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Adhesives Ingredients

Surfactants in Adhesives & Sealants: Where to get started with selection?

Surfactants are used in both water-borne and solvent-based adhesive formulations. They added to formulations to provide characteristics like reduce surface tension, improved flow and wetting without negatively impacting adhesion. Learn about the classification of surfactants along with their mechanism in detail. Also, get selection & formulation tips for surfactants you can benefit from and the trends driving developments of new surfactants.

Overview

Advantages and Disadvantages of Surfactants

Advantages and Disadvantages of Surfactants

Surfactants are used in both waterborne and solvent-based adhesive formulations. In solvent-based systems, their primary use is as dispersing agents.

In adhesive formulations, surfactants are used to change many applications and end properties. They are used in the adhesive formulations to provide the following characteristics without negatively impacting adhesion.

  • Reduce surface tension to extremely low values for improved substrate wetting
  • Help to avoid defects occurring in the adhesive coating - especially on contaminated or difficult surfaces
  • Improve flow
  • Promote wetting and dispersion of additives
  • Optimize stability of pigments and latex particles
  • Overcoming foaming issues

They are also used by the latex raw material manufacturing to emulsify polymers in their liquid state and to provide the following characteristics:

  • Micelles formulation, where the polymerization reaction takes place
  • Protection of the polymer particles from agglomeration due to external stress (e.g., temperature during storage, high shear during application, etc.)
  • Significant reduction in surface tension
  • Prevent excessive foaming

Drawbacks of Using Surfactants in Adhesive Formulations


The major disadvantage of using surfactants is that they generally increase the water sensitivity of the adhesive. The surfactant also may not stabilize a latex in difficult situations, such as when the product is applied at high speed or when mixed with other systems.

Due to these factors and the thousands of surfactants that are commercially available, the selection process is difficult. Also, the formulator often needs to turn to trial-and-error.

Surfactants in Adhesives & Sealants: Where to get started with selection?

Let's discuss each and every factor you should consider while selecting a suitable surfactant for your formulation in detail.


Classification of Surfactants

Classification of Surfactants

To understand how surfactants operate and to select a surfactant for a specific purpose, it is necessary to classify surfactants according to their structural features. From the commercial point of view, surfactants are often classified according to their use. However, this is not very efficient because many surfactants have several uses.

For example, surfactants can be used as emulsifiers in one application and as wetting agents, dispersants, or stabilizers in another. A more accepted approach to classifying surfactants is by their structure and chemistry.

Structure of a Surfactant


A surfactant molecule consists of two key groups in its structure.

  • Polar hydrophilic head groups – It makes the surfactant soluble in polar solvents such as water.
  • Non-polar hydrophobic tail groups – It makes the surfactant soluble in non-polar solvents and oil.

The relative sizes and shapes of the hydrophobic and hydrophilic parts of the surfactant molecule determine many of its properties. The hydrophobic group in the surfactant structure is made up of hydrocarbon chains, fluorocarbon chains, and a combination of fluorocarbon and hydrocarbon chains or silicone chains.

However, surfactants are also characterized by the chemical structure of their hydrophilic groups, either ionic or non-ionic. This is depicted in the figure below.

Classification of Surfactants based on Head Type
Surfactant classification according to the composition of their head:
from top to down respectively non-ionic, anionic, cationic, and amphoteric

Ionic surfactants can, unlike non-ionic surfactants, dissociate into ions in an aqueous medium. The hydrophobic part can belong to a negative or positive ion.

Surfactants can generally be classified into four types:

  1. Anionic surfactants – The hydrophobic part is an anion, for example I-
  2. Cationic surfactants – The hydrophobic part is a cation, for example Na+
  3. Amphoteric surfactants – They have at least one anionic and one cationic group
  4. Non-ionic surfactants – They have neither positive nor negative charge

The hundreds of commercially available surfactants can be divided into the basic classes described above which makes the selection process much easier. The most important classes for adhesive and emulsion formulations are non-ionic and anionic.

Let's take a deeper look at these classes.

Anionic surfactants


Anionic surfactants contain negatively charged functional groups at their head. Examples of anionic surfactants are:

  • Sulfates
  • Carboxylates, and
  • Phosphate esters

These are the most common surfactant in general use (detergents, cleaners, etc.) and many find use in emulsion polymerization. This is because of their affinity for hydrogen bonding with the aqueous medium.


Cationic surfactants


Cationic surfactants contain positively charged functional groups at their head. Cationic surfactants are typically amine derivatives, such as quaternary ammonium compounds. Most of these surfactants are used as anti-microbials and anti-fungals. Cationic surfactants are less commonly used in adhesive formulations because of their certain limitations, such as:

  • High cost
  • Inefficient emulsifying capability, and
  • Undesirable effects on initiator decomposition

Cationic surfactants are avoided for being applied in waterborne systems. However, they are successfully used in solvent-borne systems, for instance to support the wetting and dispersing process.


Non-ionic Surfactants


Non-ionic surfactants (alcohol ethoxylate, EO/PO types, etc.) can be differentiated from ionic surfactants in important ways.

  • They do not dissociate into ions.
  • Since they do not dissociate into ions in water, they are less sensitive to electrolytes and pH changes.
  • They are soluble in acid and alkaline medium and are compatible with ionic and amphoteric species.
  • Unlike ionic surfactant, these surfactants are not preferentially adsorbed on charged surfaces.
  • Their solubility decreases with increasing temperature and at the cloud point, the aqueous solution becomes turbid.

Non-ionic surfactants are commonly used in adhesive formulations. However, in emulsion polymerization, they are rarely used alone due to their inferior efficiency in creating stable emulsions in comparison to anionic surfactants. Because of this, non-ionic surfactants are usually used with anionic surfactants and impart a second method of colloidal stabilization. Latexes that require stability over large pH ranges use larger non-ionic to anionic surfactant ratios.

Efficient Selection of Bio-Based Surfactants for Emulsion PolymerizationThe main classes of non-ionic surfactants are polyglycoether derivates such as:

  • Alkyl- and alkyl-aryl polyethylene glycol ether (alkyl PEG)
  • Polypropylene glycol ether, and
  • Block copolymers of polyethylene glycol and polypropylene glycol

Many long chain alcohols exhibit non-ionic surfactant properties.

For non-ionic surfactants, the chemistry and length of the hydrophilic chain can be varied to modify what is called the hydrophile-lipophile balance (HLB) for the surfactant. This is the ratio based on molecular weight of the oil loving (hydrophilic) to the water loving portion (lipophile). HLB affects interfacial behavior and the stabilization of emulsions and is important in selecting a non-ionic surfactant.

Considering all industries, there are thousands of surfactants that are commercially available. Within the adhesives industry non-ionic surfactants along with specialty surfactants such as fluoro- and silicone-based surfactants are the most commonly used. Anionic surfactants are also used primarily in emulsion polymerization processes.

Descriptions of >400 surfactants are contained in the SpecialChem Adhesives Additives Database. They include the various types of surfactants that are shown in table below and focused on in the remainder of this guide.

Anionic  Cationic  Non-ionic
Other
  • Alkyl ether sulfates
  • Phosphate esters
  • Alkylammonium salts
  • Acetylenics
  • Alcohol Ethoxylates
  • Alcohols
  • Alkyphenol ethoxylates
  • Amides
  • Amines
  • Amine oxides
  • Copolymers
  • Fatty acids
  • Nonylphenol ethoxylates
  • Fluorosurfactants
  • Silicone-based 
Types of Surfactants


The description and example of commercial surfactants within types mentioned above is given in the table below,

Surfactant Type Characteristics Example Product
Anionic Surfactants
Alkyl ether sulfates
  • Used as co-emulsifier for the manufacture of emulsion polymers used in adhesives
  • Provides good mechanical stability and high resistance to electrolytes
Alkylaryl polyglycol ether
Phosphate esters
  • VOC-free
  • NPE-free
  • Used as a highly hydrophilic emulsifier for alkyd resin and tackifier resin emulsions for adhesives
  • Offers high efficiency, very good long term stability and high compatibility
  • Can be used alone as single emulsifier or in combination with the anionic surfactants
  • Can be a UV curable additive
EO phosphoric acid ester
Cationic Surfactants
Alkylammonium salts
  • Used as emulsifier in adhesives
  • Stabilizes the polymer dispersion during polymerization and beyond - throughout the packaging, transportation, mixing and application stages
Anionic ammonium lauryl sulfate
Non-ionic Surfactants
Acetylenics
  • Low-VOC
  • Low-foam
  • Non-ionic wetting agent and surfactant
  • Used in waterborne systems
  • Possesses surfactant, low foam and low
  • water-sensitivity properties
  • Offers advantages such as enhanced dispersion quality and increased stability
Acetylenics
Alcohol Ethoxylates
  • Acts as an emulsifier or surfactant and also as a dispersant or dispersing agent
  • Acts as a defoamer / antifoam agent and low foam surfactant
  • Shows excellent solvency, low foam characteristics, chemical stability and other performance properties
POE-cetyl alcohol
Alcohols
  • Acts as a non-ionic surfactant,
  • Has good wetting and emulsifying properties
  • Dispersant for organic and inorganic particles
POE-tridecanol
Alkylphenol ethoxylates
  • Solvent free, proprietary surfactant blend, non-ionic/anionic and wetting agent
  • Used in adhesives
Alkylphenolethoxylate
Amides
  • Used as curing agent and surfactant for liquid epoxy resins in waterborne and solvent-free sealants
Modified polyamide/epoxy adduct
Amine Oxides
  • Provides emulsion stability and long term pH control for water emulsions
  • Neutralizes waterborne resins
  • Improves long-term stability
  • Controls viscosity stability
  • Can also aid in pigment dispersion and acts as a thickener activator
Low toxicity trifunctional amine.
Amines
  • Acts as a very good cross-linker in PU systems improving water and solvent resistance
  • Low foaming water soluble surfactant used in multiple applications as emulsifier or dispersant
Alkoxylated ethylene diamine
Copolymers
  • Acts as a defoamer / antifoam agent and low foam surfactant
  • Shows excellent solvency, low foam characteristics, chemical stability and other performance properties
  • Can be used as a stabilizer in waterborne pressure sensitive adhesives
  • Enhances the colloidal stability of the latex and improves dry film properties
  • Reactive towards vinyl unsaturated monomers
Linear EO/PO block copolymers
Fatty Acids
  • Used as a pigment wetting and as a dispersing agent in water-based adhesives and sealants
  • Offers compatibility with:

    • Water reducible resins
    • Pure acrylic
    • Styrene acrylic
    • Polyvinyl acetate and copolymers
    • Polyvinyl alcohol
    • Vinyl acetate-ethylene pressure polymers
    • Casein and polymer emulsion-silicate combinations
Formulation of surfactant and modified fatty acids
Nonylphenol Ethoxylates
  • Used in adhesives and emulsifier for the production of emulsion polymers such as:
    • Vinyl acetate
    • Vinyl chloride
    • Acrylates and acrylic copolymers and 
    • Styrene copolymers
  • Acts as a non-ionic surfactant
  • Soluble in organic
  • polar solvents and water
  • Versatile emulsion polymerization
  • surfactant and latex post-stabilizer
Sodium nonylphenolether sulphate
Other Surfactant Chemistries
Fluorosurfactants
  • Provides surface tensions as low as 15 dynes/cm in water at very low concentrations
  • Has excellent dynamic surface tension properties
  • Imparts excellent wetting; spreading, leveling and flow control properties on various types of water-based as well as solvent-based systems
  • Typical uses include leveling and anti-static agents for adhesives and caulks
  • Applications are generally those in which typical hydrocarbon surfactants are found to be inadequate
Short-chain perfluoro-based amphoteric fluorosurfactant
Silicone-based
  • Acts as a superwetting agent
  • Contains no added:
    • Hazardous air pollutants (HAPs)
    • Alkylphenol ethoxylates (APEs) and
    • Volatile organic compounds (VOCs)
  • Provides a superior balance of equilibrium, dynamic wetting, system compatibility and low foam when compared to traditional siloxane surfactants
  • Primarily recommended for high-quality waterborne adhesives
Siloxane based surfactant
Polyamide / Acid Ester Salts
  • Used as a lead-free, high-efficiency activator for foam compositions
  • Can be used as an activator in plastic foams
  • EPDM, and PVC/nitrile sponge compounds
  • Applications: closure sealing gaskets for food containers
Stearic acid salt
Description and Examples of Common Surfactants Used in Adhesives and Emulsions

Surface active adhesive additives are rarely mono-molecular products; they are mainly polymeric. These are preferred for reasons of providing:

  • Best performance
  • Best film integrity
  • Low risk of being extracted from the dried film and minimal side effects


Working Mechanism of Surfactants

Working Mechanism of Surfactants

The term surfactant is the acronym of surface active agent. Surfactants are materials that lower the surface tension (or interfacial tension) between two liquids or between a liquid and a solid. The surface tension is defined as "the force which acts in a material to adapt the smallest possible surface under the set conditions".

In the general sense, any material that affects the interfacial surface tension, can be considered a surfactant. But in the practical sense, surfactants may act as wetting agents, emulsifiers, foaming agents, and dispersants. Surfactants reduce the surface tension of water by adsorbing at the liquid-air interface.

Surface activity is achieved when the number of carbon atoms in the hydrophobic tail is higher than 8.

  • Surfactant activities are at a maximum if the carbon atoms are between 10 and 18 at which level a surfactant has good but limited solubility in water
  • If the carbon number is less than 8 or more than 18, surfactant properties become minimal
  • Below 8, a surfactant is very soluble and above 18, it is insoluble

Thus, the solubility and practical surfactant properties are somewhat related.

Micelle Formation


Many surfactants can also assemble in the bulk solution into aggregates. Such aggregates are known as “micelles”. The concentration at which surfactants begin to form micelles is known as the critical micelle concentration (CMC). When micelles form in water, their tails form a core that can encapsulate an oil droplet or polymer product, and their (ionic/polar) heads form an outer shell that maintains favorable contact with water. The formation of micelles leads to the stabilizing effect provided by surfactants in solution.

Structure of Micelle
Micelles Around a Polymer Particle Provide Protection

The hydrophobic tails form the core of the aggregate and the hydrophilic heads are in contact with the surrounding liquid. The shape of the aggregates depends on the chemical structure of the surfactants, namely the balance in size between hydrophilic head and hydrophobic tail. A measure of this is the HLB, hydrophilic-lipophilic balance.

Most waterborne adhesives are an emulsion of polymer particles dispersed in water. So surfactants are added by the emulsion manufacturer to lower interfacial tension and stabilize polymer particles to prevent demulsification.


What are the Properties Affected by Surfactants?

What are the Properties Affected by Surfactants?

Surfactants affect a wide array of physical properties in adhesive systems. Surfactants affect the behavior of the adhesive not only during the formulation and application process but also during the lifetime of the bonded joint.

For example, surfactants are used to stabilize the dispersion of polymer particles during emulsion polymerization. The addition of surfactants improves:

  • Mechanical stability
  • Freeze-thaw stability, and
  • Shelf-life of paints

The addition of surfactants also allows the adhesive to coat and wet a surface more easily. This is because surfactants increase the wetting of a solution.

However, the addition of surfactants does not always have a positive effect on all properties. The water resistance of the coating can be decreased with surfactant addition. This is because surfactants can be very water-soluble and will easily migrate out of the adhesive bond during service. The type and amount of surfactant will determine which water properties are affected and the extent of the change.

Fluorocarbon and Silicone-based Surfactants


Fluorocarbon and silicone-based surfactants have a unique place in the surfactant industry. These surfactants in water and non-aqueous systems reduce the surface tension lower than the hydrocarbon chain surfactants. Both fluorocarbon and silicone chain surfactants have better thermal and chemical stability than hydrocarbons. Also, they provide excellent wetting for low-energy surfaces. However, due to their costs, these surfactants are used in limited applications.

Surfactants may be added before the emulsion polymerization process or to already manufactured emulsions to further improve their properties. A mixture of anionic and non-ionic emulsifiers is generally used.

Surface Active Properties of Surfactants


The principal surface active properties exhibited by surfactants are listed below1. Many surfactants possess a combination of these properties.

  • Wetting
  • Foaming / defoaming
  • Emulsification / demulsification of emulsions
  • Dispersion / aggregation of solids
  • Solubilization due to hydrotropic properties
  • Adsorption
  • Micellization
  • Detergency (which is a complex combination of several properties)
  • Synergistic interactions with other surfactants

In addition, depending on the chemical composition of a particular surfactant, some products may possess important secondary properties including:

  • Corrosion inhibition
  • Biocidal properties
  • Lubricity
  • Stability in highly acidic or alkaline media
  • Viscosity modification
  • Conformance to FDA or BGA regulations for some applications, e.g. direct/indirect food contact

From this list one can immediately see the great number of functions that a surfactant can provide. Also, the difficulty inherent in selecting a surfactant for a particular formulation or set of requirements. As a result, the formulator must know what properties need to be adjusted by the use of the surfactant additive.

Emulsion adhesive films prepared with conventional surfactants can show increased weight by up to 120%. This is due to water uptake, especially at high surfactant concentrations. The water uptake leads to general degradation in both adhesive and cohesive properties of the emulsion film.

In addition to increase in water sensitivity, surfactants may migrate if incompatible, to the adhesive surface. This causes a decrease of tack. Surfactants that are compatible with the adhesive generally act as plasticizers. They may increase tack and peel adhesion and decrease shear resistance. Table below shows the effect of some surfactants on the properties of a pressure sensitive adhesive.

Surfactant Type Amount, phr Surface Tension
dynes/cm
180 Degree Peel Strength
N/m
Shear Creep Resistance
Hours
Rolling Ball Tack
cm
No surfactant 0 48.7 426 11.0 3.0
Fluorocarbon 0.02 45.9 404 8.0 3.0
Non-ionic 0.2 46.0 481 6.7 3.6
Anionic 0.2 40.0 393 6.4 5.9
Effect of Surfactants on the Physical Properties of Pressure Sensitive Adhesives



Surfactant Selection and Formulation Guidelines

Surfactant Selection and Formulation Guidelines

The chemical structure of a surfactant is not the only important factor in selecting surfactant candidates for a given application. Economic, ecological, regulatory, and other considerations such as functionality are also important in surfactant selection. The relative role of the surfactant must be evaluated along with its compatibility with other formulation ingredients.

If the cost of the surfactant is significant compared to that of other components of a system, the least expensive material producing the desired effect will usually be preferred, all other things being equal. However economics cannot be the only factor, since the final performance of the system will be of crucial importance.

To make a rational selection of a surfactant, without resorting to an expensive and time consuming trial-and-error approach, the formulator must have some knowledge of the following.

  1. The surface and interfacial phenomena that must be controlled in the specific application.
  2. The relationships among the structural properties of the available surfactants and their effects on the pertinent interfacial phenomena to be controlled.
  3. The characteristic chemical and physical properties of the available surfactant choices.
  4. Any special chemical or biological compatibility requirements of the system.
  5. Any regulatory limitations on the use a given class of materials (toxicity, allergenic reactions, ecological impact, etc.).
  6. Public acceptance - ‘‘Natural’’ versus ‘‘Synthetic’’2.

Unfortunately, there is no universal surfactant. The selection of the optimal additive and its incorporation into an adhesive formulation requires special consideration. Generally, the selection will depend mainly on factors, such as:

  • Compounding and application requirements
  • End-use requirements
  • Type of carrier (specific solvent or water)
  • Nature of suspended particles, and
  • Nature of the resin or emulsion and other ingredients in the formulation (to a lesser extent)

The selection of a surfactant is based on:



Selection Based on Adhesive Type and Form of Rheology


Tables below provides a guide as to the surfactants that have been typically been used with various adhesive systems. Since there is a broad range of surfactant chemistries available, the formulator should discuss the optimal candidate for specific formulations with the surfactant supplier.

Adhesive System Acetylenics Alcohol Ethoxylates Alcohols Alkyl -Ether Sulfates Alkyl-ammonium Salts Alkyl-phenol Ethoxylates Amides
Acrylic and acrylic copolymers
Aminoplasts / phenoplasts
Epoxies
Ethylene co-terpolymer emulsions
Ethylene co-terpolymer solids
Natural rubbers
Polychlorovinyls
Polyesters
Polyolefins
Polyurethanes
Polyvinyl acetate emulsions and derivatives
Polyvinyl alcohol
Styrene copolymers
Synthetic rubbers
Surfactants for Specific Adhesive Chemistries (Part 1)


Resins Amines Co-polymers Fatty Acids Fluoro-surfactants Nonyl-phenol Ethoxylates Phosphate Esters Silicone-Based Polyamides /Acid Ester Salts
Acrylic and acrylic copolymers
     ✔
Aminoplasts / phenoplasts
Epoxies
Ethylene co-terpolymer emulsions    
Ethylene co-terpolymer solids  
Natural rubbers    
Polychlorovinyls  

Polyesters  
Polyolefins  
Polyurethanes    
Polyvinyl acetate emulsions and derivatives    ✔

Polyvinyl alcohol

Styrene copolymers      
Synthetic rubbers    
Surfactants for Specific Adhesive Chemistries (Part 2)

Surfactants are supplied in several forms. The choice of form is mainly dependent on the compounding processes used by the formulator and whether it is waterborne, solvent based, or solventless system.

Table below shows the forms that are typically available for common surfactants. Again, since there is a broad range of surfactants and forms available, the formulator should discuss the optimal form for specific formulations with the supplier of the surfactant.

Surfactants Flak-es Gel Dispe-rsion Emul-sion Gran-ules Pellets/ Beads Various Liquid Powder Solid
Acetylenics                 ✔    ✔
Alcohol Ethoxylates                ✔
   
Alcohols                 ✔    ✔
Alkyl Ether Sulfates                 ✔
   
Alkylammonium Salts
               ✔
   
Alkylphenol Ethoxylates               ✔
 ✔
   
Amides       ✔
     ✔
 ✔
 
 ✔
 
Amines                ✔
   
Copolymers           ✔
     ✔
   ✔
Fatty Acids   ✔
   ✔
         ✔
   ✔
Fluorosurfactants     ✔
         ✔
 ✔
   
Nonylphenol Ethoxylates
               ✔
   
Phosphate Esters
   ✔
       ✔
   ✔
 ✔
 
Silicone-Based
       ✔        ✔  ✔  
Polyamides / Acid Ester Salts                 
 ✔
 
Physical Form of Common Surfactants Used in Adhesive Systems 


Selection Based on Performance Properties


Performance considerations for selecting a surfactant include the criteria listed in table below.

Required Performance as a Liquid and Coating Required Performance Properties in a Joint
  • Appearance (uniformity, transparency, color stability, etc.)
  • In-can stability (resistance to agglomeration, sedimentation, and separation)
  • Ease of incorporation(mixing requirements, pumpability, etc.)
  • Wetting of the substrate
  • Flow and leveling of applied adhesive coating
  • Application performance(spray, brush, roller, etc.)
  • Defoaming
  • Viscosity modification
  • Moisture resistance
  • Durability
  • Adhesion
  • Minimal negative effect on other physical properties
  • Conformed to FDA or other regulations
Selection Considerations for Surfactants in Adhesives and Sealants 

The comparative properties of the various surfactants are generally provided in the discussions above and can be better defined by the surfactant supplier. These can be condensed into the following criteria for both waterborne and solvent based formulations.

  • Rheological requirements of the liquid formulation (during all stages of its product life)
  • Ease of incorporation into the formulation
  • Physical properties of the adhesive coating or sealant after it is immediately applied
  • Permanence and durability after it is applied and during its service life
  • Total cost of the formulation (materials, processing, energy, waste, etc.)

Due to the extreme variations in possible surfactant chemistry and in specific adhesive formulations, it is not possible to list the preferred properties of every surfactant. However, this can be generalized. The overall properties of the two most common surfactants for adhesives (anionic and nonionic) are summarized in table below:

Property Surfactant Type
Anionic Non-Ionic
Wetting ability Good Fair
Resistance to moisture Poor Fair
Resistance to foaming Poor Fair
Shear stability Best Fair
Chemical stability Good Best
pH stability Good Best
Discoloration resistance Good Good
Resistance to micro-organisms Fair Fair
Comparative Properties of Surfactants Commonly Used In Adhesive Formulations

For the successful broad application of emulsion adhesives, it is important to eliminate the detrimental effect of surfactants such as moisture resistance. The type and amount of surfactant used has an effect on moisture resistance as well as other properties. However, the major approaches have been to use surfactants that are less sensitive to moisture or less likely to migrate. This has generally followed one of two paths:

  • Use of reactive or polymerizable surfactants that become chemically bound to the polymer particle. The surfactant then remains in the film and phase separation is no longer possible.
  • Use of fugitive surfactants that evaporate from the coating during the drying process.


Formulation Guidelines for Surfactants


Non-ionic surfactants may be classified based on their percent hydrophile using the HLB (hydrophile-lipophile balance) scale. Thus, the more hydrophilic the surfactant, the higher the HLB value. To calculate HLB value, the molecular weight of the hydrophile is divided by the total molecular weight of the surfactant molecule, giving the percent hydrophile. This is arbitrarily divided by 5 to convert the percent hydrophile to a scale of 0 to 20.

Surfactants within different ranges of HLB value may be loosely categorized for different end uses as shown in table below:

HLB Value Optimal Application
0-3 Antifoaming agent
1-3 Mixing unlike oils together
4-6 Mixing water-in-oil emulsions
7-9 Wetting powders into oils
7-10 Making self-emulsifying oils
8-16 Making oil-in-water emulsions
13-15 Making detergent solutions
8-18 Mechanical stabilization
13-18 Solubilizing oils into water
Non-Ionic Surfactants Uses by Typical HLB Value Range 

New research demonstrates that traditional methods of using surfactants at the end of the formulation process limited their effectiveness in solving issues facing today’s low-VOC adhesive formulation needs. Although they have been traditionally used to correct performance near the end of the formulation process.

Scientific research shows more and more evidence that, surfactants are most effective when incorporated early during the initial design of the adhesive formulation. This allows formulators to take out unnecessary (redundant) additives to achieve the best results.

This is particularly important in formulating low- and zero-VOC coatings. Fluorosurfactants have been shown to be especially effective when this strategy is used.3

Trends Driving Development of New Surfactants

Trends Driving Development of New Surfactants

The recent trends in the development of new surfactants have been mainly related to the issues as discussed below.



Trend 1: Environment Safe Surfactant


Recognition of the environmental issues surrounding higher chain length fluoropolymers has led producers to increase research efforts. The hunt is for the identification of short chain alternatives that provide similar performance characteristics. These efforts will result in the development of additional new fluorochemicals and other surfactant chemistries to ensure the continued growth of the surfactant market.

Growing demand for biosurfactants in developed economies of Europe and North America is expected to create new avenues for industry participants. This is on account of growing consumer awareness and regulatory pressure to reduce reliance on their synthetic counterparts. Governments across these regions have also been promoting the use of biosurfactants which promotes industry participants to increase its production.


Trend 2: Surfactant with Low VOC Level


Most of the efforts in adhesive and coating formulation development have been to reduce volatile organic compound (VOC) emissions. This is done by decreasing the amount of solvent. This has resulted in development and close analysis of surfactants in these formulations in high-volume adhesive systems such as latex emulsions for tape converting which meet strict VOC standards.

Sometimes surfactants used as wetting, flow and leveling agents are fugitive. This implies that they no longer serve a useful function after performing their primary function. Also, they can move about the bulk or surface of any object into which they are formulated. This can have two undesirable consequences:

  1. The unexpected presence of a surfactant at an inappropriate interface can cause the surface to be much more hydrophobic or hydrophilic than expected for the base formulation.
  2. The fugitive surfactant can enter the eco-sphere and if toxic create health and safety issues.

Related Read: Formulating Adhesives and Sealants with VOC Restrictions


Trend 3: Surfactant with Low Migration


The optimum path to permanence is through the use of a reactive surfactant. This is accomplished by addition of a curable functional group such as a reactive acrylate that can homo-polymerize (forming an interpenetrating network) or react with other functional groups present in the binder resin.

The surfactant market is extremely diverse and includes many primary product manufacturing industries and segments. Surfactants are used in formulated adhesive products to provide optimum performance. The trends noted above will result in continued development of new products and added value propositions for the adhesive formulator.


References
  1. Karsa, D. R., “History and Applications of Surfactants” Chapter 1 in Chemistry and Technology of Surfactants, edited by Richard J. Farn., Blackwell Publishing Ltd., 2006.
  2. D. Myers, Chapter 2 “The Organic Chemistry of Surfactants”, in Surfactant Science and Technology, 3rd ed., John Wiley & Sons, Inc., 2005, p. 33.
  3. Meng, J., “Novel Applications for Fluorosurfactants in Low-VOC Coatings”, Paint & Coatings Industry, April 2007, pp. 84-88.

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