Relative Contributions of Viscoelasticity and Aging to the Relaxation of Rubber Vulcanizates

Abstract Relaxation in relatively stable, gum natural rubber vulcanizates has been studied to determine the effects of viscoelasticity and aging, respectively, using a dark, air-oven. A quantitative analysis of experimental results shows that, in the case of a dicumyl peroxide vulcanizate at 100° C, relaxation is caused by aging, except in its initial stages. Stress decreases as a linear function of time, in agreement with theoretical assumptions. Conversely, at 30° C, the effect of aging is negligible. At this temperature the difference between actual stress and stress extrapolated to infinite time, is proportional to a negative power of time. At intermediate temperatures, both phenomena occur simultaneously over a time interval ranging from. 3 minutes to 150 hours.

Download Full-text

Relative Contributions of Viscoelasticity and Aging to the Relaxation of Cured Rubber

Rubber Chemistry and Technology ◽

10.5254/1.3540353 ◽

1964 ◽

Vol 37 (3) ◽

pp. 617-626 ◽

Cited By ~ 7

Author(s):

P. Thirion ◽

R. Chasset

Keyword(s):

Quantitative Analysis ◽

Natural Rubber ◽

Time Interval ◽

Dicumyl Peroxide ◽

Infinite Time ◽

Negative Power ◽

Theoretical Assumptions ◽

The Difference ◽

Natural Rubber Vulcanizates ◽

Actual Stress

Abstract Relaxation in relatively stable pure gum natural rubber vulcanizates has been studied to determine the effects of viscoelasticity and aging, respectively, using a dark air oven. A quantitative analysis of experimental results shows that, in the case of a dicumyl peroxide vulcanizate and at 100° C, relaxation is caused by aging, except in its initial stages. Stress decreases as a linear function of time, in agreement with theoretical assumptions. Conversely, at 30° C, the influence of aging is negligible. At this temperature the difference between actual stress and stress extrapolated to infinite time, is proportional to a negative power of time. At intermediate temperatures, both phenomena occur simultaneously over a time interval ranging from 3 minutes to 150 hours.

Download Full-text

Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates

Rubber Chemistry and Technology ◽

10.5254/1.3542442 ◽

1959 ◽

Vol 32 (3) ◽

pp. 739-747 ◽

Cited By ~ 4

Author(s):

J. R. Dunn ◽

J. Scanlan

Keyword(s):

Stress Relaxation ◽

Natural Rubber ◽

Protective Action ◽

Dicumyl Peroxide ◽

Vulcanized Rubber ◽

Aging Properties ◽

Photochemical Aging ◽

Natural Rubber Vulcanizates

Abstract The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.

Download Full-text

The Crosslinks in TMTD-Zinc Oxide-Natural Rubber Vulcanizates

Rubber Chemistry and Technology ◽

10.5254/1.3542155 ◽

1960 ◽

Vol 33 (2) ◽

pp. 394-397 ◽

Cited By ~ 1

Author(s):

C. G. Moore

Keyword(s):

Zinc Oxide ◽

Natural Rubber ◽

Appreciable Amount ◽

Dicumyl Peroxide ◽

Swelling Properties ◽

Tetramethylthiuram Disulfide ◽

Chemical Studies ◽

The Subject ◽

Natural Rubber Vulcanizates ◽

Recent Experimental Work

Abstract The mechanism of vulcanization of natural rubber (NR) by means of tetramethylthiuram disulfide (TMTD) and zinc oxide has been the subject of much recent experimental work and speculation. While such studies have clarified the kinetics and stoichiometry of TMTD decomposition and zinc dimethyldithiocarbamate formation, they have not directly aided our knowledge of the nature of the crosslinks in the resultant vulcanizate. It was earlier suggested that the vulcanizate contained only C—C crosslinks, comparable with those formed by means of di-tert-alkyl (and aralkyl) peroxides, while more recently, disulfide crosslinks have been proposed. However, neither of these views has been confirmed by direct chemical studies of the vulcanizate. Evidence is now presented which shows that there can be no appreciable amount of C—C crosslinking by the TMTD-ZnO combination, and this is consistent with the view that sulfur crosslinks predominate. This conclusion is based on the respective swelling properties in n-decane of dicumyl peroxide vulcanizates (containing only C—C crosslinks) and TMTD-ZnO vulcanizates, which have been treated with methyl iodide in vacuo at 80° C. This reagent is known to cause the fission of C—S and S—S bonds in variously constituted organic mono- and polysulfides and should therefore cause the fission of sulfur crosslinks in a vulcanizate with consequent degradation of the network (cf. Ref. 8), whereas there is no evidence that di-allylic C—C crosslinks can be similarly degraded.

Download Full-text

The Determination of Network Chain Density and the Chemical Stress Relaxation of Crosslinked Polymers

Rubber Chemistry and Technology ◽

10.5254/1.3542917 ◽

1973 ◽

Vol 46 (2) ◽

pp. 477-482

Author(s):

Saburo Tamura ◽

Kenkichi Murakami

Keyword(s):

Stress Relaxation ◽

Natural Rubber ◽

Main Chain ◽

Chemical Stress ◽

Dicumyl Peroxide ◽

Constant Independent ◽

Crosslinked Polymers ◽

Network Chain ◽

The Difference ◽

Entanglement Network

Abstract Both initial network chain densities nM(0) and nS(0) of dicumyl peroxide- cured natural rubbers were determined from the tensile stress and swelling method, respectively. The difference between nM(0) and nS(0) was usually constant, independent of the magnitude of network chain density. That is, it was found that the number of entanglement network chains in the crosslinked natural rubber was usually constant, independent of network chain density. The entanglement network chain density nII(0) was 0.7×10−4 mole/cc. This led to the supposition that the molecular weight between entanglement points Me would be about 9000. Although this value is far from exact, it does not differ too greatly from the value found for noncrosslinked natural rubber. Next, in order to calculate the number of main-chain scissions of crosslinked polymers from their chemical stress relaxation, we proposed our modification of Tobolsky's equation. Using our equation, it was found that the scission of dicumyl peroxide-cured natural rubber occurred in the main chain only. Furthermore, this value agreed with the one obtained from the oxidation of toluene solution of noncrosslinked rubber under the same conditions.

Download Full-text

Wiener–Hopf Method Applied to the X-ray Edge Problem

International Journal of Modern Physics B ◽

10.1142/s0217979297001696 ◽

1997 ◽

Vol 11 (29) ◽

pp. 3433-3453 ◽

Cited By ~ 3

Author(s):

V. Janiš

Keyword(s):

Integral Equations ◽

Time Limit ◽

Time Interval ◽

Infinite Time ◽

Effective Lifetime ◽

X Ray ◽

Edge Problem ◽

Long Time ◽

The Difference ◽

Hopf Method

We apply the Wiener–Hopf method of solving convolutive integral equations on a semi-infinite interval to the X-ray edge problem. Dyson equations for basic Green functions from the X-ray problem are rewritten as convolutive integral equations on a time-interval [0,t] with t→∞. The long-time asymptotics of solutions to these equations is derived with the aid of the Wiener–Hopf method. Although the Wiener–Hopf long-time exponents differ by a factor of two from the solution of Nozières and De Dominicis we demonstrate how the latter and the critical exponents of measurable amplitudes from the X-ray problem can be derived from the former. We explain that the difference in the exponents arises due to different ways of performing the long-time limit in the two solutions. To enable the infinite-time limit in the defining equations a new infinite-time scale τ→∞, interpreted as an effective lifetime of the core-hole, must be introduced. The ratio t/τ decides about the resulting critical exponent. The physical relevance of the Nozières and De Dominicis as well as of the Wiener–Hopf exponents is discussed.

Download Full-text

Crosslink Formation during Aging of Natural Rubber Vulcanizates

Rubber Chemistry and Technology ◽

10.5254/1.3535658 ◽

1965 ◽

Vol 38 (2) ◽

pp. 374-378

Author(s):

L. J. Maisey ◽

J. Scanlan

Keyword(s):

Stress Relaxation ◽

Natural Rubber ◽

Cross Linking ◽

Crosslinking Reaction ◽

Oxidative Reactions ◽

Relaxation Measurements ◽

Equilibrium Swelling ◽

Form Part ◽

The Difference ◽

Natural Rubber Vulcanizates

Abstract The effect of antioxidant on the crosslinking reaction occurring during the oxidation of sulphur vulcanizates of natural rubber was investigated by using both continuous and intermittent stress relaxation measurements. Similarly, by means of continuous stress relaxation and equilibrium swelling measurements the cross-linking reaction in vacuum was followed. The presence of antioxidant or removal of air reduced considerably both continuous and intermittent relaxation and also the difference between them, which measures the crosslinking. The crosslink formation must therefore form part of the sequence of oxidative reactions.

Download Full-text

The Oxidative Aging in Ultraviolet Light of Dicumyl Peroxide Vulcanizates of Natural Rubber in Presence of Various Antioxidants

Rubber Chemistry and Technology ◽

10.5254/1.3540238 ◽

1961 ◽

Vol 34 (2) ◽

pp. 686-696 ◽

Cited By ~ 3

Author(s):

J. R. Dunn

Keyword(s):

Natural Rubber ◽

Ultraviolet Light ◽

Protective Action ◽

Phenolic Antioxidants ◽

Dicumyl Peroxide ◽

Oxidative Aging ◽

Natural Rubber Vulcanizates ◽

Accelerate Degradation

Abstract The oxidative aging of natural rubber vulcanizates at 25° C under irradiation by ultraviolet light of wavelength 365 mµ has been described in a number of communications from this laboratory. At this wavelength naphthylamines were shown to accelerate degradation of peroxide vulcanizates while substituted p-phenylenediamines inhibited it; α-naphthol and a variety of dithiocarbamates were also found to have a protective action. Since some amines and phenolic antioxidants do not absorb light of wavelength 365 mµ but do absorb in the region of 313 mµ, investigations have now been made of the effect of a large number of additives on aging at the shorter wavelength, so that predictions might be made of the most suitable materials to employ in protecting unfilled vulcanizates against crazing in sunlight.

Download Full-text

Vulcanization Studies of Elastomers Using Solid-State Carbon-13 NMR

Rubber Chemistry and Technology ◽

10.5254/1.3538176 ◽

1983 ◽

Vol 56 (5) ◽

pp. 971-994 ◽

Cited By ~ 28

Author(s):

Dwight J. Patterson ◽

Jack L. Koenig ◽

J. Reid Shelton

Keyword(s):

Fourier Transform ◽

Free Radical ◽

Solid State ◽

Natural Rubber ◽

Fourier Transform Infrared ◽

Difference Spectrum ◽

Dipolar Interaction ◽

Infrared Analysis ◽

Dicumyl Peroxide ◽

The Difference

Abstract With the use of solid state carbon-13 NMR, changes in the structure of natural rubber and cis-polybutadiene were observed spectroscopically. Cis-trans conversion has been shown to occur in the naturaal rubber by the rearrangement of the allylic free radical. At least four structurally different methyl groups have been detected in the crosslinking of natural rubber by dicumyl peroxide, which indicates that the simple combination of allyic free radical is an oversimplification of the curing process. Quaternary aliphatic carbons have been detected which results from double bond migration. Polybutadiene showed only methine and methylene carbons present in the crosslinked network with a small amount of methyl end-groups. The increase in the line width of the highly crosslinked elastomers was shown to be dominated by the carbon-hydrogen static dipolar interaction. Fourier-transform infrared analysis observed the formation of a molecular complex between dicumyl peroxide and polybutadiene. The formation of trans double bonds was observed in the infrared spectra of polybutadiene. Weak broad bands around 1320 cm−1 were observed in the difference spectrum of cured rubbers and were assigned to carbon-carbon crosslinks. From the structural interpretation of spectra obtained from solid state carbon-13 NMR and Fourier-transform infrared, models are proposed for the crosslinked networks of natural rubber and polybutadiene, obtained from peroxide vulcaniation.

Download Full-text