The Role of Oxygen in the Vulcanization of Natural Rubber

1955 ◽  
Vol 28 (3) ◽  
pp. 785-787
Author(s):  
A. S. Kuzminskii˘ ◽  
V. F. Cheetkova
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Atmospheric Oxygen ◽  
Three Dimensional ◽  
Large Degree ◽  
Work Capacity ◽  
Dimensional Structure ◽  
Oxidative Destruction ◽  
Rubber Mixture ◽  
Chain Molecules

Abstract A three-dimensional structure is formed during the vulcanization of rubber. The complex processes of formation, rupture, and regrouping of bonds during vulcanization lead finally to union of the long chain molecules into a compact network. The density of the network formed during vulcanization and the distribution and degree of sulfide formation by the bonds govern to a large degree the work-capacity of vulcanizates. Structure formation in vulcanizates is manifest by the change of their tensile strength, elasticity, swelling, and solubility. During the vulcanization of natural rubber, an optimum is observed in the change of tensile strength and other technically important properties of the material. The decrease of tensile strength of vulcanizates by overvulcanization is usually ascribed to the oxidative destruction of the molecular chains of the rubber. The strong influence which has been observed of oxygen on the tensile strength of natural rubber and its vulcanizates is the basic argument in favor of oxidative destruction. This influence, however, only appears when the rubber is in direct contact with oxygen or air. When, in the rubber industry, vulcanization is carried out in presses, the surface of the rubber mixture is isolated from atmospheric oxygen, and, consequently, destruction in this case can be caused only by the oxygen dissolved in the rubber mixture.

Mechanochemical Devulcanization of Vulcanized Gum Natural Rubber

2005 ◽  
Vol 21 (3) ◽  
pp. 183-199
Author(s):  
G.K. Jana ◽  
C.K. Das
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Natural Rubber ◽  
Three Dimensional ◽  
Elongation At Break ◽  
Tear Strength ◽  
Vulcanized Rubber ◽  
Dimensional Network ◽  
Polymeric Chains ◽  
Cure Time

De-vulcanization of vulcanized elastomers represents a great challenge because of their three-dimensional network structure. Sulfur-cured gum natural rubbers containing three different sulfur/accelerator ratios were de-vulcanized by thio-acids. The process was carried out at 90 °C for 10 minutes in an open two-roll cracker-cum-mixing mill. Two concentrations of de-vulcanizing agent were tried in order to study the cleavage of the sulfidic bonds. The mechanical properties of the re-vulcanized rubber (like tensile strength, modulus, tear strength and elongation at break) were improved with increasing concentrations of de-vulcanizing agent, because the crosslink density increased. A decrease in scorch time and in optimum cure time and an increase in the state of cure were observed when vulcanized rubber was treated with high amounts of de-vulcanizing agent. The temperature of onset of degradation was also increased with increasing concentration of thio-acid. DMA analysis revealed that the storage modulus increased on re-vulcanization. From IR spectroscopy it was observed that oxidation of the main polymeric chains did not occur at the time of high temperature milling. Over 80% retention of the original mechanical properties (like tensile strength, modulus, tear strength and elongation at break) of the vulcanized natural rubber was achieved by this mechanochemical process.

The Structure of the System: Filler Rubber. An Electron-Microscopic Study

1954 ◽  
Vol 27 (1) ◽  
pp. 1-11 ◽  
Author(s):  
Friedrich Endter
Keyword(s):  
Natural Rubber ◽  
Microscopic Study ◽  
Electron Microscopic Study ◽  
Three Dimensional ◽  
Electron Microscopic ◽  
Rubber Mixture ◽  
Dimensional Network ◽  
Bound Rubber ◽  
Microscopic Investigations

Abstract Electron microscopic investigations of the benzene-extraction residues of filler-natural rubber mixtures which are used for the determination of bound rubber, give a pattern of a three-dimensional network consisting of filler and bound rubber. The unchanged benzene-soluble rubber is present in the interstices of the network in the untreated filler-rubber mixture.

X-Ray Study of the Crystallization of Vulcanized Rubber during Stretching. II.

1951 ◽  
Vol 24 (3) ◽  
pp. 541-549 ◽  
Author(s):  
V. I. Kasotochkin ◽  
B. V. Lukin
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Crystal Formation ◽  
Oxidative Destruction ◽  
Ray Method ◽  
X Ray ◽  
Vulcanized Rubber ◽  
Crystal Content

Abstract 1. The relation between the crystal content of stretched vulcanizates to the time of vulcanization for different mixtures of natural rubber was studied by the x-ray method. 2. It was shown that the tensile strength is a function of the crystal content of the stretched vulcanizate and of the total time of vulcanization. 3. The nature of crystal formation depends on the following factors: changes of density of the network of sulfur bridges, their distribution, the degree of oxidative destruction, and the quantity of bound sulfur which has not formed bridges between the molecular chains.

scholarly journals The three dimensional structure of astronomical sources through optimal inversion

1991 ◽  
Vol 131 ◽  
pp. 228-232
Author(s):  
Eric Keto ◽  
William Jeffrey
Keyword(s):  
Goodness Of Fit ◽  
Three Dimensional ◽  
Large Degree ◽  
Dimensional Structure ◽  
Physical Parameters ◽  
Correlated Errors ◽  
Sampled Data ◽  
Astronomical Data ◽  
Three Dimensional Structure ◽  
General Terms

AbstractWe explore the application of optimal inversion techniques to astronomical data with a goal of developing a set of procedures for the determination of the three dimensional structure of astronomical sources. Astronomical data present a particularly difficult problem in inversion because: In any observation, 3 of 6 spatial and velocity dimensions are lost in projection onto the plane of the sky and the line of sight velocity. In any inversion, we would like to solve for a number of physical parameters. Generally, these parameters are closely related in their effect on the single observable, the sky brightness.The dimensional deficiency leaves us with an unavoidably large degree of ambiguity (non-uniqueness) in any solution, while the inter-related parameters lead to a high probability of correlated errors and hence instability in the presence of to noise.We show how constraints of symmetry and smoothness source allow us to handle an inversion with an insufficiently sampled data base and mutually dependent solution parameters (mathematically ill-posed and ill-conditioned). The constraints represent a priori information incorporated into the solution; thus very highly constrained inversions are similar to model fitting. In any case the inversion procedure provides us with quantitative statistics on the goodness of fit which may be used to assess the degree of ambiguity in a particular model, and the expected errors and cross-correlated errors on the parameters defining the source structure.We briefly discuss the background and motivation, and outline the procedure in general terms. We refer to papers published in the Ap. J. where different aspects of the inversion are applied to observational data bases collected at the VLA.

The Nature of Optimum Vulcanization in Natural Rubber

1959 ◽  
Vol 32 (2) ◽  
pp. 562-565
Author(s):  
A. S. Kuzminskiĭ ◽  
V. F. Chertkova
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Three Dimensional ◽  
Oxidative Degradation ◽  
Substantial Effect ◽  
Considerable Change ◽  
Network Density ◽  
Tetramethylthiuram Disulfide ◽  
Series Of Experiments ◽  
Set Up

Abstract The vulcanization of natural rubber is accompanied by a considerable change in mechanical properties as the vulcanizate is formed. With sulfur as the vulcanizing agent an optimum is observed in the change in tensile strength and other physical properties. In many studies the presence of an optimum vulcanization has been considered as the result of the superimposition of two processes: (1) the structure-forming action of sulfur and (2) the degrading action of the oxygen, which causes a reversion of vulcanizates. We have established2 that the oxidative degradation of natural rubber in the vulcanization process proceeds extremely slowly and cannot have any substantial effect on the tensile strength of vulcanizates. To resolve the question as to the true causes of the reversion of vulcanizates in “overvulcanization”, several series of experiments were set up. In the first series the mobility of sulfur bonds was studied in natural rubber vulcanizates containing various accelerators by the use of the sulfur radio-isotope S35 with a method described earlier. The results of these experiments shown in Figure 1 indicate the “concentration” of mobile links in the vulcanizate to change proportionately with the change in tensile strength and the maximum density of mobile polysulfide links thus corresponds to optimum vulcanization according to tensile strength. The modulus likewise changes during the course of vulcanization, proportionately to the density of the intermolecular crosslinks formed. The formation of a complex three-dimensional network proceeds continually through all the various stages of the process up to the optimum. The increase in network density in the vulcanizates being formed, up to the optimum, is accompanied by a steady substantial rise in tensile strength. Further vulcanization, however, causes a decrease in network density and a drop in tensile strength. In a second series of experiments with vulcanizates at various stages of the process the polysulfide bonds were removed by extraction with sodium sulfite. When this occurred a decrease in the tensile strength of the vulcanizates was observed, which was especially marked at optimum vulcanization (Figure 2, Curve 2). In a third series of experiments, vulcanization was achieved with tetramethylthiuram disulfide (TMTD) without added sulfur. It is known that TMTD forms monosulfide bonds in rubber which are stable under the usual vulcanization conditions (a temperature of 143° C). Figure 2 (Curve 3) shows that no reversion is observed in vulcanization with TMTD.

Conformation of Ribosomes from Escherichia Coli

1974 ◽  
Vol 32 ◽  
pp. 210-211
Author(s):  
M. Boublik ◽  
W. Hellmann ◽  
F. Jenkins
Keyword(s):  
Binding Sites ◽  
Ribosomal Proteins ◽  
Fluorescent Dyes ◽  
Protein Biosynthesis ◽  
Three Dimensional ◽  
Spatial Arrangement ◽  
Dimensional Structure ◽  
Complete Understanding ◽  
And Function

The present knowledge of the three-dimensional structure of ribosomes is far too limited to enable a complete understanding of the various roles which ribosomes play in protein biosynthesis. The spatial arrangement of proteins and ribonuclec acids in ribosomes can be analysed in many ways. Determination of binding sites for individual proteins on ribonuclec acid and locations of the mutual positions of proteins on the ribosome using labeling with fluorescent dyes, cross-linking reagents, neutron-diffraction or antibodies against ribosomal proteins seem to be most successful approaches. Structure and function of ribosomes can be correlated be depleting the complete ribosomes of some proteins to the functionally inactive core and by subsequent partial reconstitution in order to regain active ribosomal particles.

Three-Dimensional Reconstruction Using Stereo Pairs from Serial Thick Sections

1977 ◽  
Vol 35 ◽  
pp. 562-563
Author(s):  
Robert Glaeser ◽  
Thomas Bauer ◽  
David Grano
Keyword(s):  
Three Dimensional ◽  
Dimensional Structure ◽  
Serial Sections ◽  
Thin Sections ◽  
3 Dimensional ◽  
Transmission Electron ◽  
Freeze Dried ◽  
Dimensional Reconstruction ◽  
Stereo Imagery ◽  
Whole Mounts

In transmission electron microscopy, the 3-dimensional structure of an object is usually obtained in one of two ways. For objects which can be included in one specimen, as for example with elements included in freeze- dried whole mounts and examined with a high voltage microscope, stereo pairs can be obtained which exhibit the 3-D structure of the element. For objects which can not be included in one specimen, the 3-D shape is obtained by reconstruction from serial sections. However, without stereo imagery, only detail which remains constant within the thickness of the section can be used in the reconstruction; consequently, the choice is between a low resolution reconstruction using a few thick sections and a better resolution reconstruction using many thin sections, generally a tedious chore. This paper describes an approach to 3-D reconstruction which uses stereo images of serial thick sections to reconstruct an object including detail which changes within the depth of an individual thick section.

Electron Microscopy of Cytoplasmic Contractile Proteins

1978 ◽  
Vol 36 (3) ◽  
pp. 606-614 ◽  
Author(s):  
T.D. Pollard ◽  
P. Maupin
Keyword(s):  
Electron Microscopy ◽  
Actin Filaments ◽  
Three Dimensional ◽  
Uranyl Acetate ◽  
Contractile Proteins ◽  
Dimensional Structure ◽  
X Ray Diffraction ◽  
Cytoplasmic Matrix ◽  
Computer Image Processing ◽  
Nonmuscle Cells

In this paper we review some of the contributions that electron microscopy has made to the analysis of actin and myosin from nonmuscle cells. We place particular emphasis upon the limitations of the ultrastructural techniques used to study these cytoplasmic contractile proteins, because it is not widely recognized how difficult it is to preserve these elements of the cytoplasmic matrix for electron microscopy. The structure of actin filaments is well preserved for electron microscope observation by negative staining with uranyl acetate (Figure 1). In fact, to a resolution of about 3nm the three-dimensional structure of actin filaments determined by computer image processing of electron micrographs of negatively stained specimens (Moore et al., 1970) is indistinguishable from the structure revealed by X-ray diffraction of living muscle.

A New 1000kv Electron Microscope

1969 ◽  
Vol 27 ◽  
pp. 100-101
Author(s):  
J.L. Williams ◽  
K. Heathcote ◽  
E.J. Greer
Keyword(s):  
Electron Microscope ◽  
Direct Observation ◽  
High Voltage ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Specimen Thickness ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
Dynamic Experiments ◽  
Conventional Instrument

High Voltage Electron Microscope already offers exciting experimental possibilities to Biologists and Materials Scientists because the increased specimen thickness allows direct observation of three dimensional structure and dynamic experiments on effectively bulk specimens. This microscope is designed to give maximum accessibility and space in the specimen region for the special stages which are required. At the same time it provides an ease of operation similar to a conventional instrument.

High-voltage electron microscopy of maxillary gland of spirochete-infected brine shrimp: lesion of efferent tubule

1988 ◽  
Vol 46 ◽  
pp. 362-363
Author(s):  
G. E. Tyson ◽  
M. J. Song
Keyword(s):  
Electron Microscopy ◽  
High Voltage ◽  
Brine Shrimp ◽  
Natural Populations ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
High Voltage Electron Microscopy ◽  
Voltage Electron ◽  
High Voltage Electron ◽  
Infected Adult

Natural populations of the brine shrimp, Artemia, may possess spirochete- infected animals in low numbers. The ultrastructure of Artemia's spirochete has been described by conventional transmission electron microscopy. In infected shrimp, spirochetal cells were abundant in the blood and also occurred intra- and extracellularly in the three organs examined, i.e. the maxillary gland (segmental excretory organ), the integument, and certain muscles The efferent-tubule region of the maxillary gland possessed a distinctive lesion comprised of a group of spirochetes, together with numerous small vesicles, situated in a cave-like indentation of the base of the tubule epithelium. in some instances the basal lamina at a lesion site was clearly discontinuous. High-voltage electron microscopy has now been used to study lesions of the efferent tubule, with the aim of understanding better their three-dimensional structure.Tissue from one maxillary gland of an infected, adult, female brine shrimp was used for HVEM study.

Sign in / Sign up

Export Citation Format

Share Document