biocidal coatings through self- segregating additives · biocidal coatings through self-segregating...

Biocidal Coatings Through Self-

Segregating Additives

JA Orlicki, JA Escarsega, AM Rawlett, JL Leadore,

GR Martin, A Farrell, AA Williams, E Napadensky

U.S. Army Research Laboratory

Aberdeen Proving Ground, MD 21005 [email protected]

National Meeting of the American Chemical Society

28 March 2012

San Diego, CA

Content approved for public release

Outline

Technology Overview

– Hyperbranched polymer (HBP) additives

- Basic concept

- Tech demonstrations/ applications

- Antimicrobial Surfaces


Motivation and Background

• Changing threats dictate new approaches to asset protection

– Increased threat of biological attack

– Broad spectrum decontamination against chemical threat is

challenging

• Expanding capabilities of military topcoats to include autonomous

reactivity may address these issues

• Reduce asset susceptibility to non-conventional attacks

StaphStaph VxVx


Critical performance characteristics

• Topcoats are complex

multirole formulated

systems

– Camouflage

– Corrosion protection

– Low sorption

– Materials limitations

– Cost effective

• Approaches for surface

modification

– Plasma treatment

– Self-assembly

– Additive incorporation

Environmental

DurabilitySurvivability

Affordability

Affordable

Multifunctional

Military

Coatings

VOC/HAP Reduction

Cr(IV) and heavy

metal elimination

UV Resistance

Flexibility

Corrosion resistance

Chemical agent

protection

Camouflage

SubstratePretreatment

Epoxy Primer

Topcoat

~2 mils

~1 mil

~400

mg/ft2

SubstratePretreatment

Epoxy Primer

Topcoat

~2 mils

~1 mil

~400

mg/ft2


Polymer additives in the bulk additives may

not control surface properties effectively

• Techniques are known for surface segregation and

environmental response, but inefficient to utilize

Surface Segregation

Asymmetric response

desired to maximize

additive impact

Low cohesive energy groups

drive segregation

Localized triblocks show

interaction with environment

Koberstein, J.T., et al., Macromolecules, 2003, 2956

Ward, T.C., et al., J. Polym. Sci. Part A, Polym. Chem., 2000, 3742


Hyperbranched polymers (HBPs) provide

readily available scaffolds for additives

Desired characteristics

Low chain entanglements

High solubility

Large number of reactive sites

•Residual, non-functionalized chain ends

•-OH, NH2

•Installed functionality

•Epoxy, (meth)acrylates, isocyanate


Cast films of thermoplastic polyurethane show

migration based on functional group density

10

30

50

70

90

0 1 2 3 4 5

% HBP in TPU

Ad

van

cin

g C

on

tact

An

gle

(wate

r)

Unmodified PEI 10% wf CFx

20% wf CFx 30% wf CFx

40% wf CFx ~20% wf CFx, ~40% alkyl

Boxed points

highlight the

increasing

influence on

surface properties

at reduced

loading

Orlicki, J.A., et al., Polymer, 2007, 2818. Content approved for public release

X-ray photoelectron spectroscopy analysis of

HBP modified urethanes (TPUs)

300 295 290 285 280

0

3000

6000

9000

12000

15000

18000

Inte

nsity (

CP

S)

Binding Energy (eV)

N O

O

H

CH2

C O

C

C N

C 1s peak, TOA = 90°

TPU matrix

300 295 290 285 280

0

3000

6000

9000

12000

15000

18000

Inte

nsity (

CP

S)

Binding Energy (eV)

C 1s peak, TOA = 90°TPU w/ HBP additive

N O

O

H

CF2

CF3

CH2

C O

C

C N

F N

Thr. 0.5 % 5.0 % Thr. 0.5 % 5.0 %

Additve Bulk 90° 30° 90° 30° Bulk 90° 30° 90° 30°

TPU 0.00 0.00 0.00 0.00 0.00 2.04 2.04 0.93 2.04 0.93

PEI 0.00 0.00 0.00 0.00 0.00 3.53 2.46 1.93 3.94 3.18

HBP 1 0.23 0.40 0.86 2.57 4.78 3.38 2.54 1.75 4.98 4.54

HBP 2 0.45 0.76 2.83 6.95 10.27 3.24 4.06 3.32 8.44 5.71

HBP 3 0.68 3.46 6.99 9.02 14.22 3.09 4.26 4.08 8.90 7.47

HBP 4 0.90 5.36 10.27 14.00 20.19 2.95 4.46 3.39 8.67 7.90

HBP 5 0.48 2.92 8.22 5.75 13.11 2.63 7.85 6.67 7.09 6.47

XPS is convenient tool to

examine changes in surface

composition

Depth limited to ca. 10 nm for

90° take off angle


Influence of HBP core depends on MW, hydrophilicity

decreases as molecular weight increases

Polyester core, variable molecular weight

0

20

40

60

80

100

120

PE-1 PE-2 PE-3 PE-4

HBP Additive (1%) in EstaneA

dvan

cin

g C

on

tact

An

gle

(°)

Matrix contact angle

HBP-

TPU film C O F N

Estane 80.6 17.2 0.0 2.2

PE-1 60.7 18.8 18.4 1.5

PE-2 60.3 19.5 17.8 1.8

PE-3 59.0 19.1 20.6 1.1

PE-4 59.5 19.6 19.1 1.3

Influence of polyester core molecular weight

HBP Additive, 1% in TPU A

dva

nc

ing

Co

nta

ct

An

gle

(°)

Increasing core weight

Variation of surface elemental

composition is unlikely to cause

observed trend. Changes in core

dynamism is root of changing

contact angle values.

O

O

OH

n

O

HO C11H23O

HO C7F15

O

O

O

n

170 °C, cat. acid

R

O

R = 20% PFOA 20% Aliphatic 60% Hydroxyl


Depth profile was visualized with Rutherford

Backscatter Spectrometry, agrees with XPS

base polymer

POM + TPU

POM-HBP + TPU

base polymer

POM + TPU

POM-HBP + TPU

Approx depth (nm)

10002000 0

Approx depth (nm)

10002000 0

•HBP-POM complex demonstrates migration, ~ 10 fold increase in surface

concentration with XPS

•RBS results correlate, show ~11 fold increase in surface concentration of metal

catalyst sites

•He+

Soluble complex

when protonated

•H5PV2Mo10O40


Expanded palette of functional groups/active

sites are being investigated

• AgNP have also been delivered; nice model system, but cost and long-term stability remain question marks

• Commercial options for antimicrobials and chemical decon groups are low probability solutions

– Silver zeolites– leaching, sorption

– Small molecule biocides– leaching, porosity

– MxOy nanoparticles for chemical decon (Al, Mg, Zn, Cu)– deactivation

– TiO2 particles– long term coating stability, light driven

• ARL developing library of mixed end-group additives with specific functionality

– Quaternary ammonium salts (in conjunction with TSI, Inc.)

– Biguanides (in conjunction with TSI, Inc.)

– Alkanolamines

– N-halamines, hydantoins

NR1

Br

NH

H2N N NH

NH2

RHN

HO

R1 N

N

OO

Cl

Cl

Chen, et al. Biomacromolecules, 2000, 1, 473-480. Content approved for public release

Modification of Functionalized PEI

step 1step 2

RNH (CH2)3 Br

O

NH2

R) ) RNH N

+(CH2)3

OCH3

CH3

(CH2)15CH3) Br-

step 1step 2

RNH (CH2)5 Br

O

NH2

R) ) RNH N

+(CH2)3

OCH3

CH3

(CH2)9CH3) Br-

Step 1. Br(CH2)5COCl, THF, RT

Step 2. Alkyl-N(CH3)2, DMAC reflux at 80 ºC, 50 hr

NH NH NH

NH NH

NH2NH2

step 1

step 2

RNH (CH2)3 Br

O

NH2

R) )

+

)

n

nHCl

(CH2)3

NH NH NH

(CH2)3

NH2NH

NH NH

RNH (CH2)3

O

Step 1. Br(CH2)3COCl, THF, RT

Step 2. PHMB, K2CO3, MeOH reflux at 75-80 ºC, 55 hr

PEI’s were first functionalized with ca. 20% lauric, 20% PFOA amides based on 1° amine composition.

Functionalization with halo-alkane via amidation installed group for quaternization.

Biguanide functionalization followed similar route.

Materials obtained as orange powders, somewhat hygroscropic.


Antimicrobial activity in TPU was assayed

using an array of techniques to show efficacy

ASTM E2180 test for hydrophobic surfaces challenged

with E. coli, S. aureus, C. albicans, P. aeruginosa

AATCC Method 100, adapted for hydrophobic surfaces

challenged with S. aureus, K. pneumoniae

Kirby-Bauer test for leaching of additives

challenged with E. coli and S. aureus

HBP

Additive

%

Reduct.

Candida

albicans

%

Reduct.

Escherichia

coli

%

Reduct.

Staphylococcus

aureus

%

Reduct

MRSA

%

Reduct.

Pseudomonas

aeruginosa

PEI None NR 21.8 NR NR NR

PEI C10 Quat 100 99.99 100 52.51 NR

PEI Biguanide 65.99 99.93 100 70.07 25.25

PE None NR 94.10 60.63 48.60 NR

PE C10 Quat 99.54 86.05 55.95

• ASTM E2180 test w/ 1% additive in TPU, 24 h exposure







challenged with E. coli and S. aureus

• ASTM E2180 test w/ 1% additive in TPU, 24 h exposure

HBP

Additive

%

Reduct.

Candida

albicans

%

Reduct.

Escherichia

coli

%

Reduct.

Staphylococcus

aureus

%

Reduct

MRSA

%

Reduct.

Pseudomonas

aeruginosa

PEI None 21.8 NR

PEI C10/C4 100 99.99 100 52.51 NR

PEI C10/C6 Q 18.45 65.22 57.59

PEI C16/C4 Q 9.22 NR 52.04









challenged with E. coli and S. aureus Wt % Additive % Reduction

MRSA

% Reduction

P. aeruginosa

1 PEI-Q C10 52.51 NR

2 PEI-Q C10 97.78

3 PEI-Q C10 NR

5 PEI-Q C10 NR

1 PEI-B 70.07 25.25

2 PEI-B 100

3 PEI-B 91.18

5 PEI-B 94.12

2 1 % PEI-Q

1 % PEI-B

93.85

• Increased

efficacy at

elevated additive

levels

• Reasonable

activity in TPU

proxy system




Materials reported in literature may also be

suitable for this approach

NR1

Br

Park, D; Wang, J; Klibanov, AM. Biotechnol. Prog.,2006, 22, 584-589.

2% Loading in TPU, cast from THF

Demonstrated 6-log kill against E. coli

4-6 log kill against S. aureus

25 kDa, 750 kDa PEI backbone

Hexyl hydrophobic tail

Full series has since been synthesized


Antimicrobial activity is very high for PEI-based

additives in thermoplastic urethane

NR1

Br

Additive Composition Staph Aureus Escheria Coli

1.3 KDa PEI, hexyl 6.00 3.41

25 KDa PEI, hexyl 6.00 6.00

750 KDa PEI, hexyl 6.00 6.00

1.3 KDa PEI, dodecyl 6.00 3.55

25 KDa PEI, dodecyl 6.00 2.35

750 KDa PEI, dodecyl 6.00 3.72

Sample % C % O % N % Br % I

Estane Control 78.1 +/- 0.2 18.5 +/- 0.5 3.4 +/- 0.4

1.3 KDa PEI, hexyl 78.5 +/- 0.6 11.1 +/- 1.0 8.2 +/- 0.6 1.7 +/- 0.1 0.6 +/- 0.1

25 KDa PEI, hexyl 78.6 +/- 0.3 11.6 +/- 0.1 7.6 +/- 0.3 1.8 +/- 0.1 0.5 +/- 0.0

750 KDa PEI, hexyl 77.3 +/- 0.4 11.3 +/- 0.9 9.1 +/- 0.3 1.8 +/- 0.4 0.5 +/- 0.1

1.3 KDa PEI, dodecyl 82.9 +/- 0.5 8.8 +/- 0.2 7.0 +/- 0.5 1.0 +/- 0.2 0.4 +/- 0.1

25 KDa PEI, dodecyl 84.5 +/- 0.8 7.0 +/- 0.6 6.4 +/- 0.2 1.7 +/- 0.1 0.6 +/- 0.1

750 KDa PEI, dodecyl 82.5 +/- 0.5 7.7 +/- 0.5 7.8 +/- 0.4 1.5 +/- 0.2 0.4 +/- 0.0

ASTM-E2180 Assay

Surface composition of TPU films determined using XPS


Adapting technology to military systems presents

new technical barriers & performance requirements

• Additive reacts during cure, potential

for anchoring additive at surface, may

also influence cure kinetics and

migration efficiency

Substrate

Solvent Evaporation

r = CS

Pigment Settling

r = P

R’OH

HBP surface-segregation

R’OH

H2O

Pigment

N C O

R

NH2R

Key performance metrics

include

Corrosion protection

Signature/gloss

Abrasion resistance

Long-term stability


XPS provides most direct method to ascertain

surface composition of additive, monitoring fluorine

PUrth PE-HBP + PUrth

Bulk concentration of fluorine ~0.3 %,

observed ca. 7% at surface of coating


Candidate HBP scaffolds in a range of coatings

demonstrate migration, ca. 10 – 20 fold increase

Coating HBP F 1s N 1s

Polyurea None 0.0 5.22

Polyurea PEI-F-Alk 2.01 7.36

Epoxy None 0.0 3.15

Epoxy PE-F-Alk 7.18 3.16

Polyurethane None 0.0 4.62

Polyurethane PE-F-Alk 9.62 5.80

Polyurethane PEI-Alk 0.0 5.64

Polyurethane PEI-F-Alk 0.62 5.14

Polyurethane PEI-F-Alk-Quat 0.32 5.58

Solvent-

based primer

Water-based

primer

Water-based

topcoat

• Most HBP segregated to surface of coatings using PEI and PE-based

additives:

– Coating/PE bulk Fluoro conc. = 0.3 mol%

– Coating/PEI bulk Fluoro conc. ~ 0.07 mol%


Integration into CARC coatings

Control

Coatings with HBP

2 Component

Polyurethane

CARC

2 Component

Epoxy CARC

• Negligible difference in appearance of coatings with and w/o HBP

– Draw-down

– Spray coat

• Acceptable coating properties

– Gloss

– Color

– Adhesion

1 Component

Polyurea

CARC


Acceptable performance of 2-component

polyurethane topcoat against initial tests

Test Polyure-

thane PUrth + PEI-F

PUrth + PEI-aliph.

PUrth + PE-F

PUrth + PEI-Quat.

Color Pass Pass Pass Pass Pass

Gloss 1.3/1.1 1.2/1.1 1.2/0.8 1.2/1.0 1.3/1.1

DFT 3.1-3.6 3.1-3.7 2.1-2.9 2.5-2.7 2.7-3.7

MEK Dbl Rub 200+ 200+ 200+ 200+ 200+

Impact Resistance, lb-in, direct/reverse

40/20 40/20 40/20 40/20 40/20

Cross-cut adhesion WET/DRY

5B/5B 5B/5B 5B/5B 5B/5B 5B/5B

QUV (cyclic test) 600 h

Pass/no change

Pass/no change

Pass/no change

Pass/no change

Pass/no change

STB Pass Pass Pass Pass Pass

Flexibility/DFT Pass Pass Pass Pass Pass

Water Resistance

Pass Pass Pass Pass Pass


CARC HBP &

Additive

% Reduct.

C. albicans

% Reduct.

E. Coli

% Reduct.

S. aureus

% Reduct.

MRSA

Epoxy

(primer)

PEI C10

C4 Q X 18.54

(99.99)*

5.41

(100)*

X

Epoxy

(primer)

25kDa PEI,

C12 quat X 17.70 6.58 X

Polyurea

1 wt%

PE C10

C4 Q 99.68 98.02

(99.54)*

100

(86.05)*

X

Polyurea

2 wt%

PEI C10

C4 Q X 100 100 100

Polyurethane PEI C10

C4 Q X 18.29

(99.99)*

25.44

(100)*

X

Polyurethane PE C10

C4 Q X NR

(99.54)*

5.92

(86.05)*

X

Polyurethane PEI B 94.26

(65.99)*

25.65

(99.93)*

43.66

(100)*

X

Int. Epoxy

2 wt%

PEI C10

C4 Q X 90.26 100 X

• Q denotes quaternary ammonium salt (values in (x) from TPU system)

• B denotes biguanide group

HBPs incorporated into reactive coatings exhibit

variable activity, improved at 2% loading


Conclusions

• Demonstrated repeatable 10+ X self segregation of active components to the air/polymer interface in coatings

• HBP scaffold provides flexible platform. Favorable for attachment of myriad reactive species.

• Transitioned to low VOC TPU coating systems

• Antimicrobial functional groups demonstrated strong activity (99.9999 % kill) towards environmental hazards: S. aureus, C. albicans, E. Coli, MRSA

• Antimicrobial HBPs compatible with existing coating systems, including water dispersible polyurethanes, but suffer reduced activity

• The search continues for non-leaching contact antimicrobial that functions well in a cross-linked topcoat.


Acknowledgements

• Jim Hirvonen

• J. Derek Demaree

Triton Systems Inc. (quat,

biguanide studies)

• Norm Rice

• Lawino Kagumba

• Arjan Giaya

• Macromolecular Science &

Technology Branch

• ISN 6.2 Research Program

• Defense Threat Reduction

Agency

• Jeff Owens, Eileen Shannon,

AFRL

• Jim Wynn, NRL

• Rod Fry, William Creasy,

Chris Giannaras, ECBC


biocidal coatings through self- segregating additives · biocidal coatings through self-segregating...

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