Antimicrobial Copper Containing Coatings for Food and Health Industries

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dc.contributor.advisor Gao, W en
dc.contributor.advisor Silva, F en
dc.contributor.advisor Farid, M en
dc.contributor.advisor Lin, R en
dc.contributor.author Wei, Xiaojin en
dc.date.accessioned 2014-11-30T19:58:40Z en
dc.date.issued 2014 en
dc.identifier.citation 2014 en
dc.identifier.uri http://hdl.handle.net/2292/23623 en
dc.description.abstract Many diseases spread due to the bacterial infections, which have caused significant economic and personal losses. Contact with infected surfaces is likely to catch infections, and antimicrobial surfaces may play an important role in preventing the spreading of disease and infection in public health. Some techniques including coating have been used in developing antimicrobial surfaces. Copper (Cu) has a broad spectrum of intrinsic antimicrobial functions and long been considered safe for everyday and external application. The surface containing Cu can provide sustained protection against microbial contamination. In the present study, the polymer-Cu and polymer-Cu salt, polymer-Cu/TiO2, and Cu-Bi composite coatings were developed, effectively applied onto metallic or non-metallic substrates. These coatings can be used in indoor or outdoor environments with effective antimicrobial and other properties. The present research started with a polymer based coating system containing mixtures of fine particles of Cu and Cu salt separately. These polymer based coatings have good compatibility with various substrates, including nonmetallic substrates such as wood, glass, and plastics. These Cu containing coatings display good antimicrobial properties. Coatings with embedded fine Cu salt showed higher antimicrobial property than the coating with only Cu due to the higher Cu ion releasing rate than the coatings only contain Cu. The total elimination of 106 bacteria by contacting the polymer-metallic Cu coatings needs 8 h, while contacting with the polymer-CuCl2 coatings took only 20 min to kill the same amount of bacteria. Single bacterial cell membrane changes could be clearly observed by using transmission electron microscopy (TEM) and synchrotron infrared microscopy techniques coupled with cellular Deoxyribonucleic acid (DNA) analysis. The death of Escherichia coli (E. coli) after contacting with polymer-Cu coatings occurred mainly because of the damage to the cell membrane integrity. In contrast, after contacting with Cu salt containing coatings, E. coli became inactive possibly due to the loss of DNA integrity and cell membrane integrity. The antimicrobial property and mechanical properties of Cu containing coatings were further investigated by adding TiO2 nanoparticles. TiO2 is a wide band-gap semiconductor with photocatalytic properties. The addition of TiO2 enhanced the antimicrobial property under sunlight, which provided extended applications in outdoor environment. The elimination of 106 bacteria by contacting the polymer-Cu coatings without TiO2 need 5 h, while contacting with the Cu/1 wt.% TiO2 took only 2 h to kill the same amount of bacteria. The addition of TiO2 also enhanced hardness and wear resistance of the polymer based coatings. Synchrotron Infrared Microscopy was used to in-situ and in-vivo study the bacteria killing process. The real-time chemical images of bacterial activities showed that the bacterial cell membranes were damaged by the Cu and TiO2 containing coatings. Cu-Bi is another type of coating that was originally developed for mechanical applications as Cu and Bi do not dissolve to each other at ambient temperature. This coating was produced using electroplating method which is widely used in industry. With a small addition of Bi, the microhardness and wear resistance of Cu coating significantly increased from 165 to 250 HV50. The Cu-Bi coating has a two-phase mixed microstructure. X-ray Diffraction (XRD) analysis indicates that the Bi addition did not produce lattice distortion in the Cu matrix as Bi and Cu do not form solid solution. The electrical conductivity therefore has no measurable change. This Cu-Bi composite coating may extend the service life of Cu coatings when used as electric contacts. These coatings show good antimicrobial properties and have stronger antimicrobial properties against gram-negative bacteria than gram-positive bacteria. Bacterial surface property, roughness and wetting property were systematically studied to illustrate the antimicrobial mechanism of Cu coating. Two types (wild-type and mutant strain with exopolysaccharide overproduction) of bacteria were used to investigate the killing rate and mechanisms. The results showed that mutant strain was more sensitive to Cu containing coating than the wild-type strain. The bacteria with more cell surface components were killed faster. More Cu ions released on Cu containing coating surface after contacting with the mutant strain comparing with the wild-type strain. The antimicrobial Cu containing composite coating systems that have been developed in this work are weather resistant, low-cost and easy to apply. These Cu containing antimicrobial coatings can greatly reduce the contact-transfer of infectious diseases, and will help reduce their health hazard significantly. These antimicrobial Cu containing coatings are proposed to have a wide range of applications not only in the food and health industries, but also in many public sectors such as schools, airports, railway stations, and libraries. The future work could be focused on designing different coating compositions for different applications. The processing and coating properties will also be systematically investigated and optimized, which will provide a reliable basis for coating industries. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof PhD Thesis - University of Auckland en
dc.rights Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.title Antimicrobial Copper Containing Coatings for Food and Health Industries en
dc.type Thesis en
thesis.degree.grantor The University of Auckland en
thesis.degree.level Doctoral en
thesis.degree.name PhD en
dc.rights.holder Copyright: The Author en
dc.rights.accessrights http://purl.org/eprint/accessRights/OpenAccess en
pubs.elements-id 464488 en
pubs.record-created-at-source-date 2014-12-01 en
dc.identifier.wikidata Q112907596


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