Permanent Set in Vulcanized Rubber

1949 ◽  
Vol 22 (4) ◽  
pp. 1036-1044 ◽  
Author(s):  
L. Mullins
Keyword(s):  
Plastic Flow ◽  
Room Temperature ◽  
Elastic Recovery ◽  
The Other ◽  
Initial Length ◽  
Chain Molecules ◽  
Permanent Set ◽  
Vulcanized Rubber ◽  
Rate Of Recovery ◽  
Long Chain

Abstract The residual extension which remains after a sample of rubber has been stretched for some period, then released and allowed to recover, is popularly called permanent set. This set, however, is far from being permanent since it continuously decreases with the period of recovery; furthermore, after the rate of recovery has become exceedingly slow and is no longer readily observable, an increase in temperature will usually result in a sharp increase in the rate of recovery. It has been usual to identify this set with irreversible plastic flow, but it will be immediately evident that this can rarely be justified for, owing to incomplete high-elastic recovery, the measured value of set is a combination of both plastic flow and high-elastic deformation which has not completely recovered. Thus before any attempt is made to discuss the interpretation of the results of set tests, a study must be made of the significance of set. Treloar has investigated this phenomenon in raw natural rubber and has shown that entanglements or cohesional linkages may form while the rubber is stretched, and these oppose recovery; further, although van der Waals forces between the long-chain molecules largely control the rate and the amount of recovery, the crystallization of rubber produced by stretching may profoundly influence the set. On the other hand Tobolsky has studied the set which results from stretching rubber vulcanizates at high temperatures ; in such cases the amount of set is controlled by two processes which take place while the rubber is stretched; one of these involves the oxidative breaking of network chains, the other the oxidative cross-linking of network chains. Although these ideas are well founded, they do not provide a completely satisfactory basis for the understanding of set, and the purpose of this work is to extend these ideas and to explain the significance of the results of normal set tests ; in these tests rubber samples were extended at room temperatures to moderate elongations for relatively short periods of time. Most of the tests performed in this investigation were made on dumbbell shaped samples, which were extended by 200 per cent of their initial length for fifteen minutes at room temperature and then allowed to recover for one hour at room temperature; the residual extension was then noted and expressed as a percentage of the initial length. These tests will be referred to as normal set tests. In some tests various periods and temperatures of extension and recovery were used.

Phase Changes in Fe(III)OCl–RNH2-Intercalation Complexes

1984 ◽  
Vol 39 (9) ◽  
pp. 1193-1198 ◽  
Author(s):  
Armin Weiss ◽  
Jin Ho Choy
Keyword(s):  
Room Temperature ◽  
Host Lattice ◽  
Phase Changes ◽  
Temperature Dependent ◽  
Chain Molecules ◽  
Intercalation Complexes ◽  
Long Chain

Iron(III)oxide chloride is capable of intercalating ammonia and amines into its layer lattice. Long chain molecules form bilayers with extended chains almost perpendicular to the host lattice layers at room temperature (intercalate composition): FeOCl · (0.54 ±0.03)n -CxH2x+1NH2 with x ≥ 12) and tilted by 57° at about 100-110 °C (intercalate composition: FeOCl · (0.45 ±0.02)n-CxH2x+1NH2 with ≥12). The temperature-dependent changes in basal spacings between 20 and 110 °C are complex. Above 120 °C the layers of the host lattice are altered irreversibly by substitution and HCl-release to FeOCl1-y(-NHCxH2x+1)y with y ≤ ca. 0.4.

Plasticization of Natural and Synthetic Rubbers. II. GR-S

1949 ◽  
Vol 22 (2) ◽  
pp. 518-534 ◽  
Author(s):  
G. H. Piper ◽  
J. R. Scott
Keyword(s):  
Natural Rubber ◽  
Plastic Flow ◽  
Elastic Recovery ◽  
Mechanical Action ◽  
Shear Stresses ◽  
Mechanical Working ◽  
Chain Molecules ◽  
Peptizing Agent ◽  
Set Up ◽  
Internal Mixer

Abstract Continuing the work described in Part I, experiments have been made to determine the separate effects of heat, oxidation, mechanical working on rolls or in an internal mixer, peptizing agents (used in hot milling), and absorption of softener on the softness, elastic recovery, and plastic flow relation (between applied force and rate of flow) of GR-S. Heat alone, without oxygen or mechanical action, does not soften GR-S, but makes it harder and more elastic, presumably by inducing cross-linking of the chain molecules; GR-S thus differs fundamentally from natural rubber, which can be softened by heat. Absorption of softener (mineral oil) softens GR-S and reduces its recovery, but these effects are too small to form a practicable plasticizing method. Either oxidation or mechanical working softens GR-S considerably, reduces its elastic recovery, and brings its plastic flow relation nearer to that of well masticated natural rubber, i.e., approaching ordinary viscous or Newtonian flow (flow rate proportional to stress). Peptizing agents such as benzaldehyde phenylhydrazone or iron naphthenate promote the effect of hot milling, presumably by accelerating oxidation, which is shown to occur during hot, but not appreciably in cold, milling. Of the methods tried, those which plasticize GR-S most quickly are (1) hot milling with a peptizing agent, and (2) oxidation at 125° C and 15 lb. per sq. in. oxygen pressure ; if the latter is continued too long, however, hardening sets in. The results show that GR-S, like natural rubber, can be plasticized by mechanical breakage of the chain molecules by the shear stresses set up during mastication, as well as by oxidation, which presumably causes breakage of the molecules at the double bonds. Mechanical and oxidative treatments, however, do not give the same properties ; mechanical breakdown in the cold gives a product completely soluble in benzene, whereas oxidation does not, and is less effective in reducing recovery, and there may be other differences not yet revealed. In view of these differences and the fact that heat has effects opposite to oxidation or mechanical working, it follows that the various possible ways of plasticizing GR-S, since they involve heat, oxidation, and mechanical action in different combinations and degrees, give plasticized batches with very different properties, even if the length of the treatments is so adjusted as to give, say, the same Williams or Mooney plasticity reading. These differences are fully discussed in the present paper; the main conclusions are:

scholarly journals The torsional flexibility of aliphatic chain molecules

1940 ◽  
Vol 174 (956) ◽  
pp. 137-144 ◽  
Keyword(s):  
Room Temperature ◽  
Threshold Energy ◽  
Chain Molecule ◽  
Aliphatic Chain ◽  
Chain Molecules ◽  
Distortion Effect ◽  
A Chain ◽  
Single Bonds ◽  
Long Chain ◽  
Made In

The rotation of the CH 3 groups round the single C—C bond in ethane is associated with a threshold energy of about 3000 gcal./gmol. or 2 x 10 -13 erg/mol. (Schäfer 1938; Kistiakowsky, Lacher and Strutt 1939). In an aliphatic CH 2 chain where the carbon atoms are linked together by single bonds the corresponding energy must be of the same order and is most likely rather smaller. Supposing we consider any particular C—C bond in the chain and treat the two parts at each side of this bond as rigid rotators, then their kinetic energy would be 2 x 1/2 kT which at room temperature amounts to about one-fifth of the threshold energy. It seems very likely under these circumstances that a chain molecule of say ten to twenty carbon atoms should already at room temperature show signs of distortion due to internal rotation. If this is true, then the previously observed increase of the crystal symmetry at the melting-point of paraffins (Müller 1930, 1932) and the corresponding changes of the polarization of long-chain ketones (Müller 1937, 1938) can no longer be ascribed entirely to a rotation of the molecule in the field of the surrounding molecules but must at least partly be due to this internal distortion. It is clear that a distortion of this type tends to destroy the anisotropy of the molecule and to give an apparent isotropy to the crystal. The present experiments were made in order to obtain an estimate of the magnitude of the distortion effect. It is found to be surprisingly large.

Pressure crack-figures on diamond faces II. The dodecahedral and cubic faces

1955 ◽  
Vol 230 (1182) ◽  
pp. 294-301 ◽  
Keyword(s):  
Plastic Flow ◽  
Room Temperature ◽  
The Body ◽  
The Other ◽  
Surface Level ◽  
Cube Face ◽  
Different Types ◽  
Formation Of Cracks ◽  
Ring Crack ◽  
Surface Distortions

The study of pressure figures on diamond is extended to the cubic and dodecahedral faces. The formation of cracks on a sawn but unpolished dodecahedral (two-point) face is first studied. The loads required for the initiation of cracks, using a diamond ball, were between 7 and 24 Kg. Two different types of cubic face were available, one on a natural cubic boart stone, the other a polished approximation to a cube face secured by truncating an octahedral stone. The loads required to initiate cracks were of the order 20 to 30 Kg. All the cracks observed were specifically oriented in accordance with crystallographic expectations of easy cleavage directions. The cracks were accompanied by permanent surface distortions which were studied by multiple-beam interference methods. The permanent distortions broadly resemble those found in part I for octahedral faces. There is one important difference in that for both the cube faces studied, the surface level within the perimeter of the ring crack is appreciably depressed, being some 800 Å below the outer undisturbed level. This is considered to offer further evidence for the existence of plastic flow in diamond at room temperature. For the polished cube face studied observations could also be made on the accompanying internal cracking effects within the body of the crystal.

A Mathematical Treatment of a Theory of Rubber Structure

1935 ◽  
Vol 8 (1) ◽  
pp. 23-38
Author(s):  
T. R. Griffith
Keyword(s):  
Elastic Modulus ◽  
Plastic Flow ◽  
Strain Curve ◽  
The Other ◽  
Stress Axis ◽  
Mathematical Treatment ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Joule Effect ◽  
Vulcanized Rubber

Abstract A brief consideration of the work that has been done on the structure of rubber convinces, one that the elasticity is wholly or at least mainly explained by a consideration of the kinetics involved. The fact that when a strip of stretched rubber, one end of which is free, contracts when it is warmed, contrary to the behavior of most bodies, and that it becomes warmed on stretching, commonly known as the Gough-Joule effect, pp. 453–461, would lead one to suspect .that there is a connection between the kinetic energy of the rubber molecule and its elasticity. Lundal, Bouasse, Hyde, Somerville and Cope, Partenheimer and Whitby and Katz have reported observations, principally stress-strain curves, which show that vulcanized rubber has a lower modulus of elasticity at higher temperatures, i. e., it becomes easier to stretch as the temperature is raised. On the other hand, Schmulewitsch, Stevens, and Williams found that the elastic modulus increases with the temperature. Williams shows that the softening of vulcanized rubber with rise of temperature is due to an increase of plasticity. In order to get rid of plastic flow, he first stretches the specimen several times to within about 50 per cent of its breaking elongation, and then obtains an autographic stress-strain curve of the rubber stretched very quickly. He finds that in this case the rubber actually becomes stiffer with rise of temperature, increasing temperatures causing the stress-strain curves to lean progressively more and more toward the stress axis. He concludes that rise of temperature has two effects, one a softening due to increase of plasticity, rendering plastic flow more easy, the other an actual stiffening of the rubber due to rise of temperature. It is not easy to explain the latter effect on any theory which does not take kinetics into account.

Semi-Ebonite. Part 1

1935 ◽  
Vol 8 (4) ◽  
pp. 554-570 ◽  
Author(s):  
P. A. Gibbons
Keyword(s):  
Tensile Strength ◽  
Plastic Flow ◽  
Room Temperature ◽  
Constant Load ◽  
Vulcanized Rubber ◽  
Large Elongation ◽  
Soft Rubber

Abstract Hitherto two products of the reaction between sulfur and rubber have been studied and used commercially, soft rubber and ebonite. Few publications have appeared concerning the products obtained by vulcanization of proportions between 5 and 30 parts of sulfur with 100 parts of rubber. Before the introduction of organic accelerators of vulcanization the coefficient of vulcanization was considered a satisfactory criterion of the quality of soft vulcanized rubber. Mixes of rubber and sulfur vulcanized to a coefficient of more than 3.5 to 4 were usually considered overvulcanized in that experience showed that the optimum properties as regards tensile strength and elongation at rupture occurred at this degree of vulcanization. Semi-ebonites differ from soft rubber and ebonite in as much as they are extremely sensitive to small changes in the time of vulcanization. Their plasticity is such that the velocity of plastic flow just prior to break is relatively great, and thus they may experience a large elongation at constant load. Their plasticity decreases with further vulcanization, in fact, with advance in vulcanization they become almost rigid at room temperature. The decrease in plastic flow is accompanied by an increase in hardness and brittleness and the ultimate stage in the rubber-sulfur reaction, ebonite, is reached.

An X-Ray Investigation of Crystallinity in Rubber

1939 ◽  
Vol 12 (4) ◽  
pp. 706-718
Author(s):  
S. D. Gehman ◽  
J. E. Field
Keyword(s):  
Crystalline Structure ◽  
Polymeric Materials ◽  
The Other ◽  
X Ray Diffraction ◽  
Random Orientation ◽  
Chain Molecules ◽  
Micellar Structure ◽  
X Ray ◽  
Recent Developments ◽  
Long Chain

Abstract The crystalline structure which rubber exhibits under certain circumstances has come to be regarded as associated with a secondary or micellar structure of long chain molecules. The exact mechanism by which the localized ordered regions appear is a speculative subject in recent developments of the micellar theory of long chain polymeric materials. The views of various workers on this subject have been summarized by other authors. The crystalline structure of rubber displays varying degrees and types of orientation of the crystal units, depending on the conditions under which crystallization occurs. The amorphous x-ray diffraction pattern of unstretched rubber is shown in Figure 1, the unoriented crystalline diagram for frozen rubber in Figure 2. When crystallization is induced by stretching, the crystallites are aligned along the axis of stretching, giving the fiber diagrams of Figures 3 and 4. In this case there is random orientation of the other two axes of the crystallites. “Higher orientation,” in which all three axes of the crystallites are aligned, gives the diagram of Figure 15 and can be secured with suitable dimensions of the stretched piece.

Infra-Red Spectra of Rubber and High Polymers

1941 ◽  
Vol 14 (3) ◽  
pp. 572-579
Author(s):  
W. C. Sears
Keyword(s):  
Methyl Methacrylate ◽  
Fair Agreement ◽  
Chain Molecules ◽  
Rubber Industry ◽  
Vulcanized Rubber ◽  
Gutta Percha ◽  
Infra Red ◽  
Related Compounds ◽  
Long Chain ◽  
High Polymers

Abstract The rubber industry is interested in all methods for studying the structure of highly polymerized substances. Infra-red spectroscopy has been recognized by recent workers as a possible means for determining the valence forces in long chain molecules. Accordingly, the infra-red spectra of rubber and related compounds have been measured by several workers. An investigation of rubber, gutta percha, indene, polyindene, styrene, polystyrene, polyvinylacetate and polyvinylchloracetate has been carried out by Stair and Coblentz. Later Williams measured natural and vulcanized rubber, rubber hydrochloride, isoprene, styrene and polymerized butadiene in the region between 2.5µ and 9µ, but his spectra of rubber did not agree with that of Stair and Coblentz. Williams and Taschek reported that the bands in rubber become broader with increasing stretch. Recently a rough survey of the infra-red transmission of rubber, Pliofilm, Vinylite XYSG, Shawinigan V-15, polystyrene, methyl methacrylate polymer and Cellophane has been made by Wells. The Raman data of rubber obtained by Gehman and Osterhof are in fair agreement with the infra-red results of Stair and Coblentz.

scholarly journals The Tensile Strength of Rubber and Rubber Molecule

1950 ◽  
Vol 23 (3) ◽  
pp. 581-586
Author(s):  
Chullchai Park ◽  
Usaburo Yoshida
Keyword(s):  
Tensile Strength ◽  
Low Temperature ◽  
Room Temperature ◽  
Chain Molecule ◽  
Chain Molecules ◽  
Vulcanized Rubber ◽  
A Chain

Abstract The tensile strengths of crystallized crude rubber and vulcanized rubber are remarkably different from each other at room temperature, but are found to be almost the same at the temperature of liquid air. By assuming that the tensile strength of crystallized rubber at this low temperature is entirely due to its chain molecules, the forced needed to break a chain molecule of rubber at its weakest point is estimated.

Effect of Particle Size and Polarity of Long-Chain Molecules in Polymeric Films on the Supercooling Temperature

1997 ◽  
Vol 9 (4) ◽  
pp. 369-383 ◽  
Author(s):  
Yoshihiko Hotta ◽  
Ryota Hiraoka ◽  
Tsuguo Yamaoka
Keyword(s):  
Particle Size ◽  
Behenic Acid ◽  
Polymeric Films ◽  
The Other ◽  
Recording Media ◽  
Chain Molecules ◽  
Effect Of Particle Size ◽  
Size Of Particles ◽  
Supercooling Temperature ◽  
Long Chain

We studied the effect of particle size and polarity of long-chain molecules on supercooling when dispersed in polymeric films. Supercooling of the molecules of greater than 20 °C, which plays a key role in the thermoreversible response of recording media, was not observed for the molecules alone but occurred only when the molecules formed particles dispersed in a polymer. As the size of particles grew from 0.1–1.0 μm to 3.5 μm, the degree of supercooling of behenic acid dispersed in a copolymer of vinyl chloride and vinyl acetate decreased from 30–40 °C to about 20 °C. The degree of supercooling also decreased from 21–41 °C to 8–17 °C as the polarity of the molecules decreased from fatty acids to fatty alcohols to alkanes. On the other hand, the degree of supercooling increased from 20 °C to 43 °C as the polarity of the polymer matrix increased. This large supercooling effect may be caused by the interaction between the molecules and the polymers which depends on the polarity of both the long-chain molecules and the polymers.

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