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Article

Changes in Chemical Composition, Crystallizability, and Microstructure of Decayed Wood-Fiber-Mat-Reinforced Composite Treated with Copper Triazole Preservative

by
Minzhen Bao
1,*,
Rongqiang Tang
2,
Yongjie Bao
1,
Sheng He
1,
Yuhe Chen
1 and
Neng Li
1
1
Key Laboratory of High Efficient Processing of Bamboo of Zhejiang Province, China National Bamboo Research Center, Hangzhou 310012, China
2
Zhejiang Academy of Forestry, Hangzhou 310023, China
*
Author to whom correspondence should be addressed.
Forests 2022, 13(9), 1387; https://doi.org/10.3390/f13091387
Submission received: 25 July 2022 / Revised: 17 August 2022 / Accepted: 24 August 2022 / Published: 30 August 2022
(This article belongs to the Section Wood Science and Forest Products)
Browse Figures
Versions Notes

Abstract

:
Wood-fiber-mat-reinforced composites (WFMRCs) possess excellent physical and mechanical properties and provide high structural performance, making them a suitable engineering structural material. However, WFMRCs are susceptible to biological attack by fungi and insects when they are used in outdoor environments. In this study, the efficacy of copper triazole (CuAz) preservative treatment in protecting WFMRC against decay by white- and brown-rot fungi (Trametes versicolor and Gloeophyllum trabeum, respectively) was evaluated. Both fungi caused a mass loss in the untreated scrimber of more than 15%, while the CuAz preservative treatment reduced the mass loss to 5%. The measurement results show that CuAz treatment could effectively reduce the degradation rate of three major components of wood; inhibit fungal colonization and degradation; and improve the decay resistance of WFMRC. The atmospheric impregnation of CuAz preservative is more suitable for the material features of WFMRC than vacuum impregnation and can be considered for practical industrial applications. This study provides technical support for the protection and outdoor application of WFMRCs.

1. Introduction

Wood, as a renewable resource, is an important structural material for both indoor and outdoor applications. It possesses excellent construction properties, such as good machinability, favorable aesthetics, and high strength. Wood can be converted into engineered products with standardized dimensions, such as oriented strand board, glued laminated wood, and reconstituted wood lumber. Wood-fiber-mat-reinforced composite (WFMRC), as a novel engineered scrimber composite, consists of oriented fast-growing wood fiber mats bonded with phenolic resin under hot or cold pressing [1]. The density of scrimber composite can be up to three times the density of virgin timber [2]. The output of scrimber products increased to 1.53 million m3 by 2021 in China. Scrimber composite has emerged as a competitive substitute for traditional engineered wood products.
When used outdoors, engineered wood composites are often affected by temperature, humidity, and biological agents. In particular, exposure to molds and decay fungi under appropriate humidity and temperature conditions can affect the color, morphology, and mechanical properties of timber [3,4,5]. White- and brown-rot fungi can degrade the polysaccharides and lignin in wood [6]. Witomski et al. [7] reported that Scots pine wood lost up to 20% of its bending strength and compressive strength with only 7% mass loss. Fungal decay inflicts severe damage to timber and limits its outdoor application. Therefore, engineered wood composites made of timber with poor durability, especially those made from fast-growing species, requires protective measures to be used outdoors.
Preservative treatments can significantly improve the decay resistance of wood-based materials [8]. The durability of biomass materials can be enhanced by treatment with preservatives, such as disodium copper dimethyldithiocarbamate, disodium octoborate tetrahydrate, triazole fungicide, and chitosan–copper complexes [9]. Water- and solvent-based preservatives can protect wood against fungal decay and extend its service life. However, some water-based wood preservatives, such as chromated copper arsenate (CCA), have negative effects on the environment and are now forbidden in some countries [10,11]. Other copper-based preservatives, such as ammoniacal copper quaternary (ACQ), copper dimethyldithiocarbamate (CDDC), micronized copper quaternary (MCQ), and copper azole (CuAz), have less impact on the environment [12,13]. They are suitable for use against fungal attack because quaternary ammonium salts and copper bind to the wood, providing an excellent antifungal effect [14]. ACQ, MCQ, CDCC, and CuAz have gradually replaced CCA and are widely used for the protection of wood-based materials. Preservatives may have chemical interference with the adhesive cure. Compared with other organic acid salt preservatives, CuAz does not significantly affect the performance of wood-based panels or the curing of the thermosetting adhesive [15]. CuAz can decrease the curing temperature and accelerate the curing of the thermosetting adhesive [16,17]. In particular, CuAz has a low toxicity and high efficiency. Therefore, CuAz was chosen to protect WFMRCs based on phenolic-resin-impregnated wood fiber mats.
In order to expand the applicability of WFMRC to outdoor flooring and buildings, more attention should be paid to the decay resistance of WFMRC. Because WFMRC is mainly made of non-durable fast-growing wood, it requires special protection unlike traditional engineered wood products. Fortunately, CuAz preservative does not affect the bonding property of phenolic-resin-based polymer composite, and it also has an excellent antifungal effect. The objective of this study was to investigate the changes in the chemical composition, crystallizability, and microstructure of CuAz-treated WFMRCs exposed to white- and brown-rot fungi (Trametes versicolor and Gloeophyllum trabeum, respectively). The results provide a basis for the use of CuAz preservative treatment for WFMRCs in outdoor applications.

2. Materials and Methods

2.1. Materials

Poplar wood (Populus × canadensis Moench) was purchased from Langfang Senyuan Wood Co., Ltd. (China). A low-molecular-weight (Mw ≈ 420 g/mol) phenol formaldehyde resin with a pH of 10.5, solid content of 45.6%, and viscosity of 40.2 mPa·s was supplied by Dynea Chemical Industry Co., Ltd. (Guangdong, China). CuAz-B preservative with a concentration of 10.2 wt.% was purchased from Sanyu Chemical Co., Ltd. (Shenzhen, China). The weight ratio of copper/ammonia/tebuconazole/propiconazole in the CuAz-B preservative was 30:15:1:1.

2.2. Preparation of WFMRCs

WFMRCs were prepared through a series of processes, including rotary cutting, shaping, fluffing, flattening, impregnating, drying, assembling, and hot pressing, according to a previously published method [2]. According to the porous characteristics of fluffed wood fiber mats, two available impregnation treatments of CuAz preservative, namely, atmospheric impregnation (AI) and vacuum impregnation (VI), were employed. Briefly, poplar log was peeled into veneers and then split along the grain direction to produce oriented fiber mats (600 × 180 × 6 mm3). Next, the air-dried fiber mats (moisture content of 12%) were impregnated with the CuAz preservative (concentration of 10.2 wt.%). The target retention of the treated wood fiber mats was 1.0 kg/m3 according to the specification for preservative-treated wood described in the Chinese Standard GB/T 27651-2011 [18]. Subsequently, the CuAz-impregnated fiber mats were air-dried to a moisture content of 12%. Next, the air-dried mats were immersed in diluted PF resin (concentration of 20 wt.%) for 6 min at room temperature to obtain a resin content of 13 wt.% based on the mass of the dried mats. Thereafter, the resin-impregnated wood fiber mats were air-dried again to obtain a moisture content of 12 wt.%. Finally, the WFMRC was manufactured by assembling mats symmetrically along the grain and hot pressed at 140 °C for 30 min. The WFMRCs (500 × 150 × 18 mm3) with a density of 1.00 g/cm3 were prepared by adjusting the mass of the mats. Untreated fiber mats were also used to produce untreated (control) WFMRC samples. In total, 18 specimens of WFMRCs (6 replicates per treatment) were trimmed into the required dimensions and stored at 20 °C and 65% relative humidity (RH) for 2 weeks prior to further experiments.

2.3. Fungal Durability Experiment

The CuAz-impregnated WFMRC samples (20 × 20 × 10 mm3) were tested against selected decay fungi. The untreated WFMRC and poplar wood with the same dimensions were used as control and reference samples for the biodegradation experiments. For the fungal decay tests, white-rot T. versicolor fungi or brown-rot G. trabeum fungi were inoculated on malt agar medium and pre-incubated for 10 days until the mycelium had covered the entire surface of the medium. Then, 6 test blocks from each group were placed in separate pre-inoculated culture vessels and incubated on sterile glass sticks for 12 weeks at 28 °C and 80% RH according to the Chinese Standard GB/T 13942.1-2009 [19]. After incubation, the decayed samples were gently cleaned to remove the mycelium adhered to the surface of the samples and oven-dried at 103 °C to a constant mass. The percentage of mass loss (ML) of the samples was calculated after 12 weeks.
M L   =   M 1 − M 2 M 1   ×   100 %
where M1 is the mass of the samples before decay, and M2 is the weight of the samples after 12 weeks of incubation.
According to the ML values, the decay resistance can be divided into four classes: highly resistant (0%–10%), resistant (11%–24%), slightly resistant (25%–44%), and non-resistant (>45%).

2.4. Chemical Analysis

Chemical analyses of the wood cell walls were conducted in 2 replicates according to TAPPI standards following the fungal decay tests. Before chemical analyses, all specimens were oven-dried, ground, and screened through a 40-mesh sieve. Acid-insoluble lignin, holocellulose, and α-cellulose analyses were carried out following the TAPPI T 222 om-06 [20], TAPPI T 249-75 [21], and TAPPI T 203 om-93 [22] procedures, respectively.

2.5. Fourier Transform Infrared Spectroscopy (FTIR) Analysis

Infrared spectra of the untreated and CuAz-treated WFMRCs before and after 12 weeks of incubation with T. versicolor and G. trabeum fungi were obtained using an FTIR spectrometer (Vertex 70, Bruker, Japan). The specimens were prepared by finely grinding the WFMRC samples and preparing KBr disks containing 1% WFMRC. Each spectrum was recorded in absorbance units from 1800 to 800 cm−1 as an average of 16 scans at a spectral resolution of 4 cm−1. The spectra were baseline corrected and smoothed using OMNIC software.

2.6. X-ray Diffraction (XRD) Analysis

XRD patterns of the samples were recorded on an X-ray diffractometer (Bruker, D8 Advance) with Ni-filtered Cu Kα radiation (λ = 1.5404 Å) at an accelerating voltage and beam current of 40 kV and 40 mA, respectively. Scattered radiation was detected in the 2θ range of 10–80° at a rate of 2° min−1. The degree of relative crystallinity (Cr) of the samples was measured before and after fungal decay.
C r   =   A crystalline A total   ×   100 %
where Acrystalline is the sum of all areas of crystallographic reflections, and Atotal is the total area of both the crystalline and amorphous contributions.

2.7. Scanning Electron Microscopy (SEM) Analysis

SEM images of wood fiber mats atmospheric impregnated with CuAz and sputter-coated with gold were observed using a scanning electron microscope (SEM, SU8010, Hitachi, Tokyo, Japan) equipped with energy-dispersive X-ray spectroscopy (EDS). The surface morphologies of the untreated (control) and decayed AI WFMRC samples were also investigated using SEM equipment (Hitachi S4800, Japan) in the low-vacuum mode with a SE detector.

2.8. Statistical Analysis

A descriptive analysis was conducted (mean and standard deviation) between undecayed and decayed samples. An analysis of variance (ANOVA) was applied to verify the effect of the treatment with the CuAz preservative. Duncan’s test was performed (95% confidence level) to determine the statistical difference between the means.

3. Results and Discussion

3.1. Mass Loss Analysis

Figure 1 shows the percentage of the ML of the specimens after fungal exposure. The poplar wood specimens lost approximately 74.19% and 65.39% mass when exposed to white-rot T. versicolor fungi and brown-rot G. trabeum fungi, respectively. This result shows that fast-growing poplar is susceptible to fungal infection with white and brown fungi. When polar wood was made into WFNRC, it could be rated as resistant to biodegradation by decay fungi based on mass loss. As a rule, decay fungi are not able to easily penetrate PF-resin-bonded wood-based panels and gain access to the wood fiber [23,24,25]. Wood fiber mats compressed together densely with PF resin with the aid of temperature and pressure can contribute to the decay performance of the poplar wood, which is similar to that reported for bamboo scimber [26,27]. Exposure to T. versicolor resulted in a relatively higher mass loss than did exposure to G. trabeum fungi, indicating that poplar wood and poplar WFMRC were more susceptible to decay by white rot fungi. White-rot fungi are able to degrade polysaccharides and lignin simultaneously during decay, whereas brown-rot fungi primarily degrade polysaccharides [28,29,30]. This might explain the higher MLs of poplar wood and poplar WFMRC observed after exposure to white-rot fungi compared to those due to exposure to brown-rot fungi [31,32]. The CuAz preservative treatment had a significant effect on the ML of the WFMRC samples. The CuAz-treated WFMRC specimens exhibited a ML after fungal exposure that was lower than that of the untreated (control) WFMRC specimens. The ML caused by T. versicolor was below 5% for the treated WFMRCs, whereas that of the control specimens was significantly higher at 18.34%. After G. trabeum exposure, the ML of the treated WFMRCs was below 4%, while that of the control specimens was 15.07%. These results demonstrate that the CuAz-treated WFMRCs have greater decay resistance than the control WFMRC. The treated scrimbers could be classed as highly resistant to fungal decay (ML ≤ 10%). Jin et al. [33] reported that the mass losses caused by T. versicolor and G. trabeum of CuAz-treated poplar LVL (with a retention of 0.85 kg/m3) were 21.9% and 14.2% after 17 weeks of incubation, respectively. Copper tolerance is generally associated with brown-rot fungi, including G. trabeum fungi [34,35]. Due to the retardant effect of copper on the growth of white-rot fungi, copper azole improved the decay resistance of wood significantly [14,36,37]. The used CuAz preservative contains not only copper but also ammonia, tebuconazole, and propiconazole. The durability of wood-based materials can be improved by triazole fungicides [38,39]. The results of the present study confirm that CuAz preservative can improve the durability of WFMRC samples, even against brown-rot fungi. Therefore, the application of CuAz preservative for the biological protection of WFMRC presents a promising prospect for composite materials. Although VI treatment is more effective than AI treatment in decay resistance, the difference in the ML of the AI and VI specimens was not significant according to Duncan’s test (p ≤ 0.05).

3.2. Chemical Analysis

Microorganisms change the chemical composition of wood during decay [40]. It is not known if the cell wall components of CuAz-treated WFMRC are degraded by fungi in the same manner as that in poplar wood and untreated WFMRC. The holocellulose, α-cellulose, and acid-insoluble lignin contents of the WFMRC samples were determined before and after fungal attack. As shown in Table 1, exposure to both fungi caused a decrease in the holocellulose and α-cellulose contents. The reduction in cellulose content and the increase in lignin in the decayed WFMRC indicate that decay occurred by a cellulolytic mechanism with both fungi. There are some studies that reported that both cellulolytic and ligninolytic mechanisms were observed in wood for white-rot fungi P. ostreatus and T. versicolor [41,42]. It was observed in the present study that the carbohydrate components were degraded by T. versicolor preferentially in WFMRCs and CuAz-treated WFMRCs, although other reports have indicated that T. versicolor degrades holocellulose and lignin more or less uniformly [43,44,45]. Previous studies have shown that brown-rot fungi degrade the structural carbohydrate components and result in the accumulation of lignin in decayed wood [29,46]. According to Bouslimi et al. [47], brown-rot decay selectively removes hemicellulose and cellulose, leading to an increase in the degree of the lignin/carbohydrate ratio as decay progresses. The results of the present study confirm that the rapid and extensive depolymerization of carbohydrate components led to an increase in lignin content.
Regardless of the type of fungus used, the holocellulose and α-cellulose contents of the decayed WFMRC samples decreased with the corresponding treatment, while the corresponding acid-insoluble lignin content increased. Compared with the undecayed WFMRCs, the holocellulose content in the T. versicolor-exposed AI and VI WFMRCs was reduced by 4.20% and 3.96%, respectively, while that in the G. trabeum-exposed WFMRCs was reduced by 4.96% and 4.78%, respectively. These results demonstrate that the holocellulose content of the VI WFMRC decreases less than that in the AI WFMRC after fungal decay, which indicates that the VI WFMRC has better decay resistance. The amount of holocellulose in the CuAz-treated WFMRCs decomposed by G. trabeum was greater than that in the CuAz-treated WFMRCs decomposed by T. versicolor, indicating that CuAz could inhibit the growth of white-rot T. versicolor. These observations are also in agreement with previous findings that copper has an effective effect on the growth of white-rot fungi [14,36,37].

3.3. FTIR Test

The FTIR spectra collected from the control WFMRC and CuAz-treated WFMRC before and after 12 weeks T. versicolor and G. trabeum fungi attack are shown in Figure 2. The FTIR spectra of the decayed samples show significant changes in the fingerprint region (1800 to 800 cm−1) [13]. Regardless of the type of fungus, the intensity of each characteristic peak decreased to some extent after fungal decay. Changes in the relative intensities of the different peaks were less pronounced in the CuAz-treated specimens than in the control specimens after fungal exposure. This confirms the effectiveness of the CuAz treatment for inhibiting decay.
The intensity of the unconjugated stretching C=O band at 1740 cm−1 was reduced in the decayed WFMRC, which indicates that hemicellulose in wood is degraded by fungal attack [48]. The decrease in the intensities of the bands at 1600, 1510, and 1462 cm−1, which correspond to the aromatic skeletal stretching vibrations of lignin, signifies the changes in lignin in the exposed specimens [49]. The relative changes were smaller for the CuAz-treated specimens than that for the control WFMRC after fungal exposure. The peaks at 1373, 1050, and 1037 cm−1 correspond to C–H and C–O bonds [50]. Thus, the decrease in the intensity of these peaks indicates that cellulose and hemicellulose were decomposed by fungal exposure. However, in the control specimens, the bands at 1268, 1103, 1050, and 1037 cm−1 almost vanished after exposure to both types of fungi.
The FTIR spectra of the untreated and CuAz-treated WFMRCs show clear differences. The intensity of the peak at 1740 cm−1 for the CuAz-treated WFMRC was reduced, showing that the acetyl and carboxyl groups of the hemicellulose change after CuAz treatment. This may be due to the degradation of hemicellulose and ligand exchange between the copper and hemicellulose molecules to form complexes [51,52]. Some functional groups of lignin react with copper to form stable compounds [53]. The absorption at 1600 and 1510 cm−1 decreased, indicating that CuAz reacts with the C=C groups in the aromatic ring. The peak at 1333 cm−1 (assigned to O–H in the aromatic ring of lignin) had a lower intensity for the CuAz-treated specimens than for the control samples, indicating that the O–H group is involved in the formation of lignin–copper complexes [54]. The bands at 1373 and 1159 cm−1, which are characteristic of cellulose and hemicellulose, also changed after the CuAz treatment [55]. These results show that the CuAz preservative reacts with the carboxyl groups of hemicellulose, phenolic hydroxyl groups, and aromatic esters of lignin to form carboxylate–copper complexes and aromatic ring–copper complexes [53,55]. These complexes can effectively inhibit fungal growth; reduce the degradation rate of the three major components in wood; and improve the decay resistance of WFMRC.

3.4. XRD Test

The XRD patterns of the untreated (control) and CuAz-treated WFMRCs after 12 weeks of fungal attack are shown in Figure 3. Typical peaks are present at 16.3° and 22.5°, which correspond to the (110) and (200) crystallographic planes of wood, respectively [56]. This reveals that the decayed WFMRC samples retain the crystalline nature of wood. After fungal decay, there was an increase in the intensity of both the (110) and (200) reflections of the CuAz-treated WFMRCs compared to those of the control (untreated) WFMRC. The intensity of these reflections was higher for the VI WFMRC than that for the AI WFMRC.
The relative Cr of the WFMRC specimens was calculated as the ratio of the area arising from the crystalline phase to the total area. After fungal decay, the relative Cr of all WFMRC samples decreased. The relative Cr of the CuAz-treated WFMRCs after 12 weeks of fungal decay was less than that of the corresponding undecayed WFMRCs (Table 2). The relative Cr was 18.26% for the T. versicolor-decayed AI WFMRC and 18.98% for the G. trabeum-decayed AI WFMRC, corresponding to decreases of 17.26% and 14.01%, respectively, when compared to that of the undecayed AI WFMRCs. A similar phenomenon was obtained with the VI WFMRC; the relative Cr values of the T. versicolor- and G. trabeum-decayed VI WFMRCs were 17.27% and 13.23% higher, respectively, than that of the undecayed VI WFMRCs. Howell reported that changes in the relative Cr were a consequence of fungal decay [57]. The fungal decay changed the crystalline area of the cellulose and caused a decline in the relative Cr [58,59]. Fungi use the small molecules of cell wall components and assimilate them as carbon sources or energy sources for growth [60,61]. However, the addition of CuAz preservative could reduce the degradation rate of hemicellulose and lignin, and decrease the degradation amount of cellulose [62]. Thus, the relative Cr in the CuAz-treated WFMRCs was higher than that in the untreated WFMRCs after fungal exposure. There is good correlation between the XRD and FTIR results.

3.5. Microscope Observation Analysis

The elemental compositions of the CuAz-impregnated wood fiber mats were determined using SEM-EDS. The presence of copper originating from the CuAz preservative is shown in Figure 4 and Figure 5. Figure 4 shows that copper was distributed in the vessels, rays, and fiber cells. Figure 5 shows that copper was distributed in the radial and transverse sections of the wood fiber mats. These observations indicate that the CuAz preservative has good permeability and is able to enter the cell walls. The distribution of copper in the cells was not uniform. Most of the copper was distributed in the vessel and ray cells, and a small amount of copper was distributed in the fiber cells. The SEM-EDS images show that the CuAz preservative adhered to the cell cavity of the ray cells and some of the fiber cells. Furthermore, the ray cells were filled with the CuAz preservative.
The element content of the wood fiber mats in the different cell types is shown in Figure 4g–i. C and O elements originated from the wood fiber mats, and Cu element originated from the CuAz preservative. The content of Cu element in vessel and ray cells was higher than that in the fiber cells, while the content of copper in fiber is the lowest (Figure 4i). The content of Cu element in vessel cells was 58.76% more than that in fiber cells. The results in Figure 5e,f show that the content of Cu element in the tangential section is 14.18% more than that in the radial section. The reason for this may be that there are more pits in the cell walls of the ray and vessel cells with large lumina fiber walls than there are in the fiber cells, which improved the permeability of the preservative.
Structural alterations in the wood cell walls of the untreated and CuAz-treated WFMRC samples exposed to T. versicolor fungi are shown in Figure 6. The untreated WFMRC showed evidence of fungal colonization and deterioration, as shown in Figure 6a–c. The T. versicolor fungi colonized the cell lumina and attacked the cell walls by thinning the cell walls and creating bore holes (Figure 6a). Erosion occurred between adjacent holes in the ray cell walls, until the holes eventually coalesced into a large hole (Figure 6b). The tangential view in Figure 6c shows the destruction of the ray cell walls, as well as the bore holes formed by fungal decay. In contrast, the change in the morphological characteristics of the CuAz-treated WFMRC samples was not as obvious, and the extent of damage was greatly reduced. Localized erosion of the cell walls was observed, and some regions were intact and had not been attacked by the fungi (Figure 6d). There was no deterioration in either the radial or the tangential walls of the CuAz-treated samples (Figure 6e,f). The structures of the ray and fiber cells were intact, and only partial damage of the ray cells was observed. The SEM images provide further evidence that shows that the extent of decay was not as pronounced in the CuAz-treated WFMRC as in the untreated WFMRC. The SEM analyses also verify the FTIR and XRD results that the CuAz treatment influenced the bioresistance of the WFMRC exposed to white-rot fungus.

4. Conclusions

Compared to the untreated WFMRC specimens, the CuAz-treated WFMRC specimens showed improved resistance against T. versicolor and G. trabeum fungal decay. The CuAz-treated scrimber specimens exhibited greater resistance than the untreated specimens against T. versicolor and G. trabeum. The relative crystallinity of the CuAz-treated scrimbers after 12 weeks of decay was greater than that of the untreated sound scrimber. The SEM analyses also confirmed that the CuAz treatment was capable of preventing the deterioration of the scrimber. The durability of WFMRC against biodegradation can be improved by using CuAz preservatives. AI, which uses a simple process, can be considered for practical industrial applications. Improving the retention of CuAz preservative to reach a good protection level will be the focus of the next research.

Author Contributions

Investigation, M.B.; writing—original draft preparation, M.B.; writing—review and editing, N.L.; validation, R.T.; visualization, Y.B. and S.H.; supervision, Y.C.; funding acquisition, M.B. All authors have read and agreed to the published version of the manuscript.

Funding

This work was supported by the Fundamental Research Funds for the Central Non-profit Research Institution of CAF (CAFYBB2021ZX001-02), the Zhejiang Provincial Natural Science Foundation of China (LQ20C160001), and the Fundamental Research Funds for the Non-profit Research Institution of Zhejiang Province (Study on Preparation and Application Technology of Bamboo Organic Anti-mildew Microcapsules).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.

Conflicts of Interest

The authors declare no conflict of interest.

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Forests 13 01387 g001 550
Figure 1. ML of poplar wood (reference), untreated WFMRC (control), and CuAz-treated WFMRCs after exposure to T. versicolor and G. trabeum fungi. AI: atmospheric impregnation; VI: vacuum impregnation. Error bars represent mean ± standard deviation. The average values with different letters (a, b, c) on the columns indicate a significant difference at the 0.05 level (analysis of variance (ANOVA), followed by Duncan’s multiple range test).
Figure 1. ML of poplar wood (reference), untreated WFMRC (control), and CuAz-treated WFMRCs after exposure to T. versicolor and G. trabeum fungi. AI: atmospheric impregnation; VI: vacuum impregnation. Error bars represent mean ± standard deviation. The average values with different letters (a, b, c) on the columns indicate a significant difference at the 0.05 level (analysis of variance (ANOVA), followed by Duncan’s multiple range test).
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Forests 13 01387 g002 550
Figure 2. FTIR spectra of (a, b) undecayed WFMRC, (c, e) T. versicolor-exposed WFMRC, and (d, f) G. trabeum-exposed WFMRC: (a, e, f) untreated (control) WFMRC and (b, c, d) CuAz-treated (AI) WFMRC.
Figure 2. FTIR spectra of (a, b) undecayed WFMRC, (c, e) T. versicolor-exposed WFMRC, and (d, f) G. trabeum-exposed WFMRC: (a, e, f) untreated (control) WFMRC and (b, c, d) CuAz-treated (AI) WFMRC.
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Forests 13 01387 g003 550
Figure 3. XRD patterns of the untreated (control) and CuAz-treated WFMRCs after 12 weeks of incubation with (a) T. versicolor fungi and (b) G. trabeum fungi. AI: atmospheric impregnation; VI: vacuum impregnation.
Figure 3. XRD patterns of the untreated (control) and CuAz-treated WFMRCs after 12 weeks of incubation with (a) T. versicolor fungi and (b) G. trabeum fungi. AI: atmospheric impregnation; VI: vacuum impregnation.
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Figure 4. (a–c) SEM images, (d–f) copper elemental maps of cross-sections of wood fiber mats ((a) vessels, (b) wood rays, and (c) fibers), and (g–i) EDS spectra and atomic percentage of each element (inset).
Figure 4. (a–c) SEM images, (d–f) copper elemental maps of cross-sections of wood fiber mats ((a) vessels, (b) wood rays, and (c) fibers), and (g–i) EDS spectra and atomic percentage of each element (inset).
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Figure 5. (a,b) SEM images, (c,d) copper elemental maps in the wood fiber mats ((c) radial section and (d) tangential section), and (e,f) EDS spectra and atomic percentage of each element (inset).
Figure 5. (a,b) SEM images, (c,d) copper elemental maps in the wood fiber mats ((c) radial section and (d) tangential section), and (e,f) EDS spectra and atomic percentage of each element (inset).
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Forests 13 01387 g006 550
Figure 6. SEM images of (a–c) untreated WFMRC and (d–f) VI WFMRC after 12 weeks of incubation with T. versicolor fungi: (a,d) transverse section; (b,e) radial section; and (c,f) tangential section.
Figure 6. SEM images of (a–c) untreated WFMRC and (d–f) VI WFMRC after 12 weeks of incubation with T. versicolor fungi: (a,d) transverse section; (b,e) radial section; and (c,f) tangential section.
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Table
Table 1. Chemical compositions of untreated (control) and CuAz-treated (AI and VI) WFMRCs before and after 12 weeks of incubation with T. versicolor and G. trabeum fungi.
Table 1. Chemical compositions of untreated (control) and CuAz-treated (AI and VI) WFMRCs before and after 12 weeks of incubation with T. versicolor and G. trabeum fungi.
SamplesFungusHolocellulose (%)α–Cellulose (%)Acid–Insoluble Lignin (%)
control—64.19 (0.13) b38.61 (0.14) b28.12 (0.11) b
AI—64.56 (0.21) c38.44 (0.32) a27.51 (0.19) a
VI—63.35 (0.17) a38.33 (0.21) a27.37 (0.23) a
controlT. versicolor61.51 (0.08) b37.85 (0.21) b32.63 (0.31) b
AI61.85 (0.16) c37.84 (0.06) b32.34 (0.25) a
VI60.84 (0.13) a37.03 (0.24) a33.69 (0.22) c
controlG. trabeum61.68 (0.11) b38.12 (0.15) b31.18 (0.31) a
AI61.36 (0.13) a38.01 (0.19) b31.60 (0.26) b
VI60.32 (0.22) a36.80 (0.05) a32.93 (0.21) b
Values in parenthesis are standard deviations. For each parameter, average values with different letters (a, b, c) in each column indicate a significant difference at the 0.05 level (analysis of variance (ANOVA), followed by Duncan’s multiple range test). AI: atmospheric impregnation; VI: vacuum impregnation.
Table
Table 2. Cr of untreated (control) and CuAz-treated (AI and VT) WFMRCs before and after 12 weeks of incubation with T. versicolor and G. trabeum fungi.
Table 2. Cr of untreated (control) and CuAz-treated (AI and VT) WFMRCs before and after 12 weeks of incubation with T. versicolor and G. trabeum fungi.
SamplesFungusCr (%)
Control—21.31
AI—22.07
VI—22.81
ControlT. versicolor16.64
AI18.26
VI18.87
ControlG. trabeum17.12
AI18.98
VI19.79
Cr degree of relative crystallinity; AI: atmospheric impregnation; VI: vacuum impregnation.
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Bao, M.; Tang, R.; Bao, Y.; He, S.; Chen, Y.; Li, N. Changes in Chemical Composition, Crystallizability, and Microstructure of Decayed Wood-Fiber-Mat-Reinforced Composite Treated with Copper Triazole Preservative. Forests 2022, 13, 1387. https://doi.org/10.3390/f13091387

AMA Style

Bao M, Tang R, Bao Y, He S, Chen Y, Li N. Changes in Chemical Composition, Crystallizability, and Microstructure of Decayed Wood-Fiber-Mat-Reinforced Composite Treated with Copper Triazole Preservative. Forests. 2022; 13(9):1387. https://doi.org/10.3390/f13091387

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Bao, Minzhen, Rongqiang Tang, Yongjie Bao, Sheng He, Yuhe Chen, and Neng Li. 2022. "Changes in Chemical Composition, Crystallizability, and Microstructure of Decayed Wood-Fiber-Mat-Reinforced Composite Treated with Copper Triazole Preservative" Forests 13, no. 9: 1387. https://doi.org/10.3390/f13091387

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