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Physical Properties of Impregnated Ganitri Wood by Furfuryl Alcohol and Nano-SiO2

Ganitri wood (Elaeocarpus sphaericus) is a fast-growing wood that has low dimensional stability and density. This study aims were to analyze the effect of Furfuryl Alcohol (FA) and nano-SiO2 impregnation on the dimensional stability and density of ganitri wood and also examine the characteristics of impregnated ganitri wood. Impregnation used three treatments, including untreated (water), FA, and 0.5% FA-SiO2. The impregnation process was initiated by giving a 0.5 bar vacuum for 60 minutes, followed by applying a pressure of 2.5 bar for 120 minutes. Weight percent gain, leachability, anti-swelling efficiency, water uptake, bulking effect, and density were affected by the treatment. It was due to the coverage of FA and nano-SiO2 on vessels of ganitri wood (SEM analysis). Also, the presence of nano-SiO2 in wood treated (SEM-EDX analysis). FT-IR showed there were no FA bonds with ganitri wood cell wall components or between Nano- SiO2 and ganitri wood. The crystallinity of ganitri wood decreases because FA is amorphous and nano-SiO2 is semi-crystalline. The optimum dimensional stability and density were obtained at FA treatment.


Introduction
Nowadays, there are many methodes for quality improvements of fast-growing wood as a substitute for high-quality wood uses. Ganitri wood (Elaeocarpus sphaericus) is planted in community forests in West and Central Java [1]. Ganitri wood is classified in the durability class V and strength class III-IV categories. Although it is not considered as commercial timber and not yet widely known, ganitri wood has many benefits. Ganitri wood is commonly used for light construction materials, tools, furniture, plywood, connecting boards, and is also used as raw material for the guitar and piano industry in Bandung, Indonesia [2,3].
Ganitri wood has a high proportion of juvenile wood which causes low physical and mechanical properties [4]. Therefore, wood modification is needed to improve the quality of ganitri wood. One of wood modification is impregnation by using Furfuryl Alcohol (FA) and nano-SiO2. FA is more environmentally friendly because made from organic materials such as agricultural waste, which is renewable and does not cause environmental pollution. Besides, FA is suitable to be applied to wood that has low density so that it can fill in the pits and make the wood denser [5].
In this study, nano particles were added to FA solutions. The nanoparticle-based treatment has several advantages, such as being more effective in coating wood surfaces and high dispersion

Materials
The sample used in this research was 6 years old ganitri wood (Elaeocarpus sphaericus) originated from community forests in Sukabumi, West Java. The tree has a 7-meters free branch height and diameters of 28 cm. The chemicals used are furfuryl alcohol (FA), nano-SiO2 (particle diameter 15 ± 5 nm; Anhui Elite Industrial Co., Ltd, China), maleic anhydride, disodium tetraborate, and distilled water. The tools used are chain saw, table circular saw, analytical balance, calipers, ovens, fans, sonicators, impregnation devices, moisture meter, and aluminum foil. The characterization of the impregnated ganitri wood was carried out with Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDX) Hitachi S-3400N Japan, X-Ray Diffraction Analysis (XRD) XRD-7000 Shimadzu Japan, and FT-IR Fourier Transform Infrared Spectroscopy (FT-IR) Perkin Elmer One Pectrum Type.

Sample Preparation
Ganitri wood is sawn without distinguishing sapwood and heartwood. The sample size was 2 cm x 2 cm x 2 cm [8], which was used to measure the weight percent gain (WPG), leachability (L), antiswelling efficiency (ASE), water uptake (WU), bulking effect (BE), and density.

Preparation of Impregnation Solutions
Two types of impregnant solutions were 50 wt% FA-distilled water solution and 50% FAdistilled water solution containing 0.5 wt% nano-SiO2 (mixed by sonication Cole Parmer, the amplitude of 40% for 30 minutes).

Impregnation Process
The samples were immersed by the impregnant solution in the impregnation devices. The impregnation process was initiated with vacuumed of 0.5 bar for 60 minutes, followed by a pressure of 2.5 bar for 120 minutes. For the polymerization, the samples were wrapped in aluminum foil and kept at room temperature for 12 hours, then put in an oven at 100 ℃ for another 12 hours. The samples were dried in an oven at 103 ± 2 ℃. Samples were measured and weighed to determine WPG, leachability, WU, ASE, BE, and density [9,10].

Characterization of Impregnated Ganitri Wood
The samples were characterized to determine the presence of a mixture of FA and nano-SiO2 particles in ganitri wood using SEM-EDX (Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy), XRD (X-Ray Diffraction Analysis), and FT-IR (Fourier Transform Infrared Spectroscopy).

Data Analysis
Data analysis used a completely randomized design with one factor that is the factor of treatment variation (2 levels). The analysis was carried out by using the IBM SPSS Statistics (Statistical Package for Service Solutions) program version 23.0, followed by Duncan's test at α = 1% [11].

Dimensional Stability and Density of Impregnated Ganitri Wood
3.1.1 Weight Percent Gain. FA and nano-SiO2 impregnation treatment significantly affected the WPG, leachability, ASE, WU, BE, and density of ganitri wood as shown in Table 1. The WPG was more than 100% because FA and nano-SiO2 had entered and penetrated all dots. This is evidenced by the increased WPG of ganitri wood after being given FA and nano-SiO2 impregnation treatment, so that causes the dots to be covered so that water is unable to penetrate the cell walls [9,12]. The WPG for wood can reach 50-200% because it uses conventional methods [13,14].

Leachability.
The lower leachability means the impregnant solutions in treated wood difficult to leach by water. The results showed that the 0.5% FA-SiO2 impregnated wood obtained the highest leachability. It is presumably because nano-SiO2 was not bound to the cell wall components of the ganitri wood. Nano-SiO2 as a bulking agent only coats the outside of the wood pits so that when the leaching test is carried out, nano-SiO2 will dissolve in water. Not many nano-SiO2 entered the lumens are thought to be due to agglomeration and did not bind to FA that entered the cell cavity and wood pits. The FA treated wood has lower leachability than 0.5% FA-SiO2 impregnated wood allegedly because the FA binds to components of wooden cell walls so that it does not leaching in the water.

Anti-swelling Efficiency.
The ASE is directly proportional to the WPG. When the cell wall is penetrated by a polymer, the polymer will fill the entire cell cavity which is usually filled by water. It also causes weight gain due to the polymer that enters the wood. The addition of nano-SiO2 to the wood also causes the ASE to increase because the wood is denser, thereby reducing the hygroscopic nature of the wood. The higher ASE means the lower wood's ability to absorb water and increase the dimensional stability of the wood [15,16].

Water Uptake.
The higher the WU, the higher the wood's ability to absorb water. More polymer will enter the cell cavity, making it more difficult for the wood to absorb water [10]. The WU of the untreated wood was very high because it was not treated with chemicals, meaning that no polymer entered the wood so that water could still enter the wood cell walls. In contrast to FA and nano-SiO2 impregnated wood which have a lower WU than untreated wood. This is because the cell cavities and lumens in the FA and nano-SiO2 impregnated wood have been covered by the polymer so that water cannot enter the cell walls.

Bulking Agent.
Ganitri wood has a low density, after wood impregnation with FA and nano-SiO2 it can increase in weight, as evidenced by the increased WPG. This indicates that FA and nano-SiO2 can function as bulking agents, causing the BE to increase. The higher the content of the bulking agent that binds to the inner cell walls of the wood, the higher the dimensional stability of the wood, thereby minimizing water absorption [16].
3.1.6 Density. The wood density after impregnation treatment increased significantly. It is caused by FA and nano-SiO2 solutions that can penetrate the cell cavity and lumens of ganitri wood as a whole so that there is a compaction of the wood structure. The WPG increases so that the density of impregnated wood also increases [17]. The addition of 0.5% nano-SiO2 did not have a significant effect on increasing the density of the 0.5% FA-SiO2 impregnated wood when compared to the FA impregnated wood.

SEM-EDX.
The morphology of impregnated ganitri wood can be seen using SEM (Figure 1). The pits that initially looked empty (Figure 1a) after being impregnated using FA were filled with FA (shown by a circle in Figure 1b). FA that enters and fills the vessel gives a bulking effect to ganitri wood. FA forms a layer like glass on the surface of the pits indicating the result of polymerization. This is what causes the weight of ganitri wood to increase so that the WPG increases. The presence of FA covering the pits is also able to prevent the entry of water into the pits on the cell wall, causing the WU of FA impregnated ganitri wood to decrease. However, not all pits are covered by FA (shown by arrows in Figure 1b) so that the water still can penetrate to the cell walls, as evidenced by the WU in FA impregnated wood which was still relatively high.
The addition of FA and nano SiO2 causes weight gain of ganitri wood which is also indicated by the increased WPG. This is evidenced by the existence of nano-SiO2 that fills the cell walls of the ganitri wood (Figure 1d). Figure 1d shows that the open pits of the Ganitri wood vessel are filled by 0.5% FA-SiO2. Nano-SiO2 appears to clump in the cell cavity indicating that some nano-SiO2 is not polymerized to form bonds among the nano-SiO2, as shown in the circle in Figure 1d. Nano-SiO2 fills the vessel cavity and covers the lumens so that the water cannot pass through the wood cavity and enter it. This proves that nano-SiO2 causes a bulking effect on 0.5% FA-SiO2 impregnated ganitri wood so that the BE increases. Untreated and FA treated ganitri wood was proven that there was no nano-SiO2 content in the wood sample, meanwhile 0.5% FA-SiO2 contains 0.13 wt.% of silicon. This is evidenced by the presence of nano-SiO2 in 0.5% FA-SiO2 wood samples that can enter the ganitri wood through FA as a solvent. The nano-SiO2 has shown in Figures 1c and 1d causes an increase in WPG, leachability, ASE, BE, density, and a decrease in WU.   Figure 2 shows the FT-IR spectrum of untreated and treated ganitri wood. The absorption band at 3386.03 cm -1 (-OH stretching) from the hydroxyl group of wood cellulose ganitri. The -OH group of nano-SiO2 is shown at 3410.67 cm -1 . The -OH group was detected in 3000-3750 cm -1 that indicates the presence of water molecules in the wood sample. The C-H functional group of ganitri wood cellulose appears at a frequency of 2915.28 cm -1 [18,19,20]. The C-H group appears in 2800-3000 cm -1 . The wave frequency was 1735.34 cm -1 , indicating the presence of C=O hemicellulose. The peak of the C=O wave experienced a shift to 1723.48 cm -1 after impregnating FA and 1734.85 cm -1 after impregnating FA-SiO2. The C=O groups appear at 1742.53 cm -1 , 1723.48 cm -1 , and 1734, 85 cm -1 . The shift in the peak of the C=O wave is formed due to the surface of the FA furan polymer hydrolytic ring and the vibration of the furan ring frame that binds to the component of the wood cell wall [9,21,22].  [13,22,23]. The discovery of the Si-O-Si group indicated the presence of silica content in FA-SiO2 impregnated ganitri wood, waves 1050-1115 cm -1 were Si-O-Si vibrations [24]. Figure 3 shows the XRD spectra of untreated and treated ganitri wood. The three highest peaks at 2θ = 22.51°, 22.53°, and 21.83° with the crystal fields I002. The presence of silica was detected at 2θ 21.83° which is close to the crystal fields I002. There are characteristics of Iβ cellulose shown at the peak angle of 2θ = 15.08°. The characteristic amorphous structure is indicated by 2θ = 18°. The cellulose peaks are shown at 2θ = 22-23°, which is a natural characteristic of cellulose I. The peaks of cellulose I α and I β are at 2θ = 14-16°. Based on JCPDS data, the peaks shown by the I 002 and I101 fields indicate the diffractogram type of cellulose [25,26]. There is also a shift in 2θ from 15.08° to 14.67° that indicates a decrease in the intensity of FA impregnated ganitri wood. This is due to the amorphous FA covers the crystalline cellulose area [9]. There is also a peak of 2θ 19.82° which is thought to arise as a result of silica activity in the ganitri wood.

XRD.
Additional information regarding XRD test data can be seen in Table 2. There was a decrease in the degree of crystallinity in the FA and 0.5% FA-SiO2 impregnated ganitri wood samples [9]. In FA impregnated ganitri wood samples, the presence of this amorphous FA was able to cover the crystalline area, causing the crystalline area in the ganitri wood to decrease. Therefore, the crystallinity of FA impregnated wood decreases. Nano-SiO2 is semi-crystalline, causing the crystallinity degree of FA-SiO2 impregnated ganitri wood to decrease. The properties of nano-SiO2 are thought to be caused by the ultrasonication treatment [27].  Figure 3. XRD spectra of ganitri wood with various treatments The XRD analysis results indicate that there is an effect of the addition of FA and nano-SiO2 on the WPG, leachability, BE, WU, ASE, and density. This effect is supported by the presence of nano-SiO2 peaks which correspond to the diffraction field according to the JCPDS data.

Conclusion
FA and nano-SiO2 impregnation have a significant effect on WPG, leachability, ASE, WU, BE, and density of ganitri wood. The increase of WPG, BE, ASE, leachability, and density indicates that FA and nano-SiO2 can fill all the lumen cells so that causing the WU to decrease. The SEM analysis results of impregnated ganitri wood showed that the pits were covered by FA and nano-SiO2 and also strengthened by the results of EDX analysis which stated that there was a silica content in the pits. The degree of crystallinity of untreated, FA, and 0.5% FA-SiO2 ganitri wood was decreased due to FA is amorphous and nano-SiO2 is semi-crystalline characteristics. FTIR analysis showed that there was no chemical bonding of both FA and nano-SiO2 on ganitri wood. Ganitri wood with the best dimensional stability and density was obtained in the FA treatment. The addition of FA and nano-SiO2 with a concentration of 0.5% was not sufficient to significantly increase dimensional stability and density.