Non-Migratory Surfactants in Emulsion Polymerization

ASC Fall Conference

October 18, 2016

By : Dr. Steven Y. Chan

Agenda

• Introduction

• Surfactants in Emulsion Polymerization

• Non-Migratory Surfactants (NMS)

• Reactivity of NMS

• Dry Film Properties (Clear)

• Performance Testing in PSA

• Conclusion

Introduction

• Global Adhesives and Sealant Market by 2020• 15 million metric tons/ $60 billion

• Waterborne Systems Replacing Solventborne as Result of VOC Directives and Legislation

• Majority of Waterborne Systems Utilize Emulsion Polymers• WB Pressure Sensitive Adhesives at $8.5 billion by

2020

• Tends to have Worse Water Resistance • Presence of water sensitive materials like surfactants

Surfactants In Emulsion Polymerization

• Adsorption on Surface and Interfaces

• Particle Size Nucleation and Colloidal Stability

• Energy Barrier to Prevent Particle Flocculation or

Coagulation

D.C. Blackley Emulsion Polymerization, Theory and Practice, London: Applied Science Publishers., 1975

Conventional Surfactants

• Physical Adsorption via Hydrophobic Interaction (Weak)

• Emulsion Stability Failure

• Desorption of surfactant due to external stresses

• Shear, temperature, formulation ingredients

• Water Sensitivity

• Release of surfactant during drying/film formation

• Surfactant accumulation

• Surface effects - gloss, adhesion, blocking & water resistance

• Bulk effects - water uptake, protection, pigment binding, swelling

Non Migratory Surfactants (NMS)

• Co-Polymerizable Surfactants

• Irreversibly Grafted through Covalent Linkage

• Strong Chemical Bond Gives Superior Colloidal

Stability

• No Surfactant Release During Drying

• Homogeneous Distribution of Surfactant Improves Dry

Film Properties

Non-Ionic NMS • Non-Ionic Polymerizable Surfactant (N-NMS)

• Alkenyl/Carboxyl Functional Ethoxylate

• Molecular Weight of 1100 (N-NMS1) and 1600

(N-NMS2)

• Steric StabilizersCOOH

(EO)n-X

Steric

Stabilization

Anionic NMS

• Anionic Polymerizable Surfactants (A-NMS)

• Modified Alcohol Ethoxylate Phosphate Ester

• Electrostatic and Steric Stabilizer

• Efficient during particle nucleation and growth stage

(EO)n-OPO3H

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Electrostatic

Repulsion

Experimental

• Seeded Semi-Continuous Emulsion Polymerization

• In-situ or separate seed

• Neat monomer feed or pre-emulsion feed

• Process Optimization

• pH control to avoid aqueous phase polymerization

• Semi-continuous feed to avoid excessive burial of

surfactant

• Starved feed conditions to maximize grafting

Surfactant Reactivity

• BA/MMA/AA, Conventional Anionic in Seed Stage, N-

NMS1 in Pre-Emulsion

• Unreacted Surfactant Separated from Polymer with

Ultrafiltration and Quantified via HPLC

• 70% of N-NMS1 Reacted after post-cooking with

monomer starved conditions

0

0.2

0.4

0.6

0.8

1

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6

Feed 4 hr

Xsurf 4 hr

Feed 2 hr

Xsurf 2 hr Xa

ccu

m

Relative Time

En

d o

f fe

edin

g t

ime

Reactivity of A-NMS

• BA/MMA/MAA, All A-NMS Emulsion

• 45% Polymer Solids and 2.5 phm or 1.14wt%

Surfactant on total

• Unreacted Surfactant Separated via

Ultracentrifugation and Quantified via ICP-MS

• Only 0.096 wt % Recovered or 8.5%

• >90% A-NMS Reacted

NMS Effect on Reaction Kinetics

Degradative Chain Transfer Observed for Competitive Allylic and

Propenylic NMS Surfactants Resulting in Lower Molecular Weight

SAT = Saturated Alcohol Ether Phosphate

Allyl/Propenyl = Competitive Reactive Surfactants

0

50

100

150

200

250

300

350

400

450

500

M. W

t.,

g/m

ole

x10

3

Mn Mw

Surfactant Exhudation

NPE-30 N-NMS-1

AFM of Styrene Acrylic Film Dried and Washed with Water

Pinholes Observed None

Better Water Whitening

0

10

20

30

40

50

60

70

80

90

100

0 1 24Tra

nsm

iss

ion

Ha

ze (%

)

Immersion time (hrs)

A-NMS R A-NMS ISO Linear

A-NMS, KPS initiated, A-NMS R, t-BPB initiated vs

linear and isobranched alcohol ether phosphates, all

2.5 phm

Linear: 1 days

A-NMS : 7 days

Lower Water Transmission

Rate

UpperAir

LowerSubstrate

BA/MMA/AA Latex Film –

High Water Diffusion Rates with

Conventional Surfactant Suggest

Poor Protective Properties

Water Transmission Rates

Lower Interface Upper Interface

NPE-30 14.11 183.5

SLS 13.6 103.4

N-NMS1 9.84 35.77

N-NMS2 13.92 34.31

Improved Water Repellency

Water Runs Off much Faster from a Film Based on A-NMS

Contact Angle : A-NMS = 71°, Conventional = 43°

for Sodium Alkyl Diphenyl Disulfonate (r)

A-NMS NaDPDS

Increased Hydrophobicity in

Acrylic Emulsion

Conventional Competitive Maxemul 6106

76.2° 78.4° 91.4°

Contact angle of water droplets on dried emulsion

films prepared with different emulsifiers

Higher contact angle indicates more hydrophobic

film, leading to better water resistance

Lower Foam

• 50 ml of Emulsion in a 4 oz Jar

• Hand Shaken 5 times

NaDPDSA-NMS

NMS in PSA - Shear Strength

• Tensile Strength (kN) or in-plane Cohesion Failure

• Test Conditions• Films obtained from a 60/40

PSA/Ethanol mix

• Applied on polyester substrate

• Cured for 5’ at 120°C and 24hrs at ambient

• Contact area: 20mm x 20mm, 5 kg loaded for 60 sec

100

150

200

250

300

Max lo

ad

(N

)

Wet film thickness

BA/MMA/MAA/HEA

Allylic NPEs

A-NMS

Improved Shear Strength

Effects of Film Thickness and Polymer Composition

• Wet film thickness from 50 to 200 µm, dry films obtained from

a 60/40 PSA/Ethanol mix

• Surfactant @ 3.21 phm

Higher shear strength for A-NMS vs allylic NMS and conventional

0

50

100

150

200

250

300

Max l

oad

(N

)Wet film thickness

BA/MMA/MAA

A-NMS 3.21 HEA free

A3232 HEA free

Conclusion

• Non-Migratory Surfactants are Effective in Emulsion

Polymerization

• Chemically Grafted to Emulsion Particles

• Improved Performance in Dried Film

• Water whitening, water retention, WTR, high contact angle,

lower foaming tendency

• Better Properties in PSA

• Water immersion, cohesion

• Improve the Performance of Waterborne Systems to the

Next Level that Conventional Surfactants cannot.

Acknowledgement

• Jo Grade from Gouda, Netherland

• Nathan Noyes, New Castle, DE

Thank You !