CURE CHARACTERISTICS OF DEVULCANIZED RUBBER:THE ISSUE OF LOW SCORCH

2017 ◽  
Vol 90 (3) ◽  
pp. 536-549 ◽  
Author(s):  
Anu Mary Joseph ◽  
Benny George ◽  
K. N. Madhusoodanan ◽  
Rosamma Alex
Keyword(s):  
Solvent Extraction ◽  
Natural Rubber ◽  
Main Chain ◽  
Process Safety ◽  
Original Sample ◽  
Vulcanized Rubber ◽  
Sulfur Vulcanization ◽  
Natural Rubber Vulcanizates ◽  
Devulcanized Rubber

ABSTRACT We investigate the reasons behind the observed low scorch during the revulcanization of devulcanized rubber. Mechanically devulcanized carbon black filled natural rubber vulcanizates originally cured by conventional vulcanization (CV), semiefficient vulcanization (semi EV), efficient vulcanization (EV), and peroxide systems as well as buffing dust obtained from pre-cured tread with known formulation were used. Revulcanization of these devulcanized samples using sulfur/sulfonamide system led to the following observations; irrespective of the type of sulfur cure system used for the initial vulcanization of the rubber, (i) the devulcanized samples cured without pre-vulcanization induction time and (ii) devulcanized samples prepared from peroxide vulcanized rubber cured with scorch safety. Based on the earlier reports that solvent extraction of devulcanized rubber did not improve the scorch time during revulcanization, the role of zinc bound non-extractable moieties was investigated using devulcanized rubber prepared from activator-free vulcanizates, which disproved the role of such moieties. This confirmed that the scorch reducing moieties should be attached to the rubber main chain, which can be unreacted crosslink precursors and cyclic sulfides left after the initial accelerated sulfur vulcanization of the original sample. The ability of pre-vulcanization inhibitor to induce scorch safety when devulcanized rubber is revulcanized as such, without adding any virgin rubber, proved that mercaptobenzothiazole (MBT) generated from crosslink precursors is the cause of low scorch. Acetone extracted devulcanized rubber samples prepared from tetramethyl thiuramdisulfide (TMTD) cured natural rubber, which does not follow the MBT pathway when revulcanized, cured with scorch safety, which further proved the role of MBT. Based on the previous reports and our results, it is obvious that powdering of rubber vulcanizate and devulcanization processes have no role on the low process safety of these materials, but it is inherent to the initial accelerated sulfur vulcanization chemistry undergone by these materials.

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.

Role of geopolymer as a cure activator in sulfur vulcanization of epoxidized natural rubber

2019 ◽  
Vol 137 (17) ◽  
pp. 48624
Author(s):  
Hassarutai Yangthong ◽  
Skulrat Pichaiyut ◽  
Suwaluk Wisunthorn ◽  
Claudia Kummerlöwe ◽  
Norbert Vennemann ◽  
...  
Keyword(s):  
Natural Rubber ◽  
Epoxidized Natural Rubber ◽  
Sulfur Vulcanization ◽  
Cure Activator

Relaxation Processes in Vulcanized Rubber. II. Secondary Relaxation Due to Network Breakdown

1963 ◽  
Vol 36 (2) ◽  
pp. 389-398 ◽  
Author(s):  
A. N. Gent
Keyword(s):  
Molecular Structure ◽  
Experimental Study ◽  
Natural Rubber ◽  
Relaxation Process ◽  
Relaxation Processes ◽  
Secondary Relaxation ◽  
Oxidative Deterioration ◽  
Vulcanized Rubber ◽  
Oxidation Inhibitors ◽  
Natural Rubber Vulcanizates

Abstract An experimental study is described of a “secondary” relaxation process in stretched vulcanizates, which becomes dominant after long periods at normal temperatures. It is shown to be affected markedly by the temperature, the atmosphere in which the test is conducted, and the presence of oxidation inhibitors. It is therefore attributed to oxidative deterioration of the molecular structure. In some vulcanizates, however, a similar or even greater relaxation is found to occur in vacuo, and this is attributed to the failure of specific crosslink structures. The extent of recovery on releasing the extended testpieces has also been investigated for a number of natural rubber vulcanizates.

ZINC OXIDE VERSUS MAGNESIUM OXIDE REVISITED. PART 1

2012 ◽  
Vol 85 (1) ◽  
pp. 38-55 ◽  
Author(s):  
Manuel Guzmán ◽  
Berta Vega ◽  
Núria Agulló ◽  
Ulrich Giese ◽  
Salvador Borrós
Keyword(s):  
Zinc Oxide ◽  
Environmental Impact ◽  
Natural Rubber ◽  
Metal Oxides ◽  
Environmental Effects ◽  
Model Compound ◽  
Rubber Industry ◽  
Sulfur Vulcanization ◽  
Activator System

Abstract Zinc oxide is a widely used compound in the rubber industry due to the excellent properties that it shows as activator, and consequently, its role in the mechanism of accelerated sulfur vulcanization has been extensively studied. Due to the increased concern about its environmental effects, several research studies have been carried out in order to substitute it with different metal oxides such us MgO. The effect of the activator system in order to minimize the environmental impact of the rubber goods has been explored. The work developed is presented in two parts. In Part 1, the influence of different mixtures of ZnO and MgO on the vulcanization of natural rubber has been investigated. In Part 2, model compound vulcanization has been used to study the role of MgO on the mechanism to gain a better understanding of the differences shown in Part 1.

ZINC OXIDE VERSUS MAGNESIUM OXIDE REVISITED. PART 2

2012 ◽  
Vol 85 (1) ◽  
pp. 56-67 ◽  
Author(s):  
Manuel Guzmán ◽  
Berta Vega ◽  
Núria Agulló ◽  
Salvador Borrós
Keyword(s):  
Zinc Oxide ◽  
Environmental Impact ◽  
Natural Rubber ◽  
Metal Oxides ◽  
Environmental Effects ◽  
Model Compound ◽  
Rubber Industry ◽  
Sulfur Vulcanization ◽  
Activator System

Abstract Zinc oxide is a widely used compound in the rubber industry due to the excellent properties that it shows as an activator and, consequently, its role in the mechanism of accelerated sulfur vulcanization has been extensively studied. Due to the increased concern about its environmental effects, several research studies have been carried out in order to substitute it with different metal oxides such us MgO. The effect of the activator system in order to minimize the environmental impact of the rubber goods has been explored. The work developed is presented in two parts. In Part 1, the influence of different mixtures of ZnO and MgO in the vulcanization of natural rubber has been investigated. In Part 2 of the study, model compound vulcanization has been used to study the role of MgO on the mechanism to gain a better understanding of the differences shown in the first part.

Effect of Curing Systems on Fatigue of Natural Rubber Vulcanizates

1966 ◽  
Vol 39 (3) ◽  
pp. 785-797 ◽  
Author(s):  
W. L. Cox ◽  
C. R. Parks
Keyword(s):  
Fatigue Life ◽  
Natural Rubber ◽  
Main Chain ◽  
Accelerated Aging ◽  
Chain Scission ◽  
Rapid Loss ◽  
Effective Antioxidant ◽  
Natural Rubber Vulcanizates ◽  
Aging In Air ◽  
Oxidative Effect

Abstract The fatigue life of natural rubber-HAF black vulcanizates showed maxima when plotted as a function of crosslink concentration as did other properties related to a tearing process such as tensile strength, crack growth, and tear strength. Accelerated-sulfur vulcanizates were superior to peroxide and nonelemental-sulfur cures; this can be attributed to an exchange of polysulfide crosslinks under stress. An effective antioxidant was essential for maximum fatigue resistance. Accelerated-sulfur systems, although having a higher original fatigue life than peroxide or nonelemental-sulfur cures, showed a rapid loss on accelerated aging in air. This would indicate that an oxidative effect was involved. Sulfur group analyses of the flexed samples showed an increase in the concentration of RSSxSR linkages but a decrease in the total polysulfide sulfur, Sx, with no change in the crosslink densities. This suggests that the polysulfide linkages not only underwent exchange during the fatigue process but also homolytic cleavage to polythiyl radicals. These radicals can add to double bonds and in the presence of oxygen initiate oxidation chains which would lead to main chain scission.

Investigation of the Role of Intermolecular Forces in the Mechanism of High-Elastic Deformation. VII. The Effect of Molecular Interaction on the Fatigue Resistance of High Polymers Having Highly Developed Spatial Structures

1954 ◽  
Vol 27 (2) ◽  
pp. 363-373
Author(s):  
V. E. Gul ◽  
D. L. Fedyukin ◽  
B. A. Dogadkin
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Fatigue Resistance ◽  
Dibutyl Phthalate ◽  
Intermolecular Forces ◽  
Spatial Structures ◽  
Paraffin Oil ◽  
Degree Of Swelling ◽  
Natural Rubber Vulcanizates

Abstract It is shown experimentally that an irregular change of the fatigue resistance of loaded natural-rubber vulcanizates with increase of the degree of swelling in paraffin oil and in dibutyl phthalate is caused by the superposition of two processes: the increase of fatigue resistance, as a result of the reduction of mechanical losses, and the decrease of fatigue resistance due to the decrease of tensile strength proportional to the higher degree of swelling.

Role of eco-friendly Molasses carbon powder as a filler in natural rubber Vulcanizates

2017 ◽  
Vol 4 (5) ◽  
pp. 6450-6457 ◽  
Author(s):  
Thanunya Saowapark ◽  
Suwimon Plao-le ◽  
Ekrachan Chaichana ◽  
Adisak Jaturapiree
Keyword(s):  
Natural Rubber ◽  
Carbon Powder ◽  
Natural Rubber Vulcanizates

Structural Characterization of Natural Rubber Vulcanizates

1963 ◽  
Vol 36 (2) ◽  
pp. 547-557 ◽  
Author(s):  
C. G. Moore ◽  
M. Porter
Keyword(s):  
Natural Rubber ◽  
Main Chain ◽  
Structural Complexity ◽  
Chain Scission ◽  
Reaction Products ◽  
Chemical Reagents ◽  
Pendent Groups ◽  
Cure Time ◽  
Conjugated Triene ◽  
Natural Rubber Vulcanizates

Abstract The three principal approaches used in the structural resolution of sulfur vulcanizates of natural rubber are described and exemplified by their application to three systems: an unaccelerated sulfur system and two mercaptobenzothiazole (MBT)-accelerated sulfur systems, one of which makes very efficient use and the other inefficient use of the sulfur crosslinking. The ultimate aim of such studies is to relate vulcanizate structure to the physical properties and aging behavior of the vulcanizates during service. The first approach, which gives an overall measure of the structural complexity of the network, involves the determination of the crosslinking efficiency, (E), that is, the number of sulfur atoms combined in the network for each physically-effective, chemical crosslink formed. Crosslinking efficiencies of networks vary with increasing cure time from ca. 6-1.16 for the efficient-MBT system to 55-40 for the unaccelerated sulfur system. Between these extremes, it is found that variations of reactant concentrations and of temperature and time of cure lead to large variations in crosslinking efficiency and therefore of network complexity. Related work not reported here indicates that the latter features are also dependent on the type of accelerator used. More detailed information on network structure is obtained from analysis of reaction products of low molecular weight analogs of natural rubber with the vulcanizing agent and ancillary ingredients. Such studies reveal that the poor efficiency of the unaccelerated sulfur system is due to sulfur being combined wastefully in (i) long polysulfidic crosslinks of alkenyl t-alkyl structure, (ii) vicinal crosslinks which behave physically as one crosslink, and (iii) a large proportion of cyclic monosulfide groups which constitute an important modification of the main rubber chains. Conjugated triene groups, cis, trans-isomerized isoprene units, and main chain scission represent other possible types of modification. In contrast with this complex network, efficiently-cured MBT-accelerated sulfur vulcanizates contain, at early stages of cure, polysulfidic crosslinks of dialkenyl type which decrease with time to mainly monosulfide crosslinks; conjugated triene units are also present but little or no cyclic monosulfides, vicinal crosslinks, or main chain scission. Other accelerated sulfur vulcanizates possess structures intermediate between these two extremes, except that the crosslinks are generally of dialkenyl type and pendent groups terminated by accelerator residues constitute an additional possible type of modification. Knowledge from model olefin studies of the different types of sulfurated groups present in vulcanizates has led to the development of the third experimental approach, i.e. use of chemical reagents (‘chemical probes’) to determine specific groups. This approach is exemplified by reaction with actual vulcanizates of triphenylphosphine which removes sulfur atoms in excess of one or two from polysulfides; as cure proceeds in unaccelerated sulfur vulcanization, the proportion of combined sulfur present in cyclic sulfide groups rises from 75% to 95% while the average number of sulfur atoms in each crosslink unit falls from 12–13 to 2–4. Comparable data for the efficient MBT system confirm the essential simplicity of the network in this case.

The Dynamic Properties of Carbon Black-Loaded Natural Rubber Vulcanizates. Part I

1963 ◽  
Vol 36 (2) ◽  
pp. 432-443 ◽  
Author(s):  
A. R. Payne
Keyword(s):  
Thermal Treatment ◽  
Carbon Black ◽  
Natural Rubber ◽  
Dynamic Modulus ◽  
Dynamic Properties ◽  
Viscosity Change ◽  
Vulcanized Rubber ◽  
Elastic Responses ◽  
Natural Rubber Vulcanizates

Abstract The dynamic properties of a natural vulcanized rubber containing carbon black were studied for dynamic tensions of amplitude varying greatly. It was shown that both the elastic responses and viscosity change with amplitude of oscillation and with concentration and type of carbon black. The effects of thermal treatment on the dynamic modulus were also studied. Beginning with conditions of equilibrium between the hard and soft regions of the vulcanizate for very weak stresses, the values for the formation of hard regions from soft regions were determined by means of the Van't Hoff isochore.

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