Hybrid Cellulose-Copper Nanoparticles Embedded in Polyvinyl Alcohol Films for Antimicrobial Applications

Transcription

1 Hybrid Cellulose-Copper Nanoparticles Embedded in Polyvinyl Alcohol Films for Antimicrobial Applications Speaker: PhD Student Tuhua Zhong Advisor: Dr. Gloria S. porto Division of Forestry and Natural Resources West Virginia University SWST 2015 International Convention, June 7-12, 2015, Wyoming 1

2 UTLINE Introduction and goals 1. Materials and Methods 2 Results and Discussion 3 Conclusions 4 2

3 1. Introduction and goals Specific goal: 1. Evaluate cellulose/nanocellulose as template for the synthesis of copper nanoparticles and improve the antimicrobial performance of their films. 2. Characterize the films in terms of their thermal and mechanical standpoint. 3. Evaluate changes in terms of copper crystal structure and oxidation states when combined with cellulose-based materials. 3

4 1. Introduction Antimicrobial Copper Copper An Ancient biocide (Borkow and Gabbay 2009) February 2008, The Environmental Protection Agency (EPA) approved the registration a copper as an antimicrobial material. Reduce bacteria linked to potentially fatal microbial infections: Food-borne pathogens: E.coli 157:H7, Salmonella, Listeria Hospital-acquired pathogens: Methicillin-resistant Staphylococcus aureus (MRSA). MRSA can be eliminated within 10 min upon contact of copper surface. 4 Borkow and Gabbay, Current Chemical Biology, 2009, (3),

5 1. Introduction Antimicrobial Copper Copper Nanoparticles High surface areas and unusual crystal morphologies with numerous reactive surface sites Potent Biocides Drawbacks: Prone to aggregate on the nanoscale 5

6 1. Introduction Cellulose: A Template For Copper Nanoparticles Molecular structure of cellulose (Adapted from Moon et al. 2010) TEMP* Nanofibrillated Cellulose (TNFC) and Carboxymethyl Cellulose (CMC) Cu Cu Cu H H H Cu Cu Cu TNFC Native cellulose CMC 6 Moon et al. Chem. Soc. Rev., 2011, 40, *TEMP: (2,2,6,6-Tetramethyl-piperidin-1-yl)oxyl

7 1. Introduction PVA Composite Film Cellulose: Light weight High strength Biocompatible Biodegradable Cellulose-Copper nanoparticles: Antimicrobial & Reinforcing Polyvinyl Alcohol (PVA): Biodegradable Copper: Potent Antimicrobial PVA Composite film: Good Antimicrobial Properties? Enhanced Thermal and Mechanical Performances? 7

8 2. Materials and Methods Fabrication of PVA/TNFC-Cu Film PVA/TNFC-Cu Film Without Cellulose Template With TNFC Template 8

9 2. Materials and Methods Fabrication of PVA/CMC-Cu Film 9

10 XPS 2. Materials and Methods Characterizations xidation states of copper on film surface PVA Composite Films Thermal properties Antimicrobial Testing Antimicrobial Properties Dynamic mechanical property 10

11 3. Results and Discussion: Morphology of Copper Nanoparticles on Cellulosic Templates Copper nanoparticles on TNFC Copper nanoparticles on CMC 10 nm 11

12 3. Antimicrobial Properties as a Function of Copper Content Log Microbial Reduction Log microbial reduction riginal E.coli Concentration: 10 8 CFU/mL* Copper loading: 0.6 wt% Exposure Time: 1-week PVA PVA/TNFC 0.4 wt% PVA/TNFC-Cu wt% PVA/TNFC-Cu0.5 PVA/TNFC-Cu0.6 * CFU/mL: Colony-forming units per milliliter 0.7 wt% PVA/TNFC-Cu0.7 Log microbial reduction = log 10 A log 10 B Where A is the counts of test E.coli culture (unit: CFU/mL), B is the counts of survival E.coli after fixed exposure time log E.coli DH 5a Reduction 2-log 3-log 4-log 5-log % 6-log 12

13 Log microbial reduction Copper concentration (ppm) 3. Antimicrobial Activity and Copper Ion Release as Function of Exposure Time Copper content: 0.6wt. % E. coli reduction increased over time for both PVA composite films and had similar trend with the rate of copper ion release. Table 1 Weight percentage (wt. %) of main element to the total weight of PVA, cellulose and copper. Sample Code PVA (wt. %) Cellulose (wt. %) Copper (wt. %) PVA/TNFC-Cu PVA/CMC-Cu

14 Representative examples for bacterial enumeration of the survival E.coli PVA/TNFC-Cu Too Numerous To Count 3 PVA/CMC-Cu0.6 6 Non-detectable

15 Intensity (counts) Intensity (counts) 3. Results and Discussion xidation States of Copper XPS spectra for PVA/TNFC-Cu0.6 XPS spectra for PVA/CMC-Cu ev Cu 2+ (from Cu) ev Cu 2+ (from Cu) Cu was found on film surface for both PVA composites. Table 2 Binding energy (Cu2p 3/2 ) for copper different oxidation states (McIntyre and Cook, 1975). Chemical state Formula Binding energy, Cu2p 3/2 (ev) Cu metal or (Cu 0 ) Cu ± 0.15 Cu(I) oxide or (Cu + ) Cu ± 0.2 Cu (II) oxide or (Cu 2+ ) Cu ± 0.2 Cu hydroxide or (Cu 2+ ) Cu(H)₂ ± 0.2 McIntyre and Cook Anal. Chem., 1975, 47(13),

16 Intensity (counts) 3. Results and Discussion Crystalline Structure of Copper Park et al. Environmental Science & Technology, 2012, 46(20), XRD patterns for PVA composite films The intensity of characteristic peaks for crystal Cu 2 within PVA/CMC-Cu0.6 film is much stronger than that in PVA/TNFC-Cu0.6, suggesting: Higher amount of crystal Cu 2 was present in PVA/CMC-Cu0.6 film than that in PVA/TNFC-Cu0.6 film; Cu 2 and Cu (I) ions are more toxic than Cu and Cu (II) ions (Park et al. 2012); This may explain why PVA/CMC-Cu0.6 inactivated more E.coli. 16

17 3. Results and Discussion Thermal property DTG Curve T max 260 o C for PVA 278 o C for PVA/TNFC-Cu o C for PVA/CMC-Cu0.6 The thermal decomposition of PVA/TNFC-Cu and PVA/CMC-Cu films shifted toward higher temperature Higher thermal stability. T max : The decomposition temperature corresponding to the maximum weight loss 17

18 3. Results and Discussion Dynamic mechanical property Storage modulus (MPa) Increase up to 217 % for PVA/CMC-Cu0.6 Increase up to 164 % for PVA/TNFC-Cu0.6 PVA The storage modulus for both PVA/TNFC-Cu0.6 and PVA/CMC- Cu0.6 has significantly enhanced. 18

19 4. Conclusions The optimum copper loading for antimicrobial efficacy in the PVA/TNFC matrix is 0.6 wt%; Both PVA composite films containing 0.6 wt % copper possessed strong antimicrobial activities against E.coli DH 5a, over % of E.coli were inactivated after 3-day exposure of E.coli to either PVA/TNFC-Cu0.6 film or PVA/CMC-Cu0.6 film; 19

20 4. Conclusions Approximately 90 % less cellulosic material is required when using TNFC as copper template compared to CMC template to get similar film antimicrobial performance; Antimicrobial activities depend not only on the amount of copper ion release, but also on the oxidation states of copper; The incorporation of cellulose-copper nanoparticles improves the thermal stability and enhances the film mechanical performance. 20

21 ACKNWLEDGMENTS NIFA McStennis Project WVA00098 USDA NIFA Award No