Chain Scission Efficiency in the Oxidation of Natural Rubber Vulcanizates

1957 ◽  
Vol 30 (4) ◽  
pp. 1146-1161
Author(s):  
A. G. Veith
Keyword(s):  
Natural Rubber ◽  
Elevated Temperatures ◽  
Density Ratio ◽  
Direct Consequence ◽  
Chain Scission ◽  
Polymer Chains ◽  
Published Report ◽  
Relaxation Measurements ◽  
A Chain ◽  
Chain Scission Reaction

Abstract Natural rubber when it degrades under the action of oxygen does so primarily by a chain scission reaction. A technique has been developed by Tobolsky and coworkers for assessing the magnitude of this chain scission reaction in vulcanizates by means of continuous stress relaxation measurements. Since the result of the oxygen attack on the rubber is a chain scission reaction, the question of the efficiency of the reaction comes to mind. The influence of antioxidants is of importance in this regard as is the type of vulcanizate or network structure. This paper describes some measurements of the chain scission efficiency of a simple benzothiazolyl disulfide (MBTS) vulcanizate and the effect of several antioxidants on this chain scission reaction. Some of the complications inherent in this type of measurement are discussed. The first published report on the efficiency of the chain scission reaction in vulcanizates was given by Tobolsky, Metz, and Mesrobian in 1950. A more recent publication is that of Baxter, Potts, and Vodden in 1955. Tobolsky has interpreted the stress decay of gum vulcanizates at elevated temperatures as a direct consequence of the cutting of polymer chains of the network. The reduced stress is postulated as being equal to the chain density ratio:

Chain Scission in the Oxidation of Polyisoprene

1977 ◽  
Vol 50 (2) ◽  
pp. 373-396 ◽  
Author(s):  
J. L. Morand
Keyword(s):  
Natural Rubber ◽  
Chain Scission ◽  
Vinyl Ketone ◽  
Methyl Vinyl Ketone ◽  
Alkoxy Radical ◽  
Methyl Vinyl ◽  
Protective Agents ◽  
Volatile Products ◽  
A Chain ◽  
Oxidation In Air

Abstract The composition of the mixture of volatile products formed during the oxidation in air of natural rubber or synthetic cis-polyisoprene in the raw state was investigated in order to obtain further information on the mechanism of chain scission. An important observation was made: in order to obtain, by means of gas chromatography, the peaks of all the constituents, a completely anhydrous solution of the trapped mixture must be used. If the water liberated by the oxidized polyisoprene is present, the peaks of some constituents do not appear. By removing this difficulty, four new less volatile compounds which could result from chain scission were detected on heating extracted polyisoprenes which do not contain protective agents. The concentrations of these four compounds are similar to those of levulinaldehyde, methacrolein, or methyl vinyl ketone, and the structures which were identified correspond to a γ-substituted γ-butyrolactone, a primary γ-ketol, and probably a tertiary γ-aldol and a secondary γ-ketol. These components could arise from a chain scission between two isoprene units, due to a β-scission process of an alkoxy radical. Natural rubber or synthetic polyisoprene which contain protective agents give off mainly the lactone and the tertiary γ-aldol, but levulinaldehyde is produced in small amounts, and methacrolein and methyl vinyl ketone are absent.

PHOTOLYSIS OF POLYACRYLONITRILE

1961 ◽  
Vol 39 (10) ◽  
pp. 2056-2068 ◽  
Author(s):  
H. H. G. Jellinek ◽  
I. J. Bastien
Keyword(s):  
Double Bond ◽  
Ethylene Carbonate ◽  
Bond Formation ◽  
Chain Scission ◽  
Photochemical Reactions ◽  
Polymer Chains ◽  
Small Quantum ◽  
Model Substance ◽  
Cross Links ◽  
Chain Scission Reaction

The photolysis of polyacrylonitrile has been investigated in solution (80:20 by weight of ethylene carbonate to propylene carbonate), in powder form, and as a film. Experiments have been carried out in vacuum and in the presence of oxygen. All polymer samples were exposed to ultraviolet light of wavelength 2537 Å. In solution a random chain-scission reaction with a small quantum yield (ca. 10−4 main chain bonds broken/quantum absorbed) takes place; at the same time, photochemical reactions occur involving side groups of the polymer chains, as evidenced by the change in the ultraviolet spectra of the polymer solutions. It seems likely that double-bond formation, both conjugated and isolated, and cyclization are responsible for the change in spectra. Infrared spectra do not show any change. Exposed polymer films become cross-linked and exposed powder also cross-links and evolves small molecules, such as nitriles, particularly HCN. Degradation in oxygen suppresses what is believed to be double-bond formation as evidenced by ultraviolet absorption spectra. The photolysis of glutaronitrile as a model substance has also been studied.

Stress Relaxation during the Thermal Oxidation of Vulcanized Natural Rubber

1960 ◽  
Vol 33 (2) ◽  
pp. 423-432
Author(s):  
J. R. Dunn ◽  
J. Scanlan ◽  
W. F. Watson
Keyword(s):  
Free Radical ◽  
Stress Relaxation ◽  
Natural Rubber ◽  
Thermal Aging ◽  
Elevated Temperatures ◽  
The Other ◽  
Tetramethylthiuram Disulfide ◽  
Oxidative Aging ◽  
Relaxation Measurements ◽  
Cross Links

Abstract The photoinitiated oxidative aging of peroxide vulcanized natural rubber (which contains only carbon-carbon cross-links) was found by stress relaxation measurements to be autocatalytic and to be sensitive to the presence of free radical retarders and catalysts. Similar behavior would be expected in thermal aging. However, earlier work in these laboratories indicated that the thermal aging of peroxide vulcanizates was not autocatalytic. Because of this discrepancy the stress relaxation of peroxide vulcanizates at elevated temperatures has now been reinvestigated and the study has been extended to include also the aging of the other types of networks which are produced on vulcanization by tetramethylthiuram disulfide in the absence of sulfur, by sulfenamide-sulfur, and by sulfur alone.

scholarly journals Preparation and characterization of liquid natural rubber through oxidative degradation with phenyl hydrazine and benzoyl peroxide-oxygen

2021 ◽  
Vol 912 (1) ◽  
pp. 012098
Author(s):  
Tamrin ◽  
S Leny ◽  
Eddiyanto
Keyword(s):  
Natural Rubber ◽  
Benzoyl Peroxide ◽  
Oxidative Degradation ◽  
Chain Scission ◽  
Phenyl Hydrazine ◽  
Vacuum Oven ◽  
Liquid Natural Rubber ◽  
Chain Scission Reaction ◽  
Rubber Product

Abstract The aim of this research was to synthesize liquid natural rubber (LNR) from Natural rubber (SIR-20) by chain scission method in the presence of oxygen gas and difference of peroxides, phenyl hydrazine and benzoyl peroxide. The chain scission reaction was conducted in solution of xylene in close system. SIR-20 was diluted xylene before flushing with oxygen and the addition of the peroxide. The degradation oxidation by the oxygen and the peroxides was processed at 60°C for 24 hours. The degradative oxidation product was re-precipitated by adding the excess of methanol and filtrated before dried in vacuum oven 60°C for 24 hours. The dried product was characterized by Fourier Transform Infra Red (FTIR). It was found that the liquid natural rubber product successfully degraded by chain scission process as shown the change of the peak area intensity of infrared absorption. It was showed the peaks area intensity of O-H and carbonyl group of liquid natural rubber spectra increased.

Effects of Frequency and Sonication Time on Ultrasonic Degradation of Natural Rubber Latex

2013 ◽  
Vol 747 ◽  
pp. 721-724 ◽  
Author(s):  
S. Utara ◽  
U. Moonart
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Average Molecular Weight ◽  
Natural Rubber Latex ◽  
Gel Permeation Chromatography ◽  
Chain Scission ◽  
Polymer Chains ◽  
Rubber Latex ◽  
Ultrasonic Degradation ◽  
The Fourier Transform

Ultrasonic degradation of fresh latex was investigated at frequencies of 20 and 25 kHz, at a constant temperature of 25o C (±1o C) to avoid temperature-related effects. The time-dependent evolution of the molecular weight of the natural rubber latex was determined using gel permeation chromatography, and its structure by means of the fourier transform infrared (FTIR) technique. A 10 minute period of sonication resulted in reduction in the molecular weight of both the 20 and 25 kHz treated samples, the lowest average molecular weight () being obtained in the case of the 25 kHz sample. The of the 25 kHz sample also decreased with increasing latex concentration. However, after 30 minutes, fluctuations had occurred in both samples with respect to the and and also the molecular weight distributions, an effect possibly explained by the competing processes of chain scission and radically-induced cross-linking of the polymer chains. The FTIR results also suggest that the structure of polyisoprene is unaltered by ultrasonic wave treatment at these frequencies.

The Thermal and Oxidative Stability of Chlorosulfonated Polyethylene Vulcanizates as Measured by Stress Relaxation

1971 ◽  
Vol 44 (5) ◽  
pp. 1410-1420
Author(s):  
F. Haaf ◽  
P. R. Johnson
Keyword(s):  
Stress Relaxation ◽  
Elevated Temperatures ◽  
Oxidative Degradation ◽  
Activation Energies ◽  
Polymer Chains ◽  
Chlorosulfonated Polyethylene ◽  
Thermal And Oxidative Stability ◽  
Relaxation Measurements ◽  
Accelerator System ◽  
Interchange Reactions

Abstract Stress relaxation measurements of chlorosulfonated polyethylene vulcanizates show that curing with m-phenylene-bis-maleimide gives thermally more stable crosslinks than the conventional metal oxide/sulfur accelerator system. The superior thermal stability of the bis-maleimide cure is based on the covalent nature of the crosslinks. In conventionally cured vulcanizates interchange reactions of the metal sulfonate and polysulfide crosslinks occur at elevated temperatures. The interchange reactions of the crosslinks cause a rapid stress decline at the beginning of the stress relaxation process. Over longer aging periods stress relaxation due to oxidative degradation becomes apparent in vulcanizates of both types. The activation energies of oxidative stress relaxations are very similar for the bis-maleimide and the conventional cure. The similarity of the activation energies indicates that oxidative degradation follows the same path. The site of the oxidative attack is established for bis-maleimide cured vulcanizates. Oxidative degradation is found to occur in the polymer chains rather than in the crosslinks. The effects of fillers and stabilizers are investigated and their mode of action is explained on the basis of the stress relaxation results.

A Peroxide Curing Butyl Rubber

1969 ◽  
Vol 42 (4) ◽  
pp. 1147-1154 ◽  
Author(s):  
C. E. Oxley ◽  
G. J. Wilson
Keyword(s):  
Natural Rubber ◽  
Chain Scission ◽  
Butyl Rubber ◽  
Polymer Chains ◽  
The Other ◽  
Cross Linking ◽  
Ethylene Propylene ◽  
Peroxide Curing ◽  
Polymer Reactions ◽  
Crosslinking Reactions

Abstract The reactions of peroxides with polymers have been studied for some time. They form an extensive part of vulcanization technology. Two types of reactions are generally recognized, those leading to crosslinking between polymer chains and those leading to scission of the chains. Natural rubber, polybutadiene and ethylene-propylene rubber are examples of polymers in which crosslinking reactions take place to a greater extent than reactions leading to chain scission and these polymer reactions with peroxides form a useful method of vulcanization. On the other hand, polyisobutene is an example of a polymer which degrades extensively and for polyisobutene and butyl rubber, peroxides have not found use as cross-linking agents.

scholarly journals Evaluation of Electron Induced Crosslinking of Masticated Natural Rubber at Different Temperatures

Polymers ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1279
Author(s):  
Huang ◽  
Gohs ◽  
Müller ◽  
Zschech ◽  
Wießner
Keyword(s):  
Natural Rubber ◽  
Elevated Temperatures ◽  
Sol Gel ◽  
Complex Viscosity ◽  
Chain Scission ◽  
Nitrogen Atmosphere ◽  
Size Exclusion ◽  
Reactive Blending ◽  
Exclusion Chromatography ◽  
Branched Chains

In this work, natural rubber (NR) was masticated using an internal mixer to fit the requirements of reactive blending with polylactide and characterized by size exclusion chromatography (SEC), Fourier-transform infrared (FT-IR) spectroscopy and dynamic rheology measurements. Subsequently, the effect of elevated temperatures (25 °C, 80 °C, and 170 °C) on the electron beam (EB) induced crosslinking and degradation of masticated natural rubber (mNR) in a nitrogen atmosphere without adding crosslinking agents has been investigated. The sol gel investigation showed that the gel dose of mNR slightly increased with increasing irradiation temperature, which is also confirmed by the swelling test. The chain scission to crosslinking ratio (Gs/Gx) was found to be less than 1 for irradiated mNR at 25 °C and 80 °C, suggesting a dominating crosslinking behavior of mNR. However, a significant increase of Gs/Gx ratio (~1.12) was observed for mNR irradiated at 170 °C due to the enhanced thermal degradation behavior at high temperature. A remarkably improved elasticity (higher complex viscosity, higher storage modulus, and longer relaxation time) for EB modified mNR was demonstrated by dynamic rheological analysis. Particularly, the samples modified at higher temperatures represented more pronounced elasticity behavior which resulted from the higher number of branches and/or the longer branched chains.

Formation and structure of polymeric carbons

1972 ◽  
Vol 327 (1571) ◽  
pp. 501-517 ◽  
Keyword(s):  
Glassy Carbon ◽  
Molecular Orientation ◽  
Early Stage ◽  
Structural Difference ◽  
Direct Consequence ◽  
High Resolution Electron Microscopy ◽  
Polymer Chains ◽  
Resolution Electron ◽  
Ribbon Structure ◽  
Phenolic Polymer

Glassy carbon has been prepared in the shape of disk and fibre by direct pyrolysis of a phenolic resin. Carbonization studies indicate that the unique structure of the final glassy carbon is a direct consequence of the production of very stable aromatic ribbon molecules by the coalescence of phenolic polymer chains at an early stage of pyrolysis. It is shown that molecular orientation induced in the initial polymer before pyrolysis is 'memorized’ to some extent after carbonization. Molecular orientation imposed in this type of carbon is not an intrinsic structural feature, but a physical characteristic which can be varied by the formation process or by extension at high temperatures; there is no essential structural difference apart from preferred orientation between polymeric units or microfibrils in well-oriented carbon fibres and isotropic glassy carbon. High resolution electron microscopy confirms this directly. We thus identify a new class of ‘polymeric carbons’, that consist of intertwined microfibrils comprising stacks of narrow graphitic ribbons. The fibrils are held together with covalent interfibrillar links of strength lower than that in the ribbons themselves. A ribbon structure has been proposed previously by Ruland (1971) for the specific case of high modulus carbon fibre. The structure is elaborated and extended here to cover all polymeric carbons and the steps in its development during carbonization are decisively detailed.

Graft Polymers Derived from Natural Rubber

1956 ◽  
Vol 29 (1) ◽  
pp. 99-105 ◽  
Author(s):  
G. F. Bloomfield ◽  
F. M. Merrett ◽  
F. J. Popham ◽  
P. Mc L. Swift
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Methyl Methacrylate ◽  
Transfer Reaction ◽  
Polymer Chains ◽  
Vinyl Monomers ◽  
Grafted Polymer ◽  
Polymeric Chains ◽  
Graft Polymers ◽  
Direct Growth

Abstract Graft polymers result when vinyl monomers are polymerized in the presence of natural rubber, either in solution or as latex, and some of the polymeric chains become attached to the rubber molecules. The properties of the natural rubber can be widely modified according to the nature and the amount of the grafted polymer. The polymer-modified natural rubber appears to be produced by direct growth of polymer chains on to rubber molecules rather than by a transfer reaction involving the rubber. Graft polymers of styrene and methyl methacrylate with natural rubber can be compounded and cured to give light-colored articles of good tensile strength, and rubber-methyl methacrylate graft polymers have outstanding flex-cracking and fatigue resistance.

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