Biodegradation of CNT-polymer. The Influence of CNTs

Transcription

1 Biodegradation of CNT-polymer nanocomposites The Influence of CNTs Howard Fairbrother Department of Chemistry Johns Hopkins University

2 Why add CNTs to Polymers? Structural Properties 1 Functional Properties 2 Wt % MWCNT in Polycarbonate Chitosan: Poor Properties, Limited Usability Polycarbonate: Property Enhancement, Multifunctional 1) Wang et al., Biomacromolecules, 2005, 6, ) Potschke et al., AIP Conf. Proc. 2004, 43, 3247.

3 Biodegradable Polymers Often cheap but without CNTs, poor properties can preclude the use of these polymers in products Synthetically Derived Bio-Derived PES Cellulose PBS PVOH PCL Chitosan PLA PHA Starch PHA Copolymer 3

4 Life Cycle Perspective Polymers & NPs Polymer Nanocomposite Incineration Discharge/wa ste Weathering Disposal Use Wear/ abrasion Biodegradation UV Washing 1 µm

5 Motivation If the polymer matrix is biodegradable: How does the presence of CNTs impact the biodegradability? Does biodegradation lead to CNT release?

6 Synthesis of CNT Composites Solution Blending CNT Loading

7 Influence of CNTs on Polymer Biodegradation Two Case Studies: 1. PCL/Single Culture 2. PHA/Mixed Culture

8 Characterization: Does the Inclusion of CNTs Change Crystallinity? Crystallinity (%) Addition of CNTs does not change crystallinity MWCNT Loading, % w/w

9 Experimental Approach Pure PHB 0.1 wt% CNTs 0.5 wt% CNTs 1 wt% CNTs 2 wt% CNTs Add & Incubate Measure %Mass Loss Biodegradation of PCL and 2% w/w O-MWNT/PCL 100 Remove & Weigh % Mass Loss Microorganism Time (Weeks)

10 One end of the spectrum: Polycaprolactone (PCL) CNT Composites PCL 0.1 wt.% O-MWNT in PCL 2 wt.% O-MWNT in PCL 10 mm

11 Microorganism Single Culture Pseudomonas aeruginosa 1 Model, gram negative microorganism commonly found in soil Flow Cell 1) Madigan et al. Brock Biology of Microorganisms. 12th ed.,san Francisco, ) McCarty, P. L., Environmental biotechnology: principles and applications, ) Lallai & Mura, The Chemical Engineering Journal, 1989, 41, (3), B55-B60. 4) Fierer & Jackson, PNAS, 2006, 103, 626.

12 Biodegradation: CNT Content Matters % Mass Loss R 2 =0.98 R 2 =0.98 PCL PCL R 2 =0.84 R 2 =0.94 1% w/w 2% w/w % Mass Loss PCL PCL 5% w/w 10% w/w Time (Weeks) Time (Weeks)

13 CNT Content Matters k (weeks -1 ) LO-MWCNT Loading (% w/w)

14 Does Biodegradation of the Polymer Nanocomposite Lead to CNT Release?

15 Detection of SWNTs at environmentally relevant concentrations by monitoring residual trace metal catalysts using single particle ICP-MS Metal Nanoparticle Catalyst

16 Using Mo to Detect MWCNTs 16

17 No Measureable ( < 200 µg/l) MWCNT Release During Biodegradation 17

18 The Other end of the Spectrum: Polyhydroxyalkanoates (Bio-polymer) R O OH Biodegradation studies using primary effluent (mixed culture) Pristine MWCNTs Rapidly Biodegraded PHA 0.5 wt% 1 wt% 2 wt% 5 wt% 10 wt% 18

19 Microorganism Mixed Culture Aerobic: Primary effluent (wastewater after settling of solids) 4 1) Madigan et al. Brock Biology of Microorganisms. 12th ed.,san Francisco, ) McCarty, P. L., Environmental biotechnology: principles and applications, ) Lallai & Mura, The Chemical Engineering Journal, 1989, 41, (3), B55-B60. 4) Fierer & Jackson, PNAS, 2006, 103,

20 Mass Loss of MWCNT/PHA Nanocomposites % mass loss entire nanocomposite % mass loss polymer matrix % Mass loss Elapsed time (days) 5 20 s) PHA 0.5% MWCNT/PHA 5% MWCNT/PHA 10% MWCNT/PHA % Mass of PHA loss 100 % Mass loss y x R² Elapsed time (days) CNT loading, % 20

21 Nancomposites at the End of Biodegradation

22 Physical Transformation of Nanocomposites Despite >90% mass loss, all CNT/PNCs of varied CNT loading remained intact after biodegradation in mixed culture. 0.5% w/w MWCNT/PHA 5% w/w MWCNT/PHA 2% w/w MWCNT/PHA 10% w/w MWCNT/PHA

23 Summary Degradation of CNT polymer nanocomposite causes a compressed structure to form that still retains its basic shape No obvious release of CNTs even when > 95% mass loss is observed (strength of CNT-CNT interactions through London dispersion forces)

24 Inhibitory Effect of CNTs Mass Loss PCL/Single Culture Conclusions? PHA/Mixed Culture Polymer Biodegredability

25 Acknowledgements: Johns Hopkins University David Goodwin Professor Edward J. Bouwer Duc Phan Colorado School of Mines: Jim Ranville JJ Wang