摘要:

AbstractDepartures from behavior predicted by the statistical theory of rubberlike elasticity, which occur at high extensions, are ascribed to the finite extensibility of network chains. By use of a non‐Gaussian statistical theory, a relation is obtained between the extension ratio λ*, the extension at which departures are small but significant and the degree of crosslinking. Experimental results on the dependence of λ*on the degree of crosslinking and on the degree of swelling are in good agreement with theoretical predictions. It is shown that the additional determination of λ*permits the calculation of both the degree of crosslinking and the extent of network flaws due to chain ends, from a single simple extension stress‐strain curve. The calculation of these two basic parameters has hitherto been unattainable from measurements on vulcanized rubbers alone. This development provides a new technique of particular value in studies of the degradation of vulcanized ne

ISSN:0021-8995    

DOI:10.1002/app.1959.070020601

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractThe mechanism of water transport across cellulosic membranes under high pressure differentials was studied in an attempt to explain the semipermeability of these films when used as osmotic membranes for ionic solutions. Diffusion coefficients and activation entropy values for the diffusion of water and other fluids through various polymer films were determined, and compressive deformation of cellulose acetate and cellophane films was measured. Activation entropy values for the diffusion of water across both cellulose acetate and cellophane films illustrated that water molecules are constrained to states of high order as they are transported across the membrane under high pressure differentials. Activation entropy values for the diffusion of methanol through cellulose acetate film failed to support the proposition that chains of this polymer may actually be crosslinked by hydrogen‐bonded water. It appeared, rather, that but one hydrogen of the water molecule was involved in hydrogen bonding to the polymer. A significant reorientation of the polymer in the pressure interval in which cellulose acetate film is induced into a semipermeable condition was indicated by pressure‐dependent fluctuations of diffusion coefficients and activation entropy values in this interval. The greater elastic modulus of wet cellulose acetate film under a compressive force applied normal to the film surface demonstrated a strong interaction between water and polymer chains in the cellulose acetate‐water structure. The capacity of the film for bound water was also increased by repeated compression while wet. Wet cellophane films deformed plastically under compression. Crosslinking polymer chains of cellophane film with cupric ions prevented plastic flow and, at the same time, increased the semipermeability of the film for sodium chloride solu

ISSN:0021-8995    

DOI:10.1002/app.1959.070020602

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractA method for determining molecular weight distributions is presented, based upon the partition of polymer molecules between gel and sol in a partly crosslinked system. It is assumed that the polymer sample consists of a series of molecular weight species, and analysis of previously developed theories covering this situation yields an expression which equates the weight fraction of gel to a summation involving the weight fraction of the material in each species and the number of crosslinked units in the sample. The data are presented in the form of a graph showing how the weight fraction of gel varies as a function of the number of crosslinked units in the sample. Data for the graph are obtained from swelling measurements made in the usual manner. The procedure is outlined for using the information from the graph to make a step‐by‐step evaluation of the fractional weight of each molecular weight species in the sample for as many fractions as may be arbitrarily chosen. Both a first approximation method and a more refined second approximation method are outlined. The procedure has been applied to samples of natural rubber, synthetic rubbers, and to two known molecular weight distributi

ISSN:0021-8995    

DOI:10.1002/app.1959.070020603

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractAs evidenced by formation of peroxides and carbonyl, reaction occurs during the oxidation induction period of polyethylene. The meaning of the term oxidation induction period is revealed by the tremendous change in melt index, carbonyl, density, color, tensile, and elongation occurring towards the end of this time period. Hydroperoxide forms long before the end of the oxidation induction period even in the presence of an antioxidant. At any temperature both chain scission and crosslinking occur simultaneously. The rate of oxidation is accelerated by increasing temperature, unsaturation, and branching. Molecular weight seems to have no effect.

ISSN:0021-8995    

DOI:10.1002/app.1959.070020604

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractThe machanical anisotropy of several thermoplastic polymers has been investigated, and the relationship with a practical dart drop impact measurement has been explored. It has been shown that the unnotched Izod impact strength of a specimen taken perpendicular to flow orientation can be correlated with the dart drop impact strength. Further, the effect of several dart drop test variables, such as drop height, dart tip radius, and specimen size, have been investigated and reported. It has been concluded that the conventional strength measurement of injection‐molded specimens may lead to erroneous appraisal of the practical strength of a material. Testing at an orientation normal to flow or by multiaxial stressing as in a dart drop test is suggeste

ISSN:0021-8995    

DOI:10.1002/app.1959.070020605

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractThe manner in which changes in air pressure affect the thermal and oxidative degradation of a methylphenylsilicone was investigated as a function of time. A closed, gas‐circulating system of 1500‐cc. volume, incorporating a magnetic balance for following loss of weight in the sample, was employed. Finely ground samples were heated at 400°C. for 7 hours with initial pressures of air ranging from 700 to 50 mg. Hg. Mass spectrometric and infrared analyses identified the gaseous and the volatile products. At all pressures, low molecular weight silicones represented a major portion of the weight loss. Final weight losses in air approximated 10%, and approached, at the lowest pressure (50 mm.), the 7% observed in argon. Water and benzene were evolved, the latter at a rate that decreased with decrease in pressure. Traces of phenol, formaldehyde, propane, and higher molecular weight hydrocarbons were also given off. The evolution of carbon dioxide, carbon monoxide, methane, and hydrogen and the consumption of oxygen were followed in detail. Changes in air pressure from 700 to 300 mm. did not alter appreciably the rates of product evolution, oxygen consumption, and of weight loss. At lower presures (300 to 50 mm.), however, the molar ratio of the total noncondensed gases generated to total oxygen consumed increased, indicating a possible change in reaction mecha

ISSN:0021-8995    

DOI:10.1002/app.1959.070020606

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractCinnamic acid esters of poly(vinyl alcohol) and of cellulose are insolubilized by ultraviolet radiation. This response may be increased by the inclusion of simple organic compounds such as Crystal Violet carbinol and Michler's ketone. A method of measuring this response (in terms of a sensitivity value,S) based upon photographic sensitometry has been devised. Preliminary study indicates that an increase inSis accompanied by an increase in response to the longer wavelengths of light.

ISSN:0021-8995    

DOI:10.1002/app.1959.070020607

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractIt was reported in Part I of this series that coatings of various polymers containing cinnamic ester groups are rendered insoluble by exposure to ultraviolet radiation, and that the rate of insolubilization may be increased by the inclusion of certain organic compounds. A continued systematic examination of the behavior of several hundred organic compounds has revealed that the ability to sensitize to some degree is quite general, provided that no complicating factors are present. The sensitivity of poly(vinyl cinnamate) is decreased by the presence of reducing groups in the addend, and sensitizing activity is lowered by interaction between adjacent groups. It is enhanced by the introduction of increasing conjugation and of ketone, nitro, or amino groups. Spectrograms of polymer‐sensitizer combinations indicate that, with increasing sensitivity value, the sensitivity shifts towards, and, in some cases, into, the visible portion of the spectru

ISSN:0021-8995    

DOI:10.1002/app.1959.070020608

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractA technique is described for the small scale evaluation of plastisol formulations for molding, casting, coating, and foam applications. The technique described rapidly measures and automatically records the viscosity of a plastisol as a function of temperature by means of a Bendix Ultra‐Viscoson and thermocouple. The measurements are made under conditions that closely approach process conditions. Small changes are accurately followed and the portion of the curve in the vicinity of gelation is amplified. The shape and position of the viscosity‐temperature plot are dependent on the chemical nature of the plasticizer as well as the intrinsic viscosity and molecular weight distribution of the dispersed polymer. The resulting curves can be used to choose plastisol compositions for a given application. The application of the curves to foam and rotational casting formulations is outli

ISSN:0021-8995    

DOI:10.1002/app.1959.070020609

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY

摘要:

AbstractThe method of continuous and intermittent stress relaxation measurements on rubber vulcanizates developed by Tobolsky and co‐workers has been modified by the introduction of intermittent tangent modulus measurements during the continuous relaxation experiments. This allows rate of scission and crosslinking to be determined simultaneously and on the same specimen. The method is based on the use of small or moderate extension ratios α and on the fact that in this case the stressfin actual rubbers is represented more closely by the empirical relationshipf= 3G(1−1/α) than by the theoreticalf=G[α−(1/α2)], where 3Gdenotes Young's modulus at infinitesimally smal

ISSN:0021-8995    

DOI:10.1002/app.1959.070020610

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1959

数据来源: WILEY