E. Sahle-Demessie1, Changseok Han2, Eunice Varughese1

1U.S. Environmental Protection AgencyOffice of Research and Development, Cincinnati, OH

sahle-demessie.endalkachew@epa.gov

2Department of Environmental Engineering, INHA University, Incheon 22212, South Korea

1

Environmental Degradation of Polymer

Nanocomposite: release, detection, and

toxicity of nano-fragments

Nano-composites -“Nano-effect”

Polymer Nanofiller Tg (oC)

Polystyrene SWCNT 3

Polycarbonate SiC (0.5-1.5 wt%) (20-60

nm)

Nochange

Poly(vinyl chloride) Exfoliated clay (MMT)

(<10wt%)

-1 to -3

Poly(dimethyl siloxane) Silica (2-3 nm) 10

Poly(propylene carbonate) Nanoclay

(4 wt%)

13

Poly(methyl methacrylate) Nanoclay

(2.5 -15 wt%)

4-13

Polyamide MWCNT

(0.25-6.98 wt%)

-4 to 8

Polystyrene Nanoclay (5 wt%) 6.7

Natural rubber Nanoclay (5 wt%) 3

Poly(butylene

terephthalate)Mica (3 wt%) 6

Polylactide Natural clay (3 wt%) -1 to -4

SWCNT = single wall carbon nanotube, MMT = montmorillonite, MWCNT = multi-walled CNT

Nanofillers changes glass Transition (Tg) temperatures

Paul and Robeson, Polymer 49 (2008) 318-3204

• NP inclusion in polymer matrix

enhanced properties of

nanocomposites

• E.g. improved mechanical,

thermal, membrane, electrical

properties,

• Changes in crystallization & Tg →

suggested polymer’s properties

affected at nanoscale→ nano-effects

• Tg – decreases surface wetting,

density changes

• ENM-polymer large quantity of

interfacial area relative to the volume

of the material.

• Macroscale composite structures

• Exfoliate and clustering of nanoparticles -micron scale

• Interface - affected zones - several to tens of nanometers - gradient of properties

• Polymer chain immobilization at particle surface is controlled by electronic and atomic level structure

• Does the nanoscale interaction between polymer and nanofiller affect the aging, the fragmentation and nano-release during weathering?

10 -12 s

10 -9 - 1 s

1 s - 1h

Multi-scale system of nanocomposites

Macroscale

Material Scale

Mesoscale

Nanoscale

Molecular dynamicsmodeling

Material configuration

Elemental design

Objectives Weathering Study

• Discover and mitigate, reduce the risk of product failure

• Meet product codes and compliance requirements

• Demonstrate durability and performance for various climates

• Predict service life

• Improve product or reduce cost

• Assess possible risks to human and the environment

Needed: Quantitative predictive model for release process

based on structure-function relationship of representative

material systems

Studying degradation pathways of polymers

Polymeric material

Change in chemical functionality

degradation leaching of additives

transformation / degradation

macro (> 5 mm), Meso ( 5mm> 1 mm), Micro (1mm to 0.1 mm), Nano ( 0.1 mm)

Nano release

binding to natural colloids

aggregation

sedimentationbinding to NOMnatural colloids

Mn

+dissolution

Mn+Mn+

Transformation:biological degradation, photolysis, hydrolysis

weathering and

degradation

Cracking and de-bonding

Surface Weathering

UV exposure

Defect evolution in polymer layers

hn

Mechanism of Matrix Degradation

Polymer nanocomposite

O2 O.2

H2O

Reactive species

Primary mechanism for nanorelease

Polymer structural degradation Surface erosion

Microplastics release

Nanoparticle release

ToxicityFate/

Transport

Nano release

Weathering

Temp, UV dose, time

Composite

Changes

Nanocomposite

(thickness, wt% NM)

Nanomaterial

(CNT-X wt%)EPOXY

CharacterizationPhyso-

chemical,

structural

Size, composition

Aging & release

studies

Effect

studies

Water filtration

Porous media

channels

Predictive

model

ROX,

Cell viability

In vitro

Hazard Assessment of Nanomaterials Consumer Nanomaterials Research

Develop a predictive model

EPON-862

Epikure

Nanocomposite Filler

( 1 wt%)

Dimensions TEM HD TEM Glass trans.

Temp, Tg, (oC)

Neat-Epoxy(EP)

None - - - 137.44 4.35oC

Epoxy-CNT(EPC)

NanoCyl-NC7000TM

D=10 nm,L = 1.5 mm

ABET = 250 m2/g Metal < 1%

141.54 5.92oC

Epoxy-CNT-COOH(ECC)

NanoCyl-NC3151TM

D=9.5 nm,L = 1.5 mm

ABET = 250 m2/g Metal < 1%

139.23 5.92oC

Epoxy-CNT-NH2

(ECN)

NanoCyl-NC3152TM

D=10 nm,L = 1.5 mm

ABET = 250 m2/g Metal < 1%

140.27 5.91oC

Materials Tested

Preparation of Epoxy-MWCNT composites

Primary Weathering Factors

Polymer Composite

Formation of Ozone During Weathering

Vacuum Pump

Buffered potassium iodide (KI) solution

Flow Meter

Weathering Chamber

1. The air next to polymer samples was taken out and bubbled into KI solution for 15 hr.

2. Perform “Iodometric Method” test for O3. a. 2.5 mL of 4.5 M H2SO4 was added in 100 mL

of the bubbled water. a. 0.1 M Na2S2O3 solution was added to the

acidified water (#2).a. Observe color changes of the solution from

transparent to pale yellow.

Procedure Results

❖ Due to dissolved O3, the color became pale yellow.

Air-bubbled water

Vent

Laboratory Accelerated Weathering System

❑ Xenon arc weathering – simulates terrestrial solar irradiation❑ Irradiation: 700 W/m2 and Wavelength: 300-800 nm ❑ Chamber temp: 33-37 oC, Black substance temp.: 65 oC, air-cooled❑ Standard method- ISO – 4892-2/2013

Effects of Physical Properties polypropylene on WeatheringN

o C

NT

Ad

de

d2

wt%

CN

T A

dd

ed

Surface Roughness of Pristine and Aged PP and PP-MWCNT

No

CN

T A

dd

ed

2 w

t% C

NT

Ad

de

d

Pristine - SEM Aged-SEM Aged-OEM

PPO1

PPO3

PPO2

t = 1512 h

t = 2268 h

t = 3024 h

t = 1512 h

t = 2268 h

t = 3024 h

SEM and Optical Microscope Images of Pristine and Environmentally-aged Samples

PP-MWCNT Composite Samples

Unaged

t = 0

Aged

t = 756 h

Agedt = 1551 h

Crack depth 77 mm

hn

Weathering of Polymer Nanocomposites

Temperature (oC)100 105 110 115 120 125 130

Heat

flo

w (

mW

)

0

2

4

6

8

10

12

14

EXO

Decreasing recrystallization temperature by weathering

Surface Degradation by Weathering

Conversion (

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Acti

vati

on

en

erg

y (

KJ/m

ol)

100

150

200

250

300

0 h 756 h 1512 h 2268 h 3024 h

Changing activation energy by weathering

Han, Sahle-Demessie, Carbon, Vol 129, pp 137-151, April, 2018 Han, Sahle-Demessie, NanoImpact, Vol. 9, pp 102-113, January 2018.

Modified Experimental Setup

❑ Total Irradiance (MJ/m2): 6588❑ Solar Irradiance (W/m2): 700 ❑ Black Substrate Temperature (oC): 65❑ Weather: 111 min of daylight and 9 min of rainModified ISO 4892-2:2013 (E)

PE-3 months (1) PE-6 months (2) PE-12 months (3) EPC-3 months (4)

ECC-6 months (8) ECC-3 months (7) EPC-12 months (6) EPC-6 months (5)

ECC-12 months (9) ECN-3 months (10) ECN-6 months (11) ECN-12 months (12)

Sample location

❖ Sample positions were rotated daily to ensure even spraying

Weight changes of aged samples during weatheringSamples 1, 4, 7, and 10 were taken out.

Samples 2, 5, 8, and 11 were taken out.

5%

Pure Epoxy

Epoxy-Pure CNTs

Epoxy-CNT-COOH/NH2

Aging time equivalent to actual solar exposure (Month)

0 1 2 3 4 5 6 7 8 9 10 11 12

W/W

0

0.90

0.91

0.92

0.93

0.94

0.95

0.96

0.97

0.98

0.99

1.00

1 (Pure Epoxy)

2 (Pure Epoxy)

3 (Pure Epoxy)

4 (Epoxy-Pure CNT)

5 (Epoxy-Pure CNT)

6 (Epoxy-Pure CNT)

7 (Epoxy-CNT-COOH)

8 (Epoxy-CNT-COOH)

9 (Epoxy-CNT-COOH)

10 (Epoxy-CNT-NH2)

11 (Epoxy-CNT-NH2)

12 (Epoxy-CNT-NH2)

Aging Time (month)

0 2 4 6 8 10 12

Th

ick

ne

ss

Ch

an

ge

(C

/C0)

0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

1.02

Pure Epoxy Epoxy-Pure CNT Epoxy-CNT-COOH Epoxy-CNT-NH2

Sample thickness during the weathering

Aging time equivalent to actual solar exposure (month)

0 2 4 6 8 10 12

Co

nta

ct

an

gle

(o)

0

20

40

60

80

100

120

Pure Epoxy Epoxy-Pure CNT Epoxy-CNT-COOH Epoxy-CNT-NH

2

Changes of contact angle during weathering

Raw Epoxy Epoxy (3 month)

Epoxy (12 month)

Raw Epoxy-CNT-

COOH

Epoxy-CNT-COOH(3 month)

Epoxy-CNT-COOH(6 month)

(One month in aging chamber three month solar exposure)

FTIR analysis of surface of aged Epoxy plates

O 3 month 6 month 12 month

Surface FTIR analysis of aged epoxy-composites

EP-CNT-NH2

EP-CNT-COOHEP-CNT

Raw 3 month 6 month

SEM Images of surface morphology of Epoxy composites

Raw

Raw 3 month

3 month

3 month

Epo

xyEp

oxy

-CN

TEp

oxy

-CN

T-C

OO

HEp

oxy

-CN

T-N

H2 Raw

6 month

6 month

6 month

Unaged 3 month aged

6 month aged

Pure Epoxy-Cross section

6.4 µm

3.3 µm

𝑇𝑂𝐿 ≅ Φ−1 =𝐷

𝑘

Τ1 2

Thickness of oxidation layer

O2 penetration is the controlling factor for

degradation within the sample thickness

Sahle-Demessie, et al. Envi. Science: Nano, 6, 1876 – 1894, 2019.

Raw 3 month

6 month

Epoxy-Pure CNT-Cross section

33.3 µm

8.3 µm

Raw 3 month

6 month

Epoxy-CNT-COOH-Cross section

28.9 µm

2.7 µm

Raw 3 month

6 month

Epoxy-CNT-NH2-Cross section

20.6 µm

15.5 µm

Epoxy

aged

EP-CNT

aged

Imaging using Fluorescent Dye

Zyglo Fluorescent Penetrant, lpeak = 365 nm, Laser Confocal microscopy, 40X

10mm 10mm

10mm 10mm10mm

10mm

Epoxy

3 month 12 month6 month

Unaged epoxy

cracks

Cracks

widened with

extended

weathering

crack

❑ Water from each flask sample in the SunTest chamber were collected every day (avg

200 ml), and transferred to bottles, and gradually evaporated by bubbling nitrogen.

❑ Water temperature in the bottles was 60-65 oC. Wash water collected for 12 test

days (150 ml) is reduced to 150 ml, were store in air tight jars (4 oC )

Water Evaporation Setup

Wash Water Samples Collected in Individual Sample Beakers

EPON 862Curing agent

Bisphenol A – common leachate organic from epoxy based polymers – LC-MS-MS

Release of pollutants from aged epoxy composites

Compound Structure

nonylphenol monoethoxylate

Nonyl phenols

Bisphenol A

trichlorocarbanilide

carbazepine

Nanomaterial Release and polymer

fragments

OrganicRelease

High levels

Analysis of pollutants from aged epoxy composites with Agilent 6540 UHD Accurate-Mass Q-TOF

UV-vis spectroscopy leachate and released particles

Epoxy-CNT-COOH

Epoxy-CNTEpoxy

Epoxy-CNT-NH2

Epoxy-pure CNT

Wavelength (nm)

200 250 300 350 400 450A

bso

rb

an

ce (

a.u

.)

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 day 1 day2.2 days 5 days 7 days 20 days 70 days

Water

50 oC

Wavelength (nm)

200 250 300 350 400 450

Ab

so

rb

an

ce (

a.u

.)

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 day 1 day 2.2 days 5 days 7 days 20 days 70 days

No IrradiationIrradiated

12 month3 month

EPOXY

EPOXY-CNT

EPOXY-CNT-COOH

EPOXY-CNT-NH2

TEM Images of Released Materials

polymer fragment

CNT

514 nm Ar-ion laser-for excitation useful for nanostructured forms of sp2 carbon materialG band – at 1580 cm-1 in-plane vibration of C-C bond

D band – at 1350 cm-1 presence of disorder in carbon

G’ band –at 2698 cm-1 overtone of the D band

The Raman band of the functionalized NTs shifted to a higher wavenumber → inter-tube interaction is less than the physical interaction with the polymer

Fewer CNT-COOH detected

CNT CNT-

COO

H

CNT-

NH2

CNT CNT-

COO

H

CNT-

NH2

CNT CNT-

COOH

CNT-

NH2

G peak

wave

Number

(cm-1)

1580 1586 1590 1575 1580 1586

D peak

Wavenum

ber (cm-1)

1351 1359. 1359. 1348 1339 1362 1359 1356 1362

Raman Spectroscopic Characterization of Released MWCNTs

DG

GD

G’

CNT

CNT-COOH

CNT-NH2

MWCNT

Release NM 1000 h

exposure

Release NM 3000 h exposure

No

rma

lize

d C

ou

nts

No

rma

lize

d C

oun

tsN

orm

aliz

ed C

oun

ts

(a)

(b)

(c)

CNT-NH2

CNT-COOH

CNT

Cytotoxicity studies of released fragments from weathering

▪ Oxidative stress (reactive oxygen species [ROS]) and the production of inflammatory cytokines responses resulting from exposure to superoxide, H2O2, and OH-

→ in vivo and in vitro toxic effectsSin-1 = positive control, generated NO, superoxide

▪ Cell based assays used to measure cell proliferation in response to toxicity of released materials direct cytotoxicity→ cell death on A549 alveolar epithelial cells

https://www.slideshare.net/apparajuvijay/reactive-oxygen-species

In vitro Assessment of Toxicity

Measuring the ability of nanoparticles to cause cell death or damage to basic cellular functions.

Cell Viability & Activity (MTS Assay)Oxidative Stress Measurement via

Detection of Reactive Oxygen Species (DCF Assay)

Viable Cell Dead Cell

Tetrazolium salt (MTS)

Tetrazolium salt (MTS)

More viability

More FormazanViability measured

at O.D. 490 nm

ROS Present

H2DCF(Non- Fluorescent)

No ROSCellular Esterase Activity

H2DCF(Non- Fluorescent)

ROS

Presence of ROS

H2DCF Rapidly oxidized to DCF

DCFExcited with 485-495 nm &

Emission at 517-528 nm

(24 hr test)

Cell Viability & Activity (MTS Assay)

Toxicity Assays of NM released from aged Polypropylene-CNT composite → No measured toxicity

Cell Activity

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Positive Control (CdSO4)

PP01 - 0 h

PP01 - 1215 h

PP02 - 0 h

PP02 - 2268 h

PP03 - 0 h

PP03 - 3024 h

PP41 - 0 h

PP41 - 3024 h

PP42 - 0 h

PP42 - 3024 h

Negative Control

Han, Sahe-Demessie, Environmental Science: Nano, 2019, 6, 1876 - 1894

Unaged and aged pp-MWCNT

Unmodified PP: Unaged and aged

Little toxicity of released MWCNT to A594 adenocarcinomichuman alveolar basal epithelial cell

PP01

PP03

PP02

PP41

PP42

PP43

Cell Viability & Activity (MTS Assay)

Cell Activity

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

Pos. Cntrl (CdSO4)

PE-6

PE-12

EPC-3

EPC-6

EPC-12

ECC-3

ECC-6

ECC-12

ECN-6

ECN-12

Negative

Epoxy

Epoxy-CNT-COOH

Epoxy-CNT

Epoxy-CNT-NH2

Epoxy CNTs show moderate levels of Toxicity

Epoxy CNTs show some levels of Toxicity

Oxidative Stress Measurement via

Detection of Reactive Oxygen Species (DCF Assay)

Detection of ROS

0.2 0.4 0.6 0.8 1.0 1.2

Positive Control (Sin-1)

PE-3

PE-6

PE-12

EPC-3

EPC-6

EPC-12

ECC-3

ECC-6

ECC-12

ECN-3

ECN-6

ECN-12

Negative

Epoxy

Epoxy-CNT-COOH

Epoxy-CNT

Epoxy-CNT-NH2

Summary

➢ Main factors affecting the degradation of polymers are the polymer matrix, the UV dose, → surface cracks increased and deepened with UV dose

➢ Degradation is not significantly influenced by the type functionalized CNT

➢ Weathering of epoxy-CNT composites released phenolic and aromatic compounds and nanomaterials

➢ Release from epoxy and epoxy-CNT show moderate cytotoxicity –based on ROS generation, cell activity and viability tests

➢ For epoxy-CNT composites the toxicity appears to be more responsible due to organic components than released nanomaterials.

Disclaimer

The findings and conclusions of this presentation have not been formally disseminated by U.S. EPA and should not be understood to represent any agency determination or policy. The views expressed in this presentation are those of the authors and do not necessarily represent the views or policies of the U.S. Environmental Protection Agency.

Thank yousahle-demessie.endalkachew@epa.gov

Raw 3 month

6 month

Pure Epoxy-Surface morphology

Raw 3 month

6 month

Epoxy-Pure CNT-Surface morphology

Raw 3 month

6 month

Epoxy-CNT-COOH-Surface morphology

Raw 3 month

6 month

Epoxy-CNT-NH2-Surface morphology