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 !