Mechanical stability ethylene oxide-fatty alcohol

Wherever possible, the soaps and surfactants were added to the natural rubber latex as dilute aqueous solutions. The cases where this was not possible were (a) ethylene oxide-fatty alcohol condensates of low ethylene oxide fatty alcohol mole ratio, and (b) sparingly-soluble fatty-acid soaps such as lithium laurate and calcium soaps. The former were added as pastes with water, the latter as dry powders. In all cases, the latex samples were allowed to mature for about three days at room temperature before their mechanical stabilities were determined. This allowed some opportunity for the attainment of adsorption equilibrium. 

Effects of ethylene oxide-fatty alcohol condensates upon the mechanical and chemical stability of natural rubber latex (10)... 

The results summarised in Figure 7 show that small additions of ethylene oxide-fatty alcohol condensates to natural rubber latex generally cause the mechanical stability of the latex to fall. This phenomenon is attributed to the displacement of adsorbed proteinaceous molecules by the condensate molecules. Although the latter are more surface active than the former, they are presumably less effective in conferring mechanical stability upon the rubber particles, perhaps because, unlike the proteinaceous molecules, they are not ionised. 

Figure 7. Effect of added ethylene oxide-fatty alcohol condensates upon mechanical stability of natural rubber latex ( 0). Levels of condensate are expressed in parts by weight. Numbers appended to curves indicate overall mole ratio ethylene oxide fatty alcohol in condensate.

We interpret this observation as implying that, for these condensates, the effect upon mechanical stability is determined primarily by the binding of water to the ethylene oxide units which are anchored to the rubber-water interface by the fatty-alcohol moiety of the condensate. In the case of condensates for which the overall mole ratio of ethylene oxide to fatty alcohol exceeds ca. 30, the effect upon mechanical stability is much greater than would be expected on the basis of the total amount of ethylene oxide which has been added to the latex, as evidenced by the... 

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