Gel Formation in the Mastication of Natural Rubber, and Its Influence on Vulcanizate Strength

1960 ◽  
Vol 33 (4) ◽  
pp. 940-941 ◽  
Author(s):  
B. A. Dogadkin ◽  
V. N. Kuleznev
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Insoluble Fraction ◽  
Gel Formation ◽  
Spatial Structures ◽  
Molecular Weights ◽  
Mechanical Dispersion ◽  
Major Significance ◽  
The Common ◽  
Maximum Content

Abstract Angier and Watson observed formation of spatial structures (gels) in neoprene rubber, certain SBR fractions, and butadiene-acrylonitrile rubber, under the influence of powerful shearing forces during treatment in a specially designed scroll-type masticator. This gel formation was considered to be a specific characteristic of synthetic rubbers ; no one has reported gel formation in the mastication of natural rubber (NR). In our experiments an insoluble gel was formed in NR. Weighed samples of extracted smoked sheet were masticated in an argon atmosphere containing not more than 0.05% oxygen, on specially designed rolls, with 0.12 mm gap between the rolls cooled intensive with water. The formation of an insoluble fraction (gel) at the early stages of mastication was established in repeated experiments. Its maximum content (after 10 minutes of mastication) reaches 20%, and further milling results in mechanical dispersion of the gel fraction, so that after 60 minutes of mastication the rubber is again completely soluble in the common solvents. However, the masticated rubber contains formations branched to such an extent that most of them (∼80%) are precipitated from octane solution by centrifugation at 12,000 rpm for an hour. Molecular weight determinations, based on changes in the light scattering of the solutions at an angle of 90°, showed that the molecular weights of the sol fractions of the masticated samples increase during mastication, reaching 2,500,000 after 60 minutes. The true molecular weight of the particles is apparently of major significance, as a correction for the asymmetry of the scattering particles was not applied.

Relation between Molecular Weights and Physical Properties of Rubber Fractions

1941 ◽  
Vol 14 (3) ◽  
pp. 580-589 ◽  
Author(s):  
G. Gee ◽  
L. R. G. Treloar
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Physical Properties ◽  
High Molecular Weight ◽  
Elastic Properties ◽  
Elastic Material ◽  
Experimental Results ◽  
Molecular Weights ◽  
High Elasticity ◽  
Latex Rubber

Abstract As high elasticity is a property possessed only by substances of high molecular weight, it is of interest to enquire into the relation between the elastic properties of a highly elastic material such as rubber and its molecular weight. An investigation on these lines has been made possible through the work of Bloomfield and Farmer, who have succeeded in separating natural rubber into fractions having different average molecular weights. The more important physical properties of these fractions have been examined with the object of determining which of the properties are dependent on molecular weight and which are not. Fairly extensive observations were made on the fractions from latex rubber referred to as Nos. 2, 3 and 4 by Bloomfield and Farmer, and some less extensive observations were carried out on the less oxygenated portion of fraction No. 1 obtained from crepe rubber (called hereafter 1b) . Before considering these experimental results, and their relation to the molecular weights of the fractions, it will be necessary to refer briefly to the methods used for the molecular-weight determinations, and to discuss the significance of the figures obtained.

Temperatures of Vitrification and Fluidity of Natural Rubber of Different Molecular Weights

1956 ◽  
Vol 29 (1) ◽  
pp. 95-98
Author(s):  
A. Tager ◽  
M. Iovlova ◽  
T. Kantor ◽  
L. Muzheva
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Vitrification Temperature ◽  
Molecular Weights

Abstract The vitrification temperature of natural rubbers does not change with change of molecular weight, whereas the higher the molecular weight of the rubber, the higher is its fluidity temperature.

scholarly journals Microinjection of ubiquitin: intracellular distribution and metabolism in HeLa cells maintained under normal physiological conditions.

1987 ◽  
Vol 104 (3) ◽  
pp. 537-546 ◽  
Author(s):  
N Carlson ◽  
M Rechsteiner
Keyword(s):  
Molecular Weight ◽  
Protein Synthesis ◽  
Size Distribution ◽  
High Molecular Weight ◽  
Hela Cells ◽  
Insoluble Fraction ◽  
Nuclear Fraction ◽  
Molecular Weights ◽  
Differential Sedimentation ◽  
Triton X

Radioiodinated ubiquitin was introduced into HeLa cells by erythrocyte-mediated microinjection. Subsequent electrophoretic analyses revealed that the injected ubiquitin molecules were rapidly conjugated to HeLa proteins. At equilibrium, 10% of the injected ubiquitin was conjugated to histones and 40% was distributed among conjugates of higher molecular weight. Although the remaining ubiquitin molecules appeared to be unconjugated, the free pool of ubiquitin decreased by one-third and additional conjugates were present when electrophoresis was performed at low temperature under nonreducing conditions. Molecular weights of these labile conjugates suggest that they are ubiquitin adducts in thiolester linkage to activating enzymes. Despite the fairly rapid degradation of injected ubiquitin (t1/2 approximately 10-20 h), the size distribution of ubiquitin conjugates within interphase HeLa cells remained constant for at least 24 h after injection. The intracellular locations of ubiquitin and ubiquitin conjugates were determined by autoradiography, by differential sedimentation of subcellular fractions in sucrose, and by extraction of injected cells with buffer containing Triton X-100. Free ubiquitin was found mostly in the cytosolic or Triton X-100-soluble fractions. As expected, histone conjugates were located predominately in the nuclear fraction and exclusively in the Triton X-100-insoluble fraction. Although high molecular weight conjugates were enriched in the Triton X-100-insoluble fraction, their size distribution was similar to that of soluble conjugates. When injected HeLa cells were exposed to cycloheximide to inhibit protein synthesis, the size distribution of ubiquitin conjugates was similar to that found in untreated cells. Moreover, high molecular weight conjugates decreased less than 20% after inhibition of protein synthesis. These results indicate that most ubiquitin conjugates are not newly synthesized proteins which have been marked for destruction.

The Structure of Neoprene. I. The Molecular-Weight Distribution of Neoprene Type GN

1949 ◽  
Vol 22 (3) ◽  
pp. 680-689
Author(s):  
W. E. Mochel ◽  
J. B. Nichols ◽  
C. J. Mighton
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Osmotic Pressure ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Distribution Curve ◽  
Pressure Measurements ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Good Agreement

Abstract Polychloroprene rubber (Neoprene Type GN) was fractionated by partial precipitation from dilute solution in benzene and the fractions were examined both osmotically and viscometrically in benzene solutions. The molecular-weight distribution curve for Neoprene Type GN based on osmotic pressure measurements shows a pronounced maximum at 100,000, but has a long extension to molecular weights of over one million, indicating the presence of branched or cross-linked material which is still soluble. The uniformity is somewhat less than that of sol natural rubber, while in shape the Neoprene distribution curve resembles more closely that of peptized natural rubber than fresh sol rubber. Observed variations in the slopes of the π/c vs. c and the ηsp/c vs. c curves also indicate the presence in solution of complex, branched and (or) cross-linked molecules. Calibration of the intrinsic viscosity-molecular weight relationship by osmotic pressure measurements gave good agreement with the equation: [η]=KMa, where K=1.46×10−4 and a=0.73.

Gel Permeation Chromatography of Natural Rubber

1972 ◽  
Vol 45 (1) ◽  
pp. 346-358 ◽  
Author(s):  
A. Subramaniam
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Weight Distribution ◽  
Hevea Brasiliensis ◽  
Distribution Curve ◽  
Gel Permeation Chromatography ◽  
Bimodal Distribution ◽  
Fractional Precipitation ◽  
Molecular Weights ◽  
Gel Permeation

Abstract The Waters Model 200 Gel Permeation Chromatograph has been used to study the molecular weight distribution of natural rubber. The cumulative weight distribution curve of synthetic cis-polyisoprene from the GPC method showed fair agreement with the distribution obtained by fractional precipitation. For natural rubber the agreement was not so good. Natural rubber samples from six clones of Hevea Brasiliensis were examined with the GPC. Differences were observed in their distributions. Five clones showed a distinct bimodal distribution. The weight and number average molecular weights from the GPC were found to be too low. Some possible reasons for this have been suggested.

Mastication of Elastomers I. Natural Rubber in Nitrogen

1962 ◽  
Vol 35 (4) ◽  
pp. 896-905 ◽  
Author(s):  
G. M. Bristow
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Gel Formation ◽  
Theoretical Expectation

Abstract In accordance with theoretical expectation, the mastication of acetone extracted natural rubber in the absence of radical acceptors leads to gel formation. Unextracted rubbers undergo no gelation. The extent of gelation is determined almost entirely by the initial molecular weight of the rubber: under the conditions studied here rubbers of initial molecular weight less than ca. 3×105 do not gel on mastication. Only very small quantities of radical acceptors are required to repress gelation suggesting that acetone extracted rubber still contains appreciable quantities of such materials.

Determination of the Molecular Weight of Rubber and Polystyrene by the Methods of Light Scattering and Osmometry

1950 ◽  
Vol 23 (1) ◽  
pp. 89-97
Author(s):  
B. Dogadkin ◽  
I. Soboleva ◽  
M. Arkhangel'skaya
Keyword(s):  
Molecular Weight ◽  
Light Scattering ◽  
Natural Rubber ◽  
Satisfactory Agreement ◽  
Molecular Weights ◽  
Molecular Compounds

Abstract 1. Experiments on the determination of the molecular weights of natural rubber and other high-molecular compounds by the methods of light scattering and osmometry are reported. 2. An osmometer of new design, suitable for determining molecular weights, is described. 3. It is shown that the method of light scattering yields values for molecular weights which are in satisfactory agreement with those obtained by the method of osmometry.

scholarly journals Use of Rubber Process Analyzer for Characterizing the Molecular Weight Parameters of Natural Rubber

2015 ◽  
Vol 2015 ◽  
pp. 1-6 ◽  
Author(s):  
Tianming Gao ◽  
Ruihong Xie ◽  
Linghong Zhang ◽  
Hongxing Gui ◽  
Maofang Huang
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Milling Time ◽  
Laser Light ◽  
Average Molecular Weight ◽  
Gel Permeation Chromatography ◽  
Sweep Frequency ◽  
Weight Average Molecular Weight ◽  
Molecular Weights ◽  
Strain Sweep

The aim of this work is to introduce a simple and rapid method for characterizing the molecular weight parameters and other molecular structure parameters of natural rubber (NR) using a rubber process analyzer (RPA). In this work, NR of different molecular weights was prepared by milling. Molecular weight parameters were measured by gel permeation chromatography coupled with laser light scattering (GPC-LLS) for comparison with RPA results. It was verified that increasing of milling time leads to a decrease of the number-average molecular weight (M-n), weight-average molecular weight (M-w), and molecular weight distribution (MWD). The dynamic and rheological properties were evaluated on RPA by tests of strain sweep, frequency sweep, and stress relaxation. These results were used to characterize the average molecular weight, MWD, and viscosity of NR and were found to agree with those from GPC-LLS. This convenient and rapid technology for characterizing NR molecular weight parameters would be especially useful in the elastomer industry.

Investigation by HPLC of the Catabolism of Recombinant Tissue Plasminogen Activator in the Rat

1988 ◽  
Vol 60 (01) ◽  
pp. 107-112 ◽  
Author(s):  
Roy Harris ◽  
Louis Garcia Frade ◽  
Lesley J Creighton ◽  
Paul S Gascoine ◽  
Maher M Alexandroni ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Plasminogen Activator ◽  
Tissue Plasminogen Activator ◽  
Half Life ◽  
Recombinant Tissue Plasminogen Activator ◽  
Rat Plasma ◽  
High Molecular Weight Complex ◽  
Molecular Weights ◽  
Major Activity ◽  
Tissue Plasminogen

SummaryThe catabolism of recombinant tissue plasminogen activator (rt-PA) was investigated after injection of radiolabelled material into rats. Both Iodogen and Chloramine T iodination procedures yielded similar biological activity loss in the resultant labelled rt-PA and had half lives in the rat circulation of 1 and 3 min respectively. Complex formation of rt-PA was investigated by HPLC gel exclusion (TSK G3000 SW) fractionation of rat plasma samples taken 1-2 min after 125I-rt-PA injection. A series of radiolabelled complexes of varying molecular weights were found. However, 60% of the counts were associated with a single large molecular weight complex (350–500 kDa) which was undetectable by immunologically based assays (ELISA and BIA) and showed only low activity with a functional promoter-type t-PA assay. Two major activity peaks in the HPLC fractions were associated with Tree t-PA and a complex having a molecular weight of ̴ 180 kDa. HPLC fractionation to produce these three peaks at various timed intervals after injection of 125I-rt-PA showed each to have a similar initial rate half life in the rat circulation of 4-5 min. The function of these complexes as yet is unclear but since a high proportion of rt-PA is associated with a high molecular weight complex with a short half life in the rat, we suggest that the formation of this complex may be a mechanism by which t-PA activity is initially regulated and finally cleared from the rat circulation.

Permeability Enhancing and Chemotactic Activities of Lower Molecular Weight Degradation Products of Human Fibrinogen

1981 ◽  
Vol 45 (01) ◽  
pp. 090-094 ◽  
Author(s):  
Katsuo Sueishi ◽  
Shigeru Nanno ◽  
Kenzo Tanaka
Keyword(s):  
Molecular Weight ◽  
Degradation Products ◽  
Electron Microscopic Observation ◽  
Chemotactic Activity ◽  
Lower Molecular Weight ◽  
Electron Microscopic ◽  
Human Fibrinogen ◽  
Rabbit Skin ◽  
Molecular Weights ◽  
Active Fragments

SummaryFibrinogen degradation products were investigated for leukocyte chemotactic activity and for enhancement of vascular permeability. Both activities increased progressively with plasmin digestion of fibrinogen. Active fragments were partially purified from 24 hr-plasmin digests. Molecular weights of the permeability increasing and chemotactic activity fractions were 25,000-15,000 and 25,000 respectively. Both fractions had much higher activities than the fragment X, Y, D or E. Electron microscopic observation of the small blood vessels in rabbit skin correlated increased permeability with the formation of characteristic gaps between adjoining endothelial cells and their contraction.These findings suggest that lower molecular weight degradation products of fibrinogen may be influential in contributing to granulocytic infiltration and enhanced permeability in lesions characterized by deposits of fibrin and/or fibrinogen.

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