Agriculture Science Developments, 2(11) November 2013, Pages: 116-119
TI Journals
ISSN
2306-7527
Agriculture Science Developments
www.tijournals.com
Study of Microscopy Properties of Wood Impregnated
with Nanoparticles during Exposed to White-Rot Fungus
Maliheh Akhtari *1, Mehdi Arefkhani 2
1
Assistant Professor of Wood Science & Technology, Department of Natural Resources and Agriculture, Bojnourd Branch, Islamic Azad
University,Bojnourd , Iran.
2
Technical and vocational Training Organization, North khorasan, Iran.
AR TIC LE INF O
AB STR AC T
Keywords:
This research evaluated the microscopic features of Paulownia fortunei wood treated with nano
particles of silver, copper, and zinc oxide followed by decay with the white rot fungus Trametes
versicolor. Wood specimens were pressure impregnated with a 400 ppm aqueous suspension of
nanoparticles. Specimens were the inoculated with the fungus and incubated for sixteen weeks in
accordance with the EN113 standard. At the retention levels tested all three of the micronized metals
were very effective in weight loss after 2 months and preventing decay by this fungus. In the untreated
specimens, SEM observation visualized that fungus caused cavities in the cell wall and distinct
physical changes. Changes were minor in samples impregnated with nanoparticles after exposed
during Exposed to White–Rot fungus.
SEM
Nanosilver
Nanocopper
Nanozinc oxide,
Trametes versicolor
Percentage weight loss
© 2013 Agric. sci. dev. All rights reserved for TI Journals.
Introduction
1.
Wood is degraded by microorganisms, when moisture, oxygen and other environmental factors favor microbial growth. Biodeterioration
represents a complex of natural physical and chemical spoilage processes in various materials, caused by the growth of very different
organisms. These are generically called biodeteriogens, but they are all characterized by the saprotrophic ability of using substrates to
sustain their growth and reproduction [1]. The growth characteristics of the microorganisms in wood and the type of degrading system
produce different decay patterns [2]. Depending on the type of decay, different physical, chemical and morphological changes occur in
wood [3].There are reports that white rot fungi produce extracellular -OH, but they also secrete eroxidases, laccases and celluloses, which
undoubtedly participate in lignocelluloses degradation[4]. Wood decay can be prevented by treating wood with toxic preservatives such as
creosote, arsenic, zinc, copper, and chromium which have been solubilized in a solvent prior to impregnation [5]. Recently, commercial
metallic systems have been formulated by grinding fungicidal metals down to sub-micron size and then dispersing the particles in water.
These are called micronized, particulate or dispersed preservatives [6]. Nano-metals are totally different from solubilized metallics and
may, in turn, perform in an unusual manner. Nano-metal preparations have several characteristics that may improve their performance in
wood protection applications [7]. Preparation of nanometer-size metal particles essentially increases the effective surface area of the metal
in an evenly dispersed layer [8]. In a study on the microdistribution of copper-carbonate and iron oxide nanoparticles in treated wood,
Matsunaga et al [9] suggested that nano-Cu preservatives are able to deliver bioactive components only into parenchyma wood cell walls
because the majority of copper particles are too large to penetrate the cell wall’s nanocapillary network. In another study Matsunaga et al
[10] they concluded that small nanoparticles (2-4 nm) are able to penetrate ray parenchyma cell walls, but are excluded from lignified
tracheid walls. The spectra of specimens impregnated with nanoparticles showed no significant changes in their relative peak intensities of
lignin and carbohydrates after exposure to T. versicolor. This can indicate fungicide effects of the metal nanoparticles on T. versicolor [11].
Paulownia is a fast growing tree. If appropriate conditions are provided, the tree can reach about 15–25 m high in a 5-year period.
Paulownia wood is used for a variety of applications such as furniture, construction, musical instrument, shipbuilding, aircraft, packing
boxes, coffins, paper, plywood, cabinetmaking, and molding [12,13]. In this study we investigated the biological resistance and microscopy
properties of Paulownia wood treated with nano silver, nano copper, and nano zincoxide after exposure to a white-rot fungus (Trametes
versicolor). Knowing the morphological and structural changes of the wood decayed by this fungus and its deterioration potential is
essential both for understanding the ageing of wooden cultural heritage objects and for conducting the antiquating process of wood by
various techniques [14].
2.
Methodology
2.1 Materials
Boards were cut parallel to the grain from logs obtained from three sample trees. The boards were dried in a conventional kiln to a moisture
content of approximately 12%. Samples, 5×2×1.5 Cm3 were prepared from sapwood portion of Paulownia fortunei wood in accordance
with the EN113 standard. The specimens were free of knots, visible concentration of resins, and infection by mold, stain, or wood* Corresponding author.
Email address: [email protected]
Study of Microscopy Properties of Wood Impregnated with Nanoparticles during Exposed to White-Rot Fungus
117
Agri culture Scienc e Developments , 2(11) Nove mber 2013
destroying fungi. The density of Paulownia wood was 0.37gr/cm3. Test specimens were randomly separated into four groups with 10
replications. These included untreated samples and samples for treatment with nanosilver, nanocopper and nanozincoxide. The average
particles size for the nano-metals was 10 - 80 nm.
2.2 Impregnation process
The treating solutions were aqueous dispersion containing 400 ppm nanosilver, nanocopper and nanozincoxide particles. The test
specimens were impregnated with 400 ppm aqueous nanoparticle solutions in a pressure vessel by the Rueping (empty cell) process with no
initial or final vacuum at 2.5 bar pressure for 20 minutes. After treatment the specimens were stored for 1.5 months in a constant
temperature/relative humidity room (30°C and 45–50% relative humidity) where they attained a final moisture content of 8.5%. Retentions
for each compound were calculated based on initial and final weight of each wafer and the treating solution concentration.
2.3 Wood decay by fungi
The white-rot fungus (Trametes versicolor), was used in the decay test. The Fungus was maintaining at 4˚C on malt extract agar (48g/lit)
plates, until the fungal mycelium completely covered the plates. Malt-extract agar culture bottles were prepared and autoclaved at 120 ˚C
for 20 minutes. Culture bottles were inoculated with 1 cm3 of active mycelium fungus one week prior to the test. The samples were
supported on glass rods to avoid contact with agar and stored at 26˚C and 65% relative humidity for 16 weeks in accordance with the
EN113 standard. After this exposure, the mycelium was removed from the test blocks prior to oven dried to a constant weight. The weight
loss (WL) was determined for individual sample using the following equation:
WL (%) = [(Wo – Wf) / Wo ] × 100
Where Wo is oven dry weight of sample prior to exposure and Wf is the oven dry weight of samples after exposure to fungus.
2.4 Scanning Electron Microscopy (SEM)
The wood samples were analyzed with a SEM JEOL-JSM-840 A. The acceleration voltage was of 15 kV. To improve the conductivity of
the samples and the quality of the SEM images, the samples were coated with a very thin layer (18 nm ± 0.2 nm) of aluminum specimen
stub, the sides were painted with silver, and the surface coated with a thin layer of gold, using a covering SEM device. The SEM
micrographs were taken at a magnification of 1000 X in the longitudinal direction of the stem.
3.
Results and discussion
3.1 Weight loss
The mean percentage weight losses for the untreated and treated samples after exposure to Trametes versicolor for sixteen weeks are given
in Table 1. Results of the analysis of variance verified that there were significant differences (p<0.01) between weight loss of treated and
untreated samples. The decayed wood was lighter in color than the normal wood, indicating a bleaching effect.
Table 1. average weight loss in specimens exposed to white-rot fungus
Samples
Control
Nanosilver
Nanocopper
Nanozinc Oxide
Nanoparticles Retentions (Kg/m3)
0.140
0.137
0.142
Weight Loss (%)
28.13
2.105
2.375
2.252
3.2 Scanning electron microscopy analysis
3.2.1 Untreated and treated Paulownia Wood
The structure elements of paulownia wood are vessel, fiber, parenchyma and ray (Figure 1). The paulownia wood contains a significant
portion of parenchyma cells and vessel elements compared to the hardwoods, which is mainly fibrous. Parenchyma is well developed
around the vessel. The cell wall of parenchyma is thinner than that of fiber. This is one of the reasons for the light weight quality of
paulownia wood [15].
The big vessels are gathered in the area of the annual ring, and others are distributed in other areas uniformly. The structure of paulownia is
ring porous wood, but it has the tendency of diffuse porous wood. The shape of the fibers is similar to the structure of a honeycomb and the
average length (1.002mm) is like the one of hardwoods. Short fibers tend to give a dense and uniform sheet structure. Figure2 illustrates the
results of the scanning electron micrograph of the Paulownia wood treated with nanoparticles. Numerous white deposits are present on the
tertiary cell wall layer adjacent to the lumens of tracheids and rays. These deposits contrast strongly with the wood cell walls. These
deposits consisted of the inorganic elements (copper, zinc and silver) found in the nano-particles preservative. The deposits consisted of
small particles, some of which appeared to be crystalline. The SEM results show that the pit structures of the undecayed samples have
nearly symmetrically round apertures, and the borders are intact and unblemished.
Maliheh Akhtari and Mehdi Arefkhani
118
Agri culture Science Developme nts , 2(11) Nove mber 2013
(a)
(b)
Figure 1. Scanning electron micrograph of Paulownia fortunei wood (500x (a), 1000x (b))
(a)
(b)
(c)
Figure 2. Scanning electron micrograph of Paulownia fortunei wood treated with nanosilver (a), nanozincoxide (b) and nanocopper (c), (5000x)
3.2.2 Decayed wood by T. versicolor
3.2.2.1 Untreated wood
The presence of the decay caused by T. versicolor has been revealed by scanning electron microscopy (Fig. 3). The cell walls showed
hyphal tunnelling along the cellulose microfibrils, resulting in the formation of holes in transverse sections. Microscopic examination
showed the degradation in the fibers of decayed wood samples and formation of typical cavities in the cell walls. Fungi are generally
characterized by their formation of cavities within wood cell walls and cause the form of erosion of fiber cell walls [16]. The penetrating
hyphae are narrow where they first advance, after which they get larger, probably because they have eroded a wider channel. As
biodegradation advances, the hyphae are strongly interconnected with the structure of wood [17].
(a)
(b)
Figure 3. Scanning electron micrograph of the surface of Paulownia fortunei wood exposed to the white-rot fungus (T. versicolor) (1000x (a), 2000x (b))
3.2.2.2 Treated Paulownia Wood with nanoparticles
The SEM photographs of the wood treated with nanoparticles exposed to the white-rot fungus (Fig.4) generally confirm the infrared results
namely that the extent of decaying is not as pronounced as in the natural wood. This had been reported previously [11]. No discernible
differences can be observed between the SEM photographs of the undecayed normal wood and the decayed treated wood, thus providing
some evidence that the treatment with nanosilver, nanocupper and nanozinc oxide effected on bioresistance of Paulownia wood after being
exposed to white-rot fungus (T. versicolor) for 16 weeks.
Study of Microscopy Properties of Wood Impregnated with Nanoparticles during Exposed to White-Rot Fungus
119
Agri culture Scienc e Developments , 2(11) Nove mber 2013
(a)
(b)
(c)
Figure 4. Scanning electron micrograph of the surface of Paulownia fortunei wood treated with nanosilver (a), nanozincoxide (b) and nanocupper (c)
exposed to the white-rot fungus (T. versicolor)
4.
Conclusion
The weight loss and morphological characteristics of wood decay by a white-rot fungus, Trametes versicolor, were studied. Mean weight
losses in Paulownia wood decayed and treated with nanosilver, nanocopper and nanozinc oxide particles were 2.105%, 2.375% and
2.252%, respectively, after 16 weeks. The extent of decay was greater in Paulownia wood untreated and decayed (28.13%). Results of the
analysis of variance showed that there were significant differences (p<0.01) between Weight loss of treated and untreated samples. SEM
showed that the hyphae grow more intensely and are more connected to the wood structure with exposure to fungi. Also, the formation of
cavities aligned along the orientation of the cellulose microfibrils was observed.No discernible differences can be observed between the
SEM photographs of the undecayed normal wood and the decayed treated wood with nanoparticles, thus providing some evidence that the
treatment with nanosilver, nanocopper and nanozinc oxide effected on bioresistance of Paulownia wood after being exposed to white-rot
fungus (T. versicolor) for 16 weeks.
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