st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Evaluation of Bioactivity of Copper Alloy Coatings
M. Nejad1, L. Pershin1, J. Mostaghimi1, and M. Ringuette 2
1
Centre for Advanced Coating Technologies, University of Toronto, Canada
2
Department of Cell and Systems Biology, University of Toronto, Canada
Abstract: Copper and copper alloys have been certified by U.S. Environmental Protection
Agency (EPA) as antimicrobial coatings. This paper is focused on evaluating bioactivity of
thermally sprayed copper alloy coated-wood and wood composites. Our results showed after
four months of exposure, copper coating had significantly improved the decay and mold resistance of wood and composite products. Also, surface roughness enhanced the biocidial efficacy of copper alloy coatings.
Keywords: Wire-arc, Bronze coating, Antimicrobial, Surface roughness
1. Introduction
The U.S. Environmental Protection Agency (EPA) has
certified few hundreds of copper-based alloys as antimicrobial with bacteria killing efficacy of 99% in two hours
of exposure [1]. Hospital acquired infections due to bacterial contamination in hospitals are often life threatening,
and require prolonged hospitalisation time. Several studies have confirmed that copper and its alloys could be
effective antimicrobial surface in reducing hospital-acquired infections [2]. However, sheet metal has limited application due to limitations in machinability and in
cost. Deposition of a thin layer of sprayed metal on polymer composites or wood fixtures is an attractive and
economical alternative to using sheet metal. Since thermal
spray technique induces relatively low heat flux to the
substrate allows depositing metal coatings on heat sensitive surfaces such as wood and wood composites. In addition, because of the nature of spray coating technique,
there are few limitations as to the shape of the substrate.
Thus it is expected that the deposition of antimicrobial
copper alloys which are non-toxic and ecofriendly on the
aforementioned substrates help prevent the spread of bacteria, mold and fungi.
Except a few durable softwood species like cedar, and
red wood most other softwoods should be treated with
preservative chemicals for decay protection [3]. In North
America, mostly copper-based preservatives are used to
treat pine, spruce and other non-durable wood species for
exterior and in-contact ground applications. Usually copper-based chemicals that work as fungicides are applied
by pressure under vacuum to penetrate deep into wood [3].
Although, pressure treated wood is protected from decay
fungi, it is susceptible to weathering degradation and
mildew growth. To protect the wood from weathering and
mildew growth, organic coatings that contain mildewcides are used [5, 6]. Addition of mildewcide to coating
formulation reduces mildew growth on the wood surface
when coated wood samples were exposed to high humidity and warm conditions.
This study is the first that focuses on measuring efficacy of copper coating in protecting wood from decay
fungi and mildew growth. Also, the effect of surface
roughness of metal coating on biocidal activity had been
investigated.
2. Materials and Methods
A twin wire arc spray system with high velocity cap
ValuArc (Sulzer Metco, Westbury, NY, US) was used
for coating deposition. Spray process parameters were as
follows: wired feed rate of 7 m/min, arc current of 280 A
and arc voltage of 27V. Feedstock material were phosphor
bronze wire and with high copper content (91.7%) and
copper alloy with Ni 18% Zn 17% to ensure antimicrobial
properties and better corrosion resistance than pure copper.
The resistance of copper-coated wood samples to mildew
growth were assessed based on AWPA E24-06 standard
test methods. Three replicate samples of mahogany, oak,
soft maple, white pine and MDF from different boards
were cut to size 12cm x 7cm x 2cm. Only one surface of
these wood samples was coated with bronze copper alloy.
Then coated samples were hung in the conditioning
chamber at 32°C and 95% relative humidity about 7 cm
above a wet unsterile soil inoculated with four mould
species: 1-Aureobasidium pullulans, 2) Aspergillus niger v.
Tiegh, 3) Penicillium citrinum Thom and 4) Alternaria
tenuissima group as shown in Fig. 1. After 4 months of
exposure samples were weighed and visually assessed for
mildew growth.
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
Fig.1 Copper coated wood samples in mildew test
The decay test was performed based on AWPA E10-06
standard in which two samples of one coated and one
uncoated wood block were placed in each glass jar (Fig.
2). Postia placenta (PP) white rot fungi, and Gloeophyllum trabeum (GT) brown rot fungi, were inoculated in
potato dextrose agar. Twelve test jars were prepared by
adding 180g of soil, 50g of distilled water, and two feeder
strips. The jars were then sterilized at 110°C for 50 minutes. A representative sample from each board of coated
and uncoated sapwood of pine wood samples were
weighed and placed in an oven at 105°C overnight until it
reached a constant weight to calculate the moisture content. Twelve replicate jars were inoculated with fungi and
placed in incubator at 25°C and 70% relative humidity for
two weeks before adding the test blocks. Three replicate
samples of each board (four boards) of both copper coated
and uncoated wood samples of 19mm blocks were prepared, weighed, autoclaved, and placed in soil jars on the
infected feeder strips. The copper coatings were applied
on all side of wood blocks. The jars were placed in incubator at 20°C and 65 % RH for four months. The mass
loss of samples calculated after 12 weeks of decay test
based on initial oven dry weight of samples (calculated
based on representative percent moisture content of samples from the same board) with their dry weight after the
decay test.
Fig.2 Copper coated and uncoated wood samples at the first
decay of decay test
2. Results and Discussion
None of the wood samples, i.e., hardwoods, softwoods
or wood composites, which were exposed to mildew tests
for four month showed any sign of mildew growth on the
copper-coated side. However, the unoctaed sides shown
hevey growth of mold. Fig. 3 shows the medium density
fiberboard (MDF, wood composite) samples after four
months of mildew test. The image on the right is copper
coated side and on the left is the back of the same sample.
The MDF wood sample is swollen almost to its double
size (thickness) and heavily infected with mildew on the
sides that were not coated. However, the Cu-coated surface of MDF sample was still free of mould and appeared
clear. The copper-coated sides of all other wood species
were free of mildew too. In some wood samples the copper coating cracked due to the stress caused by high
moisture content, but after a few days of drying there was
no sign of cracks anymore.
Fig. 3 Image of copper coated side of MDF sample (left) and
the back of another replicate of MDF coated samples (right)
after 4-month of exposure to mildew test.
Fig. 4 shows two samples from the same board one
Cu-coated and the other uncoated exposed to decay fungi
(Postia placenta) after 4 months. The uncoated sample is
completely covered with fungi while the Cu-coated sample can still be seen in the jar.
Fig.4 Image of Cu-coated and uncoated samples exposed to
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
decay test after 3 months in decay test jar.
Comparing the weight loss of oven dry samples before
and after decay test, indicates that the Cu-coating was
very effective in protecting wood from decay. The weight
losses of coated samples were 4% (±3%) and significantly
lower than the average (12 replicate each) weight loss of
uncoated samples (55% ±7%). Fig. 5 shows the two wood
samples (coated and uncoated) from the same boards after
completion of the decay test. The uncoated sample (left)
is badly damaged by decay, while the coated sample
(right) shows no sign of decay. In most cases the weight
losses of copper coated samples were zero (8 out of 12
replicates). In a closer look at those few copper coated
samples that had loss some weight some small spots were
found on their corners that were not completely covered
by copper coating that will explain that minimal weight
loss.
odically following the same protocol. Potential pathogens
were identified on chair arm cultures included: viridans
group streptococci M. luteus S. aureus, Acinetobacter and
A. viridans. Results of this study [8], which will be presented in the 53rd ICAAC (Interscience Conference on
Antibacterial Agents and Chemotherapy, September 2013,
Denver, CO, USA), consistently show that during 5
month of monitoring copper alloy coating effectively kills
bacteria.
3. Conclusion
Thermal spray copper coating on wood and wood composite proved to be an effective way of protecting these
substrates from microbial infection, decay fungi and
mold.
4. Acknowledgement
The authors would like to thank NSERC for funding this
project and also Romina Shafaghi for her help throughout
the project.
4. References
[1] D. Edwards, in, U.S Environmental Protection
Agency(EPA), (2006).
[2] A. L. Casey, et al., Role of copper in reducing
hospital environment contamination. Journal of
Fig.5 Image of un-caoted (left) and Cu-coated samples after
4-month of exposed to decay test.
The biocidal properties of the coatings demonstrated
that after two hours exposure contact killing of
gram-negative Escherichia coli and gram-positive
Staphylococcus epidermidis was 3-4-times higher than on
stainless steel. Observation under scanning electron microscope showed that when exposed to phosphor bronze
coating, E. coli were 3-4 times larger with irregular membrane morphology. The membranes of many of the S.
epidermidis were ruptured. Our data indicate that increasing the surface roughness of copper alloys had a
pronounced impact on the membrane integrity of
gram-positive and, to a lesser degree, gram-negative bacteria.it was observed that bacteria had ruptured membrane
after just 30 minutes of exposure time compared to 2
hours for brass sheet metal, details presented in [7].
Encouraging results of the lab studies allowed us to approach Toronto General Hospital for conducting the coating efficiency study in the real hospital environment. With
support of a chair manufacturer (ErgoCentric Seating
Systems, Mississauga, Ontario, Canada) 72 new chairs
were placed in the hospital waiting room. Polymer armrests on 36 of them were wire arc sprayed with copper
alloy and others used as controls were painted in similar
colour for blind testing. All armrest were swabbed peri-
Hospital Infection (2010) 74, 72-77.
[3] R.E. Ibach, Wood Preservation, in: F.P.L. (U.S.). (Ed.)
Wood Handbook - Wood as an Engineering Material,
U.S. Department of Agriculture, Washington, (1987),
pp. 28.
[4] F.P. Laboratory, in, U.S. Department of Agriculture,
Forest
Service,
Forest
Product
Laboratory,
Madison, WI, (1999), pp. 463.
[5] W.C. Feist, Journal of Coatings Technology, 68 (1996)
23-26.
[6] S. Bussjaeger, G. Daisey, R. Simmons, S. Spindel, S.
Williams, Journal of coating technolog (Technology
Forum: Wood Coatings), 71, 63 (1999).
[7] H. Gutierrez, et al., Evaluation of biocidal efficacy of
copper alloy coatings in comparison with solid metal
surfaces: generation of organic copper phosphate
nanoflowers. Journal of Applied Microbiology,
st
21 International Symposium on Plasma Chemistry (ISPC 21)
Sunday 4 August – Friday 9 August 2013
Cairns Convention Centre, Queensland, Australia
(2012)
[8] R.Peters, et al., Antimicrobial Efficacy of a
Thermal Spray Copper Alloy Coating in a
Hospital Setting, ICAAC2013, Denver, CO,
USA, Sep. 10-13, 2013