Article

The effect of percent hydrogenation and vulcanization system on ozone stability of hydrogenated natural rubber vulcanizates using Raman spectroscopy

Authors:
  • Prince of Songkla University, Pattani Campus, Thailand
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Abstract

The ozone stability of partially hydrogenated natural rubbers (HNRs) was evaluated. HNRs with the hydrogenation levels of 14, 33 and 65 mol% including with vulcanization systems of peroxide and sulfur on ozone stability comparing with natural rubber (NR) and ethylene-propylene-diene-rubber (EPDM) vulcanizates were studied. The chemical structures of rubber vulcanizates were characterized by Raman spectroscopy. The surface cracks were observed by Raman optical microscopy. The results clearly exhibited that the ozone stability of HNRs vulcanizates was much greater than that of the NR vulcanizates. The difference between the integral intensities of C=C bonds of isoprene units in rubber chains by Raman spectroscopy before and after ozone exposed was minimized with the degree of hydrogenation. The depth of cracking observed by three-dimensional (3D) modes clearly decreased with an increase in the degree of hydrogenation, while no cracks on the surface of EPDM were found. These findings indicated that ozone stability increased with the degree of hydrogenation. Regarding the effect of vulcanizing systems, sulfur cure showed greater resistance to ozone degradation than peroxide cure.

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... Vulcanized rubber has a Raman spectrum distinct from that of natural rubber (Jackson et al. 1990;Hendra and Jackson 1994;Xue 1997;Samran et al. 2004;Taksapattanakul et al. 2017). Therefore, the analysis of monkeyhair laticifers could provide the first direct evidence that the Geiseltal laticifers are sulfur-vulcanized. ...
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Chapter
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The non-catalytic hydrogenation of natural rubber (NR) and two epoxidized NRs (ENRs) i.e. ENR-22 and ENR-40 containing 22 and 40 mol% of epoxide, respectively, was carried out using p-toluenesulfonylhydrazide (TSH) as a hydrogenating agent. A two-fold molar excess of TSH compared with unsaturated units of the rubber was used. The evidence of hydrogenation is a decrease in the intensity of the characteristic signal of the carbon–carbon double bond stretching vibration of the rubber in both the Raman and FT-IR spectra. The percentage hydrogenation was successfully determined by Raman spectroscopy since the vibrational mode of the carbon–carbon unsaturation is strongly Raman active. The progress of the hydrogenation could be monitored by means of the techniques mentioned above as a function of reaction time. The maximum degree of hydrogenation of NR is ∼89% whereas in the case of ENR-22 and ENR-40 it reaches 94 and 96%, respectively. Solid-state 13C NMR spectroscopy was also used to confirm the microstructure characteristics of the hydrogenated rubbers. 13C NMR analysis showed that cis–trans isomerization of carbon–carbon unsaturations occur during hydrogenation. Copyright © 2004 John Wiley & Sons, Ltd.
Article
Hydrogenated natural rubber (HNR), providing an ethylene–propylene alternating copolymer, was prepared by the chemical modification of natural rubber latex (NRL) using diimide generated from hydrazine (N2H4) and hydrogen peroxide (H2O2), with copper sulfate (CuSO4) as catalyst. 1H-NMR analysis indicated that 48% hydrogenation was performed with a mole ratio of N2H4/double bonds = 4 and H2O2/N2H4 = 1.5 at 50°C for 7 h. The obtained HNR was subjected to a sulfur cure by using a conventional milling process. The cure characteristics, mechanical properties before and after heat aging, and abrasion and ozone resistances of HNR vulcanizate were examined and compared with those of natural rubber (NR), ethylene propylene diene terpolymer (EPDM) and 50 : 50 NR/EPDM vulcanizates. The results indicated that the cure rate of 48% HNR showed no significant change when compare to both NR and 50 : 50 NR/EPDM blends, and offered a better processing advantage over EPDM. The mechanical properties and abrasion resistance of a 48% HNR vulcanizate were comparable to those of a NR vulcanizate. Additionally, its heat and ozone resistances were better than those of NR vulcanizate, due to a reduction in the amount of double bonds in the backbone chain. Thus, hydrogenation of NR can lead to a type of rubber that has improved heat and ozone resistances while still maintaining its good mechanical properties. Consequently, it improves the properties of NR for a wide range of applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009
Article
The homogeneous catalyst precursor, OsHCl(CO)(O2)(PCy3)2, was utilized for the hydrogenation of natural rubber to convert the unsaturated structure to a saturated form, providing an alternating ethylene-propylene copolymer. A detailed kinetic investigation was carried out by monitoring the amount of hydrogen consumption during the reaction using a gas-uptake apparatus. 1H NMR spectroscopy was used to determine the final olefin conversion to the hydrogenated product. Kinetic data, collected according to a statistical design framework, defined the influence of catalyst and polymer concentration, hydrogen pressure, and reaction temperature on the catalytic activity. The kinetic results indicated that the hydrogenation rate exhibited a first- shifted to zero-order dependence on hydrogen at lower hydrogen pressure, which then decreased toward an inverse behavior at pressures higher than 41.4 bar. The hydrogenation was also observed to be first-order with respect to catalyst concentration, and an apparent inverse dependence on rubber concentration was observed due to the impurities in the rubber. The hydrogenation rate was dependent on reaction temperature, and the apparent activation energy over the temperature range of 125–145°C was found to be 122.76 kJ/mol. Mechanistic aspects of the hydrogenation of natural rubber in the presence of OsHCl(CO)(O2)(PCy3)2 were proposed on the basis of the observed kinetic results. The addition of some acids and certain nitrogen containing materials showed an effect on the hydrogenation rate. The thermal properties of hydrogenated natural rubber indicated that the thermal stability increased with increasing % hydrogenation of the rubber. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4499–4514, 2006
Article
In the presence of chlorinated solvents, the catalytic complex [Ir(COD)py(PCy3)]PF6 (where COD is 1,5-cyclooctadiene and py is pyridine) was an active catalyst for the hydrogenation of synthetic cis-1,4-polyisoprene and natural rubber. Detailed kinetic and mechanistic studies for homogeneous hydrogenation were carried out through the monitoring of the amount of hydrogen consumed during the reaction. The final degree of olefin conversion, measured with a computer-controlled gas-uptake apparatus, was confirmed by Fourier transform infrared spectroscopy and 1H-NMR spectroscopy. Synthetic cis-1,4-polyisoprene was used as a model polymer for natural rubber without impurities to study the influence of the catalyst loading, polymer concentration, hydrogen pressure, and reaction temperature with a statistical design framework. The kinetic results for the hydrogenation of both synthetic cis-1,4-polyisoprene and natural rubber indicated that the hydrogenation rate exhibited a first-order dependence on the catalyst concentration and hydrogen pressure. Because of impurities inside the natural rubber, the hydrogenation of natural rubber showed an inverse behavior dependence on the rubber concentration, whereas the hydrogenation rate of synthetic rubber, that is, cis-1,4-polyisoprene, remained constant when the rubber concentration increased. The hydrogenation rate was also dependent on the reaction temperature. The apparent activation energies for the hydrogenation of synthetic cis-1,4-polyisoprene and natural rubber were evaluated to be 79.8 and 75.6 kJ/mol, respectively. The mechanistic aspects of these catalytic processes were discussed on the basis of observed kinetic results. The addition of some acids showed an effect on the hydrogenation rate of both rubbers. The thermal properties of hydrogenated rubber samples were determined and indicated that hydrogenation increased the thermal stability of the hydrogenated rubber but did not affect the inherent glass-transition temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4219–4233, 2006
Article
Hydrogenation is an important method of chemical modification, which improves the physical, chemical, and thermal properties of diene elastomers. Natural rubber latex (NRL) can be quantitatively hydrogenated to provide a strictly alternating ethylene–propylene copolymer using a homogeneous osmium catalyst OsHCl(CO)(O2)(PCy3)2. A detailed kinetic investigation was carried out by monitoring the amount of hydrogen consumption during the reaction using a gas-uptake apparatus. The kinetic results of NRL hydrogenation indicated that this system had a second-order dependence of the hydrogenation rate on hydrogen pressure and then decreased toward a zero-order dependence for hydrogen pressures above 13.8 bar. The hydrogenation was also observed to be first-order with respect to catalyst concentration and inverse first-order on rubber concentration due to impurities present in the rubber latex. Additions of a controlled amount of acid demonstrated a beneficial effect on the hydrogenation rate of NRL. The temperature dependence of the hydrogenation rate was investigated and an apparent activation energy (over the range of 120–160°C) was calculated as 57.6 kJ/mol. Mechanistic aspects of this catalytic process are discussed on the basis of kinetic results. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 640–655, 2006
Article
Ethylene–propylene–diene monomer (EPDM) containing ENB as diene was exposed to artificial weathering environment for different periods of time. The changes of appearance, morphology, mechanical properties and chemical structures were monitored by spectrophotometer, glossmeter, microscope, computer-controlled tensile testing, hardness measurements and Fourier Transform Infrared (FTIR) spectroscopy. Crosslink density of EPDM specimens was measured by the solvent swell method. The results showed that the surface of EPDM became redder, yellower and lighter in the first stage of aging and then remained almost unchanged. The specular gloss reached a maximum when the sample was exposed for 18 days and then decreased. The aging process proceeded predominantly via crosslinking. The tensile strength increased with increase in crosslink density up to an optimum value and thereafter decreased with further increase in crosslink density. FTIR spectra confirmed the formation of carbonyl groups in an artificial weathering environment.
Article
The ageing behavior due to the effects of heat, ozone, γ- radiation, and water on ethylene propylene diene monomer rubber/styrene butadiene rubber (EPDM/SBR) blends was studied. The tensile strength, crack initiation, ozone ageing, gamma radiation, and water resistance of the blends were measured and used to determine the extent of ageing. Tensile strength of blends of different compositions increased after thermal ageing for 96 h at 100°C probably due to the continued cross-linking. It has been observed that an increase in EPDM in the blends improves the ozone resistance of the blends. Crack initiation was noted only in blends with lesser amount of EPDM and the cracks in such blends were found deeper, wider and continuous. With 15 kGy irradiation dose, the tensile strength of the blends found to be decreased while it increased with 80 kGy dosage of γ-radiation. The elongation at break showed a decreasing trend with increased dosage of γ-radiation. It has also been observed that the EPDM rich blends showed negligible water uptake. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Article
The application of FF Raman spectroscopy in the field of elastomers has been reviewed. FT Raman spectra of various natural and synthetic elastomers are presented to illustrate both the advantages and the limitations of the technique.Carbon black and some oils, when compounded with natural and synthetic elastomers, prevent the acquisition of useful Raman spectra. However, all other commercial samples studied produced excellent spectra in the raw and vulcanized states without any sample pre-treatment.This has allowed quantitative work on blends and isomeric elastomers and also the direct study of the rubber vulcanization process.Future developments of the technique are discussed.
Article
Carboxylated styrene–butadiene rubber (XSBR) is selectively hydrogenated by diimide reduction technique in latex stage using hydrazine hydrate, hydrogen peroxide and Cu+2 as catalyst. The products are characterised by IR and NMR spectroscopy. Dynamic Mechanical Properties and Transmission Electron Micrographs of the hydrogenated products confirm the existence of ionic aggregates involving carboxyl (–COOH) groups of the substrate and externally added Cu+2 ions. Longer reaction time and higher amount of catalyst are required for hydrogenation of XSBR compared to that of SBR. An increase in the amount of carboxyl group decreases the extent of reaction.
The Investigation of Rubber by Vibrational Spectroscopy
  • K S Haider
K.S. Haider, The Investigation of Rubber by Vibrational Spectroscopy, MSc. Thesis, Freie University, 2012.
Bond Dissociation Energies in Organosilicon Compounds. 23M. A. Brook, Silicon in Organic, Organometallic and Polymer Chemistry
  • R Walsh
R. Walsh, Bond Dissociation Energies in Organosilicon Compounds. 23M. A. Brook, Silicon in Organic, Organometallic and Polymer Chemistry, Wiley, New York, 1998.