Agents antistatic

Antistatic agents are added to the PVC formulation, to prevent the build-up of static electrical charges, which could lead to an electric shock or a spark causing a fire in a dusty or flammable area. Dust build-up is also reduced. 

By adding an antistatic agent (complex non-ionic or cationic materials), the surface resistivity is reduced, along with a reduction in static charge accumulation. The agent functions by the formation of an antistatic layer on the surface, which by attraction of moisture and in combination with the antistatic agent itself, conducts away charges. 

The influence of zeolites and iron oxide on the antistatic properties of PVC based composites have been established (426). 

The addition of antistatic agents can have a detrimental effect on processing, particularly heat stability, and this needs to be taken into account. 

An alternative method of achieving antistatic performance, although not so permanent, is to apply a coating after fabrication. 

Antistatic agents are amphiphilic molecules with a hydrophobic tail, which entraps into the polymer matrix, and a hydrophilic head, which migrates to the surface and absorbs a conductive layer of water. This absorbed water leaks the static charge formed on the plasticised PVC surface [51-53]. Such antistatic agents are easy to prepare and purchase, but their antistatic properties depend strongly on moisture and they do not have sufficient antistatic effect with low environmental humidity. Reducing the environmental humidity 

Antistatic agents such as carbon black, metal powders, surfactants or other hydrophilic substances can be blended with polymer matrices to dissipate electronic charge. However, carbon black makes materials black, so if a light colour is required, carbon black cannot be used. If some low-MW antistatic agents like surfactant are used, their antistatic effect is brought about by the equilibrimn moisture adsorbed on the surfactant, so sufficient antistatic effect is not achieved under low humidity. Furthermore, the surfactant is removed by rubbing or washing back and forth, and the antistatic effect disappears easily [54]. 

To solve these problems, many antistatic agents are incorporated into the polymer at the moulding process or applied to the surface of the products in a finishing process to control the surface resistivity of the moulded part to 10 -10 Q/sq [55-68]. 

One of the advantages of polymers is its inherent dielectric property, but this can be a problem when static electricity needs to be dissipated. Antistatic agents are described in Sections 3.3.8.1 and 3.3.S.2. 

The optimum antistatic effect is generally obtained after a storage period of about two or three weeks. In many cases, the optimum effect is attained only after a few days, but imder arid conditions it is reached very much later and is diminished. The antistatic 

2 Electromagnetic Interference/Radio Frequency Interference Shielding 

There might be few occasions when a reduction in the dielectric properties of PP might be desirable, e.g., antistatic properties. However, for certain applications, the reduction in surface resistivity achieved by addition of antistatic agents may not be sufficient. The two cases where greater reduction might be required are 

Antistatic agents are added to aid in the prevention of static build up and sparking in the processing and usage of final parts. This can be critical to 

Antistatic agents are usually hygroscopic compounds which readily attract moisture and so inhibit the build up of a static charge on the surface of a plastic product. They are used in many applications from the body of the humble plastic pen to numerous packaging applications. 

The selection of an antistatic agent depends greatly on the polymer matrix since a degree of incompatibility is vital to ensure that migration to the surface of the product occurs at a fast rate after manufacture. Exact chemical composition information can be difficult to obtain from suppliers and so analysis for these additives can be difficult. 

In the case of polystyrene, quaternary ammonium Column type compounds are widely used and for polyethylene, polyethylene glycol alkyl esters can be used. 

In the case of the glycol esters, these can of sufficiently low molecular weight to be extractable by solvents such as diethyl ether and then identified by a chromatographic settings  

See Aanalgesics, antipyretics, and antiinflammatory agents Immunotherapeutic agents Veterinary drugs. 

Electrification is the process of producing an electric charge on an object. If the charge is confined to the object it is said to be electrostatic. The term static electricity refers to accumulated, immobile, electrical charges in contrast to charges in rapid flow, which is the subject of electrodynamics. 

Dacron steel Velon natural mbber paper 

Odon acetate Odon, Saran polyethylene Teflon steel wood amber sealing wax hard mbber nickel, copper, brass, silver, old platinum sulfur acetate rayon polyester 

Kirk-Othmer Encyclopedia of Chemical Technology (4th Edition) 

Dacron steel VelonC natural mbber paper 

Coulomb (1736—1806) stated the law of repellency between similarly charged bodies and attraction between oppositely charged bodies, and Faraday (1791—1867) described the laws of electrostatic induction. The inductive principle known as Faraday s ice-pail method is still in use in modern measuring equipment. 

In the case of low-density polyethylene for film products, a typical antistatic agent is a long-chain aliphatic amine, e.g. Ethomeen T12, with the formula  

Improved, more permanent and durable protection against static charges can sometimes be obtained by the incorporation of an ionic copolymer. 

Poly(oxyethylene) sorbitan monolaureate is a surface active compound which is also known as an internal or external antistatic agent for a great number of plastics. It has been found that this compound provides an almost instantaneous antistatic action (14). 

Usually antistatic agents develop their full activity only after a couple of days. The almost instantaneous antistatic action is extremely important during the production of films where operators are exposed with static built up on the extrusion equipment. Thus, the additive is useful in applications where dissipative properties are important, such as supported or unsupported sheets forming 

The antistatic agent is uniformly incorporated into the copolymer by conventional melt blending techniques. For example, the antistatic agent is blended with molten copolymer in a manner to form a homogeneous blend, using for example an extruder. 

Ionomers are used in a wide field of applications, such as (15)  

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. 

A common group of cationic antistats is alkyl quaternary ammonium salts. These are mostly employed in polar substrates such as PVC and in styrenic polymers. Other types include alkyl phosphonium and alkyl sulfonium salts. Flexible PVC may contain up to 7% of these antistatics for nonfood uses, as they have not been approved by the FDA. Sodium alkyl sulfonates, similar to common detergents, have gained wide acceptance as anionic antistatic agents, and are used in PVC and styrenic polymers. Other anionic antistats include alkyl phosphonic, dithiocarba-mic, and carboxylic acids. 

For nonpolar polyolefins, nonionic antistatics are the most commonly used. These include ethoxylated fatty amines, fatty acid esters, ethanolamides, and poiy-ethylene glycol-esters. The amount used in LDPE is typically around 0.05%. For packaging of electronics, which can be highly sensitive to damage caused by static charges, considerably higher levels are used, up to 10% by weight. 

Antistats can be appiied internally or externally. Internal antistats are compounded into the resin, and act once they migrate to the surface of the poiymer. External antistats are appiied directly on the surface by spraying, or sometimes by dipping the polymer in a solution of the antistatic. Internal antistatic agents can 

An alternative to the use of antistatic additives is the incorporation of electrically conductive fillers or reinforcements into the polymer to make the whole structure conductive. Typical additives that are used for this purpose include aluminum, steel, or carbon powders, and metal-coated glass fibers or carbon fibers. Powdered fillers are generally less expensive than fibers. Maintaining the desired fiber distribution during processing is also problematic. 

The automotive industry requires static elimination in plastics used for fuel systems, electrical and electronic parts, and engine components. 

ABS is very widely used in the business machine, automotive parts and domestic appliance industry. Polyamides, in addition to their use in the critical area of carpets, also feature in business machine internal parts and to some extent in packaging. The polyolefins are widely used in packaging, pipes, storage bins and foam. PVC is used in conveyor belts, packaging and floors. Polystyrene and polycarbonate are significant materials in some of these areas. 

It will be apparent from the above examples that some applications have strict requirements for very good static dissipation performance, i.e. low surface resistivities, on safety grounds, whereas others have more modest requirements because the effect of static is mainly a nuisance. 

In order to dissipate the electrical charge on the surface of the plastic, we must render the surface electrically conducting in some way. This enables the electrons to be dissipated. There is no problem if a plastics material is already conducting, because of the additives it contains, or because the base polymer is intrinsically conducting - the latter situation is uncommon. 

One approach is to assume that static charges wiU unavoidably be accumulated, and therefore the plastic must either contain an internal additive or possess a surface coating which renders the surface sufficiently conductive to dissipate the static electricity. Other methods of dealing with the problem are available, but this article is confined to the internal additive method, which is widely used. 

Plastics are mostly electrical insulators. The development of a static charge on two plastic film surfaces during their mutual contact occurs by the transfer of electrons from one film surface to the other during rubbing or rapid separation. It is an undesirable consequence of insufficient conductivity, especially in polymers with a very low tendency to absorb moisture, and static discharges can reach several thousand volts per centimetre. This leads to  

Products especially affected by static include packaging film, automotive fuel tanks and lines, electronic device housings and associated furniture and flooring, videocassettes, domestic appliances, televisions and mobile phones, conveyor belts and chemical process equipment, or any materials used in the vicinity of flammable atmospheres. 

The cellulosics have little need of antistatic protection because they absorb moisture more than polyethylene, polypropylene and (to a lesser extent) PET. Polystyrene is difficult to protect effectively against static. 

Antistatic agents are incorporated in plastics to prevent or reduce the build-up of static charges on the surface of a product. They must be able to stand the processing temperatures used and not interact negatively with other additives (some cationic and anionic antistats interfere with PVC heat stabilisers). They must also satisfy food contact regulations, and not adversely affect performance in other ways. 

Volmne resistivities of static dissipative materials are usually between 10 and 10 ° ohm-cm, with lower values implying conductive behaviour. 

Electrostatic charges can also be produced on the surfaces of polymeric materials in the course of processing operations such as extrusion, calendering, and rolling up of plastic sheets or films. Furthermore, electrostatic charges pick up dust and dirt particles and the surfaces of charged plastics can thus become dull and dirty. 

For the application of plastic materials in atmospheres contaminated by inflammable substances, such as those in mines and in hospitals (where anaesthetics and oxygen form explosive gas mixtures), use of electroconducting ma- 

The electrostatic charges accumulated on the surface of macromolecular compounds are very difficult to eliminate because of the very low electric conductance of these materials. This is measured by the half-time electrostatic charge decay this value is given for some polymeric materials in Table 7.3 [2]. Since most of these materials have an appreciable value for the half-time charge decay, charges accumulate on them when these materials are rubbed. 

There are many ways to eliminate surface electrostatic charges, for example, by increasing the humidity or the conductivity of the surrounding atmosphere, by lowering the surface resistance of materials with the use of electroconducting carbon blacks, powdered metals, or antistatic agents [3,4]. 

Owing to its high electrical resistance, PE tends to accnmnlate electrostatic charge, as do other polymers. This is a disadvantage because dust can accumulate on articles, which is often nndesirable. Furthermore, the possibility of sparks presents a hazard in applications where explosive fnmes may be present. 

The incorporation of an antistatic agent has little or no effect on the mechanical, chemical, or thermal properties and no effect on the processing conditions. However, the presence of antistatic agents may affect the transparency and printability and may make PE non-compliant with US Food and Drug Administration (FDA) regulations, although FDA-approved antistatic agents are available. 

Plastics, being good electrical insulators retain electrostatic charges developed by friction between the plastic itself, between plastic and moving machinery, or by 

The requirements of an antistatic agent are a reasonable electrical conductivity and an ability to migrate to the surface of the plastic moulding or film as it is on the surface that the electrostatic charge concentrates. 

The selection of the types of compounds used as antistatic additives is governed by complex considerations, one of which is that it should have the correct degree of comparability with the base polymer which will enable it to migrate to the polymer surface at a controlled rate during service life. 

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A wide class of aiyl-based quaternary surfactants derives from heterocycles such as pyridine and quinoline. The Aralkyl pyridinium halides are easily synthesized from alkyl halides, and the paraquat family, based upon the 4, 4 -bipyridine species, provides many interesting surface active species widely studied in electron donor-acceptor processes. Cationic surfactants are not particularly useful as cleansing agents, but they play a widespread role as charge control (antistatic) agents in detergency and in many coating and thin film related products. 

Antistatic agents require ambient moisture to function. Consequently their effectiveness is dependent on the relative humidity. They provide a broad range of protection at 50% relative humidity. Much below 20% relative humidity, only materials which provide a conductive path through the bulk of the plastic to ground (such as carbon black) will reduce electrostatic charging. 

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