Vulcanized rubber, property stress-strain properties

ISO 37 1994 Rubber, vulcanized or thermoplastic - Determination of tensile stress-strain properties... 

ISO 7619-2 2004 Rubber, vulcanized or thermoplastic - Determination of indentation hardness - Part 2 IRHD pocket meter method ISO 7743 2004 Rubber, vulcanized or thermoplastic - Determination of compression stress-strain properties... 

The classical means for following vulcanization by physical methods is to vulcanize a series of sheets for increasing time intervals and then measure the stress strain properties of each and plot the results as a function of vulcanization time. A modification of this test generally called a rapid modulus test is widely used in the industry as a production control test. A single sample taken from a production batch of compounded rubber is vulcanized at a high temperature and its tensile modulus is measured. Temperatures as high as 380°F are used to reduce the vulcanization test time to only a few minutes. Any modulus value deviating from a predetermined acceptance limit indicates that the batch is defective and is to be rejected. 

ISO 37— Rubber, vulcanized or thermoplastic—Determination of ten.sile stress-strain properties (1994). 

ISO 37 Rubber, vulcanized or thermoplastic— Determination of tensile stress—strain properties... 

ISO 844 2001 Rigid cellular plastics - Determination of compression properties ISO 3386-1 1986 Polymeric materials, cellular flexible - Determination of stress-strain characteristics in compression - Part 1 Low-density materials ISO 3386-2 1997 Flexible cellular polymeric materials - Determination of stress-strain characteristics in compression - Part 2 High-density materials ISO 5893 2002 Rubber and plastics test equipment - Tensile, flexural and compression types (constant rate of traverse) - Specification ISO 7743 2004 Rubber, vulcanized or thermoplastic - Determination of compression stress-strain properties... 

Property Requirements of Vulcanized Rubber 2.6.1 Stress-strain Properties... 

This discovery culminated in the commercial production and the announcement (41) in 1965 of thermoplastic elastomers from block polymers of styrene and butadiene (S-B-S) and of styrene and isoprene (S-I-S). To rubber scientists and technologists the most outstanding property of S-B-S and S-I-S was the unvulcanized tensile strength compared to that of vulcanized NR and vulcanized SBR carbon black stocks. Stress-strain curves, to break, of these latter materials are compared to that of S-B-S in Figure 2. It was pointed out that the high strength of S-B-S must be due to physical crosslinks. 

The above picture of the network structure of vulcanized rubber is supported by -the success of the kinetic theory of rubberlike elasticity (see part 4, page 14) calculations based on this model agree well with experimental measurements of stress-strain curves and other properties (James and Guth, 1943 Flory, 1944). Excellent evidence that the swollen gel contains the same network as the unswollen rubber has been presented by Flory (1944, 1946), based on studies of butyl rubber. Using the network model, the number of cross-links in the structure can be calculated in three ways (o) from measurements of the proportions of insoluble (network) and soluble (unattached) material in samples of different initial molecular lengths (b) from the elastic modulus of the unswollen rubber (c) from the maximum amount of liquid imbibed by the gel when swollen in equilibrium with pure solvent. The results of these three calculations for butyl rubber samples were in good agreement. 

Elastomers are polymers with rubberlike properties. The word elastic refers to the ability of a material to return to its original dimensions when unloaded, and the term mer refers to the polymeric molecular make up in the word elastomer. Vulcanized rubber materials typically have more than 200% elongation in a tensile test and are capable of returning rapidly and forcibly to their original dimensions when load is removed. This elastic response is due to the three-dimensional cross-linked network molecular structure they have. An elastomer, on the other hand, typically has elongation rates of 100% or more and a significant amount of resilience. Resilience is represented by the area under the elastic portion of the stress-strain curve, and therefore, refers to a material s ability to undergo elastic deformations. 

Natural rubber displays elastic properties - the ability to return to its initial shape after initial stress is halted - which are remarkable in raw rubber but also when it is vulcanized (around 700% elongation at break) due to its ability to crystallize under strain (100% cis- and associative structure). Its properties are used in elastic bands but also in dipped items such as gloves. 

Elastomers are one of the most widely used industrial polymers. Historically, vulcanized natural rubbers have been used since their discovery in the 19th century. The elastic property of natural rubber, i.e. elongation up to several hundred percent with recovery of its initial state upon removal of the external stress is the characteristic property of this class of polymers. Rubbers are the only materials capable of reversible extension to strains of 6-700%. No other materials exhibit an increase in modulus with increase in temperature. 

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