Use of χ As a Function of Volume Fraction of Rubber to Determine Crosslink Density by Swelling

Abstract

A technique is described allowing a relatively simple determination of χ as a function of vr from swelling in heptane. A good measure of the true νe of the cured elastomer at all values of vr was demonstrated by substituting this relationship for χ in the Flory-Rehner (F-R) equation. The relationship was established over a wide range of vr values by using samples that had the νe of the cured elastomer determined by tensile retraction (TR). Applying this function to samples treated using the thiol probe method of Campbell gave an improved measure of the types of crosslinks present in sulfur-cured stocks. An identical equation describing χ as a function of vr in heptane was obtained with NR, EPDM and SBR containing up to a 0.31 volume fraction of carbon black (CB) and other fillers. The presence of up to 10 % of clay, talc, silica, resins or metal oxides in the CB had no noticeable effect on the relationship measured. However, when the filler contained about 50% silica a distinctly different slope in the relationship was found. The percent S1, S2 and Sx distribution measured was contrasted between measurements made by 13C NMR, swelling with χ = constant or χ as a function of vr.

Microwave‐induced devulcanization for poly(ethylene–propylene–diene) recycling

“…The crosslink density ( v e ) was estimated by a swelling test in n ‐heptane with the Flory–Rehner equation 10 and the thiol probe method of Campbell. 11 The Flory–Rehner equation, as derived from rubber elasticity theory, is as follows: where v r is the equilibrium volume fraction of rubber in the swollen state, χ is the polymer–solvent interaction parameter, and V 0 is the molar volume of the solvent.…”

“…The value of χ was calculated with the following relation, obtained from the tensile retraction measurements: χ = a ·ln v r + b, where a and b are 0.2316 and 0.8604, respectively. 10 The values of v r were determined by the following equation: 10, 12 where d r and d s are the densities of the rubber and solvent, respectively; f sol is the weight fraction of soluble material; f fil is the initial weight fraction of the filler; W s is the weight of the swollen solvent; and W D is the weight of the dry sample. The procedure derived from the Campbell theory 11 consisted of two steps: a first chemical treatment with a solution of 2‐propanethiol and piperidine for 2 h at room temperature; this broke the polysulfidic (S x > 2) bonds.…”

Study of metal poisoning in natural rubber–based tire‐tread compound

“…The swelling index of the cured samples was measured using the following formula in accordance with ASTM D3616: The volume fraction V r of the insoluble rubber fraction in the swollen gel was calculated using the following formula7–9: where V r is the volume fraction; d is the weight of the deswollen sample; h is the initial dry weight of the sample; f is the weight fraction of insolubles in solvent; s is the swollen weight of the sample; and ρ r and ρ s represent density of the rubber and solvent, respectively.…”

Broader Spectrum: Examples

“…Conversely, the network structure of a crosslinked polymer may be studied by means of its swelling characteristics in solvents. The polymer -solvent interaction parameter between a crosslinked network and its solvent has been found to vary with the volume fraction of polymer in the swelled mass, which again changes with the crosslink density of the cured compound [22] . For styrene butadiene rubber (SBR) crosslinked with different doses of sulfur/accelerator, it is possible to fi nd out the relative distribution of each type of crosslinks (polysulfi des, disulfi des, and monosulfi des) from a swelling test, considering the variation of the polymer -solvent inter action parameter with the volume fraction of polymer in the swelled mass [23] .…”