Diffusion in Rubber

F. Gruen, Diffusionmessungen an Kautschuk (Diffusion in Rubber), Experimenta 3, 490 (1947). 

TRACER DIFFUSION IN RUBBER PLUS BENZENE MIXTURES AND ITS RELATION TO MUTUAL DIFFUSION. 

The most complete and satisfactory data on solubility and diffusion in rubbers have been obtained by the second method of p. 412, depending on the time lag in setting up the stationary... 

Plasticizers reduce hardness, enhance tack and reduce cost in rubber base adhesive formulations. A plasticizer must be easily miscible and highly compatible with other ingredients in the formulations and with the surfaces to which the adhesive is applied. The compatibility and miscibility of plasticizers can be estimated from the solubility parameter values. Most of plasticizers have solubility parameters ranging between 8.5 and 10.5 hildebrands. However, the high miscibility and compatibility also lead to easier diffusion of the plasticizer to the surface, decreasing the adhesion properties. Therefore, plasticizers should be carefully selected and generally combinations of two or more of them are used. 

An antiozonant should have adequate solubility and diffusivity characteristics. Since ozone attack is a surface phenomenon, the antiozonant must migrate to the surface of the rubber to provide protection. Poor solubility in rubber may result in excessive bloom. 

MJ Hayes, GS Park. The diffusion of benzene in rubber. Trans Faraday Soc 52 949-955, 1956. 

Fig. 8.1. Toughening mechanisms in rubber-modified polymers (1) shear band formation near rubber particles (2) fracture of rubber particles after cavitation (3) stretching, (4) debonding and (5) tearing of rubber particles (6) transparticle fracture (7) debonding of hard particles (8) crack deflection by hard particles (9) voided/cavitated rubber particles (10) crazing (II) plastic zone at craze tip (12) diffuse shear yielding (13) shear band/craze interaction. After Garg and Mai (1988a).

It has also been suggested however, that even with well-separated aggregates of carbon black, flocculation may occur by diffusion in a hot rubber compound, contributing to the formation of a network and an electrically conducting structure. 

In the same manner, with decreasing of diffusion coefficient and interaction parameter, the spinodal is reached during the evolution of the system in the pregel stage. The very low values of interfacial tension in rubber modified epoxies (interfacial tension of polymer-polymer-solvent system were reported in range of 10-4-10-1 mN/m) therefore lead to an NG mechanism for phase separation. 

Eq. (18). Their experiment provided an opportunity only to fit three of the four unknown constants, namely Dg, c2, and Tg. Tg in the solution was found to be depressed below that known for the rubber. An examination of the concentration dependence of oil diffusion in the same rubber host confirmed the applicability ofEq. (17) below vdil < 0.9 and permitted a measurement ofthe fractional free volume of one or both components of the oil-rubber solution. 

The thickness of lining depends on the severity of corrosion or erosion. The diffusion of liquids is inversely proportional to the square of the thickness of the lining at a given temperature. That is to say, a 6 mm thickness is four times more resistant than a lining of 3 mm thickness. The speed of diffusion in the temperature range 30-80 deg C is proportional to the temperature increase. The fabricators of vessels are to be informed in advance that the vessel is meant for lining and should be asked to follow the standard procedure for fabrication of equipment meant for rubber lining. 

Thermal diffusivity is of little interest in many thermal insulation applications, for example civil engineering, where approximately steady state conditions normally exist. However, in rubber processing when temperatures are changing rapidly it is of more value than conductivity. 

Monomer diffusion in the rubbery phase of PVC-rich reaction products is difficult, and this was demonstrated by polymerizing vinyl chloride (200 grams) at 70°C in the presence of a crude polymerizate (360 grams) containing 9% total rubber suspended in an aqueous solution of poly-(vinyl alcohol) (1.2% with respect to the polymer + monomer weight), so as to obtain a ratio of water/crude + monomer = 2.4 and by using benzoyl peroxide (0.38% with respect to the reacting monomer). 

Nonlinear, pressure-dependent solubility and permeability in polymers have been observed for over 40 years. Meyer, Gee and their co-workers (5) reported pressure-dependent solubility and diffusion coefficients in rubber-vapor systems. Crank, Park, Long, Barrer, and their co-workers (5) observed pressure-dependent sorption and transport in glassy polymer-vapor systems. Sorption and transport measurements of gases in glassy polymers show that these penetrant-polymer systems do not obey the "ideal sorption and transport eqs. (l)-(5). The observable variables,... 

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