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Aqueous Pre-dispersions of Fumed Silica to Enhance Waterborne Adhesives and Sealants Joe Abrantes October 18, 2016

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Page 1: Aqueous Pre-dispersions of Fumed Silica to …media.mycrowdwisdom.com.s3.amazonaws.com/asc/2016 Fall...• Fumed Silica causes more energy to be required to form a crack. • Lower

Aqueous Pre-dispersions of

Fumed Silica to Enhance

Waterborne Adhesives and

SealantsJoe Abrantes

October 18, 2016

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Agenda

1. Fumed Silica Physical Properties and Capabilities

2. Fumed Silica Powder Process of Dispersion

3. Aqueous Pre-dispersions of Fumed Silica in

Waterbased Adhesives

4. Aqueous Pre-dispersion of Hydrophobic Fumed

Silica Potential in Waterbased Adhesives

5. Q&A – Session and Discussion Round

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Initially germ free; incidence of microbial contamination very low

Inert toward most active ingredients and excipients

Non-irritant and nontoxic

Regulatory Status: (Powder form only)

• Pharmacopoeias: BP, Ph.Eur., USP/NF, JP,....

• Included in the FDA Inactive Ingredients Guide

INCI name: Silica

Fumed Silica Properties

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Particle growth and formation of aggregates

Production process:

Controlled Surface Area

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.......... ...... ..... ...........

..... .... . . . .. ..

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............

.. ....... .. .....SiO2

... . . . . . .............. ..... . . .

......... ............

Reaction and

nucleation zone.

Flame tubeBurner

SiCl4 + H2 + O2

Collision of aggregates,

formation of agglomerates.

• Formation of aggregates due to delayed fusion.

• Collision of molten spherical primary particles.

• Surface area range from 50 – 380 m2/g

Down Stream Processes:

Surface Treatment – DDS, D4, HMDS, PDMS, etc.

Structure Modification - Reduced branching, High filler loading, Higher Tap Density and Reinforcement

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Primary Particle Determines the Surface Area

90

20150

14

200

12

300

7

BET Surface Area, m2/g

Theoretical Primary

Particle Size, nm

50

40

380

7

• Most common base type

• Balanced thickening and dispersibility

• Higher surface area gives better transparency

• Lower surface area allows for higher filler loading

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Structure of Fumed Metal Oxides

Primary particles

(7-40 nm)

Aggregates

(ca. 80-300 nm)

Agglomerates

(up to >100 Microns)

Energy input

at rest

in process

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Particle Modification of Fumed Oxides

Surface treatment

Hydrophilic Fumed Silica Aggregate Hydrophobic Fumed Silica Aggregate

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Fumed Silica Powder

Incorporation to Optimize

Rheology and Suspension

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When insufficient energy is put into the

system, the effect is a drastic reduction in

efficiency of fumed silica powder and the

consistency of the final product.

Higher shear rate leads to improved shelf

stability with a low drop in viscosity after 4

weeks.

The lower energy mixing will experience a

higher drop in viscosity after 4 weeks.

Note:

1- Fumed Silica should be wet in before high

shear is used.

2- The use of high energy allows for shorter

mixing time.

Influence of Shear on Storage Viscosity

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2% Fumed Silica Powder dispersion energy comparison

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The final products exhibit specks and/or other surface flaws.

The amount of Fumed Silica Powder used does not achieve the desired

thixotropic effect.

The thickened resin exhibits poor storage stability:

• sedimentation of fumed silica may occur

• viscosity deteriorates the longer the product is stored.

• Separation/ syneresis of additives and fillers under pressure and long

storage

Consequence of Inadequate Dispersion

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Proper Use Suggestions

• Equipment & Design Features

(Blade-Vessel = 1:2 – 1:3 observing a strong vortex. At 1:4 ratio material clings to vessel

sides)

• Tip Speed Considerations

(26 - 32 ft/sec)

• Length of Shearing Time

(Minimize to prevent heat build-up, RPM more critical than time)

• Temperature Build-up

(Lowers mixing viscosity)

• Sequence of Addition

(Add after oil/resin. Add preferably to film forming liquid – do not pre-disperse in solvent)

• Grind vs. Post-add

(Post add not recommended for Fumed Silica Powders)

• Hegman Grind vs. Dispersion

(Poor grinds – high values indicate silica is poorly dispersed)

• Preventing Under/Over Shear

(Under shear more common. Over shear can result in low viscosity/no thixotropy rebound)

Factors Influencing the Dispersion

of Fumed Silica Powder

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Aqueous Pre-dispersion of

Fumed Silica in Waterbased

Adhesives and Sealants

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Aqueous Pre-dispersions of Fumed Silica enhances the cohesive

properties of the film thus building a more integrated bond line for

adhesion

Aqueous Pre-dispersions of Fumed Silica eliminate the dispersing step

that is required when working with powder fumed silica. (Some

waterborne polymer systems are sensitive to shear)

Aqueous Pre-dispersions of Fumed Silica also impart the combined

properties of

• Reinforcement

• Viscosity Control

• Suspension Properties

• Improved Film Formation

Aqueous Pre-dispersion of Fumed Silica

Benefit in Waterbased Adhesives

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Aqueous Pre-dispersions of Fumed Silica

Efficiency

FS D 200m2/g (20% solids)

FS P 200m2/g : 0 sec. sonication*

FS P 200m2/g : 30 sec. sonication*

FS P 200m2/g : 60 sec. sonication*

FS P 200m2/g : 90 sec. sonication*

*Sonication power:

40 Watts, 39 KHz

The Aqueous Pre-dispersion of

Fumed Silica does not require

additional mixing/dispersion unlike

the Fumed Silica Powder.

Aqueous Pre-dispersions of Fumed

Silica are best added last in the

preparation of waterbased adhesives

and sealants.

High shear mixing is not needed for

effective distribution of Aqueous Pre-

dispersions of Fumed Silica .

FS D – Represents Aqueous Pre-

dispersion of Fumed Silica

FS P – Represents Powder fumed

silica

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Nano-structured composite film

(Resin + Fumed Silica)

Latex

+

Water

Waterborne

Formulation

Dispersed fumed

silica aggregates

Interaction of Aqueous

Pre-dispersion of

Fumed Silica with Latex

promotes formation of a

nano-structured

composite film which

improves reinforcement

Primary Attribute Reinforcement

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Information Provided by The University of Minnesota

17°C

Images of Film on Temperature Gradient Bar

EL2000 – Noveon

With 5% Aqueous

Pre-dispersion of

Fumed Silica 200

m2/g at 20% Solids

EL2000 – Noveon

Resin Only

5°C 7°C 11°C 15°C

Improved Film Formation:

Reduced Cracking Tendency with Aqueous Pre-dispersion of Fumed Silica

Improved Film Formation leads to better

adhesion

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Conclusions Based on University of Minnesota research:

• Aqueous Pre-dispersion of Fumed Silica reduce cracking tendency during film

formation.

• Fumed Silica causes more energy to be required to form a crack.

• Lower MMFT with Aqueous Pre-dispersion of Fumed Silica and reduction of crack

formation.

• Most noticeable effect in resins softer particles – MMFT <15°C

Poor film formation in these systems is due to cracking

Resins with harder particles exhibited lack of coalescence and therefore require

addition

of co-solvent

• Films with Aqueous Pre-dispersion of Fumed Silica have higher König Hardness

• Ability to reduce or replace co-solvents with Aqueous Pre-dispersion of Fumed

Silica provides potential to lower VOC’s

Improved Film Formation

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Fumed Silica improves shear

strength of adhesives by increasing

the cohesive properties of the film.

As with any shear adhesion test,

the total force is a sum of adhesive

and cohesive properties.

Formulated PSAs for general purpose and specialty

labels – PSTC 107 180° Shear Adhesion

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UCAR® Acrylic Copolymer

- PSTC 107 180° Shear Adhesion

Shear adhesion for UCAR Latex

improved when using both the

Aqueous Pre-dispersion of Fumed

Silica (FS Dispersion 200 m2/g) and

the Fumed Silica Powder (FS

Powder 200 m2/g).

The improvement was more

pronounced

when using the Aqueous Pre-

dispersion of Fumed Silica.

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FS Powder 200 m2/gFS Dispersion 200 m2/g

Flexcryl® emulsion polymers

- PSTC 107 180° Shear Adhesion

Flexcryl also shows an improvement

in 180° Shear time with the Aqueous

Pre-dispersion.

In this case, the Fumed Silica

Powder does not add to adhesion.

This may be due to a number of

factors, including shear sensitivity of

the emulsion resulting in aggregates

that are much larger than the

Aqueous Pre-dispersion of Fumed

Silica.

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Fumed Silica improves shear strength of

adhesives by increasing the cohesive

properties of the film.

Formulation changes that negatively impact

the tack properties can also affect the

adhesive properties.

However, the addition of a fumed silica can

balance these properties.

Formulated PSAs for general purpose and

specialty labels – PSTC 101 Adhesion in Peel

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UCAR® Acrylic Copolymer

– PSTC 101 Adhesion in Peel

FS Powder 200 m2/gFS Dispersion 200 m2/g

Aqueous Pre-dispersion of

Fumed Silica results in better

retention of inherent adhesive

properties when compared to

Fumed Silica Powder.

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Flexcryl® emulsion polymers

– PSTC 101 Adhesion in Peel

FS Powder 200 m2/gFS Dispersion 200 m2/g

Flexcryl® was designed for

clear label applications.

Use Aqueous Pre-dispersion of

fumed Silica shows a lower

decrease in peel adhesion

compared to Fumed Silica

Powder.

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The addition of any powder into

a PSA film has the potential to

severely impact the tack.

The use of Aqueous Pre-

dispersions of Fumed Silica

reduce this impact.

This effect is resin/formulation

dependent and the use of

Aqueous Pre-dispersion of

Fumed Silica can balance these

properties.

Formulated PSAs for general purpose and

specialty labels – PSTC 16 Loop Tack

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UCAR® Acrylic Copolymer

– PSTC 16 Loop Tack

The UCAR Latex shows only a

moderate drop in tack with the

Fumed Silica Dispersion 200

m2/g over the full range of

loading tested.

The Fumed Silica Powder

begins to show a significant

loss of tack at higher loading

levels.

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Flexcryl® emulsion polymers

– PSTC 16 Loop Tack

With Flexcryl, the loss of tack

for both materials was about

even with a slight advantage to

the dispersion.

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• Environmentally-friendly Aqueous Pre-dispersion using

hydrophobic (DDS treated) Fumed Silica at 20 % solids

• Customized structuring eliminates need for high energy mixing.

• Dispersion exhibits high stability

• Good compatibility with many coating and adhesive systems

• Efficient thickening and thixotropic agent

• Efficient anti-settling agent

• Minimal effect on the optical properties of water-based clear

coats

Aqueous Pre-dispersion of Hydrophobic Fumed

Silica (20% solids)

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Aqueous Pre-dispersion of Hydrophobic Fumed

Silica Rheology

without Fumed Silica

Hydrophobic Fumed Silica Powder:

added using bead mill

Aqueous Pre-dispersion of Hydrophobic

Fumed Silica:

added under agitation

Rheological effectiveness of Aqueous Pre-dispersion of hydrophobic fumed

silica in a water-based filler for coatings; 1 % silica

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Aqueous Pre-dispersion of Hydrophobic Fumed

Silica Thixotropy and Suspension

ReferenceFumed Silica

Dispersion

simulation of the spraying process and simulation of

the situation shortly after application

500s-1

0.5s-1

Hydrophobic fumed silica as powder

Hydrophobic fumed silica as powder + additives

Hydrophobic fumed silica dispersion

Control

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• Fumed Silica enhances the cohesive properties of the film thus building

a more integrated bond line with improved reinforcement.

• Aqueous Pre-dispersions of Fumed Silica eliminate the dispersing step

that is required when working with Powder Fumed Silica simplifying the

process while reducing mix time. It also enables the use of fumed

silica in shear sensitive waterborne polymers systems.

• Aqueous Pre-dispersions of Fumed Silica also impart the combined

properties of reinforcement with viscosity control and suspension

properties.

• Aqueous Pre-dispersions of Fumed Silica result in better retention of

inherent adhesive properties, showing a less impact on tack and peel

performance compared to Fumed Silica Powder.

• The results also indicate that each adhesive system must be studied as

results may vary based on chemistry and polymer sensitivity.

Aqueous Pre-dispersion of Fumed Silica

Benefits in Waterbased Adhesives

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Name

Date

Literature

Reference

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Literature Reference

TI 1324

AEROSIL in

waterbased

Adhesives & Sealants

TI 1279

TB 28

IB Dispersions

II 1278

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