Applications of FT-NMR to Crosslink Density Determinations in Natural Rubber Blend Vulcanizates

1992 ◽  
Vol 65 (4) ◽  
pp. 744-760 ◽  
Author(s):  
Paul S. Brown ◽  
M. John ◽  
R. Loadman ◽  
Andrew J. Tinker
Keyword(s):  
Nmr Spectroscopy ◽  
Carbon Black ◽  
Natural Rubber ◽  
Small Molecules ◽  
Crosslink Density ◽  
Chemical Shifts ◽  
Reference Position ◽  
Line Widths ◽  
Good Agreement ◽  
Crosslink Densities

Abstract Previously 90 MHz CW-NMR spectroscopy has been used to estimate the crosslink density in individual components of elastomer blends. Transfer of the technique to a 300 MHz FT instrument is not straightforward. Chemical shifts of polymer resonances in spectra of single-polymer vulcanizates are dependent on crosslink densities of the vulcanizates. Additionally, two resonances are observed for small molecules such as TMS and residual protonated solvent. The smaller resonance of each pair changes in shape and position in synchrony with the polymer signals and is considered to originate from solvent within the swollen polymer. The secondary TMS peak is used as the reference position from which to locate polymer signals in the spectrum. The position of these secondary peaks, and thus the polymer spectrum, relative to the “free” TMS is a function of crosslink density and also of carbon-black loading and type in filled vulcanizates. 13C-NMR line widths are observed to increase with crosslink density and this effect was used to study blends of NR with EPDM or a maleic acid modified EPDM. NR crosslink densities determined from 13C line-width analyses were in good agreement with those obtained from 1H-NMR and increased crosslinking in the modified EPDM was confirmed.

EFFECT OF DEVULCANIZATION ON CROSSLINK DENSITY AND CROSSLINK DISTRIBUTION OF CARBON BLACK FILLED NATURAL RUBBER VULCANIZATES

2016 ◽  
Vol 89 (4) ◽  
pp. 653-670 ◽  
Author(s):  
Anu Mary Joseph ◽  
Benny George ◽  
Madhusoodanan K. N. ◽  
Rosamma Alex
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Crosslink Density ◽  
Morphological Properties ◽  
Original Sample ◽  
Ambient Conditions ◽  
Absolute Value ◽  
Roll Mill ◽  
Percentage Retention ◽  
The Absolute

ABSTRACTCarbon black filled natural rubber (NR) vulcanizates were devulcanized at ambient temperature in a two roll mill. The effect of cure system, that is, conventional vulcanization (CV), semiefficient vulcanization (semi EV), and efficient vulcanization (EV) systems, used for vulcanization of the original sample, on the efficiency of devulcanization was studied. The efficiency of devulcanization expressed as percentage devulcanization of the samples calculated from residual crosslink density measurements was correlated with the sol fraction of the devulcanized samples based on Horikx analysis. Using chemical probe analysis, we determined (i) the crosslink distribution pattern of the original sample, (ii) the extent to which the different types of crosslinks—that is, polysulfidic, disulfidic, and monosulfidic crosslinks—have been debonded or broken during the shearing process in the two roll mill, and (iii) the pattern of bond formation during revulcanization. Mechanical shearing predominantly breaks the majority crosslink type (polysulfidic crosslinks in CV and semi EV cure systems and disulfidic crosslinks in EV samples). Irrespective of the significant reduction in total crosslink density in all three sets of samples, chain shortening reactions similar to the post-crosslinking chemical reactions at curing temperatures also occur during mechanical shear at ambient conditions, which increased the absolute value of monosulfidic links in CV and semi EV systems. However, in the devulcanized EV system, the absolute value of polysulfidic crosslinks increased, which might be due to the re-crosslinking of the cleaved bonds. All the devulcanized samples were revulcanized, and the mechanical and morphological properties were analyzed. The percentage retention of the vulcanizate properties after revulcanization of the devulcanized samples correlated very well with efficiency of devulcanization.

PROTEIN INFLUENCE ON THE MECHANICAL PROPERTIES OF NR

2021 ◽  
Author(s):  
Yayoi Akahori ◽  
Misao Hiza ◽  
Soki Yamaguchi ◽  
Seiichi Kawahara
Keyword(s):  
Mechanical Properties ◽  
Nmr Spectroscopy ◽  
Sodium Dodecyl Sulfate ◽  
Carbon Black ◽  
Natural Rubber ◽  
Hevea Brasiliensis ◽  
Sodium Dodecyl ◽  
Swelling Degree ◽  
Deproteinized Natural Rubber ◽  
Rubber State

ABSTRACT Protein effect on vulcanization of NR, obtained from Hevea brasiliensis, was investigated by analyzing the crosslinking structure of the resulting vulcanizates prepared from untreated NR, deproteinized natural rubber (DPNR), and protein-free natural rubber (PFNR) by swelling methods and rubber-state NMR spectroscopy. The proteins present in NR were removed by three methods: deproteinization with enzyme, urea, or urea–acetone in the presence of sodium dodecyl sulfate. The amount of proteins present in NR, approximately 0.238 w/w%, was reduced to 0.000 w/w% by urea–acetone deproteinization, whereas it was reduced to approximately 0.003 and 0.019 w/w% by enzyme and urea deproteinizations, respectively. Hardness, swelling degree, and crosslinking structure depended on the amount of proteins. Changes in mechanical properties for the vulcanizates prepared from not only non-filler compounds but also carbon black–filled and silica-filled compounds were attributed to the amount of proteins.

Influence of Carbon Black on Crosslink Density of Natural Rubber

2012 ◽  
Vol 51 (6) ◽  
pp. 1208-1217 ◽  
Author(s):  
Zhao Fei ◽  
Chen Long ◽  
Pan Qingyan ◽  
Zhao Shugao
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Crosslink Density

Effect of Crosslink Density on Cut Growth in Black-Filled Natural Rubber Vulcanizates

2002 ◽  
Vol 75 (5) ◽  
pp. 935-942 ◽  
Author(s):  
G. R. Hamed ◽  
N. Rattanasom
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Crack Growth ◽  
Crosslink Density ◽  
Longitudinal Crack ◽  
Test Pieces ◽  
Filled Rubber ◽  
Longitudinal Cracks ◽  
Natural Rubber Vulcanizates ◽  
High Crosslink Density

Abstract Tensile strengths, σb, of gum and N115-filled natural rubber test pieces, with and without edge pre-cuts, have been determined. At low crosslink density, the regular (uncut) σb of filled and gum vulcanizates is similar. However, at high crosslink density, the gum NR becomes brittle, while the corresponding filled rubber remains strong and resistant to cut growth. It is proposed that the tightly linked gum does not strain-crystallize appreciably during stretching, but that its filled counterpart does. Carbon black appears capable of inducing crystallization in a network that alone remains amorphous during extension. Filled vulcanizates of various crosslink densities have similar normal tensile strengths ( ≈ 30 MPa), but strengths differ, sometimes more than twofold, if a pre-cut is present. Lightly crosslinked specimens containing a small cut have strengths that depend very weakly on cut size, c. Furthermore, these develop long longitudinal cracks from which catastrophic rupture initiates. With larger cuts, strength decreases more rapidly with increasing c, there is less longitudinal crack growth, and rupture initiates near the original cut tip. In contrast, the strength of a highly crosslinked vulcanizate is sensitive to small cuts and test pieces exhibit minimal longitudinal cracking before failure.

Uncured Properties of Silica Filled ENR Compounds at High Temperature Curing

2014 ◽  
Vol 974 ◽  
pp. 102-106
Author(s):  
Mazlina Mustapha Kamal ◽  
Muhammad Zahid Zakaria
Keyword(s):  
High Temperature ◽  
Carbon Black ◽  
Natural Rubber ◽  
Physical Properties ◽  
Crosslink Density ◽  
Rolling Resistance ◽  
Curing Temperature ◽  
Rubber Mixture ◽  
Silica Filler ◽  
Work Effect

Rubber reinforcement in general depends on the type of filler used in the rubber mixture. Instead of carbon black, Silica filler has been widely accepted in tyre making due to its low rolling resistance property. In recent years, there is a trend in using higher curing temperature in order to improve productivity of vulcanisation line without drawbacks in the performance of tyres. In this work, effect of vulcanisation temperature based on the silica filled ENR curing behaviour was studied. Results indicate that time-dependant reversion behaviour of ENR was similar to that of unmodified Natural Rubber. The physical properties slowly deteriorated as the curing temperature approached 180°C which related to low crosslink density. Carbon Black filled ENR compound was used as a comparison.

Modeling the Hardness and Mechanical Properties of Moulded Natural Rubber Pad

2017 ◽  
Vol 890 ◽  
pp. 54-58
Author(s):  
Bryan B. Pajarito ◽  
Mara Angelika E. Quizon ◽  
Rofel Anne L. Marquez ◽  
Patricia Bianca C. Bermio
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Fractional Factorial Design ◽  
Empirical Models ◽  
Fractional Factorial ◽  
Paraffin Wax ◽  
Compression Stress ◽  
Tetramethylthiuram Disulfide ◽  
Compression Properties ◽  
Good Agreement

The Shore A hardness, tensile stress at specified elongation (100, 200, and 300%), and compression stress at given strain (20 and 40%) of moulded natural rubber pads were modeled as function of ingredient proportions. Nine ingredients of the rubber pad were chosen as factors and varied at two levels of proportions. A 29-5 fractional factorial design of experiment was utilized during rubber compounding. Results show hardness of rubber pads is significantly increased when proportions of carbon black, tetramethylthiuram disulfide (TMTD), and stearic acid are increased in the formulations; hardness is decreased when process oil, paraffin wax, and antidegradant are increased. The same effect of carbon black, process oil, paraffin wax, and TMTD is observed on tensile properties of rubber pads. Compression properties are improved when carbon black, zinc oxide, and antidegradant are increased; properties are lowered when process oil and paraffin wax are increased. Analysis of variance shows the variation of response with ingredient proportion is significantly linear. The derived empirical models show good agreement with experimental data.

Mechanisms Involved in the Recycling of NR and EPDM

1999 ◽  
Vol 72 (4) ◽  
pp. 731-740 ◽  
Author(s):  
M. A. L. Verbruggen ◽  
L. van der Does ◽  
J. W. M. Noordermeer ◽  
M. van Duin ◽  
H. J. Manuel
Keyword(s):  
Natural Rubber ◽  
Crosslink Density ◽  
Main Chain ◽  
Chain Scission ◽  
Ethylene Propylene ◽  
Temperature Range ◽  
Lower Reactivity ◽  
Ethylene Propylene Diene Rubber ◽  
Diene Rubber ◽  
Crosslink Densities

Abstract The thermochemical recycling of natural rubber (NR) and ethylene-propylene-diene rubber (EPDM) vulcanizates with disulfides was studied. NR sulfur vulcanizates were completely plasticized when heated with diphenyldisulfide at 200 °C. It could be concluded that both main chain scission and crosslink scission caused the network breakdown. NR peroxide vulcanizates were less reactive towards disulfide at 200 °C, and only reacted through main chain scission. For EPDM a temperature range of 200–275 °C was studied. In the presence of diphenyldisulfide at 200 °C there was almost no devulcanization of EPDM sulfur vulcanizates, and at 225 and 250 °C there was only slightly more devulcanization. A decrease in crosslink density of 90% was found when 2×10−4 mol diphenyldisulfide/cm3 vulcanizate was added and the EPDM sulfur vulcanizates were heated to 275 °C. EPDM peroxide vulcanizates showed a decrease in crosslink density of ca. 40% under the same conditions. The lower reactivity of EPDM towards disulfide compared with NR is the result of higher crosslink densities, the presence of a higher percentage of more stable monosulfidic crosslinks and the fact that EPDM is less apt to main chain scission relative to NR.

A 139La NMR study of the interactions between the La(III) cation and D-ribose in aqueous solution

1994 ◽  
Vol 72 (7) ◽  
pp. 1753-1757 ◽  
Author(s):  
Zhigang Chen ◽  
Nicole Morel-Desrosiers ◽  
Jean-Pierre Morel ◽  
Christian Detellier
Keyword(s):  
Aqueous Solution ◽  
Nmr Spectroscopy ◽  
Chemical Shift ◽  
Stability Constant ◽  
Chemical Shifts ◽  
Similar Treatment ◽  
Calorimetric Measurements ◽  
Nmr Study ◽  
The Stability ◽  
Good Agreement

The interactions of the La(III) cation with D-ribose and with D-arabinose in aqueous solution were investigated by 139La NMR spectroscopy. In the case of D-ribose, the formation of a La(III)-sugar complex was indicated by variations of the 139La chemical shift and linewidth with an increase of the sugar concentration in solution. In contrast, the complexation of La(III) by arabinose is very weak and almost undetectable by 139La NMR. On the basis of a 1:1 stoichiometry, the stability constant for the complex of La(III) with D-ribose was calculated from the observed 139La chemical shift values. A similar treatment was done for the viscosity corrected 139La linewidths using arabinose as an uninteractive reference. The stability constants, K, obtained independently from 139La chemical shifts and linewidths are in good agreement, 2.8 ± 0.5 and 2.2 ± 0.6 M−1 respectively at 299.0 ± 0.5 K. The thermodynamic parameters for the complexation of La(III) by D-ribose could also be obtained: ΔH0 = −12 ± 2 kJ mol−1, and ΔS0 = −31 ± 5 J K−1 mol−1. These values are in very good agreement with those obtained by calorimetric measurements.

Benzothiazyl Disulfide-Accelerated Vulcanization of Carbon Black Loaded Natural Rubber

1963 ◽  
Vol 36 (3) ◽  
pp. 863-874
Author(s):  
M. L. Studebaker ◽  
L. G. Nabors
Keyword(s):  
Carbon Black ◽  
Surface Chemistry ◽  
Natural Rubber ◽  
Surface Area ◽  
Crosslink Density ◽  
Lithium Aluminum Hydride ◽  
Analytical Procedure ◽  
Aluminum Hydride ◽  
Lithium Aluminum ◽  
Mercaptan Sulfur

Abstract Sulfur group analyses of reinforced MBTS accelerated vulcanizates reveal chemical differences which can be related to the surface chemistry of the carbon blacks. The analytical procedure is based on the treatment of the vulcanizate with lithium aluminum hydride followed by potentiometric titration of sulfide and mercaptan sulfur. The polysulfide crosslink density and the values of x in the R—S—Sx—S—R polysulfides are dependent upon the quinone content of the carbon black. Both the quinone content and the surface area of a carbon black appear to determine its influence on the disappearance of free sulfur and the apparent crosslinking of the vulcanizate.

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