A Vibrational Spectroscopic Analysis of the Structure of Natural Rubber

1987 ◽  
Vol 60 (4) ◽  
pp. 647-658 ◽  
Author(s):  
F. J. Lu ◽  
S. L. Hsu
Keyword(s):  
Natural Rubber ◽  
Functional Groups ◽  
Spectroscopic Analysis ◽  
Extraction Solvent ◽  
Gel Fraction ◽  
Gel Phase ◽  
Composition Structure ◽  
Vulcanization Process ◽  
Structural Aspects ◽  
Soluble Part

Abstract It is not an overstatement to say that natural rubber (NR) is one of the most used polymers. There are numerous studies dealing with the structural aspects of rubber which give rise to its elastic property. However, it should be emphasized that the majority of these studies are generally concerned with rubber in the vulcanized state or, in fact, dealing with the vulcanization process. Relatively few studies have actually been directed at a better understanding of the composition, structure, and properties of raw rubber. This area of study is also important because the composition and the structure of NR differ from synthetic polyisoprene in that the presence of functional groups on main chains and nonrubbery materials, such as proteins, can significantly affect the rheological properties and the processing conditions of rubber before the vulcanization process. Raw rubber can be divided into two different fractions, sol (soluble part) and gel (insoluble part). Of course, this definition depends somewhat on the solvent used. Even though the main chain in both portions of rubber are chemically similar, their significantly distinct mechanical properties have, in fact, been attributed to the nonrubbery materials such as proteins interacting with isoprene chains. It is generally accepted that the amount of nonrubbery materials in the gel fraction is much higher than the sol fraction. The protein apparently interacts quite strongly with specific functional groups on the isoprene chain and is difficult to remove from the gel phase by physical means. It is probable that the different properties between sol and gel rubber is due to the amount of crosslinking of the main chains, but several aspects of the structure need to be answered in greater detail. We know, for example, that the amount of gel fraction can change as a function of extraction solvent. Therefore, one cannot conclude that the interaction between rubber chains even in the gel fraction is strictly chemical in nature. Our premise is that the protein is an important component connecting the isoprene chains.

Gel Formation in Natural Rubber Latex: 2. Effect of Magnesium Ion

2003 ◽  
Vol 76 (5) ◽  
pp. 1185-1193 ◽  
Author(s):  
L. Tarachiwin ◽  
J. T. Sakdapipanich ◽  
Y. Tanaka
Keyword(s):  
Natural Rubber ◽  
Natural Rubber Latex ◽  
Storage Period ◽  
Gel Formation ◽  
Gel Content ◽  
Gel Fraction ◽  
Rate Of Increase ◽  
2So4 Concentration ◽  
Gel Phase ◽  
Long Storage

Abstract The effect of Mg2+ ions on the gel formation in fresh and commercial high ammonia natural rubber latices (FL-latex and commercial HA-latex) was analyzed from the gel content and 2+ content after treatment with (NH4)2SO4. The gel content of rubber from commercial HA-latex decreased significantly after (NH4)2SO4 treatment comparable to that of FL-latex. Long-storage commercial HA-latex containing 50% gel fraction showed no decrease in 2+ content after (NH4)2SO4 treatment. This gel fraction was not solubilized in toluene by the treatment of a proteolytic enzyme in latex or ethanol/toluene mixed solvent extraction of rubber. The 2+ content of rubber in long-storage commercial HA-latex, 0.005% (w/w rubber), decreased after treatment with (NH4)2SO4, while the same treatment showed little change on FL-latex, 0.035%. The toluene soluble fraction of these latices showed a decrease in the Mn value with an increase in the (NH4)2SO4 concentration. The gel content of FL- and HA-lattices increased with an increasing storage period in the presence and absence of (NH4)2SO4. The initial rate of increase in the gel content was slow in the case of FL-latex. These findings indicate that the gel fraction in HA-latex is partly formed by ionic crosslinks caused by 2+ ions. Whereas, the gel phase in long-storage commercial HA-latex is presumed to be a hard gel predominantly formed by covalent bonding.

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.

scholarly journals Synthesis, stability, and reactivity of mesoionic carbene iridium dihydride complexes

2020 ◽  
Author(s):  
Marta Olivares ◽  
Martin Albrecht
Keyword(s):  
Electronic Properties ◽  
Functional Groups ◽  
Pyridine Ring ◽  
Spectroscopic Analysis ◽  
Pka Values ◽  
Trans Effect ◽  
Structural Assignment ◽  
Wide Range ◽  
Hydride Metal ◽  
The Stability

Pyridyl-triazolylidene ligands with variable donor properties were used as tunable ligands at a dihydride iridium(III) center. The straightforward synthesis of this type of ligand allows for an easy incorporation of electron donating substituents in different positions of the pyridine ring or different functional groups such as esters, alkoxy or aliphatic chains on the C4 position of the triazole heterocycle. The stability of these hydride metal systems allowed these complexes to be used as models for studying the influence of the ligand modifications on hydride reactivity. Spectroscopic analysis provided unambiguous structural assignment of the dihydride system. Modulation of the electronic properties of the wingtip substituents did not appreciably alter the reactivity of the hydrides. Reactivity studies using acids with a wide range of pKa values indicated a correlation between hydride reactivity and acidity and showed exclusive reactivity towards the less shielded hydride trans to the carbene carbon rather than the more shielded hydride trans to the pyridine ring, suggesting that the trans effect is more relevant in these reactions than the NMR spectroscopically deduced hydridic character.

COOPERATIVE EFFECTS OF EPOXIDE FUNCTIONAL GROUPS ON NATURAL RUBBER AND SILANE COUPLING AGENTS ON REINFORCING EFFICIENCY OF SILICA

2014 ◽  
Vol 87 (2) ◽  
pp. 291-310 ◽  
Author(s):  
W. Kaewsakul ◽  
K. Sahakaro ◽  
W. K. Dierkes ◽  
J. W. M. Noordermeer
Keyword(s):  
Natural Rubber ◽  
Functional Groups ◽  
Coupling Agent ◽  
Silica Content ◽  
Coupling Agents ◽  
Silane Coupling Agents ◽  
Cooperative Effects ◽  
Optimal Loading ◽  
Silane Coupling

ABSTRACT Polar functionality attached onto natural rubber has a significant impact on the reinforcing efficiency of silica. Parallel studies involving various levels of epoxidation on natural rubber (ENR) in the absence of bis-(triethoxysilylpropyl) tetrasulfide (TESPT) coupling agent, as well as a combination of ENRs with different loadings of TESPT, provide a better understanding of the various factors that influence the properties of silica-filled ENR compounds. Based on the overall properties, the best possible combination to optimize processability, to reduce filler–filler interaction, and improve vulcanization rate as well as vulcanizate properties, is to use ENR with an epoxide content in the range of 20–30 mol%, together with a small portion of TESPT, that is, 2–4 wt% relative to the silica content. This leads to a reduction of approximately 60–80% of TESPT when compared with the conventional NR compounds, where the optimal loading of TESPT was 9.0 wt% relative to the silica content.

Molecular Structure and Macroscopic Properties of Synthetic Cis-Poly(Isoprene)

1974 ◽  
Vol 47 (2) ◽  
pp. 342-356 ◽  
Author(s):  
V. A. Grechanovskii ◽  
I. Ya Poddubnyi ◽  
L. S. Ivanova
Keyword(s):  
Molecular Weight ◽  
Functional Groups ◽  
Chemical Structure ◽  
Sol Gel ◽  
Average Molecular Weight ◽  
Dense Network ◽  
Green Strength ◽  
Gel Fraction ◽  
Rubber Compounds ◽  
Processing Properties

Abstract By changing the sol-gel ratio and the structure of the gel fraction it is possible to obtain various grades of synthetic cis-poly(isoprene) which show promise for different applications in the tire and mechanical rubber goods industries. The processability of commercial SKI-3 rubber (at a given average molecular weight of sol) depends mainly on the structure of the gel fraction. Thus, for example, inferior processing properties of rubber compounds is associated primarily with the presence of tight gel. The content and structure of the gel fraction also significantly affect plasto-elastic properties of raw rubbers, e.g. a low plasticity of raw rubbers owes to the increased content of gel fraction. The reduced green strength of compounds based on SKI—3 rubber is accounted for by its chemical structure. Conventional methods used to change the properties of rubbers (including the variation in molecular weight, molecular weight distribution, branching degree, and variation in the content and structure of gel fraction) cannot be considered to be adequate to tackle the problem of the green strength of SKI—3 black stocks. The way to solve the problem appears to be the introduction of functional groups into the polymer chain at the stage of synthesis or processing. These functional groups should be active as to the formation of labile rubber—carbon black—rubber and/or rubber—rubber bonds. High purity of microstructure is necessary but not sufficient for obtaining the required level of green strength of compounded SKI—3. The gel fractions of SKI—3 rubber yield vulcanizates with a more dense network than the corresponding sol vulcanizates. The temperature dependence of the tensile strength is controlled by the network density of vulcanizates from high cis-1,4 poly(isoprene).

Simulation of Irradiation-Based Processing System for Natural Rubber Vulcanization

2017 ◽  
Vol 751 ◽  
pp. 252-257
Author(s):  
Kittiya Kosaentor ◽  
Ekkachai Kongmon ◽  
Chitrlada Thongbai ◽  
Sakhorn Rimjaem
Keyword(s):  
Electron Beam ◽  
Natural Rubber ◽  
Beam Energy ◽  
Natural Rubber Latex ◽  
Processing System ◽  
Electron Beam Energy ◽  
Rubber Latex ◽  
Electron Beam Processing ◽  
Study Results ◽  
Vulcanization Process

Natural rubber is an important export product of Thailand, which presently contributes about 40% of global production and export. In order to make the natural rubber latex to be durable material, the proper vulcanization process is needed. In typical vulcanization process, chemical substances are added to improve the rubber properties. This may cause some problems e.g. toxicity, blooming effects and unpresented smell due to the additive substances. Vulcanization using an accelerated electron beam does not need to add possibly toxic chemical compounds, especially sulfur. Thus, it was proved to be an alternative method for high quality natural rubber vulcanization. This paper presents about simulation of electron beam irradiation for natural rubber vulcanization with variable electron beam energy and current of 0.5-4 MeV and 10-100 mA, respectively. These ranges of the electron beam energy and current will give adjustable absorb dose, which is the most important parameter for electron beam processing. The absorb energy and its distribution in the natural rubber latex are simulated by using a Monte Carlo method program, GEometry ANd Tracking 4 (GEANT4), with the aim to find the optimal conditions of electron beam properties for sufficient natural rubber vulcanization. Study results of the energy distribution for electron beam penetration in the natural rubber latex are presented and discussed in this paper.

The Effect of Pre-Vulcanization Temperature on Mechanical and Rheological Properties of Starch Filled Natural Rubber Latex Compounds

2013 ◽  
Vol 858 ◽  
pp. 184-189
Author(s):  
Siti Rohana Yahya ◽  
Farah Nadiah Hamdan ◽  
Azura A. Rashid ◽  
Baharin Azahari
Keyword(s):  
Natural Rubber ◽  
Rheological Properties ◽  
Room Temperature ◽  
Natural Rubber Latex ◽  
Shear Thickening ◽  
Filler Loading ◽  
Latex Films ◽  
Rubber Latex ◽  
Thickening Behavior ◽  
Vulcanization Process

The main objective of this study was to investigate the effect of the pre-vulcanization temperature on mechanical and rheological properties of starch filled natural rubber (NR) latex films. The 10 phr filler loading of starch was added into the latex prior to the pre-vulcanization process at 60°C to 140°C. The dipped films were cured in the oven at 100°C for 20 minutes and cooled at room temperature for 24 hours before stripping. The rheological properties of NR latex compounds were studied based on the viscosity measurement. The tensile and tear tests of starch filled NR latex films were also carried out. The results indicated that the rheological properties of the latex compounds showed shear thickening behavior where viscosity was increased with the increase in shear rate and pre-vulcanization temperature proportionally. The pre-vulcanization temperature at 80°C showed the optimum mechanical properties of starch filled NR latex films.

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