Swelling of rubbers

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Will strip and dissolve paint dissolves most plastic materials can cause swelling of rubber by absorption. The reactions are not hazardous Stability During Transport Stable Neutralizing Agents for Aci and Caustics Flush with water Polymerization Not pertinent Inhibitor of Polymerization Not pertinent. 

Fig. 7 Swelling of rubber samples in organic solvents measured in the Diamond TMA. NR, natural rubber NBR, nitrile butyl rubber SiR, silicon rubber HR, isobutyl rubber. (Courtesy of the PerkinElmer Instruments, Norwalk, CT.)...

Experimental Results. Equation 5 cannot be used to calculate C unless the values of the constants are known. An explicit relation for C is given by equation 6 in which the effect of the rubber pressure has been neglected. Equation 6 has been used to calculate the equilibrium amount of water absorbed by natural rubber (vulcanizate B) from a salt solution containing 10% sodium chloride. The value of A cannot be calculated since the nature and concentration of the impurity in rubber is unknown but its value was estimated from the observed equilibrium swelling of rubber in a saturated salt solution. The value of A was found to be 1.14 x 10" and the calculated value of the concentration of water in the rubber at equilibrium in the 107. salt solution was 0.0140 gm cm which was in excellent agreement with the experimental value of... 

A similar situation arises in the case of the swelling of rubber. Here the isoprene units of the rubber molecule, when not part of a rubber molecule, are soluble in aromatic hydrocarbons, but when incorporated in a polymer network they are constrained to remain as part of a gel. 

Interesting experiments on the equilibrium swelling of rubber are recorded by Gee . We know from the preceding sections that the entropy of dilution in polymer solutions is independent of the solvent it depends only on the degree of polymerisation and on the volume fraction of the solute. (See, for instance, equation 56, p. 74). 

Fig. 6. Swelling of rubbers with increasing polarity in various solvents (8 weeks at 20° C).

It would be of interest to try a quantitative theory, based on similar ideas as those which have been developed by Gee for the swelling of rubber in mixtures of two solvents (cf. Section 6, b. 2a). The solutions of sodium hydroxide of various concentrations should thereby be regarded as solvent mixtures of different composition and their thermodynamical data studied. 

Swelling of rubber (or other elastomer) gaskets, or seals, when exposed to petroleum, synthetic lubricants, or hydraulic fluids. Seal materials vary widely in their resistance to the effect of such fluids. Some seals are designed so that a moderate amount of swelling improves sealing action. Refer to Swell and Shrinkage Tests. 

Swelling of rubbers by fluids is known to be a diffusion-controlled process and, up to the equilibrium swelling, the volume of liquid absorbed is proportional to the square root of the time that the rubber has been immersed in the liquid. For most liquids, this rate also depends on its the viscosity, rather than its chemical nature. 

In recent calculations Stemstein3 has worked out the problem of swelling of rubber containing spherical filler particles subjected to the boundary conditions that the tangential strain is zero at the surface of the particle. He has obtained expressions... 

The composition and solvency is limited to prevent swelling of rubber or photopolymer-based rolls. Water, alcohols, minimal concentrations of acetates (i.e. ethyl, isopropyl alcohol), and minor levels of aliphatics such as heptane are mostly used. Acetates and aliphatics are used to solubilize polyurethane and polyamide resins used in solvent based laminating ink Only aqueous ink is discussed in this chapter. A diagram of a flexographic press is given in Fig. 5-1. 

Swelling of rubbers and polymers was mentioned in Section 2.6 in connection with cohesive energy density. Solvents may extract portions of polymer systems, for example, the plasticizer from a polyfvinyl chloride)-based system. Swelling at a surface may set up a stress that is relieved by crazing. Craze lines consist of oriented polymers. They become evident by their opacity in glassy polymers stressed by a purely mechanical couple or by surface absorption of a liquid (see Section 10.7). 

Slachmuylders, E., Numerical Prediction of Extrudate Swell of Rubber Compounds, presented at the 1997 POLYFLOW Users Meeting, Brussels, (1997). 

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