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Selection of Antistatic Agents for Polymers

Anti-static agents are used to either manage static charges during various stages of processing or to provide long-term static protection based on end-use applications.

But, searching the right additive for your product among a variety of them available in the market, could be a daunting task!

Get a comprehensive review of important aspects related to antistats and their chemistries. Also, explore the factors that influence selection of anti-static agents including their compatibility with various polymers like polyolefins, polyesters, polyamides, fluoropolymers, and more.

We would like to acknowledge Paul Seemuth for providing technical information needed to develop this guide.

Need for Anti-static Agents in Polymers


TAGS:  Surface Modification      Anti-static Agents 

Antistatic Agents in PolymersIn general, plastics are insulating materials subjected to electrostatic build-up and discharge depending on the surface resistivity of the part.

Plastics such as PP and PVC, tend to collect electrons and become negatively charged. Antistats are materials controlling the accumulation of static electrical charge especially on polymer surfaces.

This accumulation of charge at the surface makes the material prone to electric discharges, dust adhesion and static clings.

The dissipation of the static charge relies on creating conditions for unwanted electrons to move away from the surface. Most antistats make use of charge structures to dissipate the material accumulated charge. Other antistats rely solely on electronic lone pairs of electrons and/or hygroscopic properties.


In general, dissipative or ESD polymers have:

  • A surface resistivity in a range from 105 or 106 up to 1012 ohms.
  • A static discharge half-life generally inferior to 60 seconds.

According to the targeted application, beware of too low resistivity leading to conductive polymers and inherent risks. Problems are of very various seriousness, from minor to very serious and even dreadful ones:

  • Dust and other pollutants attraction with marketing, use and processing problems
  • Electrostatic build-up or discharges when touching the plastic parts: synthetic carpets, knobs, car handles
  • Painting and printing defects
  • Fire or explosion of inflammable or explosive environment, organic powders
  • TV, radio, electronic interferences

Continue reading to learn more about:


Anti-Static Strategies for Temporary or Long-Term Protection


Electrostatic build-up and discharges are widespread in:

  • Continuous processing of plastics such as films
  • Electronic manufacturing, handling and repairing
  • Electronic applications
  • Packaging of dusty organic materials
  • Aeronautics: lightning and interferences
  • Automotive: Electrostatic discharge of fuel lines leading to fires
  • Inflammable and explosive environments: healthcare, operating theatre, painting shops
  • Use in cleaning of rooms

Hence, the dissipation of the static charge relies on creating conditions for unwanted electrons to move away from the surface. Most anti-stats make use of charge structures to dissipate the material accumulated charge. Other anti-stats rely solely on electronic lone pairs of electrons and/or hygroscopic properties.

Antistatic agents may be liquids, semi-solids or solids. These materials are normally either:

  • Applied to the surface of a substrate, or
  • Can be incorporated into the materials itself

Applied anti-stats are normally for managing static charges during various stages of processing. They are considered transient use species.

Incorporation into a material matrix is required in cases where ‘lifetime’ static protection is a criterion of end-use. Examples are antistatic carpet fibers and certain composite materials prone to generating static charge.

Further, water (humidity) plays a key role in assisting anti-stats in the mechanism to dissipate charge, i.e. via conductivity.

After understanding the importance of anti-stats in polymer, let’s explore what are the main chemistries used to effective charge dissipation…



Antistatic Agents Chemistries


Anti-stats are categorized into two subsets: inorganic and organic. There is not any universal strategy to minimize the static build-up, but multiple ways are used, sometimes in combination. Hence, selection of the preferred antistats is based on need and use.

Antistatic Strategies
Anti-static Ways in Polymers


Inorganic Anti-static Agents


Inorganic salts and some basic organic elements can be incorporated into the polymer matrix to suppress long term use static accumulation. Examples include:

  • Carbon that is used in carpet fibers to produce antistatic flooring
  • Carbon used in many non-woven wipe applications for clean rooms and aerospace applications

Various salts incorporated into a polymer matrix can offer some anti-static properties. Though, lock in the matrix, the ionic nature is not readily available (ion separation) to contribute to dissipation of charge.


Organic Anti-static Agents


Organic antistats comprise the majority of materials used for assisting in conductivity of excess charge away from the polymer surface. While some can be incorporated into the solid matrix, most are used externally to control static during processing and end-use applications.

The general subset classes of the organic systems are:

  • Phosphate, normally potassium or sodium salt of the corresponding free acid;
  • Quaternary amines;
  • Non-ionic hygroscopic materials i.e. surfactants of ethylene oxide and / or propylene oxide.

For the principal antistats, phosphates and quaternary amines are organic molecules with both positive and negative charged ions. The smaller the size of the species, the greater is the observed electron density around the molecule and thus greater enhance dissipation ability.

Sulfate or sulfonated chemicals can be used though they are not especially effective. An example, di-octylsulfosuccinate potassium salt, used as a surfactant, displays weak antistatic characteristics.

Non-ionic surfactants function due to their hygroscopic character and the lone pair of electrons on oxygen. The hydrophobic side interacts with the surface of the material, while the hydrophilic side interacts with the air moisture and binds the water molecules. Again, the antistatic effect is small compared to either the phosphates or the quaternary amines.

Let’s learn about some of the organic antistats in detail…


Phosphate Acid Ester Salts


These materials are normally produced reacting an organic alcohol (ROH) with either P2O5 or POCl3. In both cases, both the mono and di-acid esters are formed (see Figure 1). In normal use, these free acid esters are transformed into the corresponding salt, preferably potassium (K+).
Phosphate Acid Ester Salts

The P2O5 route normally leads to a 55:45 mono/di ratio with small amounts of trimester. The POCl3 route tends to produce ~ 50% tri-ester, a component having little or no antistatic properties. Other aspects are outlined in the table below.

Phosphates ((RO)2P(O)O-)

Pros

Cons

Extremely Effective

Effectiveness decrease as MW increases

Wide range of phosphoric acid ester available

Solid phosphates are difficult to formulate

Potassium salts are preferred

Un-neutralized acid ester are less effective antistats

In-situ acid salt preparation is common

Many salts are not EPA and Reach compliant

Low MW phosphate salts are more effective than higher MW analogs

Low MW antistats are more likely to be absorbed in polymers esp. nylon and spandex

Phosphate ester from P2O5 preferred over POCl3

POCl3 prepared ester leave corrosive halide ion residues


Quaternary Amines


This antistat class is formed by the reaction of an appropriate amine with an alkyl halide or di-alkyl sulfate. This produces a pentavalent positively charged nitrogen coupled with the corresponding anion.

Quaternary Amines

Use and constraints for quaternary amines is outlined in the table below.

Quaternary Amines
Pros Cons
Range of systems available Limited compliance with EPA and Reach on anion selection
Readily formulated into lubricant systems Effectiveness is more % dependent than phosphates ( 1.5-2 x more )
Commonly used in cosmetics industry Less irritating than phosphates in some casesa
Lower deposition issues versus Phosphates
Several anions, esp. methyl sulfate (CH3SO3-) have H&E issues
Moderate antistat capabilities at even low RH conditions Log Rp more variable than Phosphate systems

Non-Ionic Surfactants


Non-ionic surfactant class covers a very wide variety of chemicals. These can include simple alcohols to complex bio-based polyhydric structures. For this section, focus will be on those commonly associated with applications to polymers, alcohol or acid ethoxylated or ethoxylated / propoxylated systems.

These systems tend to be hygroscopic in nature, with lone pairs of electrons available on the oxygen atoms, assist in conducting static charge away from a polymer’s surface.

The following table gives an overview of a capabilities for static control.

Non-ionics
Pros  Cons 
Large number of products available Low antistat potential vs phosphates or quaternary amines
Non-disruptive to antistat effect
Excellent for providing hydroscopic properties to enhance antistat effect Large %'s are used in formulations
Compatibility assist in formulations with phosphate or quaternary antistats

Apart from these two main classes of anti-static agents, there are some conductive fillers & additives which are widely used for ESD, EMI or RFI shielding. Explore them in detail…


Conductive Fillers and Additives


These solutions lead to volume conductive plastics that can act as conductors receiving electrons from other electrostatic materials with the known risks of electrostatic discharges.

All suitably filled plastics can be used for ESD, EMI or RFI shieldings:

  • Commodity plastics such as PE, PS, PP
  • Engineering plastics such as ABS, PA 6/6, PA 6, PC, POM, PBT, PPO, PPS
  • Specialty plastics such as PEI, PEEK
  • Alloys such as PC/PMMA, PC/ABS

For the ESD polymers, it is difficult to control the resistivity over the percolation threshold of fillers: The resistivity can be so low that the polymer becomes conductive.


Carbon Blacks


The resistivity of the final material depends on:

  • The surface area of the carbon black and the ion level on its surface
  • The level of carbon black
  • The grade of the polymer or, eventually, the alloy of polymers
  • The mixing method

  • Carbon blacks modify the other properties of the polymer especially its color.


    Conductive Fibers


    The carbon and steel fibers as well as conductive cellulose fiber highly filled with conductive carbon blacks are industrially used to make the plastics and composites conductive.

    The resistivity of the final material depends on:

    • The size, the aspect ratio, the chemical nature of the fibers
    • The level of fibers
    • The mixing method

    There are specific grades especially marketed as additives for conductive plastics and rubbers. The other properties of the final material, color, modulus, impact strength etc. are modified.

     »  Find Suitable Conductive Filler/Fiber for your Application


    Graphites


    The resistivity of the final material depends on:

    • The type of graphite: some grades are specially developed for their electric conductivity
    • The aspect ratio
    • The level of graphite
    • The grade of the polymer
    • The mixing method

    Furthermore, graphite has lubricating properties. It is claimed by certain producers that the resistivities can be in the order of those obtained with conductive carbon blacks, lower or higher according to the used grades.

    Metal Powders or Flakes


    Aluminum, copper, nickel, silver powders or flakes are used to increase the electrical conductivity.
    The resistivity of the final material depends on:

    • The particle size and form of the metal
    • The level of metal
    • The mixing method

    There are specific grades especially marketed as additives for conductive plastics and rubbers. The polymer influences the metal choice. The Sulphur vulcanization can particularly cause some troubles with metals such as copper and silver attacked by Sulphur. The other properties, color, modulus, impact strength etc. are modified.

    Some grades made of Titanium and Zirconium are specially developed for applications in polymers to obtain ESD and other antistatic materials are used into numerous plastics such as ABS, EVA, polyethylene, polypropylene, PVC, PETG, polyamide, polyethersulfone, acrylics, polyurethane.


    Carbon Nanotubes (CNT)


    CNTs are fast growing for mass-produced or specific devices. CNTs, relatively well known, are expensive despite a continuous cost drop. The very low resistivity of carbon nanotubes (CNT) allows obtaining EMI polymers with levels of CNT inferior to 1 %, far lower than used levels of conventional and conductive carbon blacks.

    Polymer Resistivity vs Carbon Loading
    Polymer resistivity Vs Carbon Loading


    Inherently Conductive Polymers (ICP)


    ICPs are the most exciting opportunities for mass produced or specific devices. They are used notably for transparent electronics, TCF (transparent Conducting Films) and photovoltaic.

    For example, PEDOT, polyaniline, IonomerPolyElectrolyte (IPE®) and so on are proposed by several companies.

    ICPs can be alloyed with various conventional plastics including, for example, ABS, acrylics, composites, polyamides, polycarbonate, polyesters, rubbers, and TPEs.


    Assessing Antistats Performance


    A common test to assess the performance of an antistatic agent is the electrical resistivity test. Result is expressed as log of resistivity. Often, antistatic performance is specified as maximum permissible log R under specific humidity conditions. The following chart gives a good idea to the range of values that reflect good antistat effect.

    Static protection vs fiber surface resistivity
    Log Rp can be obtained using a variety of instrument, Hayek-Chromey Wheel, Static Honestometer or more commonly with polymer, Rothschild’s Static Voltmeter.


    Antistatic Agents Selection Criteria


    Toyotsu Chemiplas Products
    Selection of anti-static agents would depend on the processing conditions and the nature of polymer.

    The following can have an effect on the static dissipation performance:
    • Humidity
    • Polymer Prep Temperatures
    • End-use Process Temperatures


    Impact of Humidity (RH %) on Anti-static Behavior


    While the non-ionics are less impacted by normal plant RH factors, phosphates and quaternary amines tend to exhibit marked behavior based on humidity.

    • Phosphate effectiveness significantly decreases with decreases in RH %. Decreasing RH during polymer processing from normally a 60-70% RH range to less than 45% can result in a 10 fold drop in ability to control static.
    • Quaternary amines are generally not impacted severely by humidity changes though effectiveness tends to be non-linear with MW increase.

    The following chart illustrates the RH effect on static dissipation (measured by log of resistivity) to molecular weight of species.

    Resistivity vs Molecular Weight
    Resistivity (Log R) vs Molecular Weight


    The following selection chart provides insight into dissipation performance, both within individual type and between classes.

    Type of Antistat Physical State Humidity % (RH) Polymer Prep Temperatures End-use Process Temperatures* Storage Stability**

    High (55-70) Low (< 45) Internal use External use Internal use External use
    Inorganic Salts 3+ 3+ 5 n/a 5 n/a 5
    Carbon 5 5 5 n/a
    4 n/a
    5
    Phosphates Liquid 5 4 1 5 1 5 3+
    Semi-solid 5 4 2 5 2 5 5
    Solid 4 3 3 4 3 3+ 5
    Quaternary amine liquid 4 4 0 4 0 3+ 5
    Semi-solid 4 4 1 4 1 4 5
    Solid 3+ 3 2 3 2 2+ 5
    Nonionics Liquid 2 2 -2 2 -1 2 3
    Semi-solid 2 2 -1 2 -1 2 4
    Solid 1+ 1+ 1 2 -1 1+ 5
    *Normal process temperatures for most all classes of polymers

    **Normal warehouse; For staple, POY and PU polymer products, low MW phosphates are especially prone to absorb into polymer structure, thus losing capability to function optimally.


    Anti-stat Selection based on Type of Polymer


    The general classes of polymers function well in combination with the antistats. The inorganic salts and carbon are considered fully compatible in use with all polymer systems if incorporation is feasible.

    The following guide shows the ability to dissipate static relative to physical form and polymer types. (5 being excellent, -5 v. poor).

    Polymer Type Phosphates** Quaternary Amine Non-ionics
    Liquid Semi-solid Solid Liquid Semi-solid Solid Liquid Semi-solid Solid
    Polyolefin 5 3+ 2 4 3 0 -1 -1 -1
    Polyester 5 5 5 4 4 3 1 1 -2
    Polyamide* 4+ 5 3+ 4 3+ 2+ 1 1 -2
    Aramid 5 5 5 4 4 4 1 1 1
    Polyurethane -1 1 3 -1 1 3 1 1 1
    Polyketone 5 5 5 4 4 3 1 1 0
    Fluoropolymers 5 5 5 4 4 4 2 1 0
    Carbon Fiber 5 5 5 4 3 3 2 1 0


    * POY and staple nylon (6 & 6,6) more sensitive to low MW absorption issues than FDY. MW esters of less than C12 will result in only short-term static protection and long storage times will result in poor processing.

    ** Physical form by themselves - normally K or Na neutralized salts


    Commercially Available Antistatic Agent Grades






     »  Explore Latest Developments in Surface Modifying Technologies


    Paul Seemuth

    Paul SeemuthPaul Seemuth is Chief Executive Officer at Tribology Consulting International. Dr. Seemuth, who holds a PhD in Organic Chemistry, has more than 30 years of experience in tribology and lubrication of polymers. His fields encompass, but not limited to, organic chemistry, fiber lubrication technology and formulations, catalysis, polymer processing, specialty chemicals, fuel and oil additive formulations.

    Work experience include global technology leader at DuPont Fibers Finish Technology Group, responsible for global Fiber Finish technologies and strategies, related plant designing and plant start-ups, VP - Global Technology at SSC Industries and an Associate Professor at Chattanooga State in the Departments of Chemistry and Chemical Engineering.

    A Fellow of the Royal Society of Chemistry (FRSC), he is a recognized world expert in the field of Tribology, the study of friction and wear. Paul has over thirty publications and over 15 patents covering scientific endeavors on automotive additives, lubricant technologies, fiber finish formulations, polymer production processes, heterogeneous catalysts and supercritical fluid applications. Recently, he completed a major chapter on Textile Fibers / Fabrics” in the Handbook of Lubrication and Tribology, Volume I Application and Maintenance, Second Edition, then served as Section Editor for the Encyclopedia of Tribology along with a contribution on Fiber Boundary Tribology.

    Dr. Seemuth consults both domestically and internationally. He also presents regular presentations on scientific topics related to lubrication and surface science.

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    2 Comments on "Selection of Antistatic Agents for Polymers"
    Tukaram J Jul 15, 2019
    How to achieve a surface resistivity in a range from 105 or 106 ohms with PET film ?
    Nicholas P Jul 23, 2018
    What kind of Antistatic agent should I use for RTV silicones? Thank you

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