摘要:

AbstractStress‐strain cycling of natural rubber to high strains produces greater softening than amorphous rubbers, but only if the force on the sample is relaxed below a certain value during the cycle. This phenomenon, attributed to crystallization shows why nonrelaxing tests give a longer fatigue life than relaxing test

ISSN:0021-8995    

DOI:10.1002/app.1967.070111001

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe stresses and energy losses during simple extension cycles up to a maximum elongation of 530% have been determined for an unfilled vulcanizate of natural rubber as a function of the temperature and extension rate. At sufficiently short elongation times and low temperatures, the rate and temperature dependence of the ascending stresses are connected by the Ferry transform, and the superposition principle can be applied to them. Outside this experimental range, the stresses are increased by crystallization. The validity of the Ferry transform for the energy losses and the energy loss ratio is more restricted than for the stresses, and the losses are always higher than can be expected from a purely viscoelastic mechanism. The additional losses are tentatively ascribed to incipient crystallization and stress‐softening effects. At short elongation times and low temperatures, the losses approach the values predicted by viscoelasticity, and the loss ratio becomes independent of the maximum extension of the strain cycl

ISSN:0021-8995    

DOI:10.1002/app.1967.070111002

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

年代:1967

数据来源: WILEY

摘要:

AbstractUse of porous glass with a broad pore‐size distribution as a column packing for gel permeation chromatography has been investigated. The porous glass is readily available, and columns are packed easily and have excellent mechanical stability. Separations of polystyrene over molecular weight ranges of 500–2,000,000 have been obtained. Porous glass thus appears to be a useful packing material for gel permeation chromatogra

ISSN:0021-8995    

DOI:10.1002/app.1967.070111003

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe volume frequency size distribution of PVC latex powder was determined by means of three different methods, which all gave the same frequency maximum at about 0.8–0.9 μ diameter. While the electron microscope analysis, which allows the agglomerates to be resolved into individual primary particles, did not show any particles above 1.5 μ in a sample of 9000, both the Coulter counter and the disk centrifuge showed a considerable amount of larger partic

ISSN:0021-8995    

DOI:10.1002/app.1967.070111004

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

年代:1967

数据来源: WILEY

摘要:

AbstractCreep tests were carried out on epoxy resin specimens at room temperature and at different high stress levels under tension, compression, and flexure. Compared with the behavior at constant strain rate (CSR) reported in Part I of this work, creep strain–time curves revealed a distinct delayed yielding region of constant minimum rate (secondary creep) followed by a post‐yielding region of increasing slope (tertiary creep). In all cases, results indicate linearity between creep stress and log secondary creep rate, which is almost coincident with the corresponding relationship between yield stress and strain rate obtained in subsequent CSR loading cycles with the same specimens. The similarity in behavior under both the creep and CSR modes conforms to Eyring's theory of non‐Newtonian viscous flow at high stress levels and low temperature. Theoretical analysis yields reasonable values of the activation volume, which is unaffected by the loading and test modes or by loading history, and could thus be regarded as an intrinsic parameter of the microstructure, inherently related to the viscoplastic process involved. The above considerations indicate a deviatoric stress‐biased diffusional mechanism as the predominant factor in the yielding of an amorphous glassy epoxy

ISSN:0021-8995    

DOI:10.1002/app.1967.070111005

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe regulating efficiency of 14 dialkyl xanthogen disulfides in emulsion copolymerization of butadiene with styrene at +5°C. with the use of a diisopropylbenzene hydroperoxide–complexed ferrous iron–sodium formaldehyde sulfoxylate redox system in the presence of sodium soap of disproportionated rosin as an emulsifier, was evaluated. The apparent chain transfer constants ofn‐alkyl and isoalkyl derivatives decreased logarithmically with increasing length of the alkyl group, which seems to be related to the analogous dependency of their solubilities in water. The dialkyl xanthogen disulfides, especially the lower homologs, acted as retarders of polymerization. The retardation did not affect their regulation efficiency. On the basis of values of the apparent chain transfer constants it is possible to predict the molecular weight of polymers, except for the region where the regulation is poor and where the deteriorative influence of termination and crosslinking reactions takes place. The diisopropyl xanthogen disulfide has been selected as the most convenient of the compounds studied for molecular weight regulation of emulsion copolymerization of butadiene with styrene in the system men

ISSN:0021-8995    

DOI:10.1002/app.1967.070111006

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe influence of kind and amount of an anionic emulsifier, pH of water phase, addition of free rosin, and content of conjugated structures in rosin on the regulation efficiency of diisopropyl xanthogen disulfide in emulsion copolymerization of butadiene with styrene at +5°C. was studied. The apparent chain transfer constantCdecreased in the order: Li+>Na+>K+, for the cations with the hydrolysis of rosin soap. This soap is replaceable with other anionic emulsifiers,Cbeing dependent on the absorption area of one soap molecule. With increasing amount of soap the value ofCdecreased. With the decreasing pH of the water phase, the value ofCincreases. This fact can be explained by the increase in hydrolysis of carboxylic groups of rosin and oleate soaps and an increase in the permeability of the monomer–polymer particle surface to molecules of regulator. This tendency does not exist in the case of sulfonate‐type soaps. After addition of free rosin to the monomer phase, a similar increase inCis noted. The value ofCincreased also with an increase in the content of conjugated structures characterized by a value δ, which is related to the retardation of polymerization. The standard polymerization recipe at pH 10.8 is suitable from the point of view of using diisopropyl xanthogen disulfide as a molecular weight regu

ISSN:0021-8995    

DOI:10.1002/app.1967.070111007

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe regulating efficiency of four aliphatic mercaptans was studied in emulsion copolymerization of butadiene with styrene, at +5°C. with the use of the redox system, diisopropylbenzene hydroperoxide–complexed ferrous iron–sodium formaldehyde sulfoxylate as an initiator and the sodium soap of disproportionated rosin as an emulsifier. The apparent transfer constantsCof tertiary mercaptans decreased logarithmically with increasing length of molecule. This tendency is connected with the analogous dependency of solubilities of these compounds in water. The mercaptans did not affect the rate of polymerization. The value ofCis independent of the amount of regulator used. With the value ofC, the amount of regulator, and the conversion known, it is possible to predict the molecular weight of the polymers, except for the region of poor regulation, where the deteriorative influence of termination and crosslinking reactions takes place. The apparent transfer constant of tertiary dodecyl mercaptan decreased with increasing rate of polymerization. After elimination of diffuse processes, the value of the actual relative transfer constant was calculated. The tertiary dodecyl mercaptan has been selected as the most convenient molecular weight regulator for emulsion copolymerization of butadiene with styrene of all compounds studied for the system menti

ISSN:0021-8995    

DOI:10.1002/app.1967.070111008

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

年代:1967

数据来源: WILEY

摘要:

AbstractAvailable methods for testing the transparency of plastic sheet and film have been found inadequate as regards the correlation between measurement and visual observation. A newly developed procedure, based on the determination of light transmission within a very small angle, gives good correlation. The application of the method and its limitations, due to the difference in optical effect of small‐angle and large‐angle scattering, are discussed. A description is given of the instrument, a special feature of which is that it gives direct readings of optical density and transpare

ISSN:0021-8995    

DOI:10.1002/app.1967.070111009

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

年代:1967

数据来源: WILEY

摘要:

AbstractThe effect of60Co γ‐radiation on the thermal conductivity of polypropylene (PP) has been studied over the temperature range 0–160°C. for radiation doses of 600 and 1800 Mrad. The conductivity of unirradiated specimens rises from 4.5 × 10−4cgs units (cal./cm.‐sec.‐°C.) at 0°C. to 4.8 × 10−4cgs units at 80°C. and subsequently decreases with temperature to a value of about 3.1 × 10−4cgs units at 160°C. Upon irradiation to 600 Mrad the thermal conductivity is lowered over the 0–150°C. temperature range. Above 90°C. the conductivity decreases with temperature and becomes relatively constant at 3.4 × 10−4cgs units from 120 to 160°C. Differential scanning calorimeter (DCS) measurements from 30 to 200°C. show that irradiation to 600 Mrad lowers the energy associated with crystalline melting and shifts the endotherm melting peak from about 160 to 105°C. Irradiation to 1800 Mrad results in additional lowering of the thermal conductivity over the 50–160°C. range, a further decrease in area of the endothermic peak and a shift of its maximum peak position to about 75°C. The effects of radiation on the thermal conductivity of polypropylene are compared and correlated with the observed effects of radiatio

ISSN:0021-8995    

DOI:10.1002/app.1967.070111010

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

年代:1967

数据来源: WILEY