Effect of Temperature on Ozone Cracking of Butyl Rubbers

1968 ◽  
Vol 41 (5) ◽  
pp. 1294-1299 ◽  
Author(s):  
A. N. Gent ◽  
H. Hirakawa
Keyword(s):  
Crack Growth ◽  
Ozone Concentration ◽  
Effect Of Temperature ◽  
Segmental Mobility ◽  
Temperature Range ◽  
Styrene Copolymers ◽  
The Difference ◽  
Rates Of Growth ◽  
Rate Controlling Step ◽  
Butadiene Styrene

Abstract Rates of growth of single ozone cracks have been measured for vulcanizates of two butyl rubbers over the temperature range of 20-160° C. Over most of this range the rates are quantitatively related to the segmental mobility of the polymer and depend upon temperature in accord with the appropriate form of the WLF relation. The rates are also proportional to the concentration of ozone. It is therefore concluded that diffusion of ozone into the polymer before reaction is the rate-controlling step. This is contrasted with the behavior of butadiene styrene copolymers, for which rates of crack growth are also quantitatively related to the segmental mobility, but the rates are somewhat larger at equivalent mobilities and the dependence upon ozone concentration is smaller. The difference is attributed to different penetration distances before reaction in polymers containing low and high densities of reactive sites.

Effect of Temperature on Ozone Cracking of Rubbers

1966 ◽  
Vol 39 (3) ◽  
pp. 643-650
Author(s):  
A. N. Gent ◽  
J. E. McGrath
Keyword(s):  
Polymer Chains ◽  
Effect Of Temperature ◽  
Ozone Molecule ◽  
Segmental Mobility ◽  
Network Chain ◽  
Styrene Copolymers ◽  
Rates Of Growth ◽  
Rate Controlling Step ◽  
Limiting Value ◽  
Butadiene Styrene

Abstract The rates of growth of single ozone cracks have been measured for vulcanizates of a series of butadiene—styrene copolymers, over a temperature range from − 5° C to 95° C. The rates appear to be determined by two mechanisms. At low temperatures, near the glass transition temperature, they are quantitatively related to the segmental mobility of the polymer. The principal rate-controlling step in this case is concluded to be movement of the polymer chains after scission to yield new surface. At high temperatures the rate approaches a limiting value of 10−3 cm/sec/mg of ozone/1. This is about 1/1000 of the maximum possible value when instantaneous reaction of one incident ozone molecule causes scission of one network chain.

Properties of Ebonite. XXXVII. Electrical Properties of Synthetic Rubber Ebonites

1949 ◽  
Vol 22 (4) ◽  
pp. 1084-1091
Author(s):  
D. G. Fisher ◽  
L. Mullins ◽  
J. R. Scott
Keyword(s):  
Natural Rubber ◽  
Power Factor ◽  
Power Loss ◽  
Ionic Conduction ◽  
Effect Of Temperature ◽  
Plastic Yield ◽  
Styrene Copolymers ◽  
Synthetic Rubber ◽  
High Dielectric ◽  
Butadiene Styrene

Abstract Experiments were carried out to explore the possibility of making good electrical ebonites from various types of synthetic rubber. The ebonites produced were tested for permittivity and power factor over wide ranges of temperature and frequency. Thioplasts (Thiokols AZ and FA) apparently do not produce hard ebonitelike vulcanizates by the normal procedure. Neoprenes (GN and I) give ebonites, but with such high dielectric power loss as to be unsuitable for use as high-frequency dielectrics; moreover, if the mix contains zinc oxide, the ebonite has a very hygroscopic and therefore electrically unsatisfactory surface. Butadiene copolymers containing polar groups (butadiene-acrylonitrile types and Thiokol RD) give ebonites with high power loss, hence are not suitable for making high-grade electrical ebonites. Polybutadiene (Buna-85) and butadiene-styrene copolymers (GR-S, Hycar-EP, Buna-S) are much nearer to natural rubber as far as the radio-frequency (100 to 2,500 kc. per sec.) power loss of their ebonites is concerned. The GR-S ebonite examined was not so good as natural rubber at room temperature, but was superior above about 50° C. Buna-85 and Hycar-EP were superior to natural rubber over the whole temperature range; indeed, the high-styrene copolymers, as represented by Hycar-EP and Buna-SS, appear to be the best type of synthetic rubber for making ebonite with low power loss, especially at high frequencies and temperatures. The effects of changing temperature and frequency on permittivity and power factor are discussed. Attention is drawn to the big effect of temperature on power factor; this was less with polybutadiene and butadiene-styrene ebonites than with natural rubber ebonite, in keeping with the greater heat resistance of the former as judged by plastic yield tests. Comparison of the effects of rising temperature and decreasing frequency shows that these produce broadly similar effects on power factor, as would be expected on theoretical grounds, but that rising temperature superposes a second effect (an increase), presumably due to increased ionic conduction.

Dependence of Tack Strength on Molecular Properties

1959 ◽  
Vol 32 (1) ◽  
pp. 48-66 ◽  
Author(s):  
W. G. Forbes ◽  
L. A. McLeod
Keyword(s):  
Molecular Weight ◽  
Shear Viscosity ◽  
Catalyst System ◽  
Chain Entanglement ◽  
Molecular Weights ◽  
Styrene Copolymers ◽  
The Difference ◽  
Catalyst Systems ◽  
Time Required ◽  
Butadiene Styrene

Abstract A method has been developed for the measurement of the tack strength of fresh and reproducibly smooth rubber surfaces. Using this method the tack strength of natural rubber is shown to be independent of polymer purity, and, to a large extent, Mooney viscosity, intrinsic viscosity, gel content and molecular weight distribution. The relative tack strengths of polyisoprenes of different molecular weights prepared in different catalyst systems are measured. The results are discussed in terms of microstructure. A study of the tack strength of oil-extended butadiene-styrene copolymers indicates that relative tack strength is related to the shear viscosity of the bulk polymer. Measurements of relative tack strength on Alfin and free radical butadiene-styrene copolymers, butyl, brominated butyl and butadiene-acrylonitrile copolymers confirm the inportance of shear viscosity in controlling tack strength. Choice of catalyst system and temperature of polymerization cause the largest variation in polymer viscosity. The contact time required for the relative tack strength to become unity is shown to be inversely dependent upon the value of the relative tack strength itself. Shear viscosity measurements are given for six classes of polymer and the values shown to correlate with relative tack strength. It is postulated that molecular weight (and probably also chain entanglement) is the controlling variable. The bond strength between two different uncured polymers is shown to depend upon the difference in cohesive energy densities of the two polymers.

scholarly journals The effect of temperature on the viscosity of air

1926 ◽  
Vol 113 (763) ◽  
pp. 233-237 ◽  
Keyword(s):  
Present Author ◽  
Effect Of Temperature ◽  
Appreciable Change ◽  
Temperature Range ◽  
Higher Temperature ◽  
The Difference ◽  
Experimental Values ◽  
Coefficient Of Viscosity ◽  
Slight Alteration

In a recent paper Prof. A. 0. Rankine has put forward a number of criticisms of the results obtained from, and the experimental method employed in, the determination of the temperature coefficient of viscosity of air by the present author. In the first place, a comparison is drawn between the author’s results and those of other observers in the lower part of the temperature range, and the conclusion is drawn therefrom that there is a possibility of an error of 3 percent, in the author’s measurements throughout the whole range of temperature used. This inference is reached from the figures quoted in Table II of Rankine’s paper, in which the temperature range from 15° to 183° C. is considered. That some difference exists between the author’s results and those of other observers in the lower part of the temperature range is clear, but it must again be emphasised that the values given for low temperatures are not experimental values, but were obtained by an extension of the graph (fig. 2) for higher temperature measurements to the value of the viscosity as given by Millikanj for room temperatures. A slight alteration of the curvature of this extension would make an appreciable change in the ratios η100/η15 and η183/η15 , but this would not be sufficient to account for the curvature at B in fig. 3 of the original paper. If the values of T ⅜ /η for Breitenbach’s results at 182° C. and 302° C. are plotted on this curve, they lie above the present results and on a curve which would intersect AB at about 600° C. That part of the difference is due to this cause seems to be indicated by the fact that the difference diminishes as the temperature rises. Thus at 300° C. the following values of η300/η15 are obtained by Breitenbach, the only other worker at this temperature, and the author. The figures used are those given by Rankine.

The effect of temperature on some calcium-binding properties of troponin C and calmodulin

1980 ◽  
Vol 58 (9) ◽  
pp. 683-691 ◽  
Author(s):  
William D. McCubbin ◽  
Maxwell T. Hincke ◽  
Cyril M. Kay
Keyword(s):  
Calcium Binding ◽  
Heat Stability ◽  
Troponin C ◽  
Effect Of Temperature ◽  
Spectroscopic Techniques ◽  
Binding Properties ◽  
Tyrosine Residues ◽  
Temperature Range ◽  
Skeletal Protein ◽  
The Difference

Some calcium-binding properties of skeletal and cardiac troponin C (TnC) have been measured as functions of temperature employing several physical and spectroscopic techniques. The degree of exposure of the tyrosine residues in brain calmodulin has also been determined by a new approach. Circular dichroism thermal unfolding profiles have been established for the three cases: metal-free protein, high-affinity sites filled, and fully saturated. In addition some thermodynamic parameters have been calculated for these reversible melting processes. It was found that the calcium-binding parameters n and K, where n is the fraction of the total conformational change and K is the apparent association constant, for both skeletal and cardiac TnC, did not vary significantly over the temperature range 10–38 °C, but at 50 °C differences became quite apparent, dramatically so in the case of the skeletal protein. The technique of thermal perturbation difference spectroscopy was applied to determine the degree of exposure of aromatic chromophores for the TnC(s) and calmodulin in the absence and presence of calcium. For skeletal TnC and calmodulin the results were in good agreement with previous observations, but the reduced degree of exposure of the tyrosine residues in cardiac TnC, in the absence of Ca2+, was contrary to the earlier work. Calcium-induced difference absorption spectra have been measured for the TnC(s) over the temperature range 10–70 °C. Cardiac TnC showed greater heat stability than its skeletal counterpart, in terms of the rate and the amount of change of the difference spectral maxima.

Effect of Temperature on Deactivation Force of Three Commercial NiTi Orthodontic Archwires

2014 ◽  
Vol 1025-1026 ◽  
pp. 325-329
Author(s):  
Niwat Anuwongnukroh ◽  
Surachai Dechkunakorn ◽  
Nathaphon Tangit ◽  
Subongkoch Tongkoom
Keyword(s):  
Descriptive Analysis ◽  
Bending Test ◽  
Effect Of Temperature ◽  
Cross Sectional ◽  
Temperature Range ◽  
Significant Difference ◽  
Close Relationship ◽  
The Difference ◽  
Lower Temperature ◽  
Niti Wires

Objective: The purpose of this study was to investigate the transition temperature range (TTR) and the effect of temperatures at 10, 20, 30, 40, 50 and 60 °C on the deactivation force of three commercially available NiTi archwires. Materials and methods: Three different brands of NiTi archwires, NiTi OR (Ormco), NiTi GH (G&H) and NiTi H (Highland), with a cross sectional area of 0.016 x 0.022 inch2 were analysed for transformation temperature range (TTR) by using differential scanning calorimeter and load-deflection characteristics using a three-point bending test at temperatures of 10, 20, 30, 37, 40, 50 and 60 °C. Statistical Analysis: Descriptive analysis was used to calculate each variable and Kruskal Wallis test was performed to assess the difference in measurements among the three NiTi wires. P<0.05 was considered as statistical significant. Results: TTR showed austenitic temperature finish (Af) at 24.45 °C for NiTi OR, 27.55 °C for NiTi GH and 51.5 °C for NiTi H. The highest deactivation force was found in NiTi H followed by NiTi OR and NiTi GH at the temperatures below and higher than 37°C. There were siginificant differences (p<0.05) in the deactivation force of NiTi OR - NiTi H and NiTi GH - NiTi H at 10 °C and 20 oC, and NiTi GH – NiTi H and NiTi GH – NiTi OR at 30 °C and 37 °C. However, no significant difference was found among all NiTi wires at 40, 50 and 60 oC, except NiTi GH – NiTi H at 60 oC. A close relationship was found between temperature and unloading curves (deactivaton force); increase in the temperature led to an increase in the plateau of delivery deactivation force and decrease in temperature led to a decrease in the plateau of delivery deactivation force. Conclusion: The TTRs of commercial NiTi archwires are variable, expecially the austenitic finish temperature. The deactivation force increases in higher temperature and decreases in lower temperature.

Evaluation of Sodium-Catalyzed Copolymers of 1,3-Butadiene and Styrene

1948 ◽  
Vol 21 (2) ◽  
pp. 452-460
Author(s):  
A. E. Juve ◽  
M. M. Goff ◽  
C. H. Schroeder ◽  
A. W. Meyer ◽  
M. C. Brooks
Keyword(s):  
High Temperature ◽  
Free Radical ◽  
Low Temperature ◽  
Crack Growth ◽  
Monomer Composition ◽  
Styrene Copolymers ◽  
Identical Monomer ◽  
Emulsion Polymers ◽  
Styrene Content ◽  
Butadiene Styrene

Abstract Sodium-catalyzed butadiene-styrene copolymers (S-BS), of composition 75 weight-per cent butadiene: 25 weight-per cent styrene, have been compounded in tread type recipes. Evaluation tests showed properties significantly different from those of GR-S, the emulsion-phase free radical—catalyzed copolymers of identical monomer composition. 1. The processing characteristics of S-BS are considerably superior to those of GR-S, although one experience with a high temperature internal mix may indicate some limitation. Objective laboratory processing tests show that S-BS resembles high-styrene emulsion copolymers in that it can be satisfactorily fabricated from stocks containing less filler than is required in GR-S stocks for similar uses. 2. Stress-strain properties based on limited compounding studies are similar to those of GR-S. 3. The flex crack growth—hysteresis balance for S-BS vulcanizates is much superior to that of GR-S vulcanizates. Vulcanizates of emulsion polymers of high styrene content also had a flex crack growth—hysteresis balance superior to that of GR-S vulcanizates. 4. The low temperature properties of S-BS vulcanizates are inferior to those of GR-S vulcanizates. Brittle points and low temperature Young's modulus of S-BS vulcanizates are much higher than those of GR-S vulcanizates.

Acetylene chemisorption at palladium: Effect of temperature and structure of the surface

1984 ◽  
Vol 49 (6) ◽  
pp. 1448-1458
Author(s):  
Josef Kopešťanský
Keyword(s):  
Work Function ◽  
Atomic Hydrogen ◽  
Effect Of Temperature ◽  
Thermally Stable ◽  
Template Effect ◽  
Temperature Range ◽  
Adsorbed Layers ◽  
Different Types ◽  
Adsorption Complexes ◽  
Low Coverage

The effect of temperature and structure of the palladium surfaces on acetylene chemisorption was studied along with the interaction of the adsorbed layers with molecular and atomic hydrogen. The work function changes were measured and combined with the volumetric measurements and analysis of the products. At temperature below 100 °C, acetylene is adsorbed almost without dissociation and forms at least two different types of thermally stable adsorption complexes. Acetylene adsorbed at 200 °C is partly decomposed, especially in the low coverage region. Besides the above mentioned effects, the template effect of adsorbed acetylene was studied in the temperature range from -80° to 25 °C. It has been shown that this effect is a typical phenomenon of the palladium-acetylene system which is not due to surface impurities.

scholarly journals The Respiration of some Planktonic copepods II. The Effect Of Temperature

1953 ◽  
Vol 31 (3) ◽  
pp. 447-460 ◽  
Author(s):  
D. T. Gauld ◽  
J. E. G. Raymont
Keyword(s):  
Respiratory Rate ◽  
The Body ◽  
The Other ◽  
Effect Of Temperature ◽  
Acartia Clausi ◽  
Temora Longicornis ◽  
Different Temperatures ◽  
Planktonic Copepods ◽  
The Difference ◽  
The Relationship

The respiratory rates of three species of planktonic copepods, Acartia clausi, Centropages hamatus and Temora longicornis, were measured at four different temperatures.The relationship between respiratory rate and temperature was found to be similar to that previously found for Calanus, although the slope of the curves differed in the different species.The observations on Centropages at 13 and 170 C. can be divided into two groups and it is suggested that the differences are due to the use of copepods from two different generations.The relationship between the respiratory rates and lengths of Acartia and Centropages agreed very well with that previously found for other species. That for Temora was rather different: the difference is probably due to the distinct difference in the shape of the body of Temora from those of the other species.The application of these measurements to estimates of the food requirements of the copepods is discussed.

scholarly journals Tropism of Sub-Axial Cervical Facet Joints Is Not Related to Segmental Movement during Active Movement or Therapist-Perceived Symptomatic Locations

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 739
Author(s):  
Neil Tuttle ◽  
Kerrie Evans ◽  
Clarice Sperotto dos Santos Rocha
Keyword(s):  
Cervical Spine ◽  
Neck Pain ◽  
Active Movement ◽  
Facet Joints ◽  
Segmental Mobility ◽  
Limited Mobility ◽  
Translational Movement ◽  
The Difference ◽  
Cervical Facet ◽  
The Relationship

Tropism, or asymmetry, of facet joints in the cervical spine has been found to be related to degenerative changes of the joints and discs. Clinicians often assume that differences in segmental mobility are related to tropism. The aims of this study were to determine the relationship between asymmetry of facet joints in the sub-axial cervical spine and (1) segmental mobility and (2) spinal levels perceived by therapists to have limited mobility. Eighteen participants with idiopathic neck pain had MRIs of their cervical spine in neutral and at the end of active rotation. Angular movement and translational movement of each motion segment was calculated from 3D segmentations of the vertebrae. A plane was fitted to the facet on each side. Tropism was considered to be the difference in the orientation of the facet planes and ranged from 1 to 30° with a median of 7.7°. No relationships were found between the extent of tropism and either segmental movement or locations deemed to be symptomatic. Tropism in the sub-axial cervical spine does not appear to be related to segmental mobility in rotation or to levels deemed to be symptomatic.

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