Swollen rubber

It is also possible to estimate the cross-link density from the stress-strain data, using the statistical theory of rubber-like elasticity [47,58]. For a swollen rubber the relationship is... 

J. Prud homme, U. of Montreal, Que. Did you consider the possibility of studying swollen rubbers (vulcanized materials) to obtain better resolution ... 

Such techniques have been tried with solid propellants, but reproducible results depend on attaining complete binder-filler release and adequately measuring the binder sol fraction. Preliminary swelling studies to determine a solvent system and conditions which do not degrade the propellant are required. Common extraction techniques are used to determine the sol fraction. This determination is then applied as a correction when computing crosslink density. The force-deformation relationship for swollen rubbers is... 

Some materials might produce a unique failure surface providing measurements could be conducted under first stretch conditions in a state of equilibrium. Tschoegl (110), at this writing, is attempting to produce experimental surfaces by subjecting swollen rubbers to various multiaxial stress states. The swollen condition permits failure measurements at much reduced stress levels, and the time dependence of the material is essentially eliminated. Studies of this type will be extremely useful in establishing the foundations for extended efforts into failure of composite materials. 

Van der Hoff,B.M.E. The stress-strain relation of swollen rubbers. Polymer (London) 6,397-399(1965). 

Eq. (IV-9) as well as the stress-strain relation, which follows easily from Eq. (IV-10), lead to an upward curvature at large strains. Such an upward curvature, due to finite extensibility, is indeed found experimentally, as demonstrated in Figs. 23 and 24, taken from work of Mullins (128). In swollen rubbers the effect comes into play at an earlier stage because of the pre-stretching due to the swelling. 

Fig. 24. Mooney-Rivlin plots of extended and swollen rubbers. The upswing is again due to finite extensibility, which comes into play at an earlier stage the higher the swelling (lower curves) [Mullins 128)1...

The interaction between rubber and liquids. IX. The elastic behaviour of dry and swollen rubbers. Trans. Faraday Soc. 42, 585 (1946). 

Knibbe, D. E. Diffusion-controlled stress relaxation of swollen rubber-like networks, Rotterdam University Press 1968. 

The testing procedure of properties of elastomeric vulcanizates after immersion in organic liquids is common for both natural and synthetic rubbers. ASTM D171-66 [7] used for this purpose serves as a method for estimating the comparative ability of rubbers to withstand the effects of liquids by examination of the material after removal from the liquid. However proper testing of the physical properties on swollen rubber poses many problems. 

T2 = tensile strength of the swollen rubber specimen (in approximate units) based on original, unswollen cross-sectional area. 

Macroscopic Diffusion of Small Molecules in Swollen Rubbers... 

Studies of Network Density in Swollen Rubbers and Blends... 

Separate work on a Fourier transform (FT) NMR spectrometer revealed the presence of two peaks from the solvents from both within and outside the swollen gel [104], See below for a discussion of the origin of the NMR linewidths. The chemical shift of the olefinic peaks was found to shift down field with increasing crosslink density, and hence a modified method for determining H% was introduced. In this paper they also introduced the first 13C NMR measurements of swollen rubber blends, and again found a systematic increase in linewidth with increasing crosslink density. The higher resolution in the 13C spectrum compared with NMR allows the potential of more detailed information on rubber mixtures. 

Butadiene styrene Toluene 1. Abrasion followed by brushing. Grit or vapor blast or 280-grit emery cloth followed by solvent wipe. 2. Prime with butadiene styrene adhesive in an aliphatic solvent. 3. Etch surface for 1-5 min at RT following method 2 for natural rubber. Excess toluene results in swollen rubber. A 20-min drying time will restore the part to its original dimensions... 

NR and synthetic diene based elastomers are a very versatile material for grafting. Chain transfer grafting may be carried out by means of a functionalized monomer-initiator system in a rubber solution, in the latex phase, in swollen rubber or during vulcanization. The chain transfer can be accompanied in diene-based polymers by addition reactions involving both the starting radicals and growing polymer radicals [217]. 

If the objective of the experiment is to estimate the network chain density by the statistical theory, and if swelling is resorted to as a means for alleviating the above experimental difficulties, then the measurement of stresses becomes redundant the theory of equilibrium swelling of Flory and Rehner (127,128) makes an estimate of the desired network chain density possible with only the knowledge of the equilibrium swelling volume. The usual procedure is to calculate the volume fraction of polymer in the swollen rubber (ar) under the assumption that the filler does not swell. The Flory-Rehner theory then yields, for a network containing no sol fraction ... 

The osmotic pressure of the polystyrene solution is balanced by the elastic retractive forces of the more or less densely crosslinked rubber lamellae osmotic pressures in the swollen rubber particles are rather high because of the high positive virial coefficient of polystyrene in toluene (A2 = 5 X 10"4 mole cm3 g"2) (14). For SI = 10 (corresponding to c = 0.1 g X cm3) and M = 5 X 104, one... 

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