APPLICATION INFORMATION
ADDITIVES FOR POLYURETHANE APPLICATIONS

TS-A 8

02

Additives for polyurethane applications

Contents
03	
Introduction to polyurethaneapplications
04 Air release additives
06 Wetting and dispersing
08 Rheology
10 Surface additives
10 Processing additives

11 Viscosity reduction
12	Processing additives for
improved compatibility
15	Summary of additive
recommendations

03

Introduction to polyurethane applications
The polyurethane industry is a diversified area with manydifferent applications and their related formulations.
Polyurethane parts can be small or large, solid or foamed,flexible or rigid.
Technically, a polyurethane can be any polymer with aurethane linkage in its back­bone chain. Various problems
related to the application type and formulation often exist
for polyurethanes because of their chemical complexity
and wide range of uses.

This application information offers an overview ofadditives designed to help the fabricator or processor
deal with:•	Air entrapment, pinholes, and foam formation•	Flow and leveling as well as substrate wetting problems•	Viscosity reduction in filled and non-filled systems•	Sedimentation and floating of solid particles in filledsystems•	Viscosity differences between polyols and isocyanates•	Separation of liquid components (polyols and chainextender)
The additives listed in this guide are applicable for rigid
and elastomeric systems such as: casting, lining, flooring,
reaction injection molding (RIM), syntactic foam, spray
application (i.e. coatings and decking), foam applications,and adhesives and pigment concentrates.

For additional information
on additives and technical
topics, please contact us:
Thermosets.BYK@altana.com

Note
To ensure the best appearance
and full functionality, please
open in Adobe Acrobat.

04

Additives for polyurethane applications

Air release additives
Entrapped air bubbles are a common challenge inmanufacturing or applying polyurethane based systems.
They are difficult to remove, especially in highly thixotropic
and pseudoplastic formulations or high wet film thickness.
These same air bubbles ultimately develop into pinholes,
which increases porosity and dramatically reduces the overall
performance of the final part. Defoamers as well as air
release additives can prevent:• Blisters• Pinholes• Loss of insulation properties in electrical casting systems• Weakening of the composite structure• Poor appearance• Porosityof the final part.

Air release additives work in three steps
1. Displacing air from filler and reinforcement
materials
By reducing the interfacial tension between resin andfiller/reinforcement materials, the trapped air is displaced
into the resin.

3. Bubbles burst on the surface
Bubble-stabilizing substances are displaced and thebubbles burst.

2. Smaller bubbles coalesce to form large bubbles
Bubble-stabilizing substances are displaced by the air release
additive. Smaller bubbles coalesce to form larger bubbles,
which rise to the surface faster because of their higher
buoyancy (Stokes’ law).

Air release additives work in three steps
Step 1

Step 2

Step 1

Step 3

Step 2

Step 3G. 01

05

Additives for polyurethane applications / Air release additives

Some additives are especially designed for specificrequirements, e.g. potable water, AgBB, high voltage, etc.
As regulations can change, please refer to the relevant
documents on our website or contact our product safety
department.

Air release additives can be based on (modified) polysiloxanes,silicon-free polymers, or a combination of both. Whether or
not a particular polymer can destroy foam bubbles depends
on the product compatibility and solubility in the liquidmedium. All defoamers and air release additives must havesome degree of incompatibility – managing that delicate
balance between compatibility and incompatibility. This isachieved by adjusting the molecular weight and/or polarityof the polymeric structures.

Recommendations for air release additives
SystemProductRemarks

Silicone-based

BYK-141Universal air release additive

BYK-1796

Very effective, solvent-free

BYK-A 535

Low polar, solvent-free
for food contact*

BYK-1790

Very effective, solvent-free air
release additive

BYK-088

Very effective, universal air
release additive

Optimized dosage
Silicone-free,polymer-based

BYK air release additives achieve excellent deaerationeven at small dosage levels.

Silicone/polymer
combination* F or details on food contact use, please refer to thefood contact sheet available on
www.byk.com/en/service/regulatory-affairs/food-contact.

Air release in a 2-pack polyurethane system

BYK air release additives

Without additive

Air bubbles

none

many

0.5 % BYK-088

T. 01

00.5

1
Additive (%)

G. 02

G. 03

06

Additives for polyurethane applications

Wetting and dispersing
One of the most important steps in producing filled orpigmented polyurethane systems is the homogeneous
distribution of the solid pigments and fillers within the liquid
resin solution. If this step (grinding) is not optimized, a wide
range of defects such as flocculation, flooding and floating(pigment separation), and settling can occur as well as poor
flow behavior during application. Wetting and dispersing
additives are added prior to the incorporation of the filler/pigment.

They will accelerate the wetting of solid particles, stabilize
them, and can provide the following benefits:• Viscosity reduction• Improved flow
• Increased filler load
• Reduced filler sedimentation• Color homogeneity

Viscosity

Wetting and dispersing additive: lower viscosity or higher filler load

Increasing the filler load while
maintaining the viscosity

Reduction of viscosity

Filler loadReference  

Formulation including wetting and dispersing additive

G. 04

07

Additives for polyurethane applications / Wetting and dispersing

By using wetting and dispersing additives, a lower viscosity
can be obtained. When the viscosity is reduced, the choice
between better flow or an increase of filler load can bemade (G. 04). Selecting the correct additive is dependent
on the application requirements and the raw materials.
A combination of wetting and dispersing additives with air
release additives will improve the final result.
Depending on the structure of the wetting and dispersing
additive, it can reduce the viscosity or stabilize the systemagainst sedimentation.

Anti-settlingeffect with
BYK-W 961

Viscosity (Pa·s)

Viscosity reduction ATH in polyol (60:40)
25,000Recommendations for wetting and dispersing additives
20,000

ProductRemarks

BYK-W 903

Universal, for viscosity reduction

BYK-W 940

Universal, anti-settling

BYK-W 961

Strong anti-settling

BYK-W 969

Universal, for viscosity reduction

BYK-W 980

Stabilization and viscosity reduction

BYK-W 9010

Universal, for viscosity reduction, solvent free

15,00010,0005,0000Control

BYK-W 903

BYK-W 969
G. 05T. 02

08

Additives for polyurethane applications

Rheology
Rheology is impacting many properties of polyurethane resin
systems, e.g. flow behavior, air release, or sagging andsettling issues. Furthermore, the rheological profile isconsiderably affected after mixing polyol with hardener due
to the mixing ratio and polarities of the components. Higherviscosity at low shear in combination with a high yield point
can substantially reduce both sedimentation and sagging.
This results in a longer shelf life with less settling and bettersag resistance during application. During storage, pigments
and ﬁllers in a system can settle and form sediments thatare difficult to re-disperse. This effect depends on the fillerload, type of filler, and the storage conditions (e.g.
temperature). During application on inclined and verticalsurfaces, running and sagging frequently occur at higher
film thicknesses.
To adjust rheology, BYK offers different types of rheologicaladditives:• Liquid rheology additives• Solid rheology additives• Thixotropy Booster
All of them modify the sagging and/or settling properties.

Liquid rheology additiveLiquid rheology additives are used to adjust anti-settling andanti-sagging properties. They can be added to the polyol.
Examples for this additive family are RHEOBYK-7410 ET andRHEOBYK-410.
These products are based on modified urea that forms
strong, three-dimensional network structures, thereby
creating thixotropy.

SaggingSettling

09

Additives for polyurethane applications / Rheology

Solid rheology additives

Thixotropy booster

Recommendations for rheology additives

Solid thixotrope additives are mainly used for anti-settling.
They build up a network between the single particles andare easy to incorporate. In the correct combination with athixotropy booster (e.g. RHEOBYK-R 605, RHEOBYK-R 607),
they also show an excellent sag resistance.

Optimum processability coupled with high sag resistancerequires a perfectly adjusted rheology profile, and often
mixed minerals or fumed silica are used for this. However,if the hardener is added, the viscosity spontaneously drops.
A combination of modified solid thixotropes, especially
GARAMITE-1958, or hydrophilic fumed silica in the polyol
and RHEOBYK-R 607 or RHEOBYK-R 605 can prevent this.

Product type

ProductRemarks

Liquid rheology
additives

RHEOBYK-410

Anti-sagging and anti-settling

Thixotropy
booster

RHEOBYK-R 605

RHEOBYK-R 607 enhances the network of the solid
thixotrope and leads to a very strong sag resistance (G. 07).

Solidthixotropes

GARAMITE-1958 is a solid thixotrope based on the Mixed
Mineral Technology (MMT) and can be easily incorporated
into the polyol.

RHEOBYK-7410 ET

RHEOBYK-R 607
GARAMITE-1958

Anti-sagging and anti-settlingin combination with GARAMITE
or fumed silica
Best in combination withRHEOBYK-R 605 or
RHEOBYK-R 607
T. 03

Higher sag resistance with RHEOBYK-R 607
and an additive based on mixed mineraltechnology (MMT)RHEOBYK-R 607 – mode of action

ControlWith additives

RHEOBYK-R 607

e.g. fumed
silica particle

Multiple functional groups effectively enhance the solid thixotropic network.

G. 06

G. 07

10Additives for polyurethane applications

Surface additives
Whenever a polyurethane is applied in a certain layer ona substrate, defects such as craters, Bénard cells, pinholes,
orange peel, and others can appear on the surface. Onevery significant parameter that has an impact on allthese defects is the surface tension, or more specifically,
the surface tension differences. The following additives
could be used to prevent or minimize these differencesin surface tension.

Cratering and poor leveling
Recommendations for surface additives
ProductRemarks

BYK-306

Strong surface tension reduction,
anti-cratering

BYK-330
BYK-361 N

Improved leveling

BYK-S 706
G. 08T. 04

Processing additives
BYK-P 9912 – processing additive with moldrelease properties
Composite materials made of polyurethane resins andreinforcing fibers such as glass fibers or carbon fibers areused in various applications. Especially in the automotive
industry which require short cycle times, these systems areprocessed by RTM or HP-RTM techniques. To ensure a good
demolding after curing, both internal as well as external
release agents are used in combination. The reapplicationof the external mold release agent after each part is one

step of the total cycle. BYK-P 9912 was developed inorder to reduce the cycle time and accelerate the process.
The processing additive with internal release properties
is designed for polyurethane systems to increase theproduction speed. The number of parts that can bedemolded without reapplication of the mold release agent
is increased and results in an improved potential output ofthe production process by a reduced cycle time.
BYK-P 9912 has no negative impact on the processing
parameters of the polyurethane system, such as viscosity

and reactivity. Another important feature is the excellent
surface quality directly after demolding and the power wash
process no longer being required prior to coating. Nonegative influence on the mechanical properties of thefinished part has been observed. The process additive canbe incorporated in both the polyol as well as the isocyanate
components.

11Additives for polyurethane applications

Viscosity reduction
In some non-filled applications, mixing problems occur
when the polyol is too viscous to be properly mixed with thelow viscous isocyanate. In this case, viscosity depressants
VISCOBYK-4015 and BYK-P 9915 provide an opportunity
to reduce the viscosity of the unfilled polyol and improve
its flowability during the process. VISCOBYK-4015 isalso suitable in filled systems when the filler load is low(< 30 % filler) or when a reinforcement such as mica orwollastonite is used.

Recommendations for viscosity reduction

BYK-P 9915 is an OH-functional viscosity depressant that
becomes part of the polymer chain during curing. It is thus
specifically recommended for all applications wheremigration is an issue.

Viscosity reduction of a polyol

ProductProduct typeDosage

BYK-P 9915

OH-reactive polyalkylene derivatives

0.5–5 % on polyol

VISCOBYK-4015

Aliphatic hydrocarbons

1–10 % on polyolViscosity (mPa·s)

T. 05

4,000
3,500
3,000
2,500
2,000
1,500
1,0005000012345678% BYK-P 9915 on polyol
G. 09

12Additives for polyurethane applications

Processing additives for improved compatibility
Polyurethane elastomers and foams utilize liquidcomponents such as polyol mixtures, butanediol (chainextender), and cyclopentane (blowing agent). Mixturesof these materials often exhibit phase separation becauseof their insufficient compatibility. This instability may
become obvious immediately after mixing or over time.
There are a number of compatibilizers that have been
specially developed for polyurethane systems in order toovercome this liquid/liquid separation issue.

BYK-P 9904, BYK-P 9908, and BYK-P 9909 have different
molecule structures in order to meet the requirements ofcomponents with greatly varying polarities. BYK-P 9904
is a block copolymer with alternating polar and non-polargroups, and electrical charges along the backbone.
BYK-P 9908 and BYK-P 9909 are based on the innovative
T.A.P.E. technology. The twin amphiphilic structure enablesthe additives to cover a wide range of polarities (G. 10).

BYK-P 9904 is mainly used in straight polyol blends(polyether, polyester), whereas BYK-P 9908 andBYK-P 9909 are primarily recommended for mixturesof polyols (or polyol blends) with chain extenders.

Twin amphiphilic polymeric emulsifiers (T.A.P.E.)
Arrangement of amphiphilicpolymers at the interface
BYK-P 9908
basic functional block
acidic functional group

Hydrophobic phase(polyol)

Amphiphilic block copolymer
prepared by CPT methods

Interfacial area

BYK-P 9909
acidic functional blockbasic functional group

Neutral block   

Basic group/block   

Hydrophilic phase(chain extender)

Acidic group/block   

Polymer chain

Amphiphilicpolymers

G. 10

13Additives for polyurethane applications / Processing additives for improved compatibility

Stabilization of butanediol in polyol

Processing additives

Without
additive

With
BYK-P 9908

ProductProduct type

DosageBYK-P 9904

Solution of a high molecular weight block
0.2–2 % on polyol blend
copolymer with pigment affinic groups

BYK-P 9908

Solution of an acrylate copolymer

1–3 % on total formulation

BYK-P 9909

Solution of an ammonium salt of anacrylic acid polymer

0.2–3 % on total formulation

G. 11

T. 06

Compatibilizers for polyol/chain extender blends
ProductPolyols
Polyester

Chain extenders
PolyetherPTMEG

1,4-Butanediol

Hydrophilic glycols

BYK-P 9904
BYK-P 9908
BYK-P 9909
Recommended  Suitable

T. 07

14Additives for polyurethane applications / Processing additives for improved compatibility

Today’s process

Systems house

3-pack system

Production/packaging of• Polyol• Chain extender• Crosslinker

With the new process additives BYP-P 9908 and BYK-P 9909,
this process can now be simplified. Both additives enablestable polyol/chain extender blends to be formulated, whichmakes it possible for the first mixing step (polyol + chainextender) to be accomplished in the systems house.
Therefore, the only on-site step necessary is for the polyol
blend to be mixed with the crosslinker (G. 10). Storage-stablepolyol blends, including the chain extenders, allow systems
houses to offer more innovative 2-pack systems compared totraditional 3-pack systems.

End user
Mixing of
Polyol + Chain extender

Mixing ofPolyol blend + CrosslinkerStability of polyol blend: 24 hrs

Pot life: 30 s – 2 hrs

G. 12

New process with stable polyol/chain extender blend

Systems house
Production/packaging of• Polyol blend• Crosslinker

2-pack system

End user

Mixing of
Polyol + Additive + Chain extender

Mixing ofPolyol blend + Crosslinker

Stability of polyol blend: 6 weeks

Pot life: 30 s – 2 hrs

G. 13Another important factor to consider is the benefit theadditives have on the production of the polyol blends
themselves: Some polyol systems start to separate minutes
after mixing. This distinct incompatibility means that theblends have to be continuously mixed while they are instorage or day tanks. Processing conditions and timing require
special care, especially when breaks or weekends are atodds with production schedules. BYK processing additives
offer considerable advantages. Emulsions that are stable formany days or even weeks can be produced and stored
without the need for continuous mixing. Moreover, using
processing additives leads to improved homogeneity in thereaction mix and consequently may improve the quality of thefinished part as well.

15Additives for polyurethane applications

Summary of additive recommendations
Additive recommendations for polyurethane applications
Product type

ProductRemarks

Product type

ProductRemarks

Air release,silicone-containing

BYK-141

Universal

BYK-306

Strong surface tension reduction, anti-cratering

BYK-1796

Very effective, solvent-freeSurface additives,
silicone-containing

Air release, silicone-free

BYK-088

Very effective, universal

BYK-1790

Very effective, solvent-free, for food contact

BYK-A 535

Low polar, solvent-free, for food contact

BYK-W 903

Univeral, for viscosity reduction

BYK-W 940

Universal, anti-settling

BYK-W 961

Strong anti-settling

BYK-W 969

Univeral, for viscosity reduction

BYK-W 980

Stabilization, viscosity reduction

BYK-W 9010

Universal, for viscosity reduction, solvent free

RHEOBYK-410

Anti-settling, anti-sagging

Wetting and dispersing

Liquid rheology additives

RHEOBYK-7410 ET
Thixotropy booster

RHEOBYK-R 605
RHEOBYK-R 607

Solid rheology additive

GARAMITE-1958

Anti-sagging and anti-settling in combination withGARAMITE or fumed silica
Best in combination with RHEOBYK-R 605 or
RHEOBYK-R 607

BYK-330
Surface additives,
silicone-freeBYK-361 N

Processing

BYK-P 9904

Improved leveling

BYK-S 706
Compatibilizer

BYK-P 9908
BYK-P 9909
BYK-P 9912

Processing with mold release properties

BYK-P 9915

Reactive viscosity reducer

VISCOBYK-4015

Non-reactive viscosity reducer

01/2022
TS-A 8BYK-Chemie GmbH
P.O. Box 10 02 4546462 Wesel
GermanyTel +49 281 670-0
Fax +49 281 65735

ADD-MAX®, ADD-VANCE®, ADJUST®, ADVITROL®, ANTI-TERRA®, AQUACER®, AQUAMAT®, AQUATIX®, BENTOLITE®, BYK®, BYK®-DYNWET®,
BYK®-MAX®, BYK®-SILCLEAN®, BYKANOL®, BYKETOL®, BYKJET®, BYKO2BLOCK®, BYKOPLAST®, BYKUMEN®, CARBOBYK®, CERACOL®, CERAFAK®,CERAFLOUR®, CERAMAT®, CERATIX®, CLAYTONE®, CLOISITE®, DISPERBYK®, DISPERPLAST®, FULACOLOR®, FULCAT®, GARAMITE®, GELWHITE®,
HORDAMER®, LACTIMON®, LAPONITE®, MINERAL COLLOID®, MINERPOL®, NANOBYK®, OPTIBENT®, OPTIFLO®, OPTIGEL®, POLYAD®, PRIEX®,
PURE THIX®, RECYCLOBLEND®, RECYCLOBYK®, RECYCLOSSORB®, RECYCLOSTAB®, RHEOBYK®, RHEOCIN®, RHEOTIX®, SCONA®, SILBYK®,TIXOGEL®, VISCOBYK® and Y 25® are registered trademarks of the BYK group.

info@byk.com
www.byk.com

The information herein is based on our present knowledge and experience. The information merely describes the properties of our products but noguarantee of properties in the legal sense shall be implied. We recommend testing our products as to their suitability for your envisaged purpose
prior to use. No warranties of any kind, either express or implied, including warranties of merchantability or fitness for a particular purpose, are maderegarding any products mentioned herein and data or information set forth, or that such products, data or information may be used without infringing
intellectual property rights of third parties. We reserve the right to make any changes according to technological progress or further developments.
This issue replaces all previous versions.