摘要:

Velocity and attenuation measurements were made in thin strips of rubber from 0.5 to 5 kc and from −5°C to 90°C to obtain the dynamic viscoelastic constants of butyl and GR‐S gum stocks. Above room temperature velocity and attenuation are higher in butyl gum than in GR‐S. In all cases, the velocity increases with decreasing temperature and increasing frequency. The attenuation shows a peak with temperature. For butyl the peaks are broad and occur at higher temperatures than for GR‐S. For both stocks an increase in frequency gives peaks which are higher and sharper, and shifted to higher temperatures. In some instances, there are indications of peaks in the attenuationversusfrequency at frequencies beyond our range of measurement. The behavior of the dynamic modulus in the temperature and frequency range studied is similar to that of the velocity. These results combined with low temperature static measurements and very low frequency dynamic measurements indicate a U‐shaped modulus‐temperature curve whose minimum broadens and shifts to higher temperatures with increasing frequency. This may be explained by a generalization of the kinetic theory of rubber elasticity, taking into account intra‐ and intermolecular forces, and considering time effects.

ISSN:0021-8979    

DOI:10.1063/1.1698413

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The propagation of supersonic waves in bulk rubbers has been studied from 40 kc/sec. to 10 Mc/sec. and from −60°C to 60°C. The wave velocity was found to increase with decreasing temperature, leveling off both at high and low temperatures, and was found to increase slightly with frequency. Peaks in attenuation as a function of either temperature or frequency were observed, the peaks occurring at lower temperatures for lower frequencies. The peaks for butyl, a high loss rubber, are broader and higher than those for GR‐S and Hevea, which are lower loss rubbers. The results are in qualitative agreement with data obtained by strip methods at audiofrequencies. However, for bulk waves the real and imaginary parts of two elastic constants, the bulk and shear moduli, determine wave velocity and attenuation; hence, independent measurements of shear wave properties are necessary to evaluate these constants. A three constant theory is discussed, assuming a shear viscosity only, so that an effective modulusK+4&mgr;/3 is obtained, whereKand &mgr; are the bulk and shear moduli. Relaxation times of the order 10−6to 10−8second are indicated. Approximate values of the dynamic Young's modulus are obtained from the effective modulus by assuming that the high frequency dispersion is due to the appearance of a ``crystalline'' shear elasticity. These results are correlated with low frequency data, and the dynamic Young's modulus and the loss factor are plotted. The loss factor exhibits a maximum in the dispersion region. Results are plotted in the range from 1 c.p.s. to 107c.p.s., which covers a wider range of frequency than earlier investigations. The necessary distribution of relaxation times is discussed.

ISSN:0021-8979    

DOI:10.1063/1.1698415

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Dynamic methods for measuring the elastic and dissipative properties of high polymers in fiber and film form over four decades of frequency (3 to 30,000 cycles per second) are described. The experimental quantities resulting from the three different techniques necessary to cover this range are unified by deriving in each case the parameters of an equivalent Voigt Model (elastic and viscous element in parallel) which would behave in the same way as the polymer sample. Examples of the application of these techniques to the characterization of high polymers are given. The effect of frequency and chemical and physical structure on the derived parameters are discussed, along with the question of heat losses resulting from cyclical differential deformation. In addition, the application of two of the methods to the characterization of the stiffness‐temperature behavior of high polymers is described.

ISSN:0021-8979    

DOI:10.1063/1.1698416

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

Practical considerations emphasize the desirability of formulating an adequate equation of state for polystyrene. A fairly satisfactory one is this simplified version of van der Waals' equation,(P+&pgr;)(V−&ohgr;)=nRT,where &pgr; is the internal pressure (or cohesive energy density) and &ohgr; is the volume at absolute zero, by extrapolation. Evaluating constants from thermal expansion data and expressingPin p.s.i.,Vin cc per gram, andTin degrees Kelvin, this becomes(P+27,000)(V−0.822)=11.6T.Agreement with compressibility measurements, which are described in some detail, is good. Discrepancies with room temperature values of sound velocity and cohesive energy density by swelling measurements are discussed briefly.

ISSN:0021-8979    

DOI:10.1063/1.1698417

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The anelastic behavior of polystyrene has been studied by means of creep tests under long‐time load application and by means of damping capacity tests under rapidly varying repeated loading. Tensile creep data taken at various stress amplitudes reveal that the log of the creep rate (at 1000 hours) varies linearly with the log of the stress amplitude. A similar type of variation is obtained when damping capacity or energy absorbed per cycle is plotted against stress amplitude. From these two sets of data, the creep rate is found to be proportional to the square of the damping capacity. It would thus appear possible, for polystyrene at least, to predict 1000‐hour creep rates from short‐time measurements of absorbed energy under dynamic loading conditions.The data obtained from the creep and damping tests, together with additional data from short‐time tension and compression tests, seem to be consistent with an internal structure in which the linear polymer chains and groups of chains are in ordered or partially extended positions, but in which, in the absence of stress, no preference is shown for any particular direction. Under the action of stress—particularly if the stress is maintained for a long period of time—a tendency exists for the ordered regions to orient in the direction of the applied stress. The so‐called ``crazing'' condition which has been observed to occur in the creep specimens is probably a manifestation of this orientation. X‐ray evidence appears to support this point of view.

ISSN:0021-8979    

DOI:10.1063/1.1698418

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

A general treatment of the scattering of radiation by an inhomogeneous material is developed. It is shown how scattering measurements can be used to obtain the average square of the fluctuations in refractive index or electron density and a correlation function which measures the degree of correlation between two fluctuations as a function of their distance of separation.The scattering of visible light by Lucite and two glass samples has been investigated. The data are analyzed in terms of the quantities mentioned above. It is found that the extensions in space of the inhomogeneities in the Lucite sample are much greater than those in the optical glass samples investigated. The magnitudes of the fluctuations in refractive index are found to be dependent on the composition of the sample.

ISSN:0021-8979    

DOI:10.1063/1.1698419

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The Gough‐Joule coefficients (a) at constant stress and (b) at constant strain are defined and methods of measurement of each on vulcanized rubbers are given. It is shown mathematically and experimentally that the ratio of (b) to (a) is equal to the ``tangent'' modulus. The quotient of the Gough‐Joule coefficient at constant stress divided by the stress and the quotient of the Gough‐Joule coefficient at constant strain divided by the strain are shown to be constants which are independent of the stress‐strain‐temperature conditions of the test. Experimental data are given for stocks based on Hevea, GR‐S, Neoprene GN, Butyl Rubber, and Butaprene.

ISSN:0021-8979    

DOI:10.1063/1.1698420

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The melting point of &egr;‐carbobenzoxy‐&agr;‐carboxyl‐l‐lysine anhydride stored at room temperature for one year (I) rises considerably above that of the freshly prepared compound (II) (m.p. 100°). X‐ray diffraction studies indicate: (II) is probably monoclinic,a≃90A,b=5A,c≃10A; (I) suffered disorientation giving diagrams similar to those of bulk polymer (III); threshold conditions for the disorientation process are heat‐treatment of (II) at 70° for 24 hours; the change appears to be complete when (II) is heat‐treated at 85° for 24 hours since the diagrams are similar to those of (III) and no further change is observed in the diagrams of samples treated under more severe conditions below the melting point. The largest Bragg spacing of 29A observed for (II) is of the same order of magnitude as the over‐all length of a fully extended hydrogen‐bonded dimer of (II). The smallest refractive index of (II) is parallel to thebaxis. The structure of (II) is concluded to be a triple dimer layer arrangement which would involve a relatively small entropy change on polymerizing in the solid state to give (I) and (III).

ISSN:0021-8979    

DOI:10.1063/1.1698421

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

The stiffening of rubber‐like materials at low temperature involves several different phenomena, sometimes with their effects superimposed. One of these is crystallization. This is a rate process which is generally very fast at high stresses and very slow at zero stress. In these experiments at temperatures near −25°C and under a shear stress of about 148 p.s.i. the dynamic modulus of the rubber increased at a rate convenient to study. Correlation with x‐ray data showed that crystallization was very likely responsible for the increase in stiffness. The rate of change of stiffness increased rapidly with increase in applied stress, and there was no optimum rate at −25°C as has been found for unstressed rubber. The degree of vulcanization influenced the rate of change, tighter cures giving smaller changes. Neoprene FR, GR‐S and polybutadiene, which ordinarily show little evidence of crystallization showed very definite, but small increases in stiffness. Mixing GR‐S with natural rubber seems to limit the crystallization of the natural rubber rather effectively, but apparently Neoprene FR does not mix intimately enough with natural rubber to affect the crystallization of the latter appreciably.

ISSN:0021-8979    

DOI:10.1063/1.1698422

出版商:AIP    

年代:1949

数据来源: AIP

摘要:

This paper attempts to interrelate three important aspects of plasticizer behavior:compatibilityor how much plasticizer can be added without causing phase separation;efficiency, or how much a given amount of plasticizer lowers the brittle temperature; andpermanence, or how well a plasticizer is retained by the polymer on heat aging or solvent treatment.Compatibility is discussed in terms of the Flory‐Huggins theory of the thermodynamics of polymer solutions, which relates the activity of the plasticizer to its concentration in the polymer. Efficiency is measured by how the plasticizer lowers the melt viscosity of the polymer. An empirical relationship between efficiency and &mgr; (the Huggins polymer‐solvent interaction constant) is shown. Loss of plasticizer at elevated temperatures depends in part on the effective vapor pressure of the plasticizer, and in part on how rapidly diffusion of plasticizer from the interior of the sample replenishes that lost from the surface. From the fact that diffusion constant times viscosity is a constant, it is possible to correlate measured diffusion rates with plasticizer content and with plasticizer efficiency. A linear relationship is predicted and found experimentally between logarithm of the diffusion constant and the brittle temperature. In this sense, the more efficient a plasticizer is, the more rapidly it can diffuse out of the polymer and be lost. Consideration is given to the effect of plasticizer on electrical resistance and tensile strength. A preliminary discussion of polymeric plasticizers is presented.

ISSN:0021-8979    

DOI:10.1063/1.1698423

出版商:AIP    

年代:1949

数据来源: AIP