摘要:

AbstractThe kinetics of uncatalyzed autoxidations for polyolefin films, such as atactic and isotactic polypropylene and poly‐(butene‐1) are reviewed in light of recent work. Reaction temperatures generally varied from 100 to 150°C and oxygen concentrations from 5 to 100% by volume. A general reaction scheme is suggested and kinetic expressions subsequently derived therefrom have been satisfactorily applied to account for experimental results. Linear relationships between a maximum rate and concentration of oxygen for both low and high concentrations were obtained.In the case of the catalyzed autoxidations [Co(III) acetylacetonate] the general reaction scheme was modified to take into account the presence of the catalyst. From this modified scheme, various kinetic expressions relating maximum rate and concentrations of oxygen, polymer and the catalyst were derived. First‐order reaction with respect to the concentration of the catalyst was found at low concentrations of the catalyst, and near zero‐order at relatively high catalyst concentrations. A correlation between catalytic activities of metal acetylacetonates [Co(III), Mn(III), Cr(III), Fe(III) and Cu(II)]and the oxidation‐reduction potentials has been established.Experimental dependencies of maximum carbonyl formation rates as a function of polymer concentration were found to agree well with the theoretical both for catalyzed and uncatalyzed

ISSN:0032-3888    

DOI:10.1002/pen.760110402

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe effects of polymer molecular weight, molecular weight distribution, and orientation on the rate of relaxation‐controlled sorption of n‐pentane by glassy polystyrene were studied. The sorption follows Case II kinetics but for films which sorb slowly the sorption rate increases at relatively long times until sorption is sharply terminated. This rate increase may be explained by the development of dispersed microvoids within the unrelaxed film core. Overshoot of the equilibrium n‐pentane content occurs in sorption experiments in which accelerated sorption is pronounced.The sorption rate is independent of polymer molecular weight and molecular weight distributionper seover a broad wrange of these parameters. Essentially identical vapor sorption kinetics were observed for well annealed polystyrene films of different molecular weights and distributions. Conversely, for vapor sorption by uniaxially oriented films and for liquid sorption by partially annealed films, high molecular weight film (1,880,000) exhibits greater sorption rates than low molecular weight film (ca. 200,000). These differences in rate are not due to molecular weight differencesper se, but are a consequence of the dissimilar response of free volume and strain development for films of different molecular weight prepared with a given time‐temperature‐strain history.Crazing of carefully annealed polystyrene films occurs during desorption of n‐pentane from partially saturated films. The depth of craze penetration reflects the point of advance of the discontinuous Case II sorpti

ISSN:0032-3888    

DOI:10.1002/pen.760110403

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe utility of anisotropic ultrafiltration membranes in gas separation has been examined. These membranes consist of a thin (0.2‐2μ) barrier layer supported upon a more porous supporting substructure. Gases permeate these membranes by a Knudsen diffusion mechanism. Permeabilities from 0.1 to 0.4 cm sec−1cm Hg−1were obtained. These values are 104to 105higher than most conventional gas separation membranes. These membranes may be useful in several gas separation pro

ISSN:0032-3888    

DOI:10.1002/pen.760110404

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractFibrous structures of high complexity, as introduced by ply and twist, have been subjected to high and low speed tensile tests. The ratio of strength at high speed to low speed is always greater than one, but decreases with increasing complexity of fibrous structure. The ratio of elongation to break at high speed to that at low speed is always less than one and also decreases with increasing structure complexity. The ability to absorb energy markedly increases with increasing complexity of geometry at low strain rates, characteristic of an Instron. The reasons for this additional energy absorption are discussed. Tests at high rates of strain point out the inability of many complex textile structures to translate their superior energy absorption characteristics to high strain rates. The results obtained and the principles demonstrated are applied to the development of improved materials for use in aerial delivery and ballistic applications.

ISSN:0032-3888    

DOI:10.1002/pen.760110405

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractA torsional pendulum which operates throughout the temperature range — 180° ⇄ +650°C, and permits the examination of specimens which conform to ASTM standard D2236 is reported. The same apparatus is used for torsional braid analyses for which a composite specimen is prepared by impregnating a multifilament glass braid with a solution of polymer and thermally removing the solvent. A linear‐with‐angle no‐drag optical transducer which employs the linear transmission region of a pair of polarizers is described. The apparatus has been used for examining thermo‐hysteresis effects in polymers. Hysteresis can arise in polymers from physical time‐dependent phenomena such as crystallization ⇄ fusion, dry atmosphere ⇄ water vapor, annealing ⇄ cracking, and from chemical reactions. Thermally‐induced chemical reactions can be regulated so as to freeze out preferentially longer range relaxations, thereby extending the glassy state behavior to higher temperatures. A comparison of the thermomechanical behavior of a commercially available polyimide film and of a polyimideforming varnish is reported using torsional pendulum and t

ISSN:0032-3888    

DOI:10.1002/pen.760110406

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractMelt viscosity and melt elasticity data were obtained over a broad range of temperatures and shear rates on a series of four polypropylenes of different molecular weight but approximately the same molecular weight distribution. The superposition technique was used with both temperature and molecular weight to shift flow curves for all four materials at three temperatures each along the shear rate axis to generate a master flow curve at a given temperature and molecular weight. For polypropylenes of this type, and molecular weight distribution shift, factors which can be used to extend the useful range of experimentally obtained flow data were determined. The dependency of apparent viscosity on weight average molecular weight at shear stresses as high as 106dynes/cm2is shown. The dependency of melt elasticity on molecular weight and temperature is discussed.

ISSN:0032-3888    

DOI:10.1002/pen.760110407

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

Abstract3,3,3‐Trichloropropylene oxide (TCPO) is a monomer which has the combination of a highly reactive epoxide group and a stable trichloromethyl group. The epoxy group will undergo ring opening polymerizations with itself and with a host of other compounds to yield polymeric materials. Water, alcohols, phenols, amines, carboxylic acids and many other compounds react with TCPO with the aid of Lewis acid type catalysts. The electron‐withdrawing influence of the trichloromethyl group, steric effects and the oxirane ring have a strong influence on the course of reactions, which are often radically different from that encountered with the simpler alkylene oxide monom

ISSN:0032-3888    

DOI:10.1002/pen.760110408

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractIt has been well established in the literature that the internal pressure,Pi= (∂E/∂V)T, of a polymer in the glassy state is about half the value expected from the behavior of the polymer just above the glass temperature,Tg. Consideration of this behavior in terms of a recent analysis of factors affecting internal pressures leads to the conclusion that the expression for the total energy of a glass must include a volume‐dependent stored energy term, a term not present aboveTg. This stored energy could be associated with actual bond and segment deformations in the glassy state. Brittleness and solvent cracking behavior of glasses will be strongly dependent on this stored elastic energy which can be modified by altering the molding conditions under which the glass is f

ISSN:0032-3888    

DOI:10.1002/pen.760110409

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractCiné film was employed for recording the movement of tracer particles, thus directly determining the velocity profile in the capillary flow of model materials of polybutadiene over a range of shear stresses relating to (1.) flow conditions in which there is no distortion of the regular stream of melt emerging from a capillary, (2.) severe surface fracture, (3.) elastic turbulence, (4.) oscillatory flow of melts with discontinuous flow curves. No qualitative difference was found between the velocity profiles in conditions (1) and (2); surface fracture is not related to laminar flow disturbances and originates at the capillary exit. Surface fracture must be distinguished from elastic turbulence. The streamline velocities undergo both local and time variations within the capillary under conditions of developed elastic turbulence; the wall velocity is non‐zero. A periodic pulsation of velocities occurs in the flow curve discontinuity region; it takes place throughout the capillary and is caused by stick‐slipping of polymer on the capillary wall. The frequency of velocity pulsations coincides with the frequency of extrudate variat

ISSN:0032-3888    

DOI:10.1002/pen.760110410

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractPolymethyl methacrylate, polyacetal and polypropylene samples were subjected to constant‐load uniaxial creep in tension and compression up to 3% strain in times up to 105sec. A higher creep resistance was obtained in compression compared with tension due to the influence of free volume on mobility. Square wave cyclic creep tests alternately in tension and equal compression for dwell times of 10, 100, 1000 sec were also conducted on each material up to a total time of 105sec. Under low cyclic creep stresses tension creep cancelled out compression creep in each successive half cycle so that there was no overall increase in creep strain as cycling proceeded. The unidirectional creep data was used successfully to predict this behavior. At higher cyclic stress levels creep strain range increased steadily throughout the test indicating a softening process. A few tests were conducted in unidirectional and cyclic stress relaxation on polymethyl methacrylat

ISSN:0032-3888    

DOI:10.1002/pen.760110411

出版商:Society of Plastics Engineers, Inc.    

年代:1971

数据来源: WILEY