The Effect of Additives

Low molecular weight substances offering a high dipole moment, such as nitriles, amides, nitro compounds, etc., have a strong plasticization effect on polyacrylonitrile fibers. 

What can be expected, if such molecules are introduced into the fiber The more mobile additive molecules have a greater chance to approach PAN — CsN dipoles in the most favorable direction (cf. Eq. 1) the intramolecular repulsion of adjacent — CsN groups within the polymer molecules will be partly neutralized , with the result of less resistance to an imposed stress. At the same time, part of the intermolecular dipole-dipole interactions between polymer molecules will be replaced by interactions of polymer CN groups with dipoles of the additive, which again results in reduced tensile strength. On the other hand, the presence of the plasticizing compound evidently provides increased mobility for the individual segments of the polymer molecules. 

Hydrogen-bonding substances, such as water, methanol, ethanol, acetic acid, etc., have a similar effect. Substances with more than one highly polar, or hydrogen- 

Transition metal compounds catalyze an infinite number of organic reactions. (For a recent review, see e.g. Ref. Most probably, these compounds will have an effect on the processes going on during the heat treatment of acrylic fibers, in particular on dehydrogenation reactions, provided they can be introduced into the fiber in a way such that they will not be washed out during the spinning process. 

Many industrial applications of surfactants involve the presence in the solution of cosolutes and other additives that can potentially affect the miceUization process through specific interactions with the surfactant molecules (thereby altering the effective activity of the surfactant in solution) or by altering the thermodynamics of the miceUization process by changing the nature of the solvent or the various interactions leading to or opposing micelle formation. 

Added Electrolyte. In aqueous solution the presence of electrolyte causes a decrease in the cmc of most surfactants the greatest effect is found for ionic 

FIGURE 15.12. In the presence of large, polarizable cations such as caldum nonionic POE surfactants may, under some circumstances, form complexes with the ions producing a significant change in the configuration of the ether chain and surfactant solution properties. 

A number of amphoteric surfactants have pH sensitivity related to the pK s of their substituent groups. The possibilities can be grouped in the following way  

Quaternary ammonium-strong acid salts will show little or no significant pH sensitivity. 

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