Mechanisms of Antiozonant Protection: Antiozonant-Rubber Reactions during Ozone Exposure

1984 ◽  
Vol 57 (5) ◽  
pp. 1023-1035 ◽  
Author(s):  
R. P. Lattimer ◽  
R. W. Layer ◽  
C. K. Rhee
Keyword(s):  
Chemical Reactions ◽  
Experimental Error ◽  
Chemical Structure ◽  
Model Compound ◽  
Polymer Network ◽  
Model Reaction ◽  
Ozone Exposure ◽  
Protective Film ◽  
Definitive Evidence ◽  
Unsaturated Rubber

Abstract Rubber (IR or BR) vulcanizatcs containing DOPPD antiozonant have been aged under ozone, and the soluble constituents have been removed by acetone extraction. Small amounts of nitrogen from the antiozonant remain in the rubber after extraction; this nitrogen is presumed to be chemically attached to the polymer network. Some of this “unextractable nitrogen” may be due to reaction of ozonized rubber with antiozonant, but other explanations are possible. The amount of unextractable nitrogen in the vulcanizate before ozone aging is about the same, within experimental error, as the amount remaining after static ozone aging. Model compound experiments (with cis-9-tricosene or squalene) show that chemical reactions can take place between the ozonized olefins (or unsaturated rubber) and DOPPD. The chemical structure for a model reaction product has been determined. Despite these findings, it seems unlikely that these types of reactions will play a significant role in the overall protection of rubber vulcanizates from ozone attack. That is, these products can form only after the rubber starts to become ozonized, and it has been shown that ozone attack on the rubber does not occur until after the antiozonant is nearly completely consumed. The results of this work are consistent with previous studies in our laboratory that indicate a combined “scavenger-protective film” mechanism is principally responsible for antiozonant protection. There is no definitive evidence to date to show that ozonized rubber reacts with antiozonant during ozone aging of rubber vulcanizates.

scholarly journals Density changes of aerosol particles as a result of chemical reaction

2004 ◽  
Vol 4 (5) ◽  
pp. 6431-6472 ◽  
Author(s):  
Y. Katrib ◽  
S. T. Martin ◽  
Y. Rudich ◽  
P. Davidovits ◽  
J. T. Jayne ◽  
...  
Keyword(s):  
Oleic Acid ◽  
Oxygen Content ◽  
Chemical Reactions ◽  
Aerosol Particles ◽  
Ozone Exposure ◽  
Spherical Particles ◽  
Aerodynamic Diameter ◽  
Layer Density ◽  
Aerosol Mass ◽  
Mobility Diameter

Abstract. This paper introduces the capability to study simultaneously changes in the density, the chemical composition, the mobility diameter, the aerodynamic diameter, and the layer thickness of multi-layered aerosol particles as they are being altered by heterogeneous chemical reactions. A vaporization-condensation method is used to generate aerosol particles composed of oleic acid outer layers of 2 to 30 nm on 101-nm polystyrene latex cores. The layer density is modified by reaction of oleic acid with ozone for variable exposure times. For increasing ozone exposure, the mobility diameter decreases while the vacuum aerodynamic diameter increases, which, for spherical particles, implies that particle density increases. The aerosol particles are confirmed as spherical based upon the small divergence of the particle beam in the aerosol mass spectrometer. The particle and layer densities are calculated by two independent methods, namely one based on the measured aerodynamic and mobility diameters and the other based on the measured mobility diameter and particle mass. The uncertainty estimates for density calculated by the second method are two to three times greater than those of the first method. Both methods indicate that the layer density increases from 0.89 to 1.12 g·cm−3 with increasing ozone exposure. Aerosol mass spectrometry shows that, concomitant with the increase in the layer density, the oxygen content of the reacted layer increases. Even after all of the oleic acid has reacted, the layer density and the oxygen content continue to increase slowly with prolonged ozone exposure, a finding which indicates continued chemical reactions of the organic products either with ozone or with themselves. The results of this paper provide new insights into the complex changes occurring for atmospheric particles during the aging processes caused by gas-phase oxidants.

scholarly journals A Guide through the Dental Dimethacrylate Polymer Network Structural Characterization and Interpretation of Physico-Mechanical Properties

Materials ◽  
2019 ◽  
Vol 12 (24) ◽  
pp. 4057 ◽  
Author(s):  
Izabela Maria Barszczewska-Rybarek
Keyword(s):  
Mechanical Properties ◽  
Chemical Structure ◽  
Structural Parameters ◽  
Polymer Network ◽  
Polymer Networks ◽  
Impact Resistance ◽  
Organic Matrices ◽  
Dental Restorative

Material characterization by the determination of relationships between structure and properties at different scales is essential for contemporary material engineering. This review article provides a summary of such studies on dimethacrylate polymer networks. These polymers serve as photocuring organic matrices in the composite dental restorative materials. The polymer network structure was discussed from the perspective of the following three aspects: the chemical structure, molecular structure (characterized by the degree of conversion and crosslink density (chemical as well as physical)), and supramolecular structure (characterized by the microgel agglomerate dimensions). Instrumental techniques and methodologies currently used for the determination of particular structural parameters were summarized. The influence of those parameters as well as the role of hydrogen bonding on basic mechanical properties of dimethacrylate polymer networks were finally demonstrated. Mechanical strength, modulus of elasticity, hardness, and impact resistance were discussed. The issue of the relationship between chemical structure and water sorption was also addressed.

Factors Influencing the Ozone Resistance of Neoprene Vulcanizates under Flexure

1959 ◽  
Vol 32 (4) ◽  
pp. 1117-1133 ◽  
Author(s):  
R. M. Murray
Keyword(s):  
Dynamic Testing ◽  
Constant Stress ◽  
Ozone Exposure ◽  
Surface Barrier ◽  
Limiting Factor ◽  
Surface Films ◽  
Protective Film ◽  
Dynamic Conditions ◽  
Static Conditions ◽  
Ozone Resistance

Abstract The need for dynamic testing conditions, such as mild flexing, to study the attack of ozone on elastomeric vulcanizates, has become increasingly apparent. Many rubber goods, such as belts, tire sidewalls, and hose, are subjected to intermittent or continuously fluctuating strains in service and to evaluate their ozone resistance under constant stress or strain conditions is unrealistic and often leads to entirely erroneous conclusions. For example, it is well known that under static strain a vulcanizate's ozone resistance is enhanced by compounding with a wax which migrates to its surface and forms a protective film. However, numerous investigators have reported that when a wax film is continuously ruptured by dynamic testing, the vulcanizate is even more vulnerable to ozone attack than if no wax were present. Other surface films also may act detrimentally under dynamic conditions. One such film may form under static exposure by the migration of antiozonants to the surface of a sample where they or their ozone reaction products provide a shield against ozone. Also, diene elastomers, even when not under stress, react with ozone without cracking and it has been postulated that the thin films formed as a result of this reaction are less extensible and consequently more subject to rupture on flexing than the unreacted rubber beneath them. It may well be found that the resistance of any surface barrier to dynamic stresses is the limiting factor for many products in service. Consequently, techniques for testing under dynamic conditions are needed at least to supplement testing under constant stress or strain in ozone. Ozone exposure under dynamic conditions may prove to have analytical advantages over the static method. First, because dynamic tests accelerate ozone attack over that obtained statically even though no increased strain is impressed. This permits the more ozone resistant elastomers to be tested at lower concentrations of ozone than would be possible statically. By testing in more dilute ozone, the correlation between results obtained under atmospheric exposure and the ozone cabinet should be better. Also, it seems likely that compounding ingredients which improve ozone resistance under dynamic conditions should provide improvement under static conditions as well, even though the converse is not necessarily true.

Reaction of a Thiuram and Sulfur

1955 ◽  
Vol 28 (3) ◽  
pp. 804-807
Author(s):  
G. A. Blokh ◽  
L. P. Sazonova
Keyword(s):  
Chemical Reactions ◽  
Chemical Structure ◽  
Elemental Sulfur ◽  
Practical Interest ◽  
Previous Article ◽  
Tetramethylthiuram Disulfide ◽  
Mercapto Group ◽  
Cable Industry ◽  
Isotopic Method ◽  
Vulcanize Rubber

Abstract In a previous article the occurrence of an intensive interchange between atoms of elemental sulfur when present as vulcanizing agent and the sulfur atoms of the mercapto group of mercaptobenzothiazole as accelerator was shown by the isotopic method, i.e., by the application of tagged atoms of radioactive sulfur. Thus, the existence of a reaction between the accelerator and the vulcanizing agent during the vulcanization of rubber was established. The application of isotopes as tagged atoms is an effective new method of investigating the chemical structure of substances, their reactivities, and the mechanism of chemical reactions in which they take part. This method is being successfully developed in our country, particularly by the work of Brodskii˘ and his pupils. The present study is devoted to the problem of the reaction of tetramethylthiuram disulfide (hereafter called thiuram) and elemental sulfur. Studies in this field are of great scientific and practical interest, since the mechanism of the accelerating action of thiuram is not yet clear. We assume that the chemistry of the reaction is as follows. Thiuram is decomposed during vulcanization, with the formation of a dithiocarbamate and free active sulfur. Because of this, the thiuram can vulcanize rubber without the addition of elemental sulfur to the mixture. Such vulcanizates are particularly widely used in the cable industry.

SELF-OSCILLATIONS OF HYDROGELS DRIVEN BY CHEMICAL REACTIONS

2014 ◽  
Vol 06 (03) ◽  
pp. 1450023 ◽  
Author(s):  
A. D. DROZDOV
Keyword(s):  
Chemical Reactions ◽  
Mechanical Response ◽  
Polymer Network ◽  
Kinetic Equations ◽  
Time Dependent ◽  
Material Parameters ◽  
Reference Stress ◽  
Swelling Kinetic ◽  
Stress Free State ◽  
Belousov Zhabotinsky Reaction

A model is developed for the mechanical response of hydrogels whose deformation is accompanied by swelling–shrinkage driven by the Belousov–Zhabotinsky reaction. A hydrogel is treated as a compressible network of flexible chains with a time-dependent reference (stress-free) state whose evolution is driven by oxidation of a catalyst pendent to chains. The model involves three components: stress–strain relations for deformation of a polymer network coupled with swelling, kinetic equations for chemical reactions with diffusing species, and relations connecting changes in the reference configuration with concentration of oxidized catalyst. Results of simulation confirm the ability of the model to describe autonomous oscillations of a hydrogel layer under constrained swelling. The effect of material parameters on amplitude and frequency of oscillations is studied numerically. In agreement with the available experimental data, it is shown that amplitude of oscillations decreases and their period increases when (i) elastic modulus of the polymer network grows, (ii) a good solvent is replaced with a poor one, (iii) concentration of a catalyst is reduced, (iv) size of a sample decreases, and (v) diffusivities of solvent and activator grow.

scholarly journals Density changes of aerosol particles as a result of chemical reaction

2005 ◽  
Vol 5 (1) ◽  
pp. 275-291 ◽  
Author(s):  
Y. Katrib ◽  
S. T. Martin ◽  
Y. Rudich ◽  
P. Davidovits ◽  
J. T. Jayne ◽  
...  
Keyword(s):  
Oleic Acid ◽  
Oxygen Content ◽  
Chemical Reactions ◽  
Aerosol Particles ◽  
Ozone Exposure ◽  
Spherical Particles ◽  
Aerodynamic Diameter ◽  
Layer Density ◽  
Aerosol Mass ◽  
Mobility Diameter

Abstract. This paper introduces the capability to study simultaneously changes in the density, the chemical composition, the mobility diameter, the aerodynamic diameter, and the layer thickness of multi-layered aerosol particles as they are being altered by heterogeneous chemical reactions. A vaporization-condensation method is used to generate aerosol particles composed of oleic acid outer layers of 2 to 30nm on 101-nm polystyrene latex cores. The layer density is modified by reaction of oleic acid with ozone for variable exposure times. For increasing ozone exposure, the mobility diameter decreases while the vacuum aerodynamic diameter increases, which, for spherical particles, implies that particle density increases. The aerosol particles are confirmed as spherical based upon the small divergence of the particle beam in the aerosol mass spectrometer. The particle and layer densities are calculated by two independent methods, namely one based on the measured aerodynamic and mobility diameters and the other based on the measured mobility diameter and particle mass. The uncertainty estimates for density calculated by the second method are two to three times greater than those of the first method. Both methods indicate that the layer density increases from 0.89 to 1.12g·cm-3 with increasing ozone exposure. Aerosol mass spectrometry shows that, concomitant with the increase in the layer density, the oxygen content of the reacted layer increases. Even after all of the oleic acid has reacted, the layer density and the oxygen content continue to increase slowly with prolonged ozone exposure, a finding which indicates continued chemical reactions of the organic products either with ozone or with themselves. The results of this paper provide new insights into the complex changes occurring for atmospheric particles during the aging processes caused by gas-phase oxidants.

Copolymerization Modification of PPTA with 2,5-Furandicarboxylic Acid: Towards High-Performance Material with Enhanced Solubility

2017 ◽  
Vol 898 ◽  
pp. 2174-2180 ◽  
Author(s):  
Kai Ju Luo ◽  
Yan Wang ◽  
Jun Rong Yu ◽  
Jing Zhu ◽  
Zu Ming Hu
Keyword(s):  
High Performance ◽  
Chemical Structure ◽  
Room Temperature ◽  
Furan Ring ◽  
Polymer Network ◽  
H Nmr ◽  
Good Solubility ◽  
Enhanced Solubility ◽  
Ft Ir ◽  
Furandicarboxylic Acid

The preparation and characterizations of soluble copolymers poly (p-phenylene terephthamide-co-furandicarboxylic p-Phenylenediamine)(PPTA-co-PPF) by direct polycondensation was described. The chemical structure of polyamides was investigated by 1H NMR and FT-IR. The good solubility of copolymers in organic solvents was certified at room temperature. Their thermal stability and mechanical properties were observed by TGA and tensile testing and then compared with that of traditional high performance aromatic polyamides (PPTA and PMIA, for example, with trademarks of Kevlar® and Nomex®). The furan ring incorporated polyamide was expected to form thermal reversible cross-linked polymer network through D-A reaction.

scholarly journals Toughening Hydrogels Through Force-triggered Chemical Reactions that Lengthen Polymer Strands

2021 ◽  
Author(s):  
Zi Wang ◽  
Xu Jun Zheng ◽  
Tetsu Ouchi ◽  
Tatiana Kouznetsova ◽  
Haley Beech ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Chemical Reactions ◽  
Chemical Structure ◽  
Polymer Networks ◽  
Breaking Point ◽  
Network Architectures ◽  
Material Synthesis ◽  
Double Network ◽  
Cross Links ◽  
Coupled Reactions

<p>The utility and lifetime of materials made from polymer networks, including hydrogels, depend on their capacity to stretch and resist tearing. In gels and elastomers, those mechanical properties are often limited by the covalent chemical structure of the polymer strands between cross-links, which is typically fixed during the material synthesis. Here, we report polymer networks in which the constituent strands lengthen through force-coupled reactions that are triggered as the strands reach their nominal breaking point. Reactive strand extensions of up to 40% lead to hydrogels that stretch 40-50% further than, and exhibit tear energies twice that of, networks made from analogous control strands. The enhancements are synergistic with those provided by double network architectures, and complement other existing toughening strategies. </p>

scholarly journals New Reflectable Materials on the Basis of Polyimides

2016 ◽  
Vol 6 (1) ◽  
pp. 1 ◽  
Author(s):  
Saule K. Kudaikulova
Keyword(s):  
Chemical Modification ◽  
Chemical Reactions ◽  
Model Compound ◽  
Elevated Temperatures ◽  
Amic Acid ◽  
Surface Resistivity ◽  
Visible Range ◽  
Polyimide Films ◽  
Heterogeneous Chemical

Electroconductive and reflective metallized polyimide films have been prepared by heterogeneous chemical modification of polyimide surface. By carrying out the chemical reactions <em>in situ</em> in the modified layers of polyimide surface, thereby a metal phase strongly impregnated into the polyimide surface is obtained. The steps of chemical modification have been studied on the model compound – poly(amic acid) on the basis of pyromellite dianhydride and oxydianiline, which forms insoluble sodium or potassium poly(amicacid) salts (polyamate). Metallization of Kapton HN &amp; JP (from DuPont) and Upilex S films have been carried out and the films have been characterized by XRD, XRFD, and measurements of reflectivity in the visible range and surface resistivity at elevated temperatures. It is shown that reflectivity coefficients of silvered films are 90-92% and surface resistivity is about 0.5 Ω.

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