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 2 wt% CNT Added No CNT Added Effects of Physical Properties polypropylene on polypropylene Properties of Physical Effects Weathering Surface Roughness of Pristine and Aged PP and PP-MWCNT No CNT Added % CNT Added wt 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 40 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 Epoxy-CNT-NH2 Epoxy-CNT-COOH Epoxy-CNT Epoxy Raw Raw Raw Raw SEM Images of surface morphology of Epoxy composites of Epoxy morphology surface of Images SEM 3 month 3 3 month 3 3 month 3 3 month 3 6 month 6 6 month 6 6 month 6 6 month 6 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