Powdered Thickening Agent Adds Sustainability, Safer Ingredients, and Performance

TAGS:  Sustainability / Natural Coatings     Polyurethane Coatings    

This is a sponsored article by Elementis.

A rheology modifier or thickener is the ingredient used to control the viscosity of coating or adhesive, or more precisely the rheology profile, which includes the yield stress and viscosity at different shear modes and rates.

Formulators use rheology modifiers to provide the right viscosity application profile, whether by brush, roller, trowel, or spray.

Rheology modifiers and thickeners are used in waterborne and solvent-borne coatings, adhesives, and sealants of all types. They are used extensively in waterborne formulations, and often two or more are used to achieve the required balance of properties for a particular application.

In addition to tailoring the viscosity profile, formulators also add rheology modifiers to achieve a variety of other desired characteristics such as:

• improved coating performance,
• non-sag properties,
• thickness build,
• adhesion, and
• other properties related to the flow (rheological) properties of the formulation.

The use of a rheology modifier will depend on the internal manufacturing needs of the formulator and on the end-use application requirements. Rheology modifiers offer several value propositions such as:

• Reduce settling/increase shelf life
• Reduce time and energy costs for mixing and pumping
• Increase thickening efficiency and reduce raw material costs (use less product and keep the same performance level)
• Reduce splatter during coatings manufacture and application
• Increase manufacturing or converting speed, especially in tape, label, and laminate coating processes
• Reduce penetration into porous substrates
• Increase sag resistance
• Increase coating build (thickness) per application
• Improve sprayability, brushability, and other application processes

Modern synthetic rheology modifiers are polymers that can be grouped into one of several classifications and types¹. It is possible to select the thickener dependent on the shear conditions (Table 1) that are expected. One of the most popular rheology modifiers in coatings is an associative thickener, HEURs (hydrophobically modified, ethoxylated urethane resins).

Region	Shear Rate, sec-1	Viscosity, cps	Process	Common Viscosity Measurement Instrument
Low	0.001 – 1.0	100 – 100,000	Settling, leveling, suspension, sag resistance, etc.	Brookfield DV-II+ using a spindle @ 0.3 rpm
Mild	1.0 – 1,000	10 – 10,000	Mixing, pumping, in-can appearance, consistency, etc.	Brookfield KU-1 using a paddle @ 200 rpm
High	1,000 – 1,000,000	1 - 5000	Application (brush, roller, etc.), film build, sprayability, etc.	ICI cone and plate viscometer

Table 1: Shear Regions of Concern to the Formulator
Let’s review the importance and value of rheology modifiers in waterborne adhesive formulations with an emphasis on a new family of rheology modifiers available from Elementis, which are 100% solid urethane rheology modifiers that provide high-performance and more sustainable aqueous formulations.

Powder Urethane Rheology Modifiers by Elementis

Elementis developed and patented powder nonionic synthetic associative thickeners (NiSATs) in the early years of 2000. Since then, powder NiSAT technology has been well accepted by many customers in their aqueous formulations. Common applications have been in waterborne coatings, inks, adhesives, and sealants.

These 100% active powders can easily be incorporated into paint formulations, resulting in improved handling, increased efficiency, and satisfying the latest health and safety demands. The products are supplied as a white free-flowing powder and enable formulations of odorless paints, free of organic solvent, APEO, tin, and biocides. The recent development of RHEOLATE® PHX 7025 completes the family and enables full freedom in the formulation.

	RHEOLATE® FX 1100	RHEOLATE® 208	RHEOLATE® PHX 7025
Chemistry	Polyether urea Polyurethane Associative thickener	Polyether urea Polyurethane Associative thickener	Polyether polyurethane Associative thickener
Shear profile	Low	Mid-High	High
Property profile
Use for	WB systems, like coatings and adhesives.	WB systems, like coatings and adhesives.	Designed for the use in WB systems, like coatings, adhesives and sealants, inks, textile coatings.
Details	Contributes to low shear which impacts sag resistance, higher film build and improved edge covering. Perfect partner for RHEOLATE® PHX 7025.	Very effective in small-particle-size latex emulsions and in high-volume-solid systems. Can be used as a stand-alone thickener in formulations.	Contributes very effectively to high shear which impacts flow and leveling, roller spattering and brushout. Perfect partner for RHEOLATE® FX 1100.

Table 2: Chemistry and Rheology Profiles of Elementis RHEOLATE® Powder NiSAT Rheology Modifiers
Instructions for formulation incorporation and use levels are indicated in Table 3. Since these rheology additives are 100% solid, it is recommended that they be stored in dry conditions and kept away from excess heat. Additional information relative to specific formulations or applications can be accessed by contacting Elementis.

Product	Methods of Incorporation	Use Levels
RHEOLATE® PHX 7025	Pigmented systems (mill base) — The product can be added to the mill base and should be sheared under milling conditions (e.g., 14 m/s). Adequate time will depend on the PVC of the paint. Post addition — Product can be used in the letdown. A minimum speed of 8 m/s and 30 min provides particle-free incorporation in low PVC paint. As an intermediate — Incorporation into the water at a low stirring speed is possible to allow solutions of 20% and higher. A biocide additive is recommended when used for a longer time.	Typical use levels are 0.1% to 0.6% (thickener supplied) on total system weight. A ladder-loading study test should be run to determine the most suitable dosage.
RHEOLATE® 208	Pre-dispersed — Best incorporated pre-dispersed as a water gel. The method of pre-mix is 96 pts water to 4 pts of RHEOLATE® 208. Mix at moderate speed for 15 mins. Dry addition — Under the right conditions, the product may be used as a dry addition to the mill base.	Typical use levels are 0.1% to 0.6% as delivered on the total paint weight. Must be evaluated in the complete formulation (e.g., the system’s surfactant blend may need modification for optimal properties).
RHEOLATE® FX 1100	Pre-gel — Usually added as a pre-gel or added directly to the milling paste prior to the addition of pigments and extenders. The suggested pre-gel is 97 pts water, 3 pts RHEOLATE® FX1100. Dry addition — The product can also be added as a dry powder by just mixing with the various other components – enabling high solids coatings.	In dispersion paints a concentration between 0.2 and 1.0 % RHEOLATE® FX 1100 will generally be sufficient when used as the sole thickening agent.

Table 3: Method of Incorporation and Use Levels

Associative Modification Mechanism

The Elementis powder NiSAT rheology modifiers are classified as associative thickeners. They work in a unique way compared to other rheology modifiers.

• Associative thickeners form intermolecular associations with dispersed particles (resin or filler). These interactions are the result of the presence of insoluble hydrophobic groups along the water-soluble thickener’s molecular backbone.
• Once added to water, the hydrophobic groups assemble into aggregates or micelles, and a three-dimensional network is formed which causes the medium’s viscosity to increase (Figure 1).
• The formation of hydrophobic domains is separated during shear conditions and becomes interwoven with the polymer chains.
• The domains will reform once the shear has been removed, at a recovery rate that is dependent on polymer structure, thickener concentration, and several other factors.

The thickening effect will depend on the type and number of hydrophobic groups per polymer chain and the molecular weight of the modifiers. Factors that need to be considered when formulating with associative rheology modifiers include the presence of co-solvents and the order of component addition.

• Selected co-solvents (especially alcohols) can interfere with the associative domains and suppress the associative mechanism.
• The order of addition of formulation components will have an impact on processing and may affect the overall performance of the compound.

Advantages of associative rheology modifiers

1. They are considered to be highly efficient and versatile.
2. They are especially attractive in higher viscosities at high shear rates (roll coating for example) that lead to good film build per application with little spatter.
3. They also improve the stability of the system by coating the latex particles or filler particles with a protective layer that helps to prevent coagulation and settling during storage.

Disadvantages of associative rheology modifiers

1. Hydrolytic instability,
2. Phase separation, and
3. Sensitivity to formulating changes.

Enhancing Sustainability with NiSAT Rheology Modifiers

Sustainability efforts often make good business sense, promising to deliver revenue gains, cost savings, and other benefits that lift enterprise value³. For most paint suppliers, sustainability has become an essential part of their marketing strategy. For example, sustainable certifications allow suppliers to differentiate themselves by proving that their products meet key environmental factors.

There are many ways of bringing sustainability to the coatings industry. A simple change in one minor additive in a formulation can promote sustainability downstream, all the way from the paint formulator to the end user. A rheology modifier is a good example of this. The amount usually introduced is very small, often less than 1%, however, the impact on properties and sustainability can be huge.

The use of powder NiSAT rheology modifiers in coating formulations generates several benefits in the logistic and production processes that are related to sustainability:

• By ordering a powder the transportation volume is significantly reduced. Fewer trucks are needed for the required volume, which reduces the carbon footprint on transportation by up to 80%⁴. The reduced volume requires less storing area than with the liquid thickener version, up to 5 times.
• Material moves within the manufacturer are reduced so that supply to the various processes will be faster and logistical time savings can be expected.
• Powder thickeners have long shelf lives (two years for RHEOLATE® 208 and three years for RHEOLATE® PHX 7025 and RHEOLATE® FX 1100).
• NiSAT thickeners are cost-effective powders, free of any solvents, which are highly efficient at low loading levels.
• NiSAT powder thickeners are free of emulsifiers and surfactants which can have an influence on wet and dry film properties.
• Solid powder thickeners only target rheology. High efficiency compared to liquid versions brings a reduction in the processing steps, time consumed, and cost of manufacture. A comparison of effectivity was done in an aliphatic polyurethane-alkyd dispersion, and it shows a higher effectivity of up to 18%.

Adding Safer Ingredients to the Paint Formulation

RHEOLATE® powder NiSAT provides great advantages regarding the health and safety profile of aqueous products.

• Because of the 100% solid form, biocides are not needed to preserve the material.
• They require no emulsifiers or surfactants, so the VOC content can be lowered significantly in the paint formulation.
• With safer ingredients, RHEOLATE® NiSAT powder thickeners allow the formulation of asthma and allergy-friendly paints.

Elementis RHEOLATE® powder NiSATs are free of any hazardous labels as shown in Table 4. ECO-label and other certificates show additional beneficial properties when compared to conventional liquid rheology modifiers.

		RHEOLATE® FX 1100	RHEOLATE® 208	RHEOLATE® PHX 7025
Enabling Labeling Compliance	EU Ecolabel	✓	✓	✓
	Nordic Swan	✓	✓	✓
	Blauer Engel	✓	✓	✓
	Asthma Allergy Nordic	✓	✓	✓
	French NF Environmental	✓	✓	✓
	Green Guard Gold	✓	✓	✓
	Leed 4.1	✓	✓	✓
	Declare	✓	✓	✓
	A.A.F.A (Asthma Allergy Foundation America)	✓	✓	✓
Additional Information	Biocide Free	✓	✓	✓
	VOC Content*	0%	0%	0%
	SVOC Content*	0%	0%	0%
*based on boiling points of ingredients (theoretical assumtion) Note: This document is purely meant to provide an overview for guidance purposes. It is the responsibility of the manufacturer of the final product to fulfill the compliance criteria of the respective labels in final formulation.

Table 4: Labeling Compliance of RHEOLATE® Powder NiSAT Rheology Modifiers

Improving Formulation and Performance Properties

Flexible formulation

The incorporation of powder rheology modifiers requires equipment with adequate shear forces. The Elementis RHEOLATE® NiSAT powder family is very flexible in its incorporation and can be incorporated with low shear forces. The following processes can be followed (also see Table 3):

• Mill base - The mill base process provides enough shear forces to incorporate the thickener easily and effectively. Studies in low PVC paint at a tip speed of 14 m/s for 30 min showed drawdowns free of particles.


• Post-addition - Post-addition processes are run at a lower speed than mill base processes. Internal studies in low PVC paint have revealed that 8 m/s in combination with ca. 30 min allows the incorporation of the powder thickener without remaining particles.


• Intermediate - The powder thickener family allows the creation of intermediates with different solid content. RHEOLATE® PHX 7025 can easily be introduced up to the level that is offered by the liquid version (20%). Higher contents are possible and depend on handling. It is recommended to add biocide when the intermediate is used over a long period of time.

Wet and dry film properties

The use of powder thickeners enables the improvement of wet and dry film properties. This is possible because powder thickener does not require substances such as emulsifiers and surfactants, which can have a negative influence on the wet and dry properties of the film.

Figure 2 shows a comparison of high shear thickener (HST) where color acceptance and color rub-out behavior were studied when adding a colorant to a paint based on an aliphatic polyurethane-alkyd dispersion. RHEOLATE® PHX 7025 remains stable in viscosity and provides very stable color values.


Figure 2: Color Acceptance - Rub Out [dE] / Drop KU [dKU]
A significant difference in rheology modifiers can also be noticed when block resistance is tested. Figure 3 illustrates the impact of thickeners on block resistance. RHEOLATE® PHX 7025 shows excellent block resistance when compared to other rheology modifiers.


Figure 3: Block resistance of RHEOLATE® PHX 7025
RHEOLATE® PHX 7025 can be combined with RHEOLATE® FX 1100 to influence the rheological profile at any shear rate. The influence of RHEOLATE® PHX 7025 was studied in a styrene acrylic wall paint formulation. As shown in Figure 4, the increased loading of the high-shear thickener in the thickener package helped to improve both hiding power and brush marks.


Figure 4: Effect of RHEOLATE® FX 1100 addition to PHX 7025 thickener

Conclusion

The waterborne coatings industry is constantly seeking higher-performing, safer, and more sustainable products. A simple change in rheology additive can impact the entire value chain when considering overall sustainability and property performance effects. To meet the needs of the industry, Elementis has successfully designed a family of 100% active powdered urethane rheology modifiers (nonionic synthetic associative thickeners, NiSATs).

The RHEOLATE® powder NiSAT product range (RHEOLATE® 208, RHEOLATE® FX 1100, and RHEOLATE® PHX 7025) is suitable for high-performing formulations.

• They show improved handling, increased efficiency, and the ability to meet the latest eco-labeling requirements.
• They also provide great advantages regarding the health and safety profile of resulting formulations.

Due to the 100% solid form, no biocides, emulsifiers, or surfactants are required, resulting in a VOC-free product range.

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