not change with temperature in the above range but that the curve is shifted laterally along the log time axis. This permits the construction of master curves valid in the temperature range and extends the time scale of observation. The long relaxation time end of the distribution of relaxation times is affected most by rest period, decreasing as rest period is increased, and the short time end increases as water content is decreased. Activation energies from 11 to 24 kcal per mole are calculated for relaxation from the shift of the curve on the log time axis. There is an indication that the activation energy depends on temperature and increases with rest period.A mathematical framework, based on the general Maxwell model, is discussed and the distribution function on the log time axis is interpreted in terms of viscosity and modulus of the relaxing mechanisms. Special reference is made to the ``box distribution'' and a viscosity is calculated.

ISSN:0021-8979    

DOI:10.1063/1.1721817

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Constant stress measurements have been made on lightly cross linked GR‐S and polyisobutylene of 7 million molecular weight. The modulus values as a function of temperature, time, and concentration of mineral oil plasticizer have been treated according to the ``reduced variables'' principles.Since both plasticized and unplasticized samples showed the expected equivalence of temperature and time, the modulus values could be shifted to produce master curves for each composition. In the case of GR‐S the concentration of plasticizer could be similarly reduced to yield a single curve for all the data.The polyisobutylene results, however, showed quite clearly that the plasticizer had a unique effect not paralleled by temperature or time. This effect has been attributed to the pseudoequilibrium modulus which apparently results from chain entanglements. Since the pseudoequilibrium modulus should be proportional to the number of chain entanglements per gram of polymer, it should vary as the square of the volume fraction of polymer. It is shown that a correction of this type improves the shift of the curves for polyisobutylene.Changes in activation energy with the addition of plasticizer are apparently within experimental error (±2 kcal) in all cases.

ISSN:0021-8979    

DOI:10.1063/1.1721818

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Three types of measurements have been made on concentrated polyisobutylene solutions. Dynamic measurements have been extended to low frequencies and the dynamic viscosities and rigidities determined in the region close to that in which pure viscous flow predominates. A modified Stormer viscometer has been used to determine the apparent (non‐Newtonian) viscosities of the same solutions. Pressures developed (normal stress) at the inner cylinder have also been measured in a concentric cylinder apparatus with the inner cylinder rotating. It is noted that superposition procedures currently used for dynamic data are apparently applicable to the viscosity and pressure data with the rate of shear taking the place of frequency. Relations between these phenomena are discussed in the light of a theory proposed by one of the authors.

ISSN:0021-8979    

DOI:10.1063/1.1721819

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Experimental data have been obtained on the stress‐relaxation modulusEr(t) of several copolymers in their transition regions. The new data are expressed as master curves which can be fitted to the Gauss Error Integral form of reduced equation, as previously proposed. It appears possible to characterize the time and temperature‐dependence ofErof amorphous polymers in general by means of the parameters of this equation:E1(glassy‐state modulus),E2(rubbery‐state modulus),Td(distinctive temperature, related to second‐order transition temperature),Kd(characteristic relaxation time atTd), andh(parameter related to steepness of master curve). In the butadiene‐styrene series, the effect of composition on these parameters has been determined.

ISSN:0021-8979    

DOI:10.1063/1.1721820

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Reasons are adduced for suspecting that in a raw elastomer subjected to continuous shear there exist groups of molecules which are held together by entanglement or by thixotropic attachments and move and rotate essentially as elastic solid bodies. Such coherent molecular groups are called rheological units.If an elastomer in continuous shear consists essentially of closely‐packed rheological units, such units, rolling on each other, will transfer a rubber soluble dye across the shear planes as the ink rollers transfer ink in a printing press. This predicted phenomena has been observed with a Mooney viscometer fitted with a smooth rotor, the face of which is covered with a thin film of dried cement containing a dye in high concentration. From the velocity of the color front a rough value can be computed for the mean diameter of the rheological units. The diameters for a series of different elastomers lie in the range from 1 to 35 microns.

ISSN:0021-8979    

DOI:10.1063/1.1721821

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Using the vibration tester of The Franklin Institute, a check of the proportionality between stress and strain in dynamic testing disclosed that a proportionality exists when heating is eliminated. A comparison of values of the dynamic test and steady‐state experiment in the same range of rates of shear and shearing stress showed that the behavior is basically different; whereas in the dynamic test the viscosity is independent of both amplitude and shearing stress, in the steady‐state test experiment a very high dependence exists. The curve of viscosityvsrate of shear (D) is very similar to the one of dynamic viscosityvsfrequency (f). A frequency shift of the order of two is involved in comparingDandf. The application of Ferry's method of reduced variables to a polyisobutylene solution, liquid polyesters, and solid plastics showed its validity. A precision test on the polyester showed that the temperature shift,T&rgr;/T0&rgr;0, is necessary to make experimental values at different temperatures fit. The reduced curve ofG′ vsfrequency for different plastics has anSshape with different slopes in a very wide range of frequency around 1024.

ISSN:0021-8979    

DOI:10.1063/1.1721822

出版商:AIP    

年代:1954

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1721823

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

Since the conventional elastic analysis of thermal stress problems coupled with limiting creep rates and time‐dependent fracture stresses as (inelastic) design criteria, results in design procedures for thermal stresses (in heat exchangers, nuclear reactors, flight structures at supersonic speeds, etc.) of considerable unreality, the effect of various types of rheological behavior (viscoelastic, plastic, work hardening) on the level of thermal stresses is analyzed under simplified assumptions, such as uniaxial stress and polar or cylindrical symmetry. The effect on the thermal stress intensity of the rheological behavior of the material is shown to be very significant, particularly with respect to stress relaxation and the development of residual stresses.

ISSN:0021-8979    

DOI:10.1063/1.1721824

出版商:AIP    

年代:1954

数据来源: AIP

摘要:

``Crosshead''‐slit dies are widely used for the extrusion of polymer sheeting, flat film, and blown film. In this paper we analyze the laminar flow of liquids in such dies, deriving an equation relating pressure to position along the slit for materials that obey the ``power law.'' The equation yields an index of uniformity (UI), which is the ratio of the rate of extrusion at the far end to that at the feed end, given byUI=1−[(1+0.05n)n&agr;L](n+1)/n(1+0.05n)(n+1)n,wheren=the exponent of the power law,L=the length of the die from feed end to far end, and &agr;=a parameter depending on the other die dimensions and the exponentn, having the unit (in)−1. An illustrated procedure is given for designing dies that will make film whose caliper is satisfactorily uniform over its whole width. We show that theUIfor center‐fed dies is always greater than for end‐fed dies of the same length.

ISSN:0021-8979    

DOI:10.1063/1.1721825

出版商:AIP    

年代:1954

数据来源: AIP