Influence of Copper and Biopolymer/Saqez Resin on the Properties of Poplar Wood

There is an increasing trend in the use of environmentally-friendly materials in wood protection. This includes the use of less toxic active ingredients, as well as better fixation. This study investigates the formulation based on the combination of copper and Saqez resin on the physical and biological resistance properties of poplar wood. Samples were treated by either copper-ethanolamine (Cu/MEA) and/or Saqez resin at various treatment levels. A vacuum pressure procedure was applied. The retention, weight percent gain, water absorption, volumetric swelling, and decay resistance of the samples were then determined. The highest retention and weight percent gain were obtained in the samples treated with the combination of copper-based system and Saqez resin. Additionally, the combination of the copper and Saqez improved the physical properties and decay-resistance against white-rot fungus Trametes versicolor.


Introduction
Wood, as a versatile biocomposite material has a wide variety of applications such as furniture, construct structures, artifacts, tool making for several centuries [1]. However, the application of less durable wood species in outdoor applications is frequently limited [2]. Namely, wood is susceptible to decay by wood-destroying organisms such as fungi and insects. Predominant hygroscopicity, resulting from the presence of the abundant hydroxyl groups in wood renders it susceptible to fungal infestation. Wood and wood-based products often need treatments with preservatives in order to increase durability and achieve desired service life [3][4][5]. One effective method to improve the bioresistance features of wood and wood-based products is the utilization of natural substances such as plant essential oils and resins [6,7]. There is an ever-increasing interest in the application of essential oils due to their natural safety and environmentally friendly aspects. They are effective against bacteria [8,9], fungi and moulds [10][11][12][13][14] and insects [15,16]. Su et al. [17] found that the essential oils biodegradable for preservatives has convinced scientists and technologists to examine for a new source of natural materials, as substitutes for chemical ones. The present study aimed to investigate the impact of pistachio tree resin (Saqez) alone or combined with copper-ethanolamine (Cu/MEA) and Saqez on the physical and biological properties of poplar treated wood.

Material
The boards were cut from the trunks of three 23-year-old poplar trees (Populus deltoids) located in the Khirod area (Mazandaran province, Northern part of Iran) and air-dried. Wood samples were cut from the boards for the various tests. All samples were free of defects such as knots, resin pockets and moulds and fungal infections. The wood sample sizes for the physical tests were 20l × 20r × 20t mm 3 according to ISO 13061:2016 [33]. Five replicates were cut for each test, along with five replicate control samples. For fungal durability studies, the sample size was 50l × 25r × 15t mm 3 [34] with five replicates. Before treatment, samples were oven-dried (103 °C, 24 h), to obtain constant moisture content and to determine their initial masses. The density of the oven-dried specimens was in the range of (460±20) kg/m 3 . To ensure maximum uptake of the treatment solutions, none of the surfaces of the wood samples was sealed. The copper-containing wood preservative used in this study was copper-ethanolamine (Cu/MEA) consisted of CuCO3 (Merck) and ethanolamine (C2H7NO). The resin of wild pistachio (Pistacia atlantica) trees called 'Saqez' was obtained from the area is located in Charmahal and Backtiari province, Southwest of Iran.

Methods
Before the treatment process, samples were divided into three groups. The first group was treated with copper-ethanolamine (Cu/MEA). The copper concentration was 0.5 % in all tests. This concentration is usually sufficient for the protection of wood in-ground applications. The second group was treated with various concentrations of (5, 10 and 15%) pistachio tree resin. Ethanol with 96% purity was used in the preparation of the resin. The Third group initially impregnated with Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 7 May 2020 doi:10.20944/preprints202005.0131.v1 copper amine based wood preservative, afterwards treated with resin at the concentration of 15% (Table 1).
For treatments, a vacuum pressure impregnation were applied in a pilot plant, whereby the vacuum of 0.8 bar lasted for 30 min, followed by pressure at 4 bar for 120 min. After that, samples were stored for two weeks in the lab ambience for evaporation of the solvent. The retentions for each treatment were calculated according to the Equation (1): G is the amount of treating solution absorbed the samples (kg); C is the concentration of the solution (%), and V is the volume of the samples (m 3 ).
After treatment, the oven-dry (103°C for 24 h) weight of all samples was evaluated and used to calculate the weight percent gain (WPG) (Equation 2): Where M2 is the sample weight after treatment, and M1 is the sample weight before treatment Where, WA is water absorption (%), W1 is the weight of samples after immersion; W0 is the ovendried weight before immersion.
Where VS is volume swelling (%), V1 is the volume of samples after immersion and V0 is the volume of samples before immersion.

Biological durability
Biological durability was evaluated on both of leached and unleached samples in accordance with European method [34] to assess the resistance to white-rot fungus. Where, ML is the mass loss (%), M0 is the oven dry weight of sample before fungi test (g) and M1 is the oven dry weight after fungi test (g).

Statistical Analysis
The obtained data were subjected to the analysis of variance (ANOVA). Means were analyzed and grouped using Duncan's Multiple Range Test (DMRT).

Result and discussion
Populus deltoids was chosen for this study because it is prevalently used in a wide variety of applications in Asia and Europe. The retention of preservatives is the first substantial factor that shows the quality of the impregnation. Retention of the active ingredients increases with increasing resin concentration ( Figure 1). Namely, wood treated with the lowest concentration of resin retains The highest retentions were observed at samples that were first treated with copper-based system and in the later stage with resin-based system. These kinds of impregnations are called dual treatments and are reported in the literature already [35]. Retention of wax into copper-ethanolamine based system was higher than at non-copper treated wood. It can be presumed that one of the possible reason for this occurrence, could be assigned to wood swelling efficacy of ethanolamine [36].
Wood retention data are in line with WPG data. In general WPG increases with increasing resin concentration. Similarly, as reported for retention data, the highest WPG was determined at samples treated with copper-ethanolamine solution subsequently treated with resin ( Figure 2). High WPG can be ascribed to the reaction of copper-ethanolamine complexes with wood and resin [37].  water exclusion efficacy (the ability of wood to remain dry [38]. Therefore, studies of water ability are essential. Also, water repellents can slow down copper leaching [39]. As can be resolved from   One of the prime objectives of this study was to determine the performance of the respective treatment against wood decay fungi. Samples were exposed to white-rot fungi. White rot fungi are the most important organisms degrading the hardwoods [40]. Mass loss of the leached and unleached samples was rather high, ranging between 39.3% at non-leached and 44.8% at leached specimens ( Figure 5). These data are in line with low durability classification of poplar wood [41]. whereas the mass loss of the wood treated with a similar solution with three times higher concentration was 20.4%. This mass loss is higher than the mass loss of the comparable oil or waxbased systems ( [11,42]). The major constituents in the Saqez are α-pinene (60.15%), β-pinene (8.68%), and α-terpinene (3.94%) [43][44]. The antifungal activity of Saqez resin could be related to the respective components. Antifungal activity of α-pinene, β-pinene and α-terpinene inicated in the previous study [45 -47]. Presence of copper in wood slowed down wood decay considerably. Leaching reduces the influence of copper-based system, predominately as there were no secondary fungicides present [48]. However, as can be seen from the comparison of mass losses of leached and non-leached copper and copper-Saqez treated wood, a combination of copper and Saqez acted synergistically. At the very moment, we cannot conclude whether this is because of the limited effect of Saqez resin on the fungi, or due to the limited copper leaching.

Conclusion
Synergistic effect between copper and Saqez was investigated. Saqez has positive influence on water performance. Wood treated with Saqez exhibited better water performance, which reflects in better dimensional stability and likely limits copper leaching as well. Impregnation of wood with Saqez was not sufficient to limit fungal decay. However, the combination of copper-ethanolamine based wood preservatives with Saqez has a positive effect on copper efficacy against wood decay fungi.

Conflicts of Interest:
The authors declare no conflict of interest.