The Crystallization of Weakly Vulcanized Rubber by Pressure

1940 ◽  
Vol 13 (1) ◽  
pp. 48-48 ◽  
Author(s):  
P. A. Thiessen ◽  
W. Kirch
Keyword(s):  
Melting Point ◽  
Natural Rubber ◽  
Crystalline Phase ◽  
Normal Pressure ◽  
Latex Film ◽  
X Rays ◽  
Amorphous Substance ◽  
Temperature Range ◽  
Vulcanized Rubber

Abstract Crystallization can be brought about in weakly vulcanized rubber by the method described by Thiessen and Kirsch for natural rubber. When samples of this type of vulcanized rubber were exposed to x-rays below + 6° C, but not under pressure, then Debye-Scherrer diagrams corresponding to those of a crystallized latex film were obtained. To determine the influence of pressure on these vulcanizates, samples were subjected to pressure on all sides in the chambers of the pressure apparatus described in the earlier work. After having been exposed for 100 days the sample which had been kept at + 6° C under 30 atmospheres' pressure showed a very marked Debye-Scherrer diagram, whereas samples kept at the same temperature but at normal pressure showed only the halo of an amorphous substance. Consequently pressure has an influence on the crystallization of vulcanized rubber as well as of raw rubber. The melting point of the crystalline phase lies between + 11° C. and +13° C. Obviously then an increase in pressure raises the temperature range of supercooling.

The influence of crystalline texture on the tensile properties of natural rubber. I

1974 ◽  
Vol 338 (1615) ◽  
pp. 459-478 ◽  
Keyword(s):  
Glass Transition ◽  
Natural Rubber ◽  
Tensile Properties ◽  
Amorphous Phase ◽  
Crystalline Phase ◽  
Full Range ◽  
Glassy Matrix ◽  
Tensile Behaviour ◽  
Crystalline Morphology ◽  
Temperature Range

The crystalline morphologies that are attainable in samples of natural rubber (n. r.), by extending the samples prior to crystallization, are reviewed. Specimens covering the full range of crystalline morphologies possible have been prepared and tensile tested between – 120 and – 26 °C. The tensile behaviour of crystalline samples is compared and contrasted with that of oriented, but non-crystalline, identical natural rubber in the same temperature range. It is found that the tensile behaviour of semi-crystalline n. r. is dominated by the amorphous phase throughout the temperature range – 120 to – 26 °C. At temperatures above the glass transition temperature ( T g ) of the amorphous phase, the crystalline phase acts mainly as a diluent of the amorphous phase. At temperatures below T g , where the crystalline phase is set in a glassy matrix, it is found that the crystalline morphology does significantly affect the tensile behaviour. Attempts are made to differentiate the effects of crystallinity, crystalline morphology and orientation of the amorphous phase on the tensile properties of natural rubber.

Smearing of Vulcanized Rubber

1955 ◽  
Vol 28 (2) ◽  
pp. 508-518 ◽  
Author(s):  
S. D. Gehman ◽  
C. S. Wilkinson ◽  
R. D. Daniels
Keyword(s):  
Melting Point ◽  
Thermal Degradation ◽  
Natural Rubber ◽  
Sulfur Compound ◽  
Important Variable ◽  
Cross Linking ◽  
Curing Agent ◽  
Point Bar ◽  
Tetramethylthiuram Disulfide ◽  
Vulcanized Rubber

Abstract The surface heating which occurs at the interface of rubber sliding under a load may be part of the mechanism of abrasion, especially under severe conditions. Removal of rubber by thermal degradation and a smearing process occurs if the rubber attains sufficiently high localized temperatures. A procedure, using a melting point bar, was developed for measuring the temperature at which smearing occurred for rubber vulcanizates. Smear points reproducible to about ±2° F were measured. The effect of compounding variables on the smear point was investigated. The most important variable in this category was the vulcanization system, probably inasmuch as it determined the type of cross-linking. The presence of free sulfur within the rubber also tended to increase the smear temperature. Highest smear points were obtained with mercaptobenzothiazole-tetramethylthiuram disulfide mixtures, and for a non-sulfur compound using p-quinone-dioxime as the curing agent. The highest smear point observed for natural rubber was 475° F, obtained with this system. GR-S tread compounds showed no smearing even at 560° F, which was as high as could be obtained with the apparatus used. The resistance to smearing of GR-S may be an important factor in explaining its superiority in road wear under severe conditions. Laboratory abrasion experiments were performed to illustrate the effect of smearing on the relative abrasion loss of GR-S and natural-rubber tread compounds.

Forced and Spontaneous Changes in the Arrangement of the Molecules in Stretched Rubber. Crystals and Fused Phase in Stretched Rubber

1939 ◽  
Vol 12 (4) ◽  
pp. 736-754 ◽  
Author(s):  
P. A. Thiessen ◽  
W. Wittstadt
Keyword(s):  
Natural Rubber ◽  
Mechanical Stress ◽  
Mechanical Deformation ◽  
Unsaturated Hydrocarbon ◽  
X Rays ◽  
Double Refraction ◽  
Amorphous Substance ◽  
X Ray ◽  
Space Lattice ◽  
Differences Of Opinion

Abstract An unsaturated hydrocarbon of the formula (C5H8)2x is the basis of natural rubber. Although there are still differences of opinion about the size of the molecules, it may nevertheless be accepted as fairly certain that the parent substance, the unsaturated hydrocarbon, is composed of a mixture of various steps of polymerization. At ordinary temperatures and under no mechanical stress, both vulcanized and unvulcanized rubber are isotropic glasses. Exposed to x-rays they give the diagram of an amorphous substance, i.e., a broad, diffuse ring. As a result of mechanical deformation, especially stretching, rubber becomes anisotropic. This anisotropy is manifest by the appearance of optical double refraction, as well as by an x-ray fiber diagram, which replaces the amorphous ring. This indicates orientation of the molecules and rearrangement into a space lattice, measurements of which have been made repeatedly and which make probable a rhombic structure.

The Fusion Curve of Natural Rubber

1931 ◽  
Vol 4 (2) ◽  
pp. 211-212
Author(s):  
G. v. Susich
Keyword(s):  
Melting Point ◽  
Specific Gravity ◽  
Natural Rubber ◽  
Specific Heat ◽  
Light Absorption ◽  
Temperature Range

Abstract Katz has shown that the melting point of frozen raw rubber is 35°–38° C. when determined by the disappearance of the crystal interferences upon warming. The discontinuous changes in the specific gravity, in the hardness, and in the light absorption, as well as the γ-anomaly of the specific heat, lie within this temperature range.

Crystals and Fused Substance in Stretched Rubber. (A Preliminary Communication)

1936 ◽  
Vol 9 (1) ◽  
pp. 52-54
Author(s):  
Peter A. Thiessen ◽  
Werner Wittstadt
Keyword(s):  
Natural Rubber ◽  
Mechanical Stress ◽  
Permanent Deformation ◽  
Unsaturated Hydrocarbon ◽  
Final State ◽  
Double Refraction ◽  
Space Lattice ◽  
Temperature Range ◽  
Vulcanized Rubber ◽  
Wide Range

Abstract When rubber is stretched, the arrangement of the molecules in the space lattice does not come to an end when the elongation is terminated, but continues for a certain time afterward. The final state of orientation for any elongation depends upon the temperature in the sense that within a wide temperature range there is at each temperature a definite ratio between the quantity of crystallized substance and the glass-like fused component. Within this temperature range, the proportion of crystallized substance diminishes with increase in temperature. This change is reversible, and the equilibrium is greatly influenced by the pressure. It may be considered as an established fact today that natural rubber is essentially a mixture of various polymers of an unsaturated hydrocarbon. At ordinary temperatures and in the absence of mechanical stress, it is an isotropic glass, both in the raw and vulcanized states. When deformed mechanically, particularly when stretched, it becomes anisotropic, a change which is evidenced by the appearance of an optical double refraction and an x-ray fiber diagram. This phenomenon is attributable to an orientation of the molecules in the direction of stretching and their arrangement into a space lattice which can be measured and defined accurately. The increase in double refraction as well as the clearness of the reflection interference pattern in the Roentgen diagram is proportional to the degree of elongation of both raw and vulcanized rubber, and it is reversible after a certain time of relaxation. In natural rubber, the reversibility of the phenomenon is disturbed by flow phenomena, which upon prolonged mechanical stress lead to permanent deformation. In well vulcanized rubber these phenomena are of little significance over a wide range of temperatures.

Application of Microwave Radiation in Modified Polyol Process for Synthesis Pure, Te-Doped, and Sn-Doped CoSb3 Thermoelectric Materials

2020 ◽  
Vol 302 ◽  
pp. 123-134
Author(s):  
Thammanoon Kapanya ◽  
Chanchana Thanachayanont ◽  
Adisorn Tuantranont ◽  
Thapanee Sarakonsri
Keyword(s):  
Electron Microscope ◽  
Microwave Radiation ◽  
Crystalline Phase ◽  
Synthesis Method ◽  
Normal Pressure ◽  
Solubility Limit ◽  
Heating Time ◽  
Polyol Process ◽  
Transmission Electron ◽  
Microwave Time

Synthesis routes of CoSb3 need a long reaction time, especially at high temperature and-/or high pressure. Although the modified polyol process assisted with microwave radiation can be used to solve these problems, it used the excess amount of Sb ion. Therefore, this study aimed to solve this drawback by retarding the rate of reduction. The different microwave times (0, 1, and 3 min) were investigated to find out the shortest heating duration for preparing CoSb3 nanoparticles. Te-doped and Sn-doped CoSb3 were synthesized to investigate the benefit of this synthesis method for increasing the solubility limit of Te and Sn in the CoSb3 structure. The phase and microstructure of the synthesized products were characterized by using x-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results showed that the high crystalline phase of CoSb3 (JCPDS: 78-0977) without any metallic impurity phases product was successfully synthesized in 3 minutes for a heating time at normal pressure, non-excessive addition of Sb ion precursor, and low temperature. The XRD results of Te-doped and Sn-doped CoSb3 products exhibited poor crystalline phase and hard to exactly identify. In SEM and TEM results, the CoSb3 powder consisted of very tiny spherical-like particles around 10 nanometers attaching together even at different microwave time similar to Te-doped/Sn-doped samples.

Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates

1959 ◽  
Vol 32 (3) ◽  
pp. 739-747 ◽  
Author(s):  
J. R. Dunn ◽  
J. Scanlan
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Protective Action ◽  
Dicumyl Peroxide ◽  
Vulcanized Rubber ◽  
Aging Properties ◽  
Photochemical Aging ◽  
Natural Rubber Vulcanizates

Abstract The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.

Adhesion of Vulcanized Rubber Surfaces: Characterization of Unmodified and Electron Beam Modified EPDM Surfaces and Their Co-vulcanization with Natural Rubber

2009 ◽  
Vol 23 (13-14) ◽  
pp. 1763-1786 ◽  
Author(s):  
Ganesh C. Basak ◽  
Abhijit Bandyopadhyay ◽  
Y. K. Bharadwaj ◽  
S. Sabharwal ◽  
Anil K. Bhowmick
Keyword(s):  
Electron Beam ◽  
Natural Rubber ◽  
Vulcanized Rubber

scholarly journals Physicochemical, Thermomechanical, and Swelling Properties of Radiation Vulcanised Natural Rubber Latex Film: Effect of Diospyros peregrina Fruit Extracts

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
Kazi Md Zakir Hossain ◽  
Nashid Sharif ◽  
N. C. Dafader ◽  
M. E. Haque ◽  
A. M. Sarwaruddin Chowdhury
Keyword(s):  
Natural Rubber ◽  
Natural Rubber Latex ◽  
Tensile Modulus ◽  
Decomposition Temperature ◽  
Latex Film ◽  
Cross Linking ◽  
Rubber Latex ◽  
Swelling Properties ◽  
Fruit Extracts ◽  
Control Film

A range of radiation vulcanised natural rubber latex (RVNRL) films were prepared using various concentrations of aqueous extracts of mature Diospyros peregrina fruit, which acted as a cross-linking agent. The surface of the RVNRL films exhibited an aggregated morphology of the rubber hydrocarbon with increasing roughness due to increasing fruit extract contents in the latex. An improvement in tensile strength, tensile modulus, and storage modulus of RVNRL films was observed with the addition of fruit extracts compared to the control film due to their cross-linking effect. The glass transition (Tg) temperature of all the RVNRL films was found to be at around −61.5°C. The films were also observed to be thermally stable up to 325°C, while the maximum decomposition temperature appeared at around 375°C. The incorporation of fruit extracts further revealed a significant influence on increasing the crystallinity, gel content, and physical cross-link density of the RVNRL films.

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