The Use of Antistatic Agents

The selection of an antistatic agent for a given polymer is based on its chemical composition. Accordingly, antistatic agents may be divided in many groups, as presented in the following sections [11-15]. 

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For some applications it is necessary that static charge should not accumulate on the product. This is important in such diverse applications as mine belting and gramophone records. The use of antistatic agents such as quaternary ammonium compounds has been of some limited value in solving this problem. 

In spite of the effectiveness of some carbon blacks in reducing surface charges on plastics materials, the use of antistatic agents have increased steadily. The simplest antistatic agent is water. It is adsorbed on the surface of objects exposed to a humid atmosphere, and it forms a thin electroconducting layer with impurities adsorbed from the air. Such a layer is even formed on the surface of hydrophobic plastics, probably because of the existence of a thin layer of dirt. 

Table 3.12 contains a condensed summary of t5q)es and properties of antistatic agents used in PVC. For a comprehensive review of antistatic properties, mechanisms of their action, and the use of antistatic agents, see the specialized monographic source. 

Normally, film thicknesses of 0.003-0.008 in (0.076-0.20 mm) are achieved by this method since mutual repulsion between the powder particles sets a finite limit. The film thickness can be increased by lowering the resistivity of the powder by the use of antistatic agents or by preheating the metal article. However, the powder only sticks to the object by virtue of its charge, so that it will tend to... 

A common measure to control electrostatic charges is the use of antistatic agents either in the bulk or as surface coating. Common antistatic agents are... 

Polyurethanes can be used in applications where electrical properties are important. They are not normally used for high-voltage insulation. Polyurethanes are often used directly or in combination with epoxies for encapsulation. The addition of antistatic agents to polyurethane gives a product with the correct electrical properties while retaining the excellent wear needed for a number of roller-type applications. 

Static charges on polymer surfaces can be controlled by the presence of antistatic agents that make the surface more conductive or less resistive. For example, water within a hydrophilic polymer can act as an antistatic agent and prevent static buildup. The amount of water is important for example, water in a polyamide in equilibrium with air at 65% RH acts as an antistatic agent, but at iow RH values, water is not effective. Since most polymers used in packaging are not hydrophilic, antistatic additives may be used to control static. Generally, these agents are cationic, anionic, or nonionic surfactants. 

The technique used to achieve permanence with other additives such as antioxidants and plasticisers has often been to increase the molecular weight of the additives. In the ease of antistatic agents, however, high molecular weight versions of conventional antistats require high loadings, and can significantly increase costs. 

ABS, cellulose acetate, and polycarbonate can also be modified by the addition of antistatic agents. Styrene based polymers are too readily compatible with some antistatic agents and care must be taken to ensure that the additive is chosen so that migration to the surface occurs at a sufficient rate. Glycerol derivatives and ethoxylated amines can be used. 

Surface resistivity is the leakage of current along the surface, expressed in ohms. It is also measured with a Wheatstone bridge and null detector, but with both electrodes on the same side of the sample. It is used to evaluate the effect of antistatic agents and suitability for service in charge dissipation. 

Antistats such as polyoxyethylenes (151,152) and A/-alkyl polycarbonamide (153) are added to nylon to reduce static charge and improve moisture transport and soil release in fabrics. These additives also alter the luster of fiber spun from bright polymer. Static reduction in carpets is achieved primarily by the use of fibers modified with conductive carbon black (see Antistatic agents Carbon, carbon black). 

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