E. Sahle-Demessie, Changseok Han, E. Varughese, C. Bennet-Stamper
U.S. EPA, Office of Research and Development, Cincinnati, [email protected]
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
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
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
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.
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