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:

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.

scholarly journals Rock Failure Analysis Based on a Coupled Elastoplastic-Logarithmic Damage Model

2017 ◽  
Vol 62 (4) ◽  
pp. 753-774
Author(s):  
M. Abdia ◽  
H. Molladavoodi ◽  
H. Salarirad
Keyword(s):  
Constitutive Model ◽  
Plastic Flow ◽  
Mechanical Response ◽  
Damage Model ◽  
Yield Function ◽  
Irreversible Thermodynamics ◽  
Stiffness Degradation ◽  
Shear Stresses ◽  
Rock Materials ◽  
Damage Process

Abstract The rock materials surrounding the underground excavations typically demonstrate nonlinear mechanical response and irreversible behavior in particular under high in-situ stress states. The dominant causes of irreversible behavior are plastic flow and damage process. The plastic flow is controlled by the presence of local shear stresses which cause the frictional sliding. During this process, the net number of bonds remains unchanged practically. The overall macroscopic consequence of plastic flow is that the elastic properties (e.g. the stiffness of the material) are insensitive to this type of irreversible change. The main cause of irreversible changes in quasi-brittle materials such as rock is the damage process occurring within the material. From a microscopic viewpoint, damage initiates with the nucleation and growth of microcracks. When the microcracks length reaches a critical value, the coalescence of them occurs and finally, the localized meso-cracks appear. The macroscopic and phenomenological consequence of damage process is stiffness degradation, dilatation and softening response. In this paper, a coupled elastoplastic-logarithmic damage model was used to simulate the irreversible deformations and stiffness degradation of rock materials under loading. In this model, damage evolution & plastic flow rules were formulated in the framework of irreversible thermodynamics principles. To take into account the stiffness degradation and softening on post-peak region, logarithmic damage variable was implemented. Also, a plastic model with Drucker-Prager yield function was used to model plastic strains. Then, an algorithm was proposed to calculate the numerical steps based on the proposed coupled plastic and damage constitutive model. The developed model has been programmed in VC++ environment. Then, it was used as a separate and new constitutive model in DEM code (UDEC). Finally, the experimental Oolitic limestone rock behavior was simulated based on the developed model. The irreversible strains, softening and stiffness degradation were reproduced in the numerical results. Furthermore, the confinement pressure dependency of rock behavior was simulated in according to experimental observations.

Thermal Properties and Crystallisation Behaviour of Thermoplastic Natural Rubber (TPNR) Nanocomposites

2013 ◽  
Vol 812 ◽  
pp. 125-130 ◽  
Author(s):  
Siti Norasmah Surip ◽  
Z.Y. Zhang ◽  
H.N. Dhakal ◽  
N.N. Bonnia ◽  
S. H. Ahmad
Keyword(s):  
Thermal Properties ◽  
Natural Rubber ◽  
Nucleating Agent ◽  
Preparation Technique ◽  
Preparation Methods ◽  
Blending Method ◽  
Liquid Natural Rubber ◽  
Tan Δ ◽  
Thermoplastic Natural Rubber ◽  
Internal Mixer

The effect of preparation technique on the crystallisation behavior and thermal properties of TPNR filled nanoclay nanocomposites was investigated. The nanocomposites were prepared via melt blending method using internal mixer (Haake 600P). Two types of nanocomposites preparation technique were employed which is method A and B. In method A, the nanoclay was pre-mixed with liquid natural rubber (LNR) before it was charged into the other materials. For method B, the nanoclay was directly charged into the molten TPNR matrix. The result shows, preparation methods were significantly affect the crystallinity and thermal properties of TPNR nanocomposites. DSC thermogram revealed that nanocomposites crystallinity was increased when prepared by method A but decreased with method B. An increment in polypropylene crystallinity was attributed by the nanoclay which is believed to be as a nucleating agent. DMA thermogram suggested that the preparation method has affected the storage modulus and tan δ but not the glass transition temperature (tg).

Radical Mechanisms in Saturated and Olefinic Systems. II. Disubstitutive Carbon-Carbon Cross-Linking by Tertiary Alkoxy Radicals in Isoprenic Olefins and Rubber

1951 ◽  
Vol 24 (4) ◽  
pp. 777-786
Author(s):  
E. H. Farmer ◽  
C. G. Moore
Keyword(s):  
Natural Rubber ◽  
Cross Linking ◽  
Chain Molecules ◽  
Alkoxy Radicals ◽  
Full Extent ◽  
Carbon Chains ◽  
Butyl Peroxide ◽  
High Degree ◽  
Vulcanization Process

Abstract The high degree of dehydrogenation effected by tert.-butoxy radicals at the α-methylenic groups of olefins enables these radicals to be used for the carbon-to-carbon cross-linking of unsaturated carbon chains, and especially of the polyisoprenic chains of natural rubber. Such cross-linking amounts to a vulcanization process in which the connecting links between chain molecules are just C—C bonds, which may be expected to have appropriate attributes. An examination has first been made of the cross-linking produced by tert.- butoxy radicals (from di-tert.-butyl peroxide) at 140° between the short iso-prenic chains in 1-methylcyclohexene, 4-methylhept-3-ene, 2,6-dimethylocta-2, 6-diene, and digeranyl. Cross-linking proceeds efficiently in each case, and the points of union in these isoprene units which become directly joined are not confined to original α-methylenic carbon atoms. Where the reagent radicals are in considerable deficit, e.g., one per two or three of the isoprene units present, those olefin molecules which are attacked become linked together mostly by single unions to form aggregates containing two, three or four molecules; but in the tetraisoprenic olefins the extent to which more than one union is formed between some of the directly linked molecules becomes appreciable. In natural rubber, cross-linking occurs smoothly and to nearly the full extent corresponding to the (in practice restricted) proportion of peroxidic reagent employed. Good vulcanizates can be so obtained in which the tensile stength is found to increase towards a maximum and then to decline rapidly as the degree of cross-linking steadily increases. Thus to obtain vulcanizates of the optimum physical characteristics, the degree of cross-linking must be suitably chosen. The role of the peroxidic reagent is almost entirely non-additive and non-degradative.

Toughness Enhancement of Polylactic Acid by Employing Glycolyzed Polylactic Acid-Cured Epoxidized Natural Rubber

2014 ◽  
Vol 1025-1026 ◽  
pp. 580-584 ◽  
Author(s):  
Phrutsadee Sukpuang ◽  
Mantana Opaprakasit ◽  
Atitsa Petchsuk ◽  
Pakorn Opaprakasit
Keyword(s):  
Natural Rubber ◽  
Polylactic Acid ◽  
Epoxidized Natural Rubber ◽  
Chemical Recycling ◽  
Crosslinking Reaction ◽  
Solvent Fractionation ◽  
Elongation At Break ◽  
Chemical Structures ◽  
Internal Mixer ◽  
Toughness Enhancement

Glycolyzed polylactic acid (GPLA)-cured epoxidized natural rubber (ENR) is developed for use as a toughening agent for PLA resin. GPLA is obtained from chemical recycling of PLA resin by a glycolysis reaction. GPLA-cured ENR is then prepared by the crosslinking reaction of ENR with GPLA in an internal mixer. Chemical structures of the cured products are characterized by solvent fractionation and thermogravimetric analysis (TGA). The cured ENR products are blended with PLA resin, by varying the cured ENR contents from 5 to 15% wt. Mechanical properties of the blends, and their toughening mechanisms are examined. The cured ENR materials has higher efficiency in improving toughness of PLA resin, compared to uncured ENR, likely due to their rubbery network nature and higher compatibility with the PLA matrix. The incorporation of 5% wt. GPLA-cured ENR also improves elongation at break with no adverse effect on tensile strength and modulus of PLA.

scholarly journals Autowave Physics of Material Plasticity

Crystals ◽  
2019 ◽  
Vol 9 (9) ◽  
pp. 458 ◽  
Author(s):  
Lev B. Zuev ◽  
Svetlana A. Barannikova
Keyword(s):  
Plastic Flow ◽  
Flow Localization ◽  
Plastic Properties ◽  
Plastic Flow Localization ◽  
Flow Development ◽  
Strain Invariant ◽  
Deformation Hardening ◽  
Set Up ◽  
Structure Collapse ◽  
Flow Stage

The notions of plastic flow localization are outlined in the paper. It is shown that each type of localized plasticity pattern corresponds to a definite stage of deformation hardening. In the course of plastic flow development, a changeover in the types of localization patterns occurs. The types of localization patterns are limited in number: four pattern types are all that can be expected. A correspondence was set up between the emergent localization pattern and the respective flow stage. It is found that the localization patterns are manifestations of the autowave nature of plastic flow localization process, with each pattern type corresponding to a definite mode of autowave. In the course of plastic flow development, the following modes of autowaves will form in the following sequence: switching autowave → phase autowave → stationary dissipative structure → collapse of the autowave. Of particular interest are the phase autowave and the respective pattern observed. Propagation velocity, dispersion, and grain size dependence of wavelength were determined experimentally for the phase autowave. An elastic-plastic strain invariant was also introduced to relate the elastic and plastic properties of the deforming medium. It is found that the autowave characteristics follow directly from this invariant.

The Effect of Thermal Aging on Mechanical Properties and Morphological Properties of Thermoplastic Vulcanizates Based on Natural Rubber and Polystyrene

2020 ◽  
Vol 990 ◽  
pp. 262-266
Author(s):  
Prathumrat Nu-Yang ◽  
Atiwat Wiriya-Amornchai ◽  
Jaehoon Yoon ◽  
Chainat Saechau ◽  
Poom Rattanamusik
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Impact Strength ◽  
Natural Rubber ◽  
Thermal Aging ◽  
Morphological Properties ◽  
Vulcanized Rubber ◽  
Thermoplastic Vulcanizates ◽  
Internal Mixer ◽  
Processing Properties

Thermoplastic vulcanizates or TPVs is a type of materials exhibiting excellent properties between thermoplastic and elastomer by combining the characteristics of vulcanized rubber with the processing properties of thermoplastics. This research aims to study the effect of thermal aging on the morphology and mechanical properties of thermoplastic vulcanizates (TPVs) based on a mixture of natural rubber (NR) and polystyrene (PS). TPVs samples were prepared using the internal mixer at a mass ratio of NR/PS 70/30, 50/50, 30/70 and 0/100. Tensile properties and impact strength showed that when the amount of NR increased tends of impact strength and elongation at break increased but tends of tensile strength decreased. On the other hand, tends of tensile strength for thermal aging at 70°C for 3 days increased when the amount of PS increase. The blending ratio of NR / PS at 70/30 is the best. It gave a worthy increase from 19.94 MPa to be 25.56 MPa (28.18%).

Effect of poisson's ratio strains in adherends on stresses of an idealized lap joint

1973 ◽  
Vol 8 (2) ◽  
pp. 134-139 ◽  
Author(s):  
R D Adams ◽  
N A Peppiatt
Keyword(s):  
Shear Stress ◽  
Poisson’S Ratio ◽  
Longitudinal Shear ◽  
Poisson's Ratio ◽  
Shear Stresses ◽  
Lap Joint ◽  
Stress Concentrations ◽  
Maximum Value ◽  
Set Up ◽  
Transverse Stresses

Poisson's ratio strains in the adherends of a simple adhesive lap joint induce transverse stresses both in the adhesive and in the adherends. Two simultaneous second-order partial-differential equations were set up to describe the normal stresses along and across an adherend and were solved both by an approximate analytical method and a finite-difference technique: the two solutions agreed closely. The adhesive shear stresses can then be obtained by differentiating these solutions. The transverse shear stress has a maximum value for metals of about one-third of the maximum longitudinal shear stress, and this occurs at the corners of the lap, thus making the corners the most highly stressed parts of the adhesive. Bonding adherends of dissimilar stiffness was shown to produce greater stress concentrations in the adhesive than when similar adherends are used.

Robot Controlled Rotary Peen Forming by Laser-Assisted Distance Control

2015 ◽  
Vol 651-653 ◽  
pp. 1084-1089 ◽  
Author(s):  
Markus Gottschalk ◽  
Markus Bambach ◽  
Gerhard Hirt
Keyword(s):  
Machine Design ◽  
Shear Stresses ◽  
Structural Components ◽  
Principal Stresses ◽  
Aircraft Fuselage ◽  
Innovative Process ◽  
Distance Control ◽  
Peen Forming ◽  
Set Up ◽  
Intrusion Depth

Surface curvature radii required for aircraft fuselage as well as structural components can be produced by peen forming processes. The innovative process idea of Rotary Peen Forming is a modification of the well-known Shot Peen Forming. Here, the impactors are flexibly connected to a rotating hub and thus moving on circular trajectories. As a consequence, there is no need to pressurize and recirculate the shots, as it is essential in Shot Peen Forming. Using a six axes robot, the rotating hub can be guided flexibly. The resulting machine design is more compact compared to traditional Shot Peen Forming.However, in Rotary Peen Forming not only principal stresses but also shear stresses are caused in the deformation zone which has a fundamental influence on the curvature. In order to generate defined curvatures on the workpiece, the capability to precisely adjust the intrusion depth of the impactors is essential.In this paper, a laser-assisted distance control for the Robot Controlled Rotary Peen Forming is introduced. By means of a point laser, the set-up allows for a distance control to adjust and keep a determined intrusion depth. This way, the machine design provides a mechanism to readjust the intrusion depth of the impactors while the desired curvature is formed during the process by the introduced plastic strains at the specimen’s surface. Using the distance control, the resulting curvature is two to four times bigger compared to experiments without a readjustment of the intrusion depth.

Improvement of Mechanical Properties and Water Absorption in Wheat Gluten by Epoxidized Natural Rubber

2019 ◽  
Vol 891 ◽  
pp. 163-168
Author(s):  
Kantima Chaochanchaikul
Keyword(s):  
Natural Rubber ◽  
Water Absorption ◽  
Thermal Analyses ◽  
Wheat Gluten ◽  
Research Work ◽  
Decomposition Temperature ◽  
Epoxidized Natural Rubber ◽  
Elongation At Break ◽  
Opposite Behavior ◽  
Internal Mixer

TThe aims of this research work were to improve touhgness and water resistance of wheat gluten (WG) by epoxidized natural rubber (ENR) compared to glycerol. WG specimens were mixed and prepared by internal mixer and compression molding machine, respectively. ENR and glycerol were varied from 10 to 40 wt%. Effects of modifier types and contents on WG were evaluated by tensile, impact and water absorption testings and microstructure and thermal analyses. The increase of ENR or glycerol contents led to the increase of toughness by considering the increase of impact strength and elongation at break. Glass transition temperature of WG tended to decrease with the increase of ENR or glycerol contents, especially for glycerol. The presence of glycerol affected to the decomposition temperature values whereas ENR did not affect to decomposition. ENR improved water resistant of WG specimen but trend of glycerol showed the opposite behavior. Weight loss of modified WG with glycerol was found at immersion time of 1440 min.

Sign in / Sign up

Export Citation Format

Share Document