Thermal Breakdown of Rubber

1946 ◽  
Vol 19 (2) ◽  
pp. 277-282 ◽  
Author(s):  
J. L. Bolland ◽  
W. J. C. Orr
Keyword(s):  
Degradation Products ◽  
Chain Scission ◽  
Contributory Factor ◽  
Theoretical Treatment ◽  
Thermal Breakdown ◽  
Chain Molecules ◽  
Random Fashion ◽  
Efficient Alternative ◽  
Resonance Stabilization ◽  
Insight Into

Abstract The degradation of rubber observed during various technological processes may arise from several different causes. Since one such contributory factor is possibly degradation by a purely thermal mechanism, it is of interest to estimate experimentally the importance of this type of degradation under the temperature conditions normally used in the processing of rubber. It may be stated immediately that the authors' experiments confirm that thermal breakdown of rubber is of negligible importance under such circumstances and is always overshadowed by more efficient alternative modes of degradation. The thermal degradation of rubber, constituting as it does its formally simplest chemical reaction, has real possibilities of giving insight into the chemical stability and reactivity of the rubber molecule. Moreover, the theoretical treatment of the degradation of long-chain molecules has apparently far outstripped the experimental investigation of the problem. To date, attention has been confined to long polymeric chains which are assumed to break in quite random fashion at the regularly recurring bonds joining the monomeric units, and it is of importance to see how far this simplifying suggestion regarding the manner of chain scission does in fact correspond to reality. With these two ends in view the writers have investigated the thermal breakdown of rubber in some detail. A preliminary report is now presented on certain complexities of the reaction which may, however, be resolved by consideration of the resonance stabilization of the intermediate degradation products.

Free Radicals Generated in Rubber during Fracture

1975 ◽  
Vol 48 (3) ◽  
pp. 445-461 ◽  
Author(s):  
K. L. DeVries
Keyword(s):  
Failure Criteria ◽  
Chain Scission ◽  
Systematic Investigation ◽  
Matrix Interaction ◽  
Filled Elastomers ◽  
Final Note ◽  
Ozone Stress ◽  
Type Of Failure ◽  
Insight Into

Abstract EPR has been used to measure molecular phenomena during fracture of elastomers. To date, because of various technical limitations, the studies have been largely confined to identification of the polymer chain scission site during fracture at low temperature in rubbers, to studying ozone-stress-induced cracking of rubber, to development of a micro-macro Griffith-type failure criteria for this type of failure, and lastly to systematic investigation of the role of filler-matrix interaction in fracture of filled elastomers. It is hoped that the brief outline presented here will give the reader some insight into the uses and potential of the EPR methods for the study of fracture. As a final note, while we have concentrated almost totally on EPR fracture studies in rubbers, there has been fairly extensive EPR work on fracture in oriented plastic, fibers, and films. Even though some of this knowledge may be transferable, directly or indirectly, to elastomers, it has not been reviewed here, but important aspects of these studies have been reviewed elsewhere.

Effects of Diffusion in the Oxidative Degradation of Vulcanized Rubbers. I. Rate of Chain Scission in the Steady State

1977 ◽  
Vol 50 (1) ◽  
pp. 43-48 ◽  
Author(s):  
K. Ono ◽  
A. Kaeriyama ◽  
K. Murakami
Keyword(s):  
Oxygen Consumption ◽  
Steady State ◽  
Diffusion Constant ◽  
Oxidative Degradation ◽  
Relaxation Method ◽  
Chain Scission ◽  
Simple Relation ◽  
Theoretical Treatment ◽  
Steady State Condition ◽  
True Activation Energy

Abstract The effects of diffusion in the oxidation of cis-1,4-polyisoprene vulcanizates were investigated by means of the stress relaxation method. It was assumed that the diffusion of oxygen is coupled with first-order oxygen consumption and that the rate of chain scission is proportional to the rate of oxygen consumption. The diffusion equation of this process was solved under the steady-state condition to give a simple relation between the rate of chain scission and the film thickness. The experimental results were in good agreement with the theoretical treatment. The true activation energy as well as the ratio of the rate of oxidation k to the diffusion constant D could be estimated.

scholarly journals Pigments—Lead-based whites, reds, yellows and oranges and their alteration phases

2021 ◽  
Vol 14 (1) ◽  
Author(s):  
Elisabetta Gliozzo ◽  
Corina Ionescu
Keyword(s):  
State Of The Art ◽  
Degradation Products ◽  
Raw Materials ◽  
Lead Chromate ◽  
Lead White ◽  
Mineral Phases ◽  
Starting Point ◽  
Key Concepts ◽  
Red Lead ◽  
Insight Into

AbstractThis review summarises the state-of-the-art of lead-based pigment studies, addressing their production, trade, use and possible alteration. Other issues, such as those related to the investigation and protection of artworks bearing lead-based pigments are also presented. The focus is mineralogical, as both raw materials and degradation products are mineral phases occurring in nature (except for very few cases). The minerals described are abellaite, anglesite, blixite, caledonite, challacolloite, cerussite, cotunnite, crocoite, galena, grootfonteinite, hydrocerussite, laurionite, leadhillite, litharge, macphersonite, massicot, mimetite, minium, palmierite, phosgenite, plattnerite, plumbonacrite, schulténite, scrutinyite, somersetite, susannite, vanadinite and an unnamed phase (PbMg(CO3)2). The pigments discussed are lead white, red lead, litharge, massicot, lead-tin yellow, lead-tin-antimony yellow, lead-chromate yellow and Naples yellow. An attempt is made to describe the history, technology and alteration of these pigments in the most complete manner possible, despite the topic's evident breadth. Finally, an insight into the analytical methods that can (and should) be used for accurate archaeometric investigations and a summary of key concepts conclude this review, along with a further list of references for use as a starting point for further research.

scholarly journals VopF, a type III effector protein from a non-O1, non-O139 Vibrio cholerae strain, demonstrates toxicity in a Saccharomyces cerevisiae model

2010 ◽  
Vol 59 (1) ◽  
pp. 17-24 ◽  
Author(s):  
Ranjana Tripathi ◽  
Santa Singh Naorem ◽  
Chetna Dureja ◽  
Swati Haldar ◽  
Alok K. Mondal ◽  
...  
Keyword(s):  
Vibrio Cholerae ◽  
Type Iii Secretion ◽  
Ectopic Expression ◽  
Contributory Factor ◽  
Cholerae Strain ◽  
Effector Protein ◽  
Intestinal Colonization ◽  
Type Iii Effector ◽  
Type Iii ◽  
Insight Into

VopF, a type III effector protein, has been identified as a contributory factor to the intestinal colonization of type III secretion system-positive, non-O1, non-O139 Vibrio cholerae strains. To gain more insight into the function of VopF, a yeast model was developed. Using this model, it was found that ectopic expression of VopF conferred toxicity in yeast.

A Study of the Mechanism of the Deactivation Effect

1954 ◽  
Vol 27 (1) ◽  
pp. 157-164 ◽  
Author(s):  
Jacques Le Foll
Keyword(s):  
Chemical Structure ◽  
A Priori ◽  
Natural Aging ◽  
Chain Scission ◽  
Nitro Compounds ◽  
Active Part ◽  
Relaxation Phenomena ◽  
Chain Molecules ◽  
Vulcanized Rubber ◽  
The Subject

Abstract The only method by which significant differences between the effects of antioxygenic agents and deactivating agents can be detected has been found to be a study of relaxation phenomena. An investigation by this method has also furnished further support to the theories of Tobolsky and his coworkers. The changes which take place during aging in the physical properties of vulcanized rubber are the result of two independent phenomena which occur simultaneously: (1) chain scission, and (2) formation of intermolecular bonds. As far as the aging of vulcanizates of natural rubber under normal conditions, e.g., socalled natural aging, is concerned, the chief phenomenon involved is scission of the chain molecules. In principle, therefore, there are two methods for combatting the deterioration of rubber on aging: (1) to impede chain scission by obstructing the fixation of oxygen, and (2) to promote the progressive formation of intermolecular bonds which compensate for the effects of the scission process. The first of these processes is that in which antioxygenic agents play the active part; in the second process, deactivating agents play the active part. From this viewpoint, deactivating agents play a part analogous to that of accelerators, and they may be regarded as representing a special type of acceleration. This theory makes possible a better understanding of a number of facts which, a priori, seem surprising: (1) the relationships of both chemical structure and mode of action of accelerators and deactivating agents, and (2) the protective effect of litharge, peroxides, and nitro compounds, all of which are vulcanizing agents. With respect to the intimate mechanism of the deactivating effect, one question remains unanswered, viz., how are intermolecular bonds formed under the influence of deactivating agents? This question recalls the question of the function of vulcanization accelerators, which has been the subject of many investigations, but which still remains a mystery.

scholarly journals Direct observation and kinetics of a hydroperoxyalkyl radical (QOOH)

Science ◽  
2015 ◽  
Vol 347 (6222) ◽  
pp. 643-646 ◽  
Author(s):  
John D. Savee ◽  
Ewa Papajak ◽  
Brandon Rotavera ◽  
Haifeng Huang ◽  
Arkke J. Eskola ◽  
...  
Keyword(s):  
Organic Compounds ◽  
Direct Observation ◽  
Organic Aerosol ◽  
Organic Radicals ◽  
Radical Chain ◽  
Radical Intermediates ◽  
Oxidation Of Organic Compounds ◽  
Resonance Stabilization ◽  
Kinetics Of ◽  
Insight Into

Oxidation of organic compounds in combustion and in Earth’s troposphere is mediated by reactive species formed by the addition of molecular oxygen (O2) to organic radicals. Among the most crucial and elusive of these intermediates are hydroperoxyalkyl radicals, often denoted “QOOH.” These species and their reactions with O2 are responsible for the radical chain branching that sustains autoignition and are implicated in tropospheric autoxidation that can form low-volatility, highly oxygenated organic aerosol precursors. We report direct observation and kinetics measurements of a QOOH intermediate in the oxidation of 1,3-cycloheptadiene, a molecule that offers insight into both resonance-stabilized and nonstabilized radical intermediates. The results establish that resonance stabilization dramatically changes QOOH reactivity and, hence, that oxidation of unsaturated organics can produce exceptionally long-lived QOOH intermediates.

The Statistical Theory of the Elasticity of Rubber

1939 ◽  
Vol 12 (1) ◽  
pp. 56-63
Author(s):  
H. Dostal
Keyword(s):  
Finite Size ◽  
Point Of View ◽  
Chain Molecule ◽  
Tension Zone ◽  
Single Chain ◽  
Chain Molecules ◽  
Theoretical Investigations ◽  
Statistical Behavior ◽  
Coefficient Of Elasticity ◽  
Insight Into

Abstract The theoretical investigations of various authors, with the aid of which the physical properties of rubber-like substances have become understood on a basis of intermolecular statistics, have not, at least from a quantitative point of view, kept pace with investigations relating to kinetic theories of gases. However, only the facts of rubber elasticity have become understood, and to point out one case, the coefficient of elasticity cannot be derived, and much less the tension zone, beyond proportionality. The reason for this is that, although statistics of a single chain molecule of finite size can be compiled, the bond of the chain molecule and, as a further instance, the behavior of a molecule of infinite size formed by interlacing have not been clearly understood up to the present time. Consequently, it has been possible to gain an insight into the statistical behavior of individual chain molecules much more easily than into that of a piece of rubber, and therefore to deduce with less difficulty theories of the viscosity of high molecular solutions and similar systems. In the case of rubber, progress has been more difficult in explaining the effects which take place.

High Resolution Dark Field of Poly(p-Phenylene Benzobisthiazole)

1981 ◽  
Vol 39 ◽  
pp. 342-343
Author(s):  
J.R. Minter
Keyword(s):  
High Strength ◽  
Chain Scission ◽  
Dark Field ◽  
Electron Dose ◽  
Diffraction Mode ◽  
Resonance Stabilization ◽  
Subsequent Loss ◽  
Loss Of Mass ◽  
Beam Damage ◽  
Heterocyclic Polymer

The resolution attainable in polymer samples is limited by radiation damage causing crosslinking or chain scission with subsequent loss of mass. Molecules containing aromatic groups have been found to have improved resistance to beam damage, presumably due to resonance stabilization of radicals generated by the electron beam. Poly(p-phenylene benzobisthiazole) (PBT), a wholly aromatic, heterocyclic polymer used in high modulus, high strength fibers and films has been studied by tilted beam dark fieldSamples thin enough for TEM were prepared from bulk films by extraction replication with collodion and examined in a JEOL 100 CX operated at 100 KV using Kodak 4463 film. Figure 1 shows the decay of the 2nd, 3rd and 4th equatorial reflections as a function of electron dose. The intensity was assumed to be proportional to the current on the isolated observation screen when the microscope was operated in the diffraction mode and the appropriate reflections selected with a 2.8 mrad objective aperature (see Figure 1).

Thermoelastic Properties of Rubberlike Networks and Their Thermodynamic and Molecular Interpretation

1973 ◽  
Vol 46 (3) ◽  
pp. 593-618 ◽  
Author(s):  
J. E. Mark
Keyword(s):  
Isomeric State ◽  
State Theory ◽  
Thermoelastic Properties ◽  
Chain Molecules ◽  
Rotational Isomeric State ◽  
Theoretical Investigations ◽  
Molecular Interpretation ◽  
Molecular Aspects ◽  
Insight Into ◽  
Conformational Energies

Abstract Thermoelastic measurements and their interpretation by means of rotational isomeric state theory provide a great deal of insight into both thermodynamic and molecular aspects of rubberlike elasticity. Furthermore, conformational energies obtained in part from thermoelastic studies can in turn be used in the interpretation and even prediction of a variety of configurationally dependent properties of chain molecules, as is shown in many of the theoretical investigations cited in Sections IV and VII of this review.

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