The Vulcanization of Rubber with Sulfur

1957 ◽  
Vol 30 (5) ◽  
pp. 1291-1346 ◽  
Author(s):  
David Craig
Keyword(s):  
Three Dimensional ◽  
Current Treatment ◽  
Network Behavior ◽  
Chain Molecules ◽  
Kinetic Activity ◽  
Dimensional Network ◽  
Colloid Science ◽  
The Subject ◽  
Gas Molecules ◽  
Points Of View

Abstract E. H. Farmer compiled a review of vulcanization which was published in 1946 as an important chapter in Volume II of “Advances in Colloid Science”. About two years later, Normann Bergem published a review under the same title. These authors dealt with the subject from rather fundamental points of view, but, because of more recent work from many laboratories and the increasing importance of elastomers, a fresh survey seems warranted. Accordingly, the present review aims to bring a part of the subject up-to-date. The viewpoint taken differs from those of Farmer and Bergem in some respects which seem rather important. For example, emphasis will be placed on the various rates of reactions including those of the scorch and reversion periods and on the importance of possible intermediates such as hydrogen sulfide and suitably terminated sulfur chains. The kinetic theory of elastomeric behavior constitutes the background against which any current treatment of vulcanization should be developed. Actually, vulcanization is a part of this background. Thus, Busse considered the following conditions necessary for the existence of rubberlike elasticity: (1) the presence of long chain molecules with freely rotating links, (2) the presence of weak secondary forces between molecules, and (3) the crosslinking of molecules into a three dimensional network. The three conditions taken together, at least in present day thinking, imply that long range elasticity results from the kinetic activity of segments which resembles yet differs from the kinetic activity of gas molecules. A segment is composed at most of only a few monomer units and is terminated at either end with another segment, a crosslink or an endgroup. When terminated with an endgroup, its kinetic activity may even detract from network behavior and then it is a defect. When terminated by a crosslink or another segment it is an integral part of the network and as such can contribute to the overall elasticity. It is more or less obvious that segments terminated by crosslinks and the crosslinks themselves should display an activity different from that of segments distant from crosslinks. Crosslinks, though relatively massive, are expected to move in a limited way (microBrownian) as a result of the kinetic activity of nearby segments. Crosslinks are necessary but are thus a sort of network defect. Those of lower functionality probably can contribute beneficially to the overall kinetic activity.

3D-[Pr(Im)3(ImH)]@ImH: Ein dreidimensionales Netzwerk mit vollständiger Stickstoffkoordination aus einer Imidazolschmelze / 3D-[Pr(Im)3(ImH)]@ImH: A Three-Dimensional Network with Complete Nitrogen Coordination Obtained from an Imidazole Melt

2006 ◽  
Vol 61 (7) ◽  
pp. 792-798 ◽  
Author(s):  
Klaus Müller-Buschbaum
Keyword(s):  
Crystal Engineering ◽  
Material Science ◽  
Three Dimensional ◽  
Temperature Dependent ◽  
Temperature Synthesis ◽  
3 Dimensional ◽  
High Temperature Synthesis ◽  
Dimensional Network ◽  
Bright Green ◽  
Gas Molecules

The reaction of a melt of unsubstituted imidazole with praseodymium metal yields bright green crystals of 3D-[Pr(Im)3(ImH)]@ImH. Imidazolate ligands coordinate η1 via both N atoms their 1,3 positioning within the heterocycle being responsible for the connection of praseodymium atoms. A 3-dimensional network is formed with imidazole molecules from the melt intercalated in the crystal structure. The imidazole molecules can be released and temperature dependent reversibly be exchanged with gas molecules including argon. Thus the solvent free high temperature synthesis of rare earth elements with amine melts can also be utilized for “crystal engineering” and the synthesis of compounds with material science aspects. Furthermore 3D-[Pr(Im)3(ImH)]@ImH is the first unsubstituted imidazolate of the lanthanides.

More hyperelastic models for rubber-like materials: consistent tangent operators and comparative study

2013 ◽  
Vol 22 (1-2) ◽  
pp. 27-50 ◽  
Author(s):  
Mokarram Hossain ◽  
Paul Steinmann
Keyword(s):  
Large Deformations ◽  
Pure Shear ◽  
Three Dimensional ◽  
Network Models ◽  
Polymeric Materials ◽  
Chain Molecules ◽  
Current Contribution ◽  
Dimensional Network ◽  
Analytical Expressions ◽  
Order Tangent

AbstractRubber-like materials can deform largely and nonlinearly upon loading, and they return to the initial configuration when the load is removed. Such rubber elasticity is achieved due to very flexible long-chain molecules and a three-dimensional network structure that is formed via cross-linking or entanglements between molecules. Over the years, to model the mechanical behavior of such randomly oriented microstructures, several phenomenological and micromechanically motivated network models for nearly incompressible hyperelastic polymeric materials have been proposed in the literature. To implement these models for polymeric material (undoubtedly with widespread engineering applications) in the finite element framework for solving a boundary value problem, one would require two important ingredients, i.e., the stress tensor and the consistent fourth-order tangent operator, where the latter is the result of linearization of the former. In our previous work, 14 such material models are reviewed by deriving the accurate stress tensors and tangent operators from a group of phenomenological and micromechanical models at large deformations. The current contribution will supplement some further important models that were not included in the previous work. For comparison of all selected models in reproducing the well-known Treloar data, the analytical expressions for the three homogeneous defomation modes, i.e., uniaxial tension, equibiaxial tension, and pure shear, have been derived and the performances of the models are analyzed.

Mechanisms of floc formation in sludge conditioning with polymers

1994 ◽  
Vol 30 (8) ◽  
pp. 129-138 ◽  
Author(s):  
Stefan J. Langer ◽  
Rudolf Klute ◽  
Hermann H. Hahn
Keyword(s):  
Filter Cake ◽  
Collision Frequency ◽  
Three Dimensional ◽  
Particle Collisions ◽  
Rapid Mixing ◽  
Time Period ◽  
Dimensional Network ◽  
Dilute Suspensions ◽  
The Subject ◽  
Slow Mixing

In flocculation of dilute suspensions a period of slow mixing is necessary to increase the probability of particle collisions that are necessary for flocculation to occur. When flocculating sludges, the collision frequency is so high that flocs are formed immediately after rapid mixing. However, controlled mixing of the flocculated sludge for some time period does improve dewaterability. The mechanisms that are involved have been studied in detail and the subject of this paper. The results show that after rapid mixing and initial floc formation there might still be polymer in solution, depending on polymer dose. Prolonged mixing results in breakage of large aggregates and in particle/floc surfaces that are not yet covered with polymers. Subsequently the excess polymer adsorbs onto these surfaces. From changes in sludge rheology one can see that within a period of about one half to one minute the bulk properties change dramatically. After the initial floc formation the suspension is in a state characterized by a three-dimensional network structure with strongly interacting, voluminous flocs. After the mixing period there are more discrete and less interacting flocs. Especially the properties of the filter cake from pressure filtration are then more favorable.

Stages and methods of legalization of criminal proceeds obtained as a result of economic and tax crimes

2020 ◽  
Vol 2020 (3) ◽  
pp. 148-156
Author(s):  
Pyotr Ivanov
Keyword(s):  
Law Enforcement ◽  
Money Laundering ◽  
Economic Security ◽  
Theory And Practice ◽  
Scientific Publications ◽  
The Subject ◽  
Points Of View ◽  
Internal Affairs

In this article, based on the study and analysis of operational-search legislation, scientific publications, law enforcement practice and the criminal situation in the field of legalization, the operationalsearch counteraction to the legalization of income received from the Commission of tax crimes is considered. The paper focuses on the stages (stages) of laundering, the existing points of view on this account, as well as on the methods of illegal withdrawal of funds abroad. The author of the article aimed to develop scientifically based proposals and recommendations for improving the effectiveness of this type of activity by the territorial bodies of internal Affairs and their divisions of economic security and anti-corruption. It is proposed to put forward and work out operational search versions within the subject of study, as well as to develop, taking into account the methods (schemes) used by criminals to launder criminal proceeds and illegally withdraw funds abroad for the purpose of their subsequent legalization, operational search measures to document their criminal actions. In addition, the author recommends constant monitoring of money laundering methods based on operational and investigative practices. The results and key conclusions formulated in this article can be used in the theory and practice of operational investigative activities of internal Affairs bodies to counteract the legalization of income received from tax crimes.

Development of Mucoadhesive Buccal Drug Delivery System of Propranolol Hydrochloride Using Aster ericoides Mucilage

2020 ◽  
Vol 10 (2) ◽  
pp. 133-148
Author(s):  
Ankaj Kaundal ◽  
Pravin Kumar ◽  
Rajendra Awasthi ◽  
Giriraj T. Kulkarni
Keyword(s):  
Buccal Cavity ◽  
Three Dimensional ◽  
Hot Water ◽  
Fickian Diffusion ◽  
Aster Ericoides ◽  
Dimensional Network ◽  
Buccal Tablet ◽  
Significant Difference ◽  
Volunteer Group

Aim: The study was aimed to develop mucoadhesive buccal tablets using Aster ericoides leaves mucilage. Background : Mucilages are naturally occurring high-molecular-weight polyuronides, which have been extensively studied for their application in different pharmaceutical dosage forms. Objective: The objective of the present research was to establish the mucilage isolated from the leaves of Aster ericoides as an excipient for the formulation of the mucoadhesive buccal tablet. Method: The mucilage was isolated from the leaves of Aster ericoides by maceration, precipitated with acetone and characterized. Tablets were prepared using wet granulation technique and evaluated for various official tests. Results: The mucilage was found to be non-toxic on A-431 and Vero cell lines. It was insoluble but swellable in cold and hot water. The results indicate that mucilage can form a three-dimensional network. The pH of the mucilage (6.82 ± 0.13) indicated that it might be non-irritant to the buccal cavity. The mucilage was found to be free from microbes. The release of drug was by Fickian diffusion. The in vivo buccal tablet acceptance was 80%. No significant difference between the diastolic blood pressure of standard and Aster tablets treated volunteer group was recorded. Conclusion: The mucilage was found to be non-toxic on A-431 and Vero cell lines. It was insoluble but swellable in cold and hot water. The results indicate that mucilage can form a three-dimensional network. The pH of the mucilage (6.82 ± 0.13) indicated that it might be non-irritant to the buccal cavity. The mucilage was found to be free from microbes. The release of drug was by Fickian diffusion. The in vivo buccal tablet acceptance was 80%. No significant difference between the diastolic blood pressure of standard and Aster tablets treated volunteer group was recorded. Other: However, to prove the potency of the polymer, in vivo bioavailability studies in human volunteers are needed along with chronic toxicity studies in suitable animal models.

Conflicts caused by afforestations of agricultural land in densely populated areas

1991 ◽  
Vol 56 ◽  
Author(s):  
N. Lust ◽  
B. Muys
Keyword(s):  
Nature Conservation ◽  
Agricultural Land ◽  
Agricultural Lands ◽  
Biological Value ◽  
Ecological Problems ◽  
The Subject ◽  
Points Of View

In  densely populated areas, such as Flanders, serious conflicts arise due to the  afforestation of agricultural lands. Roughly speaking, three sectors are  involved: agriculture, forestry and nature conservation. These groups do not  always share the same points of view. But even within the different sectors  there are several subgroups with their own interests and approaches.  Generally speaking, agriculture is strongly opposed, forestry has a  relatively diversified meaning, whereas nature conservation is either opposed  or in favour, depending on the region's biological value.     The policy in this matter is not forest friendly. Legislation strongly  hampers the afforestation of agricultural lands. Moreover the subject leads  to a series of ecological problems, which have not really been considered up  to now.

Geological Field Sketches and Illustrations

2019 ◽  
Author(s):  
Matthew J. Genge
Keyword(s):  
Cross Sections ◽  
Earth Science ◽  
Three Dimensional ◽  
Worked Examples ◽  
Scientific Publications ◽  
Thin Sections ◽  
Geological Features ◽  
Different Types ◽  
The Subject

Drawings, illustrations, and field sketches play an important role in Earth Science since they are used to record field observations, develop interpretations, and communicate results in reports and scientific publications. Drawing geology in the field furthermore facilitates observation and maximizes the value of fieldwork. Every geologist, whether a student, academic, professional, or amateur enthusiast, will benefit from the ability to draw geological features accurately. This book describes how and what to draw in geology. Essential drawing techniques, together with practical advice in creating high quality diagrams, are described the opening chapters. How to draw different types of geology, including faults, folds, metamorphic rocks, sedimentary rocks, igneous rocks, and fossils, are the subjects of separate chapters, and include descriptions of what are the important features to draw and describe. Different types of sketch, such as drawings of three-dimensional outcrops, landscapes, thin-sections, and hand-specimens of rocks, crystals, and minerals, are discussed. The methods used to create technical diagrams such as geological maps and cross-sections are also covered. Finally, modern techniques in the acquisition and recording of field data, including photogrammetry and aerial surveys, and digital methods of illustration, are the subject of the final chapter of the book. Throughout, worked examples of field sketches and illustrations are provided as well as descriptions of the common mistakes to be avoided.

scholarly journals Crystal structure of K[Hg(SCN)3] – a redetermination

2014 ◽  
Vol 70 (9) ◽  
pp. i46-i46 ◽  
Author(s):  
Matthias Weil ◽  
Thomas Häusler
Keyword(s):  
Crystal Structure ◽  
Room Temperature ◽  
Three Dimensional ◽  
Lattice Parameters ◽  
Bond Lengths ◽  
Dimensional Network ◽  
Anisotropic Displacement Parameters ◽  
Precision And Accuracy ◽  
Standard Deviations ◽  
Atomic Coordinates

The crystal structure of the room-temperature modification of K[Hg(SCN)3], potassium trithiocyanatomercurate(II), was redetermined based on modern CCD data. In comparison with the previous report [Zhdanov & Sanadze (1952).Zh. Fiz. Khim.26, 469–478], reliability factors, standard deviations of lattice parameters and atomic coordinates, as well as anisotropic displacement parameters, were revealed for all atoms. The higher precision and accuracy of the model is, for example, reflected by the Hg—S bond lengths of 2.3954 (11), 2.4481 (8) and 2.7653 (6) Å in comparison with values of 2.24, 2.43 and 2.77 Å. All atoms in the crystal structure are located on mirror planes. The Hg2+cation is surrounded by four S atoms in a seesaw shape [S—Hg—S angles range from 94.65 (2) to 154.06 (3)°]. The HgS4polyhedra share a common S atom, building up chains extending parallel to [010]. All S atoms of the resulting1∞[HgS2/1S2/2] chains are also part of SCN−anions that link these chains with the K+cations into a three-dimensional network. The K—N bond lengths of the distorted KN7polyhedra lie between 2.926 (2) and 3.051 (3) Å.

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