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

1961 ◽  
Vol 34 (2) ◽  
pp. 686-696 ◽  
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.

Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates

1959 ◽  
Vol 32 (3) ◽  
pp. 739-747 ◽  
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.

Oxidative Aging of Natural Rubber Vulcanizates. Part III. Crosslink Scission in Monosulfidic Networks

1969 ◽  
Vol 42 (3) ◽  
pp. 924-935 ◽  
Author(s):  
T. Colclough ◽  
J. I. Cunneen ◽  
G. M. C. Hrggins
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Chemical Structure ◽  
Spectroscopic Methods ◽  
Chemical Probes ◽  
Conjugated Diene ◽  
Strain Measurements ◽  
Oxidative Aging ◽  
Tert Butyl Hydroperoxide ◽  
Natural Rubber Vulcanizates

Abstract A natural rubber vulcanizate containing almost entirely monosulfidic crosslinks was oxidized in oxygen and with tert-butyl hydroperoxide. The changes in physical properties due to oxidation were followed by stress—strain measurements, and the changes in chemical structure were investigated with chemical probes, and by spectroscopic methods. The results show that when the oxidized vulcanizates are heated at 75° C, the monosulfidic crosslinks are broken, that crosslinks containing two sulfur atoms are formed, and that conjugated diene and triene structures are introduced into the main polyisoprene chains.

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

1963 ◽  
Vol 36 (1) ◽  
pp. 50-58 ◽  
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, 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.

The Crosslinks in TMTD-Zinc Oxide-Natural Rubber Vulcanizates

1960 ◽  
Vol 33 (2) ◽  
pp. 394-397 ◽  
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.

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

1964 ◽  
Vol 37 (3) ◽  
pp. 617-626 ◽  
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.

Oxidative Aging of Natural Rubber

1968 ◽  
Vol 41 (1) ◽  
pp. 182-208 ◽  
Author(s):  
J. I. Cunneen
Keyword(s):  
Natural Rubber ◽  
Recent Work ◽  
Structural Characteristics ◽  
Degradation Process ◽  
Antioxidant Efficiency ◽  
Oxidative Aging ◽  
Aging Studies ◽  
Different Types ◽  
Controlled Structure ◽  
Natural Rubber Vulcanizates

Abstract In the last few years several reviews and books have been published on the aging of elastomers, but the overall view which they present of the oxidation of natural rubber and its vulcanizates still contains many puzzling features. Two of these are the variation of antioxidant efficiency in different types of vulcanizate, and the extent of the involvement of crosslink scission in the overall degradation process in sulfurated vulcanizates. Sometimes apparent contradictions have arisen from a failure to appreciate that aging of natural rubber vulcanizates depends primarily on four factors; the purity and type of rubber, the presence of additives, the type and extent of vulcanization, and the purification (if any) after cure. In many cases direct comparisons have been attempted without due consideration being given to all these factors, leading inevitably to some confusion. Recent work on the structure of vulcanizates has enabled the NRPRA to embark on a program of aging studies with vulcanizates of carefully controlled structure and complexity, which has already led to a better understanding of the processes involved in vulcanizate degradation. This review will attempt to elucidate the present state of knowledge, and will therefore be largely concerned with recent work at NRPRA, and its relation to previous studies. The review is divided into two main parts, they are: the effect of vulcanizate structure on aging, and the chemistry of oxidative scission reactions. Before attempting to rationalize the effect of vulcanizate structure on aging, structural characteristics of the most important types of vulcanizate are briefly discussed.

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