E. Sahle-Demessie, Changseok Han, E. Varughese, C. Bennet-Stamper

U.S. EPA, Office of Research and Development, Cincinnati, OHsahle-demessie.endalkachew@epa.gov

Honglan ShiMissouri University of Science & Technology, Rolla, MO

1

Polymer-Nano composite degradation, release,

detection, and toxicity of nanomaterials during

accelerated aging

TransformationInteraction with:• Pollutants• NOM• Biofilm

ToxicityFate Transport

Nano release

WeatheringTemp, UV dose, time

CompositeChanges

Nanocomposite(thickness, wt% NM)

Nanomaterial

(CNT, GO, wt%)Polymer

(type) Characterization

physical

chemical

structural

Size, composition

Aging & release

studies

Effect

studies

Water filtrationPorous mediachannels

Predictive

model

ROX,Cell viabilityIn vitro

Hazard Assessment of Nanomaterials Consumer Nanomaterials Research

Develop a predictive model

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

Model Degradation of Pathways for 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

Materials Tested

Polypropylene (PP)(pristine)

PP-MWCNT4 wt.%

Epoxy

PP01, L = 0.25 ± 0.01 mm L = 0.35 ± 0.03 mm Neat

PP02, L = 0.39 ± 0.02 mm L = 0.50 ± 0.01 mm Epoxy-CNT

PP03, L = 0.69 ± 0.04 mm L = 2.07 ± 0.06 mm Epoxy-CNT-COOH

Epoxy-CNT-NH2

Epoxy-Graphene

EPON 862 DETDA

Tg = -13 oC

Tg = 60 - 110 oCEpoxy wafers 3 mm thick

MWCNT – Multiwalled carbon nanotube

Operating Conditions

Parameter Condition

A cycle of weathering 120 min (sunshine: 108 min, rain: 12 min)

Humidity 8-20% for sunshine and over 60% for rain

Solar light irradiation 700 W/m2

Wavelength of solar light 300-800 nm

Chamber temperature 33-37 oC

Black substance temperature 65 oC

June 21, clear day

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

Primary Weathering Factors

Polymer Composite

Effects of Physical Properties polypropylene on Weathering

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

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

cm

cm

cm

PP-MWCNT Composite Samples

Unagedt = 0

Agedt = 756 h

Agedt = 1551 h

Crack depth 77 mm

Carbonyl Index

𝐶𝑎𝑟𝑏𝑜𝑛𝑦𝑙 𝐼𝑛𝑑𝑒𝑥 =𝐴𝑏𝑠𝑟𝑜𝑏𝑎𝑛𝑐𝑒 𝑜𝑓 𝑐𝑎𝑟𝑏𝑜𝑛𝑦𝑙 𝑔𝑟𝑜𝑢𝑝 (−𝐶𝑂−)

𝐴𝑏𝑠𝑟𝑜𝑏𝑎𝑛𝑐𝑒 𝑜𝑓 𝑚𝑒𝑡ℎ𝑦𝑙𝑛𝑒 𝑔𝑟𝑜𝑢𝑝 (−𝐶𝐻2−)=

𝐴1775

𝐴2870

PP41

PP42

PP43

PP-MWCNT

PP01

PP02

PP03

PP

Car

bo

nyl

Ind

ex

PPO1 – crushed to pieces and removed from the test chamber at 1500 h

Released Microplastics Containing MWCNTs from Aged PP-MWCNT

(a) (b)

(c) (d)

TEM Images of MWCNTs Released from Aged PP-MWCNT Composites

(a) (b)

(C) (d)

Nanorelease: Particle Size Distribution

(a)

PP41 = 0.25 mm

PP42 = 0.50 mmUnfiltered

PP43 = 2.07 mmPP42 = 0.50 mmFiltered

Hydrodynamic Diameter, (nm)Hydrodynamic Diameter, (nm)

Hydrodynamic Diameter, (nm)Hydrodynamic Diameter, (nm)

Nu

mb

er

we

igh

t (%

)

Nu

mb

er

we

igh

t (%

)

Nu

mb

er

we

igh

t (%

)

Single particle –ICP-MS for tracking nanorelease

Sonication

Probe

ICP-MS

Background solution

Particles

Released MWCNT-aged Polypropylene-CNT Composites Determined Using single particle-ICP-MS

(c)

(b)(a)PP41

L = 0.25 mm

PP42

L= 0.50 mm

PP43

L = 2.07 mm

Cobalt used as proxy element

for CNT releaseHan, Sahle-Demessie, ES:Nano, April 2019

• Macroscale composite structures

• 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

10 -12 s

10 -9 - 1 s

1 s - 1h

Aging of Nanocomposites as a Multiscale System

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 – (12 position for rotation)

❑ 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

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

0.16

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

No IrradiationIrradiated

Release of pollutants from aged epoxy composites

Compound Structure

nonylphenol monoethoxylate

Nonyl phenols

Bisphenol A

trichlorocarbanilide

carbazepine

NanoRelease

OrganicRelease

High levels

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)

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 → intertube 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

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)

Raman Spectroscopic Characterization of Released MWCNTs

Summary

➢ Weathering of polymer composites is affected by UV-photolysis, photooxidation, ozonation, and thermal effects

➢ Main factors affecting degradation are the polymer matrix, environmental conditions

➢ Degradation rate is influenced by wafer thickness above which the process is kinetically controlled by the diffusion of O2 and H2O in the polymer

➢ Thickness of oxidized layer is order of magnitude 𝐷

𝑘

➢ Surface erosion and superficial oxidation (200 mm) causes cracks and brittle failure on the wafer/films samples → Influences the particle release per mass

➢ Organic components of polymers could be released with aging

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