Impact of Temperature on the Kinetics of Photodegradation and Nanoparticles Release in Nanocoatings

LiPiin Sung, Hsiang-Chun Hsueh Deborah Stanley Jacobs, Hsiang-Chun Hsueh, Chun-Chieh Tien and Tinh Nguyen

Engineering Laboratory (EL)

And

Justin Gorham, Savelas Rabb, and Lee YuMaterials Measurements Laboratory (MML)

lipiin@nist.gov

NanoSafe 2016

Outline

• Nanoparticle release research in EL/NIST

• Case study: Accelerating weathering a nanosilica/epoxy coating• Kinetics of photodegradation• Surface accumulation of nanoparticle• Qualification of particle release

Model Epoxy (EP)MWCNT SiO2

Release Pathways of Nanoparticles (NP) During the Life Cycle of Nanocomposites:Mechanical, Matrix Degradation, Chemical Dissolution, Fire/Incineration, etc.

Mechanical abrasion Matrix Degradation via UV

Polyurethane (PU) flooringcoatings on wood substrates

SiO2

Al2O3

Latex Coatings on a dry-wall substrate

TiO2

ZnOAg

Exterior Coatings and Paints SiO2-PU ZnO -Latex

*Abrasion after UV exposure

Airborne release particles- working with Indoor Air Quality Group/ELGoal: • To develop test methods and measurement protocols for determining the quantities

and properties of nanoparticles released from polymer nanocomposites• To understand the mechanism that causes nanoparticles to leave the polymer matrix

during exposures to the environments

Providing data needed for assessing and managing potential EHS risks of NP release during nanocomposites’ life cycles.

3

• Provide well-controlled environmental stressors (UV, T, RH, mechanical)

NIST SPHERE

Simulated Photodegradation via High Energy Radiant Exposure

UV spectra and irradiance High through-put Exposure at output: 295 nm - 450 nm Incident irradiance on sample: 140 W/m2

Chin et al, Review of Scientific Instruments

75(11), 4951-4959, 2004.

Degradation rate, mechanism, kinetics, ….

Speed# of cyclesLoadType of wheels

Matrix Degradation via UV Mechanical abrasion

Taber rotary abraser(ASTM D 4060-14, organic coatings)

NIST SPHERE High Throughput,High Intensity UV Chamber

1. Characterize abraded surfaces (LSCM, SEM, EDX)

2. Remove Particles from Abraded Surface (TEM grid pressed against the surface or using an Adhesive Tape)

3. Collect residues from abrasion wheels

2 & 3 Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), SEM/EDX

UV intensityTemperatureHumidity

To be analyzed

by ICP-OES

Simulated Rain Test (Water Spraying)

5

Case Study - a nanosilica/epoxy coating

Objective

Effect of Key EnvironmentalFactors on Polymer Degradation

(Laboratory Exposure – accelerate weathering)UV, T, RH, mechanical stress

• To better understand the degradation mechanism, surface accumulation, and possible release of nanoparticles in exterior nanocoatings.

• Acceleration effect of temperature on Kinetics of photodegradation Surface accumulation of nanoparticle Particle release

Polymer:

Amine-cured epoxy, typically used for composites, coatings, and adhesives.

Nanoparticle:

Pure SiO2 Nanoparticles (untreated)

Individual particle size: ~15 nm Diameter.

Nanocoating Preparation:

Loading: 5 % (based on polymer mass).

Thickness: ~ 7 mm on a CaF2 substrate – for UV-vis, FTIR

~125 -150 mm free-standing films – ATR-FTIR, mass loss, XPS, AFM~ 300 mm, free-standing films – for particle release study

Materials

NIST SPHERE High-Throughput High Intensity UV Chamber

Chin et al, Review of Scientific Instruments (2004), 75, 4951.

Martin and Chin, U.S. Patent 6626053

UV Radiation Exposure

Simulated Photodegradation via High Energy Radiant Exposure

12

3

4

5

6

7

89

10

11

12

17

13

14

16

15

Exposure cell – general purpose

19 mm diameter

specimens

Exposure cell for nanosilica release

Exposure Conditions and Characterization

Characterization

• Chemical Degradation (rates, mechanism)

- ATR-FTIR, UV-vis, and XPS

• Surface Morphologies (AFM)

• Release rate by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES), using specially-designed holder.

SPHERESpectral UV intensity:Wavelength: 295 - 400 nmTemp: 60 °C , 50 °C , 40 °C , 30 °C (± 0.1°C)RH: 0 % ± 0.2%

Difference ATR-FTIR Spectra Neat Epoxy 5 % SiO2-Epoxy

• The inset is a transmission FTIR spectrum of the pure, untreated silica nanoparticles• New FTIR band around 1074 cm-1 related to Si-O band in 5 % SiO2-epoxy system

UV dose[MJ/m2]

UV dose[MJ/m2]

UV doseincrease

Si-Oband

C-H stretching

1724 cm-1 Oxidation

Chain scission: 1245, 1508 cm-1

Model Epoxy-SiO2(60ºC, Dry)Photodegradation

• A substantial amount of silica nanoparticles (SiO2) has accumulated on the sample surface – mainly due to photodegradation of the matrix.

• Direct evidence of SiO2 particles release was observed during exposure of epoxy/nanosilica coatings to UV radiation.

UV

Surface accumulation of nanoparticle (60ºC, Dry)

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0 100 200 300 400

Re

lati

ve In

ten

sity

Dose (MJ/m2)

0

0,2

0,4

0,6

0,8

1

1,2

0 200 400 600 800 1000

Ab

sorb

ance

Dose (MJ/m2)

Neat Epoxy

5% SiO2

UV-vis @ = 354 nm

1724 cm-1 C=O oxidation

0 200 400 600 80020

30

40

50

60

70

Pa

rtic

le c

ov

era

ge

pe

rse

nta

ge

(%

)

Dose (MJ/m2)

Kinetics?

Temperature Effects

Arrhenius-like kinetics?

Kinetics data of polymer coatings containing nanoparticles under different UV environments is essential for better understanding the degradation mechanism and predicting the release of nanoparticesfrom exterior nanocoatings.

is the activation energyEa K: rate, T in °K

Temperature Effects: Chemical Changes (ATR-ATIR)

1060 cm-1: C-O and Si-O1245 cm-1: chain scission

1724 cm-1 C=O oxidation • IR bands 1245 cm-1 & 1724 cm-1

change rapidly at earlier exposure time/dose (< 200 MJ/m2), reach a plateau value for

dose > 400 MJ/m2

60 oC – highest degrade rate• IR bands 1060 cm-1

increases as UV dose increases no clear trends in temperature effects

All intensities were Normalized at dose = 0

-0,2

-0,15

-0,1

-0,05

0

0 200 400 600 800 1000 1200 1400 1600

Re

lati

ve In

ten

sity

Dose (MJ/m2)

30C 40C 50C 60C

0,0

0,2

0,4

0,6

0,8

1,0

1,2

0 200 400 600 800 1000 1200 1400 1600

Rel

ativ

e In

ten

sity

Dose (MJ/m2)

30C 40C 50C 60C

0

0,1

0,2

0,3

0,4

0,5

0,6

0 200 400 600 800 1000 1200 1400 1600

Re

lati

ve In

ten

sity

Dose (MJ/m2)

30C 40C 50C 60C

Two oppositely competing processes : loss of epoxy material (C-O loss) & increase of silica nanoparticles on the surface (Si-O increase).

0

0,2

0,4

0,6

0,8

1

1,2

0 200 400 600 800 1000 1200 1400

Ab

sorb

ance

Dose (MJ/m2)

0

0,2

0,4

0,6

0,8

1

1,2

0 200 400 600 800 1000 1200 1400

Ab

sorb

ance

Dose (MJ/m2)

30C

40C

50C

60C

Temperature Effects: @ = 354 nmTemperature Effects: Chemical Changes (UV-Vis)

• Absorbance increased as UV dose increased• Higher temperature had a higher rate of increase

Neat Epoxy 5 % SiO2-Epoxy

-100 0 100 200 300 400 500 600 700

0.0

0.1

0.2

0.3

0.4

0.5

0.6

30°C

Exponential Fit of Sheet1 C

C

B

Model Exponential

Equation y = y0 + A*exp(R0*x)

Reduced Chi-Sqr

1.38283E-4

Adj. R-Squar 0.99668

Value Standard Err

C y0 0.59627 0.01462

C A -0.6069 0.01452

C R0 -0.0049 3.13289E-4

Temperature Effects: Chemical Changes (UV-Vis)- data fitting

y = y0 + A*exp(R0*x)

30 40 50 60

y00.316±0.015 0.389±0.022 0.462±0.007 0.603±0.015

A -0.239±0.017 -0.399±0.022 -0.400±0.011 -0.600±0.023

R0-0.0094±0.001 -0.0098±0.0016 -0.0399±0.003 -0.027±0.003

R2 0.983 0.987 0.996 0.995

Neat Epoxy

5 % SiO2-Epoxy

30 40 50 60

y00.596±0.015 0.652±0.025 0.765±0.021 0.895±0.038

A -0.607±0.015 -0.656±0.024 -0.766±0.028 -0.879±0.059

R0-0.0049±0.0003 -0.0069±0.0007 -0.012±0.0012 -0.020±0.003

R2 0.996 0.9954 0.991 0.978

dose

Y0 values higher with SiO2

0.003004 0.003008 0.003012

0.3

0.4

0.5

0.6

0.7

0.8

0.9

EP

EP-SiO2

y0

1/T (oK)

0.003004 0.003008 0.003012

0.36788

EP

EP-SiO2

ln(y

0)

1/T (oK)

0.003004 0.003008 0.003012

0.2

0.4

0.6

0.8

1/T (oK)

- A

0.003004 0.003008 0.003012

0.36788

1/T (oK)

ln(-

A)

0.003004 0.003008 0.003012

0.01

0.02

0.03

0.04

EP

EP-SiO2

1/T (oK)

R0

0.003004 0.003008 0.003012

0.00674

0.01832

EP

EP-SiO2

1/T (oK)

ln(R

0)

Temperature Effects – with and without SiO2 (UV-Vis Data)

Y0 values higher with SiO2

y = y0 + A*exp(R0*x)

-0,5

0

0,5

1

1,5

2

2,5

0 500 1000 1500

Mas

s Lo

ss (

%)

Dose (MJ/m2)

60C

50C

40C

30C

Mass Loss Temperature Effects:

0

0,5

1

1,5

2

0 200 400 600 800Mas

s Lo

ss (

%)

Dose (MJ/m2)

5 % SiO2-Epoxy

Neat Epoxy

Linear fitArrhenius-like

kinetics

Results: XPS

• C(1s): the overall loss at 50 °C and 60 °C > that at 30 °C and 40 °C• O(1s): no significant difference for all temperatures• N(1s): %N30 °C < %N40 °C < %N50 °C ≈ %N60 °C.

Dose > 500 MJ * m-2

XPS

Dose < 500 MJ * m-2

No temperature dependence for C(1s), O(1s) and N(1s)

Surface enhancement C, O, N vs. UV dose at different T

XPS

0 200 400 600 800 1000 1200 14000

2

4

6

8

60 OC

50 OC

40 OC

30 OC

Dose (MJ/m2)

Ele

menta

l P

erc

enta

ge

Surface enhancement Si vs. UV dose at different T

Arrhenius-like kinetics

Linear fit

31 MJ/m2 30 MJ/m2 12 MJ/m2 52 MJ/m2

78 MJ/m2 104 MJ/m2 73 MJ/m2 91 MJ/m2

187 MJ/m2 253 MJ/m2 195 MJ/m2 182 MJ/m2

Surface Morphology - AFM Temperature effects:

0 200 400 600 800 10000

10

20

30

40

50

60

70

80

Pa

rtic

le S

urf

ace

Co

ve

rag

e (

%)

Dose (MJ/m2)

30oC

40oC

50oC

60oC

Remove first two points

0 200000 400000 600000 800000 1000000

20

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40

45

50

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60

65

70

Pa

rtic

le S

urf

ace

Co

ve

rag

e (

%)

Dose (MJ/m2)

30°C

40°C

50°C

60°C

0 1000000 2000000 3000000 4000000 5000000 6000000

20

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Pa

rtic

le S

urf

ace

Co

ve

rag

e (

%)

Dose (MJ/m2)

30°C

40°C shifted 1.5

50°C shifted 1.9

60°C shifted 2.9

0.0030 0.0031 0.0032 0.0033

0.0

0.2

0.4

0.6

0.8

1.0

1.2

ln (

)

1/T(oK)

Equation y = a +

Adj. R-S 0.981

Value Standard

C Interce 11.417 0.85071

C Slope -3458.4 270.0223

0.0030 0.0032

1.0

1.2

1.4

1.6

1.8

ln R

0

1/T(oK)

Surface Morphology - AFM - data fittingTemperature effects:

Shift factor

Measurement and Modeling of NanosilicaRelease from Epoxy Nanocomposite Exposed to UV at 4 Temperatures using new sample holder (below) and surface treated SiO2

Quartz cover

With surface treated SiO2

improve dispersion

Collecting Released Nanoparticles – Using ICP-OES

Large uncertainties @ high Temp !

Dispersion issue?Non-uniform degradation

0 300 600 900 1200 15000

50

100

150

200

250

Si M

ass (mg

)Dose (MJ/m

2)

30oC

40oC

50oC

60oC

1 d 3 d 7 d 10 d

Epoxy+SiO2 (treated)

Scan size : 20 mm X 20 mm

With Surface Treated SiO2 Better Dispersion

Height

Phase

Epoxy+SiO2 (untreated)– 2 d –

Epoxy+SiO2 (untreated)– 14 d –

Non-Uniform Degradation Process

surface treated SiO2

more release

less release

0 200 400 600 800 1000 12000

50

100

150

Norm

aliz

ed M

ass (mg)

Dose (MJ/m2)

30oC

40oC

50oCx

x

Except 60 oC, Release rate: no strong Temperature dependence

Linear slope:0.126 ± 0.004

Acceleration effect of temperature -Arrhenius relationship

The higher temperature, the higher photodegradationand surface nanosilica accumulation rate.

The chemical degradation rate of the matrix (FTIR data UV-Vis data)

Accumulation rate for Si on the surface (AFM and XPS data ) followed the right temperature order, i.e., 60 °C > 50 °C > 40 °C > 30 °C.

Release rate: no strong temperature dependence, except 60 oC

Summary: The effects of temperature

Summary: Temp Dependence

Slopes (k) Vs T

Linearly increasing trends: y=kt+y0

mass loseXPS Si

Exponential Decay: y=a*e-kt +y0

XPS CFTIR-ATR 1245 and 1508

Exponential Rise: y=a*(1-e-kt)+y0

AFMXPS OUV-vis

Arrhenius-like kinetics