Effect of Primary Molecular Weight on the Dynamic Properties of Cured Rubber

1959 ◽  
Vol 32 (3) ◽  
pp. 651-661
Author(s):  
E. V. Kuvshinskiĭ ◽  
M. M. Fomicheva
Keyword(s):  
Molecular Weight ◽  
Dynamic Modulus ◽  
Room Temperature ◽  
Dynamic Properties ◽  
Molecular Weights ◽  
Vulcanized Rubber ◽  
Equilibrium Modulus ◽  
Modulus Of Resilience ◽  
Molecular Weight Fractions ◽  
Butadiene Styrene

Abstract 1. Studied were the moduli of resilience and rebound elasticity of the vulcanized rubbers made from fractions of butadiene-styrene rubber “SKS-30-A” at temperatures of 20, 60, and 100° C in the region of molecular weights from 45,000 to 620,000 with various degrees of vulcanization (with variation in the pseudoequilibrium modulus from 5 to 70 kg/cm2). 2. The dynamic modulus of resilience is little dependent on the molecular weight of the original rubber both at room temperature and at higher temperatures. 3. At higher temperatures the elasticity of vulcanized rubber is mainly determined by the degree of vulcanization, the measure of which is the pseudo-equilibrium modulus, and is little dependent on the initial molecular weight. At low temperatures (20° C) elasticity increases with the degree of vulcanization, but it increases at different rates for vulcanized rubbers made from fractions with different molecular weights. At 20° C the increase in the degree of vulcanization increases the elasticity of vulcanized rubbers made from low-molecular fractions (45,000) to a lower degree than of those made from high molecular weight fractions (above 133,000). 4. The value of the maximum elasticity of vulcanized rubbers obtained from rubbers of the same molecular weight is not dependent on the type of accelerator used.

scholarly journals α-Crystallin. The isolation and characterization of distinct macromolecular fractions

1971 ◽  
Vol 124 (2) ◽  
pp. 337-343 ◽  
Author(s):  
Abraham Spector ◽  
Lu-Ku Li ◽  
Robert C. Augusteyn ◽  
Arthur Schneider ◽  
Thomas Freund
Keyword(s):  
Molecular Weight ◽  
Amino Acid ◽  
Gel Filtration ◽  
Deae Cellulose ◽  
Chemical Difference ◽  
Molecular Weights ◽  
Isolation And Characterization ◽  
Different Populations ◽  
Molecular Weight Fractions

α-Crystallin was isolated from calf lens periphery by chromatography on DEAE-cellulose and gel filtration. Three distinct populations of macromolecules have been isolated with molecular weights in the ranges approx. 6×105−9×105, 0.9×106−4×106and greater than 10×106. The concentration of macromolecules at the molecular-weight limits of a population are very low. The members of the different populations do not appear to be in equilibrium with each other. Further, in those molecular-weight fractions investigated, no equilibrium between members of the same population was observed. The population of lowest molecular weight comprises 65–75% of the total material. The amino acid and subunit composition of the different-sized fractions appear very similar, if not identical. The only chemical difference observed between the fractions is the presence of significant amounts of sugar in the higher-molecular-weight fractions. Subunit molecular weights of approx. 19.5×103and 22.5×103were observed for all α-crystallin fractions.

Nonlinearity in the Dynamic Properties of Vulcanized Rubber Compounds

1954 ◽  
Vol 27 (1) ◽  
pp. 209-222 ◽  
Author(s):  
W. P. Fletcher ◽  
A. N. Gent
Keyword(s):  
Simple Shear ◽  
Dynamic Modulus ◽  
Dynamic Properties ◽  
Mechanical Vibration ◽  
Frequency Range ◽  
Vulcanized Rubber ◽  
Rubber Compounds ◽  
Chemical Combination ◽  
Wide Range ◽  
Static Shear

Abstract Measurements are described of the dynamic properties of rubber, loaded with various amounts and types of filler, when subjected to mechanical vibration in simple shear at amplitudes from 0 to 3 per cent shear in the frequency range 20 to 120 c.p.s. The decrease of dynamic modulus with increasing amplitude is shown, for a wide range of filler types and concentrations, to be determined by the amount of stiffening produced by the filler. This relationship is not influenced by variations in the vulcanizing ingredients, reasonable variations in state of vulcanization, addition of softener, or imposition of static shear strain. Rubber compounds stiffened by mixture with, or chemical combination of, other polymers exhibit a smaller order of nonlinearity than that described above and also exhibit much lower hysteresis values within the amplitude range 0 to 3 per cent shear.

Dependence of Tack Strength on Molecular Properties

1959 ◽  
Vol 32 (1) ◽  
pp. 48-66 ◽  
Author(s):  
W. G. Forbes ◽  
L. A. McLeod
Keyword(s):  
Molecular Weight ◽  
Shear Viscosity ◽  
Catalyst System ◽  
Chain Entanglement ◽  
Molecular Weights ◽  
Styrene Copolymers ◽  
The Difference ◽  
Catalyst Systems ◽  
Time Required ◽  
Butadiene Styrene

Abstract A method has been developed for the measurement of the tack strength of fresh and reproducibly smooth rubber surfaces. Using this method the tack strength of natural rubber is shown to be independent of polymer purity, and, to a large extent, Mooney viscosity, intrinsic viscosity, gel content and molecular weight distribution. The relative tack strengths of polyisoprenes of different molecular weights prepared in different catalyst systems are measured. The results are discussed in terms of microstructure. A study of the tack strength of oil-extended butadiene-styrene copolymers indicates that relative tack strength is related to the shear viscosity of the bulk polymer. Measurements of relative tack strength on Alfin and free radical butadiene-styrene copolymers, butyl, brominated butyl and butadiene-acrylonitrile copolymers confirm the inportance of shear viscosity in controlling tack strength. Choice of catalyst system and temperature of polymerization cause the largest variation in polymer viscosity. The contact time required for the relative tack strength to become unity is shown to be inversely dependent upon the value of the relative tack strength itself. Shear viscosity measurements are given for six classes of polymer and the values shown to correlate with relative tack strength. It is postulated that molecular weight (and probably also chain entanglement) is the controlling variable. The bond strength between two different uncured polymers is shown to depend upon the difference in cohesive energy densities of the two polymers.

Effect of Initial Molecular Weight of a Rubber on the Strength and Fatigue of Its Vulcanizates

1957 ◽  
Vol 30 (1) ◽  
pp. 54-60
Author(s):  
G. M. Bartenev ◽  
A. S. Novikov ◽  
F. A. Galil-Ogly
Keyword(s):  
Molecular Weight ◽  
Dynamic Testing ◽  
Three Dimensional ◽  
Maximum Load ◽  
Testing Conditions ◽  
Maximum Deformation ◽  
Molecular Weights ◽  
Permanent Set ◽  
Dimensional Network ◽  
Equilibrium Modulus

Abstract (1) With decrease of the original molecular weight of rubber, there is a parallel decrease of the durability of its vulcanizates when they contain the same percentage of combined sulfur. On the other hand, this decrease of durability with decrease of the original molecular weight is only slight for vulcanizates having the same equilibrium modulus, i.e., the same density of crosslinks in the three-dimensional network. (2) In dynamic testing which involves repeated stretching, the durability depends on the testing conditions when the vulcanizates contain the same percentage of combined sulfur and at the same time when either the original molecular weight of the rubber is low or the equilibrium modulus is small. On the contrary, when the original molecular weight or the modulus is high, the durability does not depend on the testing conditions. When vulcanizates have the same equilibrium modulus, their durability depends on the original molecular weight. In this latter case the durability increases with increase of the molecular weight, independent of the testing conditions (given maximum load, given maximum deformation, etc.), and reaches a practically constant value at high molecular weights. (3) The fundamental influence of the original molecular weight on the strength and dynamic durability of vulcanizates containing the same percentage of combined sulfur is manifest in the retardation of the formation of a spatial network in low-molecular rubbers when vulcanized. With rubber of low original molecular weight, vulcanization leads to the formation of a thin space network and consequently a large number of molecular chain ends outside the network. For this reason, vulcanizates of low-molecular rubbers when tested are characterized by high permanent set.

A Method for Measuring the Self-Cementing Characteristics of Fly Ash Pastes

1987 ◽  
Vol 113 ◽  
Author(s):  
R. I. A. Malek ◽  
D. M. Roy
Keyword(s):  
Molecular Weight ◽  
Fly Ash ◽  
Liquid Chromatograph ◽  
Cement Pastes ◽  
Molecular Weights ◽  
Matching Process ◽  
Chromatographic Peaks ◽  
Liquid Chromatographic ◽  
Derivatives Of ◽  
Molecular Weight Fractions

SUMMARYThe development of an improved method of trimethylsilylation [1] made possible the assessment of different polysilicate fractions in hydrated cement pastes, as a means of structural characterization. Several laboratories have presented various gas-liquid chromatographic data on the polysilicate derivatives of C-S-H [2–5]. Identification of the different molecular weight fractions has been made, in most laboratories, by matching the gasliquid chromatographic peaks with the gel permeation chromatographic peaks. The success of this matching process is always dependent on type of instruments, length of columns and temperature range.In the present investigation, a mass spectrometer, in direct contact with the gas-liquid chromatograph, was used to identify the molecular weight of each of the fractions separated from the chromatograph. The technique was applied to determine the molecular weights and abundances of different polysilicate species in hydrated fly ash pastes.

Effects of Molecular Structure on Physical Properties of Butyl Rubber

1946 ◽  
Vol 19 (3) ◽  
pp. 552-598 ◽  
Author(s):  
Paul J. Flory
Keyword(s):  
Molecular Structure ◽  
Molecular Weight ◽  
Physical Properties ◽  
Small Samples ◽  
Rational Approach ◽  
Complete Evaluation ◽  
Testing Procedures ◽  
Molecular Weights ◽  
Vulcanized Rubber ◽  
Structural Variables

Abstract The investigation was undertaken in an attempt to establish the fundamental connections between the physical properties of a typical vulcanized rubberlike polymer and its chemical structure. The structural variables to be considered are the molecular weight of the “primary molecules” entering the vulcanizate, their molecular-weight distribution, and the concentration (or frequency) of cross-linkages introduced during vulcanization. The molecular weights of Butyl rubbers were determined by previously established procedures ; the effects of molecular-weight heterogeneity were suppressed by careful fractionation from very dilute solution. An indirect method, based on the theory of gelation and on the observation of critical molecular weight for incipient gelation (partial insolubility) in “vulcanisates” formed when the cross-linking capacity is fixed, was employed to determine the frequency of occurrence of cross-linked units—a quantity not hitherto evaluated in a vulcanized rubber. In representative pure-gum vulcanizates of Butyl the molecular weight per cross-linked unit ranges from about 35,000 to 20,000, depending (inversely) on the diolefin content of the raw rubber. Micro compounding and testing procedures have been devised for evaluating the necessarily small samples ob- tained in fractionation. Complete evaluation of tensile strength, stress-strain characteristics, swelling in solvents, and creep rate can be obtained with as little as 3 grams of rubber. Results are no less reproducible than those obtained with conventional procedures requiring 50 grams or more. A number of rela- tionships between vulcanizate structure and physical properties have been established. The feasibility of a rational approach to the interpretation of properties of rubber vulcanizates in terms of molecular structure has been demonstrated.

Molecular Weight Distribution of Polystyrene and of Butadiene-Styrene Copolymers Prepared in Emulsion Systems

1970 ◽  
Vol 43 (6) ◽  
pp. 1424-1438
Author(s):  
C. A. Uraneck ◽  
J. E. Burleigh
Keyword(s):  
Molecular Weight ◽  
Molecular Weight Distribution ◽  
Weight Distribution ◽  
Homologous Series ◽  
Degree Of Branching ◽  
Styrene Copolymers ◽  
Divinyl Benzene ◽  
Emulsion Systems ◽  
Molecular Weight Fractions ◽  
Butadiene Styrene

Abstract Polystyrene and butadiene—styrene copolymers (SBR) were parepared in emulsion systems with a homologous series of commercial mercaptan modifiers. The molecular weight distribution (MWD) of the sets of polymers changed in a consistant manner when the regulating index of the mercaptan was relatively low. However the shape of the MWD curves appeared distorted in comparison to theoretical curves when the modifier depleted rapidly and when divinyl-benzene was present in the system. The divergence from the theoretical curve is attributed to a higher degree of branching in the high molecular weight fractions. Differences in MWD of SBR made with n- and tert-dodecyl mercaptans was marked. Notable differences were also found for SBR 1500 samples from the industry at random, but only slight differences were seen in a set of SBR 1503 samples. This study shows how the MWD of polymers prepared in emulsions can be varied simply by use of modifiers with different regulating indexes.

Effect of Vulcanization on the Dynamic Properties of Rubber

1959 ◽  
Vol 32 (3) ◽  
pp. 662-667 ◽  
Author(s):  
E. V. Kuvshinskiĭ ◽  
E. A. Sidorovich
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Elastic Modulus ◽  
Crosslink Density ◽  
Mechanical Characteristics ◽  
Dynamic Properties ◽  
Thermostatic Control ◽  
Gap Series ◽  
Equilibrium Modulus ◽  
Butadiene Styrene

Abstract It is a known fact that the mechanical properties of rubber depend essentially upon the density (i.e., the crosslink density) of the vulcanization network. The dependence of the “equilibrium” (statistical) modulus of elasticity upon the concentration of crosslinks as well as the dependence of the tensile strength —has been studied in a series of investigations. In contrast to this, analogous investigations of the dynamic mechanical characteristics are practically nonexistent. We have undertaken our present work with the hope of filling this gap. Series of gum compounds were prepared from natural (smoked sheet) and synthetic polyisoprene (SKI), sodium butadiene (SKB), butadiene-styrene (SKS-30A), and butadiene-nitrile (SKN-26) rubbers which varied in their degree of vulcanization. The percentage of sulfur and accelerator were varied as were the temperature and the time of vulcanization. The mechanical-dynamic characteristics of the rubber at a predetermined impact pressure—the rebound elasticity and the dynamic elastic modulus were studied with the pendulum elastometer KS over a temperature range of 20–100° C. The duration of the stress was .03/.05 second. We estimated the concentration of crosslinks in the rubber samples from the magnitude of the equilibrium modulus. In order to determine this characteristic, we compressed specimens which were 20 mm in height and 10 mm in diameter 15% and studied the relaxation of stress. The specimens were also tested on the pendulum elastometer. Heppler's consistometer operating on the lever weight principle, was adapted for our measurements. The experiments were conducted at 60° C, the thermostatic control being effected with the help of Heppler's ultrathermostat.

COMPOSITIONAL HETEROGENEITY OF BUTADIENE–ACRYLONITRILE COPOLYMERS PREPARED IN EMULSION AT 5°C

1951 ◽  
Vol 29 (3) ◽  
pp. 253-269 ◽  
Author(s):  
W. H. Embree ◽  
J. M. Mitchell ◽  
H. Leverne Williams
Keyword(s):  
Molecular Weight ◽  
Weight Distribution ◽  
Viscosity Data ◽  
Reactivity Ratios ◽  
Compositional Heterogeneity ◽  
Dilute Solution ◽  
Molecular Weights ◽  
Conventional Solution ◽  
Acrylonitrile Copolymers ◽  
Butadiene Styrene

The copolymerization of butadiene and acrylonitrile is very similar to the copolymerization of butadiene and styrene. Polymers predominantly butadiene may be studied by conventional solution techniques but the study of polymers rich in acrylonitrile requires improved solvents for these materials. Polymerization rates are greatest for monomer ratios approximating equal proportions. The mercaptan modifier disappears much more slowly than in the butadiene–styrene system, the regulating index approximating unity. The number average molecular weights calculated from the mercaptan disappearance curves indicate uniform polymer molecular weights to relatively high conversions after which there is a decrease. The viscosity data indicate a rise in viscosity with conversion, which effect is overcome for charges rich in acrylonitrile by the lessening of branching, the more rapid disappearance of mercaptan at high conversion, and the tendency of polymers containing over 50% acrylonitrile to show very low dilute solution viscosities in the solvents tested. Viscosity molecular weights have been calculated and estimates of the molecular weight distribution made. These distributions appear to be quite narrow and the usual broadening at higher conversions is prevented by the increased modifier consumption and increased vinyl content of the polymer prepared with 50 parts acrylonitrile in the charge. The bound acrylonitrile has been determined at various conversions and the reactivity ratios have been found to be r1 = 0.28 and r2 = 0.02 for emulsions and r1 = 0.18 and r2 = 0.03 for oil phase portion only. Q is 0.74 and e is 1.47 as calculated by the Alfrey–Price equations.

Effect of the Molecular Weight of Rubber on the Kinetics of Vulcanization and on the Formation of a Spatial Network

1954 ◽  
Vol 27 (4) ◽  
pp. 925-929 ◽  
Author(s):  
A. S. Novikov ◽  
G. M. Bartenev ◽  
F. A. Galil-Ogly
Keyword(s):  
Molecular Weight ◽  
Sodium Sulfide ◽  
Scientific Literature ◽  
Hydraulic Press ◽  
Butadiene Rubber ◽  
Spatial Network ◽  
Molecular Weights ◽  
Equilibrium Modulus ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization

Abstract From scientific literature it is known that the rate of vulcanization and the mechanical properties of rubbers depend on the value of the initial molecular weight of the rubber. However, the cause of the slow vulcanization of olw molecular rubbers and the effect of the molecular weight of the rubber on the formation of a spatial network and the structure of the vulcanizate remain unclear. In the present work the kinetics of vulcanization of separate fractions of butadiene rubber SKS-30A of molecular weight from 100,000 to 1,170,000 was studied by measurements of the equilibrium modulus and the proportion of combined sulfur. The SKS-30A rubber was divided into five fractions of molecular weights: I 1,170,000; II 700,000; III 500,000; IV 140,000; and V 100,000. The molecular weights were calculated from viscometric data according to the formula previously established for this rubber by the authors: [η]=2.96×10−4 M0.71. In order to keep the molecular weight of the rubber constant, sheets for vulcanization were prepared from a dispersion of the ingredients in a benzene-rubber solution. The composition of the mixture was the same for all the fractions, i.e., 100 parts by weight of rubber, 3 parts of sulfur, 1 part of mercapto-benzothiazole, 5 parts of zinc oxide, 2 parts of stearic acid, and 1 part of phenyl-β-naphthylamine. The sheets were vulcanized in a hydraulic press at 143° C for various periods. The amount of sulfur combined with the rubber was determined by Bolotnikov's method, specially adapted to small batches of vulcanizate. The rubber specimens, weighing 0.2–0.3 gram, were extracted in 50 cc. of sodium sulfide, and titrated with 0.01N iodine solution.

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