The CBS-Accelerated Sulfuration of Natural Rubber and Cis-1,4-Polybutadiene

1972 ◽  
Vol 45 (1) ◽  
pp. 182-192 ◽  
Author(s):  
T. D. Skinner
Keyword(s):  
Natural Rubber ◽  
Zinc Sulfide ◽  
Chain Length ◽  
Network Formation ◽  
Reaction Times ◽  
Substantial Fraction ◽  
Chemical Complexity ◽  
Cure Time ◽  
Natural Rubber Vulcanizates

Abstract The results of characterization of the natural rubber vulcanizates are consistent with the results of characterization of the sulfidic products from 2-methylpent-2-ene. In both the model olefin system and the rubber system the initially formed crosslinks are polysulfidic but these are subsequently reduced to di- and monosulfidic crosslinks as the cure time is increased. Similar amounts of zinc sulfide are formed during the sulfuration of 2-methylpent-2-ene and during the vulcanization of natural rubber. The efficiency of sulfur utilization for crosslinking in natural rubber is approximately half that in comparable sulfurations of 2-methylpent-2-ene, i.e. approximately twice as many sulfur atoms are needed to obtain a chemical crosslink in natural rubber as are needed to obtain a crosslink in 2-methylpent-2-ene. This is presumed to be a consequence of the intra-molecular sulfuration that occurs in natural rubber. There is no evidence to indicate the presence of vicinal crosslinks in the natural rubber vulcanizates. Hence in agreement with the views of other workers it is concluded that the crosslinks present in accelerated sulfur vulcanizates of natural rubber are tetrafunctional and dialkenyl. The results of the characterization of the polybutadiene vulcanizates are not fully supported by the results of the model olefin studies. In the vulcanization of polybutadiene the initially formed crosslinks are polysulfidic. As vulcanization proceeds, the chemical complexity of the network increases. After long reaction times, however, no significant amount of monosulfidic crosslinks are present in the network and very little of the reacted sulfur is present in the form of zinc sulfide. Nitrogen analyses of the polybutadiene vulcanizates showed that a substantial fraction of the accelerator, equivalent to 80–90% of the available 2-thiobenzothiazole groups, become combined in the network during vulcanization. It is proposed that the combination of accelerator with polybutadiene prevents the desulfuration of dialkenyl polysulfides to dialkenyl monosulfides (the normally observed pathway of accelerated sulfuration of natural rubber) and allows vicinal crosslinking to proceed. Some support for this proposal is that vicinal crosslinks and a substantial amount of nitrogenous product are formed during the accelerated sulfuration of cyclohexene. The findings of Gregg and Katrenick on the MBTS accelerated sulfuration of cis-cis-1,5-cyclooctadiene are also consistent with this proposal. The nitrogen analyses of the polybutadiene vulcanizates indicate that very little of the accelerator is permanently combined in the network during the initial stages of network formation. Hence by comparison with the observed pattern of sulfuration of hex-3-ene, where it was shown that negligible amounts of nitrogenous product are present, it is proposed that dialkenyl (tetrafunctional) polysulfidic crosslinks are initially introduced into the polybutadiene network. The polysulfidic crosslinks then presumably undergo desulfuration reactions leading to dialkenyl crosslinks of reduced sulfur chain length until the desulfurating agent is, in effect, removed from the system by the 2-thio-benzothiazole groups becoming combined in the network. Once most of these groups have combined, after ca. 60 min. at 140° C, the desulfuration reactions are probably less important than the reactions leading to vicinal crosslinking, and it is likely that a well cured-polybutadiene vulcanizate contains a substantial fraction of vicinal crosslinks.

Structural Characterization of Vulcanizates Part X. Thiol-Disulfide Interchange for Cleaving Disulfide Crosslinks in Natural Rubber Vulcanizates

1970 ◽  
Vol 43 (2) ◽  
pp. 210-221 ◽  
Author(s):  
D. S. Campbell
Keyword(s):  
Natural Rubber ◽  
Exchange Reaction ◽  
Structural Characterization ◽  
Disulfide Exchange ◽  
Sulfur Vulcanization ◽  
Cure Time ◽  
Natural Rubber Vulcanizates

Abstract The thiol-disulfide exchange reaction is shown to be applicable to cleavage of disulfide crosslinks in accelerated sulfur vulcanizates of natural rubber. The reaction, in conjunction with the previously reported selective cleavage of polysulfide crosslinks, is used to determine the distribution of crosslink types for several accelerated sulfur vulcanization systems as a function of cure time. Discrepancies between the results and published results obtained using the reagent sodium di-n-butyl phosphite for disulfide crosslink cleavage are discussed.

Structural Characterization of Filled Vulcanizates Part 1. Determination of the Concentration of Chemical Crosslinks in Natural Rubber Vulcanizates Containing High Abrasion Furnace Black

1967 ◽  
Vol 40 (3) ◽  
pp. 866-882 ◽  
Author(s):  
M. Porter
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Volume Fraction ◽  
Exponential Relationship ◽  
Furnace Black ◽  
Simple Linear Relationship ◽  
Chemical Crosslinks ◽  
Natural Rubber Vulcanizates

Abstract The degree to which HAF black restricts the swelling of natural rubber vulcanizates in n-decane has been determined using a vulcanizing system in which the stoichiometry of crosslinking is unaffected by the carbon black. The dependence of the degree of restriction, as measured by the ratio of the volume fractions of rubber in the filled and unfilled vulcanizates swollen to equilibrium, on the concentration of carbon black follows an exponential relationship previously proposed by Lorenz and Parks. This is found to be equivalent to a simple linear relationship between the apparent and actual crosslink concentrations: napparent/nactual=1+Kϕ, where K is a constant characteristic of the filler and φ is its volume fraction in the vulcanizate. The relation has been used to determine actual crosslink concentrations in filled natural rubber vulcanizates. HAF black is found to cause increases of up to 25 per cent in the yield of polymer to polymer crosslinks in conventional sulfur vulcanizing systems, accompanied by changes in rate of cure and of crosslink reversion. All these are small compared with the effect of the filler on many physical properties.

Aromatic and Epoxidised Oil Curing and Rebound Resilience Characteristic and their Humidity Effect of Hardness on NR Vulcanizates

2013 ◽  
Vol 812 ◽  
pp. 138-144 ◽  
Author(s):  
Mohamed Rahmah ◽  
Wan Zain Norazira ◽  
Shafie Nur Ashyikin ◽  
Mohd Nurazzi Norizan
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Room Temperature ◽  
Rubber Compound ◽  
Humidity Effect ◽  
Humidity Level ◽  
Cure Time ◽  
Humidity Chamber ◽  
Overall Performance ◽  
Natural Rubber Vulcanizates

Recently, aromatic oil (AO) is one of the substances that is typically used as a processing aid especially for high filler loadings in formulating rubber compound. Aromatic oil has disadvantages in that, it is hazardous to environment, toxic and has been labeled as carcinogenic. In this research, an epoxidised oil (EO) and aromatic oil were used to investigate the effect incorporation of oil onto the SBR/NR natural rubber vulcanizates (NR). From the result obtained, EO showed shorter cure time and scorch time as the oil loading were increased up to 20 pphr of EO. Physical properties such as hardness and rebound resilience of NR/EO vulcanisate were also investigated upon exposure to different humidity level in humidity chamber. At room temperature, the hardness of EO loading onto the SBR/NR vulcanisate is lower than AO loadings. Hardness was slightly decreased with increasing rate of humidity. There is great difference in hardness and rebound resilience values between AO and EO. Both hardness and rebound resilience were not affected by humidity. This implies the existence of good filler interaction with EO and rubber which do not impart changes in the hardness and resilience properties of rubber compound. Epoxidised oil has great promising potential to replace the carcinogenic aromatic oil as it has good overall performance and renewable in nature .

Quantitative Characterization of Cure. II. Use of Modulus as a Measure of the State of Cure of Pure-Gum Natural-Rubber Vulcanizates

1952 ◽  
Vol 25 (3) ◽  
pp. 439-446 ◽  
Author(s):  
W. P. Fletcher ◽  
Geoffrey Gee ◽  
S. H. Morrell
Keyword(s):  
Natural Rubber ◽  
The State ◽  
Quantitative Characterization ◽  
Natural Rubber Vulcanizates ◽  
Practical Disadvantage ◽  
Practical Measure

Abstract The purpose of this investigation was to develop methods of measuring state of cure which involved only measurements normally available or very readily made. Swelling measurements, although suitable in theory, suffer the practical disadvantage of being time-consuming, but it is shown that they can be replaced very satisfactorily by modulus at 100 per cent elongation. This is a good practical measure of state of cure for most purposes, and simple corrections are developed which extend its range of usefulness. An easily constructed machine is described for the accurate measure of modulus at small elongations.

Solid-State C-13 NMR Studies of Vulcanized Elastomers XVII. Effect of Carbon Black Grade on the Network Structure in Natural Rubber Vulcanizates

1997 ◽  
Vol 70 (4) ◽  
pp. 671-680 ◽  
Author(s):  
Makio Mori ◽  
Jack L. Koenig
Keyword(s):  
Solid State ◽  
Carbon Black ◽  
Natural Rubber ◽  
Network Formation ◽  
Physical Adsorption ◽  
Nmr Studies ◽  
Carbon Black Concentration ◽  
Effective Level ◽  
The Individual ◽  
Natural Rubber Vulcanizates

Abstract The vulcanization chemistry and network formation of carbon black filled natural rubber vulcanized with sulfur and TBBS were studied using solid-state C-13 NMR and equilibrium swelling measurements. A reduction in the sulfur rank of the A1 type sulfide and increased production of B1 type polysulfide are observed when the carbon black concentration increases in natural rubber. At the same loading level, the structural property or grade of carbon black does not affect qualitatively the type of sulfide formation. The efficiency of the intermolecular crosslinking over the whole range of sulfurizations is 45.7% for the unfilled vulcanizate. The extent of the chemical sulfurization reactions (NMR result) is constant with black incorporation, while the total network (swelling result) increases with increases in the black loading. The amount of physical entanglements, estimated from the comparison of the NMR and swelling results, is found to increase linearly with the carbon black concentration. The entanglements increase as a function of the 300% modulus, which suggests that the effective level of reinforcement depends on the nature of the individual carbon black. It is assumed that physical adsorption plays a major role in the polymer-filler interactions in the natural rubber/carbon black system.

EFFECT OF CURE EFFICIENCY ON PROPERTIES OF GUM AND BLACK FILLED NATURAL RUBBER VULCANIZATES

2011 ◽  
Vol 84 (2) ◽  
pp. 229-242 ◽  
Author(s):  
Gary R. Hamed ◽  
Kanoktip Boonkerd
Keyword(s):  
Electron Microscopy ◽  
Tensile Strength ◽  
Natural Rubber ◽  
Crosslink Density ◽  
Cure Time ◽  
Cracking Pattern ◽  
Natural Rubber Vulcanizates ◽  
Scanning Electron ◽  
Fracture Specimens ◽  
Strength Effect

Abstract Effects of the sulfur cure efficiency on the reversion behavior and the normal and edge-cut tensile strength of gum and black filled natural rubber (NR) vulcanizates were studied. N, N-dicyclohexyl-2-benzothiazole sulfenamide (DCBS) was used as an accelerator. A series of five vulcanizates with high to low cure efficiencies was prepared by increasing the sulfur (S) to DCBS ratios within the range of 0.26–6.66. All vulcanizates were formulated to have the same crosslink density. The degree of reversion (%) calculated from cure curves of gum and black filled NR at 20 min above the cure time (tc100) passed through maximum with decreasing cure efficiencies. For both gum and black filled NR, the highest degree of reversion (%) was observed at the S/DCBS ratio of 1.17. The normal tensile strengths of gum and black filled NR were directly proportional to the cure efficiency. For gum NR vulcanizates, the edge-cut tensile strength was markedly influenced by cure efficiency. Similar to the normal tensile strength, the gum NR vulcanizates cured with the lowest cure efficiency showed the lowest edge-cut tensile strength. Effect of the cure efficiency on the edge-cut tensile strength was less in the case of black filled NR vulcanizates. However, the black filled NR vulcanizates cured with the lowest cure efficiency also showed the lowest edge-cut tensile strength. The cut tip characteristics of the fracture specimens were investigated using scanning electron microscopy. The gum specimens showed only the simple lateral cracking pattern, while all black filled specimens showed the longitudinal cracking pattern. Four different cracking patterns of the black filled specimens were identified. The distribution of cracking patterns depended strongly on the size of precut and the cure efficiency.

Preparation and Characterization of Epoxidized Natural Rubber

2011 ◽  
Vol 396-398 ◽  
pp. 478-481 ◽  
Author(s):  
Kui Xu ◽  
Can Zhong He ◽  
Yue Qiong Wang ◽  
Yong Yue Luo ◽  
Shuang Quan Liao ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Infrared Spectroscopy ◽  
Natural Rubber ◽  
Fourier Transform Infrared Spectroscopy ◽  
Reaction Times ◽  
Processing Technology ◽  
Epoxidized Natural Rubber ◽  
Ring Open ◽  
By Products

Epoxidized Natural Rubber is prepared with latex processing technology. The relationships of the epoxidation with the reaction times and temperature were investigated. The structure of ENR was characterized by Fourier transform-infrared spectroscopy (FIIR). It is found that, the by products, ring-open components increases with the reaction temperatures and the reaction times. It is found that as the level of epoxidation increased, the number of tetrahydrofuran ring increased.

Influence of Pyrolytic Carbon Black Prepared from Waste Tires on Mechanical Properties of Natural Rubber Vulcanizates

2017 ◽  
Vol 751 ◽  
pp. 332-336 ◽  
Author(s):  
Sarawut Prasertsri ◽  
Sansanee Srichan
Keyword(s):  
Mechanical Properties ◽  
Carbon Black ◽  
Natural Rubber ◽  
Pyrolytic Carbon ◽  
Filler Loading ◽  
Elongation At Break ◽  
Cure Time ◽  
Mooney Viscosity ◽  
Heat Build Up ◽  
Natural Rubber Vulcanizates

This research aimed to investigate the possibility of pyrolytic carbon black (PCB) used as filler in natural rubber (NR) and its effect on Mooney viscosity, cure characteristics and mechanical properties compared with commercial carbon black (N774). The results revealed that Mooney viscosity, stiffness and heat build-up tended to increase with increasing both PCB and N774 loading, whereas elongation at break decreased. However, the maximum tensile and tear strengths appeared at the optimum filler loading for both PCB and N774. At similar filler content, PCB-filled NR compounds have higher cure time, heat build-up and thermal resistance. Nevertheless, they exhibited lower Mooney viscosity and mechanical properties compared to N774-filled NR. Finally, it can be concluded that PCB could be utilized as filler in NR compound to act as semi-reinforcing filler and was classified as a filler to reduce costs.

Quantitative Characterization of Cure. III. Relation between Compound Viscosity and Vulcanizate Stiffness in Pure-Gum Natural-Rubber Vulcanizates

1952 ◽  
Vol 25 (3) ◽  
pp. 446-454 ◽  
Author(s):  
R. F. Blackwell ◽  
W. P. Fletcher ◽  
Geoffrey Gee
Keyword(s):  
Natural Rubber ◽  
Considerable Reduction ◽  
Test Compound ◽  
Quantitative Characterization ◽  
Mooney Viscosity ◽  
Natural Rubber Vulcanizates ◽  
The Relationship

Abstract The aim of this investigation was to study the dependence of vulcanizate stiffness on the compound Mooney viscosity, and if possible to derive a method by which account could be taken of variations in viscosity in order to reduce the so-called mixing error in batches of test compound. Investigations covering a range of compounds, raw rubbers, and curing times gave results which for the practical range indicated a relation between modulus at 100 per cent elongation and Mooney viscosity. Using the relationship thus established, a method of adjusting modulus results to correspond to a standard Mooney viscosity was derived. Application of the scheme to batches of ACS1 compound mixed from parts of the same lot of homogeneous raw rubber led to a considerable reduction in the range of modulus values.

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.

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