Evaluation of the antifungal activity of treated Acacia saligna wood with paraloid B-72/TiO2 nanocomposites against the growth of Alternaria tenuissima, Trichoderma harzianum, and Fusarium culmorum

Abstract

Acacia saligna wood was impregnated with 5% and 10% concentrations of Paraloid B-72/TiO2 nanocomposites using a soaking technique and evaluated for their antifungal activity against the growth of three molds in vitro, namely, Alternaria tenuissima, Trichoderma harzianum, and Fusarium culmorum. The Titanium (Ti) element peak of 0.14% and 0.23%, was found in the A. saligna wood treated with Paraloid B-72/TiO2 nanocomposites at 5% and 10%, respectively. Consolidant polymer Paraloid B-72 mixed with TiO2 nanocomposites at 5% and 10% showed antifungal activity against the three studied molds, while the linear growth of the studied molds reached the maximum in the control and Paraloid B-72 treatments. The results concluded that using synthesized Paraloid B-72/TiO2 nanocomposite could be considered as a new agent in the wood preservation field by prevention of mold fungal growth over the wood surfaces.

Full Article

Evaluation of the Antifungal Activity of Treated Acacia saligna Wood with Paraloid B-72/TiO₂ Nanocomposites Against the Growth of Alternaria tenuissima, Trichoderma harzianum, and Fusarium culmorum

Mohamed Z. M. Salem,^a,* Maisa M. A. Mansour,^b Wael S. Mohamed,^c Hayssam M. Ali,^d,e,* and Ashraf A. Hatamleh ^d

Acacia saligna wood was impregnated with 5% and 10% concentrations of Paraloid B-72/TiO₂ nanocomposites using a soaking technique and evaluated for their antifungal activity against the growth of three molds in vitro, namely, Alternaria tenuissima, Trichoderma harzianum, and Fusarium culmorum. The Titanium (Ti) element peak of 0.14% and 0.23%, was found in the A. saligna wood treated with Paraloid B-72/TiO₂ nanocomposites at 5% and 10%, respectively. Consolidant polymer Paraloid B-72 mixed with TiO₂ nanocomposites at 5% and 10% showed antifungal activity against the three studied molds, while the linear growth of the studied molds reached the maximum in the control and Paraloid B-72 treatments. The results concluded that using synthesized Paraloid B-72/TiO₂ nanocomposite could be considered as a new agent in the wood preservation field by prevention of mold fungal growth over the wood surfaces.

Keywords: Durability improvement; Molds; Paraloid B-72/TiO₂ nanocomposites; Surface characterization

Contact information: a: Forestry and Wood Technology Department, Faculty of Agriculture (EL-Shatby), Alexandria University, Alexandria, Egypt; b: Conservation Department, Faculty of Archaeology, Cairo University, Giza 12613, Egypt; c: Polymer Department, National Research Centre, Dokki, Giza, Egypt; d: Botany and Microbiology Department, College of Science, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia; e: Timber Trees Research Department, Sabahia Horticulture Research Station, Horticulture Research Institute, Agriculture Research Center, Alexandria, Egypt;

* Corresponding authors: zidan_forest@yahoo.com; hayhassan@ksu.edu.sa

INTRODUCTION

Wood is a natural material that can be attacked in service by several biological pathogens such as wood-destroying fungi and molds. Molds including Fusarium and Alternaria have been found in such places where humid conditions are available (Fogel and Lloyd 2002; Xu et al. 2013). Branches and leaves of fallen trees into water are decomposed by Fusarium sp. (Wylloughby and Archer 1973; Révay and Gönczöl 1990), where F. culmorum has been isolated from water of the Andarax riverbed in the provinces of Granada and Almeria in southeastern Spain (Palmero et al. 2009) and an aquatic system (Smither-Kopperl et al. 1998). A. tenuissima has been isolated from different wood species (Sivanesan 1991) and has been shown to cause discoloration for wood and wood-based products (Andersen et al. 2002, 2011; Yang 2005; Lee et al. 2014).

Molds such as Alternaria and Fusarium could be isolated even if preservatives have previously treated the wood (Bridžiuvienė and Raudonienė 2013). In addition, Sohail et al. (2011) found that the Alternaria species produces an enzyme that hydrolyzes cellulose into glucose. Trichoderma species have been found to colonize Pinus radiata sapwood of freshly cut timber (Butcher 1968; Dowding 1970), whereas the poles of Scots pine heartwood have little colonization (Bruce and King 1986).

Titanium dioxide (TiO₂) gel deposited in a high amount in the cell lumens of wood did help enhance the hygroscopicity of the wood; thereupon, thermal stability and stiffness of the wood cell walls were improved (Wang et al. 2012).

Nanoparticles have a broad-spectrum of uses in different areas, for example, a significant reduction in the mycelium biomass (28% to 35%) of A. niger and P. chrysogenum was found when using silver nanoparticles (AgNPs) in the growing medium (Pietrzak and Gutarowska 2015). In addition, a reduction in bacterial numbers (92.9% to 94.6%) was obtained after treating the sewage with AgNPs (Patil 2014). The resistance of coatings containing ZnO nanoparticles was improved against the microbial attack by Trichoderma reesei and Aspergillus niger (El-Feky et al. 2014). Significant antifungal activity was found against Aspergillus flavus, A. niger, and Candida albicans when using ZnO nanoparticles (Jayaseelan et al. 2012).

The treated wood with consolidants (synthetic and natural chemicals) resulted in higher strength than untreated wood, but can be attacked by fungi, molds, and insects (Clausi et al.2011). Paraloid B-72 is an acrylic resin that has been used as a wood surface consolidant (Yang et al. 2007; Vaz et al. 2008). However, this polymer at 2% or 10% has a weak resistance against the growth of fungi (Tiralová and Reinprecht 2004; Pohleven et al. 2013).

The authors’ previous studies reported F. culmorum was grown over an Acacia saligna wood surface that was treated by Paraloid B-72 (5% and 10%). Also, the enhancement of wood resistance was found with a combination of Paraloid B-72 and some natural extracts (Mansour et al. 2015; Mansour and Salem 2015). For example, the combination of Paraloid B-72 with Cupressus sempervirens wood (methanol extract) could be useful against T. harzianum (Mansour and Salem 2015), whereas borate base and voriconazole synergy effects were found useful in the inhibition of A. niger, P. chrysogenum, and Trichoderma viride (Clausen and Yang 2007). Titanium dioxide and Ag-doped titanium dioxide have been tested with consolidants and have been applied to several surface materials against biological colonization (La Russa et al. 2012; Ruffolo et al. 2013). Furthermore, the treatments of nano-compounds (CuO, ZnO, B₂O₃, TiO₂, and CeO₂) combined with Paraloid B-72 increased the biological performance of treated Scots pine wood against decay fungi tested but no improvements were obtained in mold resistance tests (Muhcu et al. 2017).

Therefore, in this present work the authors continued to increase the wood resistance by using a combination of Paraloid B-72 and TiO₂ in the form of nanocomposites to treat the wood. The antifungal activity of the treated A. saligna wood with Paraloid B-72 polymer and Paraloid B-72/TiO₂ nanocomposites is evaluated at concentrations of 5% and 10% against the growth of three molds (Alternaria tenuissima, Trichoderma harzianum, and Fusarium culmorum) in vitro.

EXPERIMENTAL

Materials

Synthesis of paraloid B-72/nano TiO₂ by in situ emulsion polymerization

A co-polymer emulsion lattice with a 50/50 composition ratio of methyl methacrylate/ethyl acrylate (MMA/EA) monomers (Aldrich, Darmstadt, Germany) was used to produce poly(MMA-Co-EA). It was prepared by an emulsion polymerization technique with different solid contents (5% and 10%) in the presence of 3% of TiO₂ nanoparticles. The polymerization was carried out according to the following procedure: in a 250-mL three-nicked flask, 1 g of emulsifier sodium dodecyl sulfate (SDS) (El Gomhouria Company, Cairo, Egypt) was dissolved in a desired amount of distilled water.

The desired amount of the monomers with the selected composition ratio (50/50 MMA/EA), was added and well emulsified for 30 min at room temperature using a mechanical stirrer (500 rpm) in the presence of 0.03 g of TiO₂ nanoparticles (a mixture of rutile and anatase nanopowder, < 100 nm particle size (BET), 99.5% trace metals basis obtained from Sigma-Aldrich, Schnelldorf, Germany). Then, the mixture was heated to 80 ºC (Shafei et al. 2008). Next, the redox initiation system composed of potassium persulphate (PPS) (0.27 g) and sodium bisulphite (SBS) (0.416 g) (Sigma-Aldrich, Schnelldorf, Germany) dissolved in 50 mL of distilled water was added dropwise to the reaction mixture under continuous stirring for 3 h. To obtain the solution of Paraloid-B72/TiO₂ nanocomposites, 100 mL of anhydrous xylene was added to the desired amount of Paraloid-B72/TiO₂ nanocomposites in the presence of N₂ and heated to 80 °C. The properties of the used concentrations are shown in Table 1.

Table 1. Concentrations of Used Coating Materials to Produce Polymer-based Inorganic Nanoparticle Composite

MMA: methyl methacrylate

EA: ethyl acrylate

Morphological analysis of the prepared nanocomposites

The morphological analyses of the prepared paraloid B-72/TiO₂ nanocomposites were investigated by transmission electronic microscopy (TEM), where the TEM images were obtained by a JEM-1230 electron microscope operated at 60 KV (JEOL Ltd., Tokyo, Japan). Before taking a TEM image, the sample was diluted at least 10 times by water. A drop of well-dispersed diluted sample was placed onto a copper grid (200-mesh and covered with a carbon membrane) and dried at ambient temperature.

The prepared Paraloid B-72/TiO₂ nanocomposite was investigated using TEM and from the figure, it was noticed that, a homogenous nanocomposite between Paraloid B-72 and TiO₂nanoparticles was prepared and the obtained particle size reached 38 nm in the case of Paraloid B-72 (5%) in presence of 3% TiO₂ (Fig. 1) and reached 54 nm in the case of Paraloid B-72 (10%) and in presence of 3% TiO₂ (Fig. 2).

Fig. 1. TEM images of nanocomposite for Paraloid B-72 (5%) in presence of 3% TiO₂; A) Photo at 500 nm of magnification and B) at 200 nm of magnification

Fig. 2. TEM images of nanocomposite for Paraloid B-72 (10%) in presence of 3% TiO₂; A) Photo at 500 nm of magnification and B) at 200 nm of magnification

Preparation and treating wood samples

Wood samples of A. saligna were prepared at the Department of Forestry and Wood Technology, Alexandria University (Alexandria, Egypt) during January 2017 with the dimensions of 0.5 cm × 1 cm × 2 cm. The wood samples were soaked for complete saturation in a solution of Paraloid B-72/TiO₂ nanocomposites (5% and 10%) and Paraloid B-72 polymer (5% and 10%) in Petri dishes for three sequential days and left to dry at room temperature for 15 days (Mansour and Salem 2015). The surfaces of the treated wood with 5% and 10% of Paraloid B-72/TiO₂ nanocomposites were examined for their elemental composition by dispersive X-ray spectroscopy (EDX) (FEI Company, Eindhoven, Netherlands) (Danilatos and Robinson 1979).

Retention value of Paraloid B-72 and Paraloid B-72/TiO₂ nanocomposite in A. saligna wood samples

The retention value was calculated based on BS EN 113 standard test method (BS EN 1997) and the recommendation of Mańkowski et al. (2015) with some modification. A. saligna wood samples were firstly weighed based on oven-dry weight, and then saturated by soaking method with the concentrated Paraloid B-72/TiO₂ nanocomposites (5% and 10%) and Paraloid B-72 polymer (5% and 10%). After all the treatments, the wood samples were air-dried in the laboratory for 48 h, then conditioned at 20 ± 2 ºC and 65 ± 5 % RH until constant weight, and the final weight after treatment was recorded, then the retention value was calculated as kg/m³.

Antifungal activity

The three common molds, namely Alternaria tenuissima, Trichoderma harzianum, and Fusarium culmorum, were used in the present study and supplied from the Regional Center for Mycology and Biotechnology, Al-Azhar University (Cairo, Egypt). Plates of potato dextrose agar (PDA) medium were prepared and inoculated with a 5-mm disc of 7-day-old culture from each of the tested molds. The treated wood samples with two levels of the concentrated Paraloid B-72/TiO₂ nanocomposites and the Paraloid B-72 polymer were put over the inoculated plates and incubated for 2 weeks at 25 °C. The fungal liner growth (mm) of the three mold fungi was measured after 14 days according to the methods described in the following sources (Satish et al. 2007; Essa and Khallaf 2014; Mansour and Salem 2015; Mansour et al. 2015; Salem et al. 2016 a, b) with some modification, where the linear growth was measured by a ruler from the fungal growth to the marge of the clear inhibition zones (no growth of fungus) formed around the treated wood once the control treatment (wood without any treatments) reached 9 cm-diameter in the growth. The wood samples were used for each treatment. Furthermore, after 6 months of inoculation at room temperature, the fungal colonization was visually evaluated (Mansour et al. 2015; Mansour and Salem 2015).

Methods

Statistical analysis

The effects of five different treatments [control (wood without any treatment), Paraloid B-72 polymer (5 and 10%), and Paraloid B-72/TiO₂ nanocomposites (5 and 10%)] on the linear growth values of A. tenuissima, T. harzianum, and F. culmorum, were statistically analyzed with one-way ANOVA using SAS version 8.2 software (2001) (Cary, NC, USA) in a completely randomized design. Least significant difference (LSD) at the α = 0.05 level was used to test the differences among the treatments.

RESULTS AND DISCUSSION

EDX Measurements of Treated Wood with Paraloid B-72/TiO₂ Nanocomposites

The elemental chemical compositions of the treated wood with Paraloid B-72/TiO₂ nanocomposites at 5% and 10% are shown in Figs. 3 and 4, respectively. The C element was 61.96% and 59.09% in wood treated with Paraloid B-72/TiO₂ nanoparticles at 5% and 10%, respectively. The Titanium (Ti) element peak was found in percentages of 0.14% and 0.23%, on the A. saligna wood treated with Paraloid B-72/TiO₂ nanocomposites at 5% and 10%, respectively.

Fig. 3. EDX analysis of treated wood with Paraloid72/TiO₂ nanocomposite at 5%

Fig. 4. EDX analysis of treated wood with Paraloid B-72/TiO₂ nanocomposite at 10%

Retention of Paraloid B-72 and Paraloid B-72/TiO₂ Nanocomposite in Wood

Table 2 presents the retention values in the Paraloid B-72/TiO₂-treated wood specimens as well as Paraloid B-72. Statistically significant higher mean of retention value was recorded after double concentration for the treated samples. These results are in agreements with Muhcu et al. (2017) and Mańkowski et al. (2015, 2016).

Table 2. Retention Levels of Paraloid B-72 and Paraloid B-72/TiO₂ Nanocomposite in Wood Specimens after Treatments

Retention levels in treated wood specimens by soaking method.

Values in parentheses are standard deviations.

Fungal Linear Growth

The linear growth of the studied three molds (Table 3) reached its highest (90 mm) in the control treatment, while it decreased significantly (p < 0.0001) to 38.3 mm, 38.3 mm, and 23.3 mm with T. harzianum, A. tenuissima, and F culmorum, respectively, as A. saligna wood was treated with Paraloid B-72/TiO₂ nanocomposites at a concentration of 5%. Furthermore, the linear growth was significantly (p < 0.0001) reduced with values of 13.3 mm, 13.3 mm, and 11.3 mm, for T. harzianum, A. tenuissima, and F culmorum, respectively, using the wood treated with Paraloid B-72/TiO₂ nanocomposites at a concentration of 10%.

Table 3. Means ± Standard Deviation (Standard Error of Linear Growth of T. harzianum, A. tenuissima, and F. culmorum as Affected by Paraloid B-72/TiO₂ Nanocomposites (5% and 10%) and Paraloid B-72

Means with the same letter within the same column are not significantly difference according to LSD at a 0.05 level of probability

From Table 3, the linear growth of the three molds incubated with the treated wood samples with Paraloid B-72 reached the maximum, which was not significantly different from the control treatments. These results are in agreement with previous works (Tiralová and Reinprecht 2004; Yang et al. 2007; Vaz et al. 2008; Pohleven et al. 2013; Mansour et al. 2015; Mansour and Salem 2015; Reinprecht and Vidholdová 2017). Also, Paraloid B-72-only treated wood specimens were observed to have the highest weight losses in decay tests (Reinprecht et al. 2015; Muhcu et al. 2017) and practically the polyacrylate Paraloid B-72 had no effects against molds (Reinprecht and Vidholdová 2017).

Several studies reported that TiO₂ applied as a coating has high photoactivity and non-toxicity, as well as a strong self-cleaning property (Meng and Lu 2010; Zawadzka et al. 2016). Suitable antifungal properties of the photocatalyst TiO₂ nanoparticles have been observed against Candida albicans biofilms (Akiba et al. 2005; Shibata et al. 2007; Haghighi et al.2013). Cotton fabric impregnated with TiO₂ nanoparticles showed a maximum zone of inhibition against Aspergillus niger and Trichoderma reesei and was demonstrated to be an effective antimicrobial agent (Durairaj et al. 2015). The poly(lactic acid)/TiO₂ nanocomposites with 8 wt.% were effective (99.99%) against Aspergillus fumigatus under the ultraviolet A (UVA) irradiation (Fonseca et al. 2015).

Nano-particle as fillers in a polymer structure combined with consolidant materials has the ability to neutralize acid, has high durability, and is a better coating (Christensen et al. 2012). The nano-materials (ZnO, TiO₂, SiO₂, CuO, Fe₂O₃) mixed consolidation products increased the biological, UV radiation scratch, abrasion and water resistance of wood (Blee and Matisons 2008; Kartal et al. 2009; Tuduce-Trãistaru et al. 2010; Clausi et al. 2011).

Unger et al. (2001) reported that Paraloid B-72 was provided some antifungal activity to the consolidated wood, but other studies have shown that Paraloid B-72 cannot protect wood itself against wood-destroying fungi and molds, which needs the additions of fungicides (Nakhla 1986), chemical preservative (Olstag and Kucerova 2009), natural products (Mansour et al. 2015; Mansour and Salem 2015), or nanoparticles (Muhcu et al. 2017). Furthermore, the choosing of ideal consolidant is very important to be compatible with wood-protecting biocides (Unger et al. 2001; Mansour et al. 2015; Mansour and Salem 2015). Therefore, the combination of Paraloid B-72 with TiO₂ nanoparticle at 5% and 10% showed strong antifungal activity against the growth of T. harzianum, A. tenuissima, and F. culmorum.

Visual Observation after 14 Days

After 14 days from the inoculation, wood samples treated with Paraloid B-72 were completely colonized by the three molds (Mansour et al. 2015; Mansour and Salem 2015). In contrast, the treated wood samples with either Paraloid B-72/TiO₂ nanocomposites at 5% or 10% showed significant inhibition to the linear growth of the three tested molds after 14 days from the inoculation. By contrast, the consolidant polymer Paraloid B-72 mixed with TiO₂ nanoparticles was shown to be a strong antifungal agent against the three studied molds.

Previous studies about using nanoparticles for preventing mold infestation showed that a 90 ppm concentration of AgNPs (10 nm to 100 nm particle size) was effective in removing the molds present on the surface of objects from six different museums and archives in Poland (Gutarowska et al. 2012). Consolidation polymers (acrylic and silicon polymers) functionalized with AgNPs were found used as a potent biocide and consolidation material for historic monuments and artifacts (Essa and Khallaf 2014). Consolidants and water repellents mixed with copper nanoparticles were effective in the protection of stones from biodeterioration (Pinna et al. 2012).

Visual Observation of the Incubated Wood Samples after 3 Months

The visual observations of the treated wood samples with Paraloid B-72/TiO₂ nanocomposites at (5% and 10%) and inoculated with T. harzianum, A. tenuissima, and F. culmorum are evaluated after Petri dishes were stored at room temperature for 3 months. It was observed that no visual growths of A. tenuissima were found on the surface of A. saligna wood samples treated with Paraloid B-72/TiO₂ nanocomposites at 10%, but some growth was observed for the treated wood with Paraloid B-72/TiO₂ nanocomposites at 5%. Some growth of T. harzianum was visually observed for both treatments (Paraloid B-72/TiO₂ nanocomposites at 5% and 10%). Growths of F. culmorum were apparent all over the surface of the treated wood samples, regardless of treatment.

CONCLUSIONS

1. Increasing saturation wood with the concentrated Paraloid B-72 solution or Paraloid B-72/TiO₂ nanocomposites significantly increased the retention values.
2. The linear growth of T. harzianum, A. tenuissima, and F. culmorum reached the maximum in the Paraloid B-72 and control treatment (wood without any treatments), while it decreased as A. saligna wood was treated with Paraloid B-72/TiO₂ nanocomposites at the concentration of 5% and 10%.
3. After 3 months from the incubation at room temperature, no visual growth of A. tenuissima was found for treated wood (Paraloid B-72/TiO₂ nanocomposites 10%), T. harzianumgrowth was visually observed (Paraloid B-72/TiO₂ nanocomposites at 5% and 10%) and growth of F. culmorum was observed regardless of treatment.
4. From the present results, these combinations of nanocomposites (Paraloid B-72/TiO₂) could be useful as a potential treatment against molds and staining fungi that colonize wood.

ACKNOWLEDGMENTS

The authors would like to extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for its funding this Research group No. RG 1435-011.

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Article submitted: May 19, 2017; Peer review completed: August 19, 2017; Revised version received and accepted: August 24, 2017; Published: August 31, 2017.

DOI: 10.15376/biores.12.4.7615-7627