Environmental Degradation of Polymer Nanocomposite: Release, Detection, and Toxicity of Nano-Fragments

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Environmental Degradation of Polymer Nanocomposite: release, detection, and toxicity of nano-fragments

E. Sahle-Demessie1, Changseok Han2, Eunice Varughese1

1U.S. Environmental Protection Agency Office of Research and Development, Cincinnati, OH [email protected]

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

1 Nano-composites -“Nano-effect”

Nanofillers changes glass Transition (Tg) temperatures Polymer Nanofiller T (oC)  g • NP inclusion in polymer matrix enhanced properties of Polystyrene SWCNT 3 nanocomposites Polycarbonate SiC (0.5-1.5 wt%) (20-60 Nochange nm) • E.g. improved mechanical, Poly(vinyl chloride) Exfoliated clay (MMT) -1 to -3 thermal, membrane, electrical (<10wt%) properties, Poly(dimethyl siloxane) Silica (2-3 nm) 10 • Changes in crystallization & Tg → Poly(propylene carbonate) Nanoclay 13 suggested polymer’s properties (4 wt%) affected at nanoscale→ nano-effects Poly(methyl methacrylate) Nanoclay 4-13 (2.5 -15 wt%) • Tg – decreases surface wetting, Polyamide MWCNT -4 to 8 density changes (0.25-6.98 wt%) • ENM-polymer large quantity of Polystyrene Nanoclay (5 wt%) 6.7 interfacial area relative to the volume Natural rubber Nanoclay (5 wt%) 3 of the material. Poly(butylene Mica (3 wt%) 6 terephthalate) Polylactide Natural clay (3 wt%) -1 to -4 SWCNT = single wall carbon nanotube, MMT = montmorillonite, MWCNT = multi-walled CNT

Paul and Robeson, Polymer 49 (2008) 318-3204 Multi-scale system of nanocomposites

Macroscale

Elemental • Macroscale composite structures design Material Scale • Exfoliate and clustering of nanoparticles - micron scale

1 s - 1h • Interface - affected zones - several to tens of Mesoscale nanometers - gradient of properties Material configuration • Polymer chain immobilization at particle surface is controlled by electronic and 10 -9 - 1 s atomic level structure

Nanoscale Molecular • Does the nanoscale interaction between dynamics polymer and nanofiller affect the aging, the modeling fragmentation and nano-release during

10 -12 s weathering? 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 weathering and macro (> 5 mm), Meso (  5mm> degradation 1 mm), Micro (1mm to 0.1 mm), transformation Nano ( 0.1 mm) / degradation Nano release

binding to NOM sedimentation natural colloids aggregation binding to natural colloids

Mn Transformation: dissolution n+ Mn++ M biological degradation, photolysis, hydrolysis Mechanism of Matrix Degradation

UV exposure hn

O2 . O 2 H O 2 Surface Reactive Weathering species Cracking and de-bonding Defect evolution in polymer layers Polymer nanocomposite

Primary mechanism for nanorelease

Polymer structural Microplastics Nanoparticle Surface erosion degradation release release Hazard Assessment of Nanomaterials Consumer Nanomaterials Research

Nanomaterial EPOXY (CNT-X wt%) EPON-862 Characterization Epikure Physo- chemical, Nanocomposite structural (thickness, wt% NM)

Aging & release studies Weathering Temp, UV dose, time

Predictive Composite Nano release Changes model

Size, composition Effect studies Fate/ Toxicity Transport Develop a Water filtration ROX, predictive model Porous media Cell viability channels In vitro Materials Tested

Nanocomposite Filler Dimensions TEM HD TEM Glass trans. o ( 1 wt%) Temp, Tg, ( C)

Neat-Epoxy None - - - 137.44  4.35oC (EP) Epoxy-CNT NanoCyl- D=10 nm, TM (EPC) NC7000 L = 1.5 mm o 2 141.54  5.92 C ABET = 250 m /g Metal < 1%

Epoxy-CNT-COOH NanoCyl- D=9.5 nm, TM (ECC) NC3151 L = 1.5 mm o 2 139.23  5.92 C ABET = 250 m /g Metal < 1%

Epoxy-CNT-NH2 NanoCyl- D=10 nm, TM (ECN) NC3152 L = 1.5 mm o 2 140.27  5.91 C ABET = 250 m /g Metal < 1% Preparation of Epoxy-MWCNT composites Primary Weathering Factors

Polymer Composite Formation of Ozone During Weathering Vent Flow Meter

Vacuum Pump

Weathering Chamber Buffered potassium iodide (KI) Procedure solution Results

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 Air-bubbled water transparent to pale yellow.

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

Weathering

NoAdded CNT

% % CNT Added

wt 2 2 Surface Roughness of Pristine and

Aged PP and PP-MWCNT

NoAdded CNT

% % CNT Added

wt 2 2 SEM and Optical Microscope Images of Pristine and Environmentally-aged Samples

Pristine - SEM Aged-SEM Aged-OEM

PPO1 t = 1512 h t = 1512 h

PPO2 t = 2268 h t = 2268 h

PPO3 t = 3024 h t = 3024 h PP-MWCNT Composite Samples

Unaged t = 0

Aged Aged t = 1551 h t = 756 h

Crack depth 77 mm Weathering of Polymer Nanocomposites

Surface Degradation by Weathering

hn Decreasing recrystallization Changing activation energy temperature by weathering by weathering 14 300

12 250 10

8 EXO 200 6 0 h

Heat flow (mW) flow Heat 756 h 4 150 1512 h 2268 h 2 (KJ/mol) energy Activation 3024 h 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 100 105 110 115 120 125 130 Temperature (oC) Conversion (

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

❑ Total Irradiance (MJ/m2): 6588 ❑ Solar Irradiance (W/m2): 700 ❑ Black Substrate Temperature (oC): 65 Modified ISO 4892-2:2013 (E) ❑ Weather: 111 min of daylight and 9 min of rain Sample location 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 positions were rotated daily to ensure even spraying Weight changes of aged samples during weathering Samples 1, 4, 7, and Samples 2, 5, 8, and 10 were taken out. 11 were taken out. 1.00

0.99

0.98 Pure Epoxy 0.97 1 (Pure Epoxy) 0.96 2 (Pure Epoxy) 0 3 (Pure Epoxy) 0.95 4 (Epoxy-Pure CNT) 5%

W/W 5 (Epoxy-Pure CNT) Epoxy-Pure 0.94 6 (Epoxy-Pure CNT) CNTs 7 (Epoxy-CNT-COOH) 0.93 8 (Epoxy-CNT-COOH) 9 (Epoxy-CNT-COOH) Epoxy-CNT- 0.92 10 (Epoxy-CNT-NH ) 2 COOH/NH 11 (Epoxy-CNT-NH ) 2 0.91 2 12 (Epoxy-CNT-NH2) 0.90 0 1 2 3 4 5 6 7 8 9 10 11 12 Aging time equivalent to actual solar exposure (Month) Sample thickness during the weathering 1.02

1.00

)

0 0.98

0.96

0.94

0.92

0.90 Pure Epoxy

Thickness Change (C/C Change Thickness Epoxy-Pure CNT 0.88 Epoxy-CNT-COOH Epoxy-CNT-NH2 0.86 0 2 4 6 8 10 12 Aging Time (month) Changes of contact angle during weathering 120 Pure Epoxy Epoxy-Pure CNT 100 Epoxy-CNT-COOH

Epoxy-CNT-NH2

) o 80 Raw Epoxy Epoxy Epoxy (3 month) (12 month) 60

Contact angle ( angle Contact Raw Epoxy- Epoxy- Epoxy-CNT- CNT-COOH CNT-COOH COOH (3 month) (6 month) 20

0 0 2 4 6 8 10 12 Aging time equivalent to actual solar exposure (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 EP-CNT-COOH

EP-CNT-NH2 SEM Images of surface morphology of Epoxy composites

Raw 3 month 6 month Epoxy

Raw 3 month 6 month

CNT

- Epoxy

Raw 3 month 6 month

COOH

CNT

- Epoxy

3 month

Raw 6 month

NH2

CNT

- Epoxy Pure Epoxy-Cross section Unaged 3 month aged

3.3 µm

6 month aged

Thickness of oxidation layer 1Τ2 6.4 µm 퐷 푇푂퐿 ≅ Φ−1 = 푘 O2 penetration is the controlling factor for degradation within the sample thickness

Sahle-Demessie, et al. Envi. Science: Nano, 6, 1876 – 1894, 2019. Epoxy-Pure CNT-Cross section Raw 3 month

8.3 µm

6 month

33.3 µm Epoxy-CNT-COOH-Cross section Raw 3 month

2.7 µm

6 month

28.9 µm Epoxy-CNT-NH2-Cross section Raw 3 month

15.5 µm

6 month

20.6 µm Imaging using Fluorescent Dye

Zyglo Fluorescent Penetrant,

lpeak = 365 nm, Laser Confocal microscopy, 40X Epoxy Unaged epoxy

Epoxy 10mm crack aged 10mm 10mm

cracks

Cracks widened with extended EP-CNT weathering aged 10mm 10mm 10mm 3 month 6 month 12 month Water Evaporation Setup

❑ 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 ) Wash Water Samples Collected in Individual Sample Beakers

Curing agent EPON 862 Bisphenol A – common leachate organic from epoxy based polymers – LC-MS-MS Release of pollutants from aged epoxy composites

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

nonylphenol monoethoxylate High levels

Nonyl phenols Nanomaterial Release and polymer Bisphenol A fragments

trichlorocarbanilide

carbazepine UV-vis spectroscopy leachate and released particles Irradiated 50 oC No Irradiation 0.14 Water 0 day 1 day 0.12 2.2 days 5 days Epoxy-CNT 7 days Epoxy 0.10 20 days 70 days

0.08

0.06

Absorbance (a.u.) Absorbance

0.04

0.02 200 250 300 350 400 450 Wavelength (nm)

0.16

0 day 0.14 1 day Epoxy-pure CNT 2.2 days 5 days 0.12 7 days Epoxy-CNT-COOH 20 days Epoxy-CNT-NH2 70 days 0.10

0.08

Absorbance (a.u.) Absorbance 0.06

0.04

0.02 200 250 300 350 400 450 Wavelength (nm) TEM Images of Released Materials 3 month 12 month

EPOXY

EPOXY-CNT

EPOXY-CNT- COOH

EPOXY-CNT- polymer fragment NH2 CNT (a) Raman Spectroscopic Characterization D G of Released MWCNTs G’ MWCNT 514 nm Ar-ion laser-for excitation useful for nanostructured forms of sp2 carbon material G band – at 1580 cm-1 in-plane vibration of C-C bond

Normalized Normalized Counts D band – at 1350 cm-1 presence of disorder in carbon G’ band –at 2698 cm-1 overtone of the D band Release NM 1000 h exposure CNT CNT- CNT- CNT CNT- CNT- CNT CNT- CNT- COO NH2 COO NH2 COOH NH2 (b) H H G peak CNT-NH2 1580 1586 1590 1575 1580 1586 wave Number CNT-COOH (cm-1) D peak 1351 1359. 1359. 1348 1339 1362 1359 1356 1362 Wavenum CNT -1 Normalized Counts Normalized ber (cm )

CNT-NH2

CNT-COOH

Normalized Counts Normalized The Raman band of the functionalized NTs shifted to a CNT higher wavenumber → inter-tube interaction is less than the physical interaction with the polymer 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 effects Sin-1 = positive control, generated NO, https://www.slideshare.net/apparajuvijay/rea ctive-oxygen-species 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 In vitro Assessment of Toxicity

Measuring the ability of nanoparticles to cause cell death or damage to basic cellular functions. Oxidative Stress Measurement via Cell Viability & Activity (MTS Assay) Detection of Reactive Oxygen Species (DCF Assay)

Viable Cell Dead Cell Tetrazolium Tetrazolium salt (MTS) salt (MTS) ROS Present No ROS Cellular H2DCF Esterase (Non- Fluorescent) Activity ROS H2DCF More viability (Non- Fluorescent)

DCF Presence of ROS More Formazan Excited with 485-495 nm & Viability measured Emission at 517-528 nm H2DCF Rapidly (24 hr test) at O.D. 490 nm oxidized to DCF Toxicity Assays of NM released from aged Polypropylene-CNT composite → No measured toxicity Unaged and aged pp-MWCNT Cell Viability & Activity (MTS Assay) PP01 PP02

Negative Control PP42 - 3024 h

PP42 - 0 h PP03 PP41 - 3024 h PP41 PP41 - 0 h PP03 - 3024 h PP42

PP03 - 0 h PP43 PP02 - 2268 h PP02 - 0 h PP01 - 1215 h Unmodified PP: Unaged and aged PP01 - 0 h Positive Control (CdSO4) Little toxicity of released MWCNT to A594 adenocarcinomic 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 human alveolar basal Cell Activity epithelial cell Han, Sahe-Demessie, Environmental Science: Nano, 2019, 6, 1876 - 1894 Epoxy CNTs show moderate levels of Toxicity Cell Viability & Activity (MTS Assay)

Negative ECN-12

ECN-6 Epoxy-CNT-NH2 ECC-12 ECC-6 ECC-3 Epoxy-CNT-COOH EPC-12 EPC-6

EPC-3 Epoxy-CNT PE-12 PE-6 Epoxy Pos. Cntrl (CdSO4)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Cell Activity Epoxy CNTs show some levels of Toxicity

Oxidative Stress Measurement via Detection of Reactive Oxygen Species (DCF Assay)

Negative ECN-12 ECN-6 Epoxy-CNT-NH ECN-3 2 ECC-12 ECC-6 ECC-3 Epoxy-CNT-COOH EPC-12 EPC-6 Epoxy-CNT EPC-3 PE-12 PE-6 PE-3 Epoxy Positive Control (Sin-1)

0.2 0.4 0.6 0.8 1.0 1.2 Detection of ROS 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 you [email protected] 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 Raw 3 month

6 month