The Reaction of Ozone with Rubber

1959 ◽  
Vol 32 (1) ◽  
pp. 269-277 ◽  
Author(s):  
Harold Tucker
Keyword(s):  
Chain Scission ◽  
Crack Development ◽  
Original Material ◽  
Protective Film ◽  
Double Bonds ◽  
Stress Strain ◽  
Ultimate Elongation ◽  
Rubber Surface ◽  
Fresh Surface

Abstract The reaction of ozone with an unsaturated elastomer is very rapid until the double bonds at the surface have reacted. Only then do the double bonds beneath the surface become available for reaction with ozone. In this respect, unstressed rubber is similar to the metals that are protected from oxidation by a film of oxide formed on the surface. When this protective film is broken and fresh surface is exposed, the reaction can continue. This is the situation that exists when the rubber is under strain. Since the entire rubber surface can be considered as under a uniform bombardment by ozone molecules, to consider cracks in stressed rubber as arising from a directed chain scission process seems unrealistic. On the assumption that the double bonds in the rubber surface are equally reactive, and that ozone does not act as a pair of chemical shears snipping double bonds at right angles to the strain, crack development must then arise from the fact that the stress-strain characteristics of the rubber-ozone reaction product are not indentical to those of the original material and that ultimate elongation decreases continuously with increasing reaction with ozone. That such a mechanism would produce the type of cracks produced by ozone reacting with rubber can be shown by modifying the nature of the surface by vulcanization.

The Ozonation of N,N′-Di-n-Octyl-p-Phenylenediamine and N,N′-Di-(1,1-Dimethylethyl)-p-Phenylenediamine

1991 ◽  
Vol 64 (5) ◽  
pp. 780-789 ◽  
Author(s):  
R. P. Lattimer ◽  
R. W. Layer ◽  
E. R. Hooser ◽  
C. K. Rhee
Keyword(s):  
Film Theory ◽  
Chain Scission ◽  
Protective Film ◽  
Self Healing ◽  
Reaction Products ◽  
Double Bonds ◽  
Final Theory ◽  
Rubber Compounds ◽  
Rubber Surface ◽  
Paraffin Waxes

Abstract Ozone attack on rubber compounds causes characteristic cracking perpendicular to the direction of applied stress. This degradation is caused by reaction of ozone with the double bonds in the rubber molecules. This causes chain scission and the formation of various decomposition products. The general subject of protection of rubber against ozone attack has been reviewed by a number of authors. In order to control the effects of rubber ozonation, either paraffin waxes or chemical antiozonants are added to unsaturated rubbers. The most effective antiozonants are N,N′-disubstituted-p-phenylenediamines (PPDAs), in which at least one of the side groups is alkyl (preferably sec-alkyl). Several theories have appeared in the literature regarding the mechanism of antiozonant protection. The “scavenger” model states that the antiozonant blooms to the surface and preferentially reacts with ozone so that the rubber is not attacked until the antiozonant is exhausted. The “protective film” theory is similar, except that the ozone-antiozonant reaction products form a film on the rubber surface that prevents (physically and perhaps chemically as well) ozone attack on the rubber. A third “relinking” theory states that the antiozonant prevents scission of the ozonized rubber or else recombines severed double bonds. A final theory states that the antiozonant reacts with the ozonized rubber or Criegee zwitterion (carbonyl oxide) to give a low-molecular-weight, inert, “self-healing” film on the rubber surface. Currently, the most accepted mechanism of antiozonant action is a combination of the scavenger and protective film theories.

Stress Relaxation of Sugi (Cryptomeria japonica D.Don) Wood in Radial Compression under High Temperature Steam

Holzforschung ◽  
1999 ◽  
Vol 53 (5) ◽  
pp. 541-546 ◽  
Author(s):  
W. Dwianto ◽  
T. Morooka ◽  
M. Norimoto ◽  
T. Kitajima
Keyword(s):  
High Temperature ◽  
Stress Relaxation ◽  
Cryptomeria Japonica ◽  
Chain Scission ◽  
Strain Recovery ◽  
Crystalline Lattice ◽  
Compressive Deformation ◽  
Radial Compression ◽  
Stress Strain ◽  
Permanent Fixation

Summary To clarify the mechanism of the permanent fixation of compressive deformation of wood by high temperature steaming, stress relaxation and stress-strain relationships in the radial compression for Sugi (Cryptomeria japonica D.Don) wood were measured under steam at temperatures up to 200°C. The stress relaxation curves above 100°C were quite different in shape from those below 100°C, showing a rapid decrease in stress with increasing temperature. In the stress-strain relationships measured above 140°C, the stress reduced as pre-steaming time increased when compared at the same strain. The recovery of compressive deformation (strain recovery) was decreased with steaming time and reached almost 0 in 10 min at 200°C. The relationship between the residual stress and the strain recovery at the end of relaxation measurements could be expressed by a single curve regardless of time and temperature. The permanent fixation of deformation by steaming below 200°C was considered to be due to chain scission of hemicelluloses accompanying a slight cleavage of lignin. In some cases, the increase in regularity of the crystalline lattice space of microfibrils or the formation of crosslinks between the cell wall polymers seemed to play an important role in the permanent fixation of compressive deformation.

Time and Temperature Dependence of the Ultimate Properties of an SBR Rubber at Constant Elongations

1961 ◽  
Vol 34 (3) ◽  
pp. 897-909
Author(s):  
Thor L. Smith ◽  
Paul J. Stedry
Keyword(s):  
Tensile Strength ◽  
Strain Rate ◽  
Temperature Dependence ◽  
Rate Dependence ◽  
Strain Rates ◽  
Type Specimens ◽  
Stress Strain ◽  
Ultimate Elongation ◽  
Tensile Tester ◽  
Ultimate Properties

Abstract A study was made previously of the temperature and strain rate dependence of the stress at break (tensile strength) and the ultimate elongation of an unfilled SBR rubber. In that study, stress-strain curves to the point of rupture were measured with an Instron tensile tester on ring type specimens at 14 temperatures between −67.8° and 93.3° C, and at 11 strain rates between 0.158×10−3 and 0.158 sec−1 at most temperatures. The tensile strength was found to increase with both increasing strain rate and decreasing temperature. At all temperatures above −34.4° C, the ultimate elongation was likewise found to increase with increasing strain rate and decreasing temperature but at lower temperatures the opposite dependence on rate was observed; at −34.4° C, the ultimate elongation passed through a maximum with increasing rate.

DO WE NEED VERY STIFF FILLERS?

2017 ◽  
Vol 90 (4) ◽  
pp. 743-750 ◽  
Author(s):  
Bing Jiang
Keyword(s):  
Material Model ◽  
Chain Scission ◽  
Rubber Matrix ◽  
Macroscopic Strain ◽  
Stress Strain ◽  
Simple Material ◽  
Strain Concentration ◽  
Trade Offs ◽  
Reinforcing Fillers ◽  
Balance Trade

ABSTRACT The influence of reinforcing fillers on the stretching of a rubber matrix is analyzed. It is shown that a filler stiffness higher than a critical stiffness does not further enhance the stiffness of the reinforced elastomer. The stiffer filler induces a higher stress–strain concentration and causes filler–rubber dissociation or chain scission at a lower macroscopic strain. Reducing filler stiffness can reduce the stress–strain concentration and therefore delay rubber chain scission or dissociation from the filler surface. Accordingly, the toughness of the reinforced elastomer could be improved. A simple material model is developed to predict the maximum macroscopic strain without bond scission in a reinforced elastomer. It is shown that reduced filler stiffness is beneficial for cases with (i) reduced bond strength, (ii) increased rubber matrix stiffness, and (iii) increased application strain of the reinforced elastomer. The model can be used to design the appropriate filler stiffness to balance trade-offs of stiffness and toughness of reinforced elastomers.

scholarly journals INVESTIGATION OF STRESS-STRAIN BEHAVIOR OF СOMPOUND ROCK BLOCKS WITH CRACK

2019 ◽  
Vol 2 (4) ◽  
pp. 107-113
Author(s):  
Andrey Krasnovsky
Keyword(s):  
Integral Equations ◽  
Work Stress ◽  
Singular Integral ◽  
Singular Integral Equations ◽  
Numerical Realization ◽  
Crack Development ◽  
Rock Block ◽  
Stress Strain ◽  
Strain Behavior

In the work stress-strain behavior of compound rock block with crack is considered. Correlations determining components of displacements and stresses at whole border of the rock block, sides of the crack and on the line of crack development and at boundary of rocks are outlined based on system of singular integral equations. Algorithm of numerical realization of these equations is built. The analysis of obtained results is carried out.

Peroxide Curing of Ethylene-Propylene Elastomers

1988 ◽  
Vol 61 (2) ◽  
pp. 238-254 ◽  
Author(s):  
Robert C. Keller
Keyword(s):  
Free Radicals ◽  
Service Life ◽  
Chain Scission ◽  
Organic Peroxides ◽  
Stress Strain ◽  
Ethylene Propylene ◽  
Compression Set ◽  
Ethylene Content ◽  
Peroxide Curing ◽  
Improved Performance

Abstract 1. Ethylene-propylene elastomers, suitably compounded for extrusion applications, can be readily vulcanized with organic peroxides to meet emerging requirements of improved performance and longer service life. 2. Aralkyl or dialkyl classes of peroxides produce the preferred cure performance, highest physical properties, and lowest compression set. Choice of peroxide governs rate of cure but not necessarily the optimum in crosslinking efficiency. 3. Coagents are essential to the development of optimum cure and stress-strain properties. The bis-maleimide is very effective in compounds that contain significant quantities of process oil, antioxidants for increased heat resistance, or other materials that consume free-radicals. 4. Ethylene-propylene compositional parameters influencing vulcanization activity are the diene, both type and concentration, and the ethylene content. Reactivity of the terpolymers is dependent on the type and amount of diene utilized in the polymer synthesis. High ethylene content improves crosslinking efficiency because there are fewer propylene sequences where chain scission can occur. 5. Increasing levels of hydrocarbon process oil needed in fast extruding compounds require higher peroxide concentrations to maintain cure and stress-strain properties.

Thermal Expansion And Viscoelastic Properties Of A Semi-Rigid Polyimide

1991 ◽  
Vol 227 ◽  
Author(s):  
Thor L. Smith ◽  
Churl S. Kim
Keyword(s):  
Liquid Crystalline ◽  
Linear Expansion ◽  
Tensile Modulus ◽  
Strain Curve ◽  
Relaxation Modulus ◽  
Superposition Method ◽  
Thermal Coefficient ◽  
Fixed Rate ◽  
Stress Strain ◽  
Ultimate Elongation

ABSTRACTStudies were made of the physical properties of the commercially available polyimide Upilex-SGA, which is prepared from biphenyl dianhydride and p-phenylene diamine. Annealing the Upilex-SGA for 2 hr Linder N2 at 400°C gave a film that expanded continuously when heated at a fixed rate, in contrast to the as-received film. The linear expansion showed a change of slope at 84°C and also at 295°C, the later being Tg. The thermal coefficient of linear expansion at all temperatures was very small, even above 295°C it is 27.8 × 10−6. Its stress-strain curve did not exhibit a yield point, even though its ultimate elongation is ˜23%. Similar behavior is shown by the PMDA-ODA polyimide, except its ultimate elongation is ˜70%,. The unusual stress- strain curves exhibited by these polyimides is undoubtedly caused by their liquid-crystalline morphology. The stress-relaxation modulus was measured at 0.5% extension and 12 temperatures from 30 to 330°C. Derived isochrones showed that the 1-s tensile modulus at 20°C is 9.0 GPa, but at 330°C it is 2.0 GPa. Creep curves were also measured at a stress of 30 MPa and at 10 temperatures from 30 to 340° C. Master curves prepared from the relaxation and creep data are discussed briefly and evidence is given which, show that the superposition method is not truly valid for this polyimide, which actually is not surprising.

Beneficial Aspects of the Environmental Instability of Materials

MRS Bulletin ◽  
1993 ◽  
Vol 18 (9) ◽  
pp. 53-57
Author(s):  
John R. Ambrose ◽  
Priya R. Bendale
Keyword(s):  
Gross National Product ◽  
Chain Scission ◽  
Transportation Systems ◽  
Original Material ◽  
Reaction Products ◽  
Oxide Formation ◽  
Environmental Instability ◽  
Engineering Materials ◽  
Degradation Of Materials ◽  
Ceramic Compounds

The environmental degradation of materials poses a serious limitation in the utility of engineering materials. The corrosion of metals, for example, has been estimated to represent a 4–5% decrease in the Gross National Product each year. To this, add losses involved in the replacement or restoration of ceramic structures such as buildings and transportation systems, i.e., the “infrastructure,” and the result is a significant sacrifice of economic strength.Most of us are familiar with the consequences of exposing materials to environments in which the materials are chemically unstable and convert into substances that are unable to perform the function for which the original material was selected. The corrosion of metals into soluble or insoluble oxidation reaction products, chain scission or molecular mutation in polymers, even hydrolysis and leaching of silicious ceramic compounds represent behavior which ultimately limits the service applications of most engineering materials. For example, aluminum and its alloys are unsuitable for use in environments where oxide formation rates are high enough to represent a problem with respect to useful service life.

Elastomer-Gasoline Blends Interactions I. Effects of Methanol-Gasoline Mixtures on Elastomers

1983 ◽  
Vol 56 (1) ◽  
pp. 135-168 ◽  
Author(s):  
Ismat A. Abu-Isa
Keyword(s):  
Tensile Strength ◽  
Ultimate Tensile Strength ◽  
Solubility Parameter ◽  
Ultimate Stress ◽  
Stress Strain ◽  
Equilibrium Stress ◽  
Ultimate Elongation ◽  
Linear Relationships

Abstract 1. Properties of most fuel resistant elastomers are degraded to a larger extent by mixtures of methanol and gasoline than by the pure components. 2. The data on all elastomers except the fluorocarbon can be explained in terms of the solubility parameter concept. 3. The ultimate tensile strength and ultimate elongation of swelled elastomer networks are quantitatively related to volume swell by simple linear relationships. 4. Ultimate stress and ultimate elongation of swelled elastomer networks obey equilibrium stress-strain relationships.

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