Abstract
Polystyrene, citric, and boric acid are capable of enhancing the quality of bamboo as a raw material for laminated board (LB). Although the characteristics of the modified LB has met the JAS 234 (2003) standard, the resistance against termite and decay attacks was still unknown. In this work, a 6-h immersion time was used to immerse bamboo lamina in polystyrene, citric, and boric acid. Laminated board comprising 3 layers of 30 cm x 15 cm x 1.5 cm (length x width x thickness) were constructed using 280 g/m2 isocyanate adhesive from bamboo lamina using double-spread adhesive method. This was followed by resistance testing against termite wood and decay caused by T. versicolor and F. palustris using the JIS K 1571 (2010) standard. Parameters calculated after testing for termite included weight loss and mortality, while weight loss was determined after evaluating the decay using JIS standard. The results showed that modification with polystyrene, citric, and boric acid slightly increased the resistance of LB from belangke bamboo against termite and decay attacks. In comparison, samples modified with polystyrene had lower weight loss than others, which showed high resistance to attacks. This showed that modification with polystyrene could be recommended to improve the quality of LB from belangke bamboo.
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Belangke Bamboo (Gigantochloa pruriens) Laminated Board Modified with Polystyrene, Citric, and Boric Acid: Resistance from Termite and Decay Attacks
Rudi Hartono,a,* Jajang Sutiawan,b Sukma Surya Kusumah,b Didi Tarmadi,c Bramantyo Wikantyoso,c Setiawan Khoirul Himmi,c Sulaeman Yusuf,c Deni Zulfiana,d Adlin Sabrina Muhammad Roseley,e and Falah Abu f,g
Polystyrene, citric, and boric acid are capable of enhancing the quality of bamboo as a raw material for laminated board (LB). Although the characteristics of the modified LB has met the JAS 234 (2003) standard, the resistance against termite and decay attacks was still unknown. In this work, a 6-h immersion time was used to immerse bamboo lamina in polystyrene, citric, and boric acid. Laminated board comprising 3 layers of 30 cm x 15 cm x 1.5 cm (length x width x thickness) were constructed using 280 g/m2 isocyanate adhesive from bamboo lamina using double-spread adhesive method. This was followed by resistance testing against termite wood and decay caused by T. versicolor and F. palustris using the JIS K 1571 (2010) standard. Parameters calculated after testing for termite included weight loss and mortality, while weight loss was determined after evaluating the decay using JIS standard. The results showed that modification with polystyrene, citric, and boric acid slightly increased the resistance of LB from belangke bamboo against termite and decay attacks. In comparison, samples modified with polystyrene had lower weight loss than others, which showed high resistance to attacks. This showed that modification with polystyrene could be recommended to improve the quality of LB from belangke bamboo.
DOI: 10.15376/biores.20.1.426-437
Keywords: Bamboo; Belangke bamboo; Laminate board; Modifications; Termite resistance; Decay resistance
Contact information: a: Forest Products Department, Faculty of Forestry, Universitas Sumatera Utara, Medan, 20155, Indonesia; b: Research Center for Biomass and Bioproducts, National Research and Innovation Agency, Cibinong, 16911, Indonesia; c: Research Center for Applied Zoology, National Research and Innovation Agency, Cibinong, 16911, Indonesia; d: Research Center for Applied Microbiology, National Research and Innovation Agency, Cibinong, 16911, Indonesia; e: Faculty of Forestry and Environment, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia; f: Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM), Shah Alam 40450, Selangor, Malaysia; g: Smart Manufacturing Research Institute (SMRI), Universiti Teknologi MARA (UiTM), Shah Alam 40450, Malaysia;
* Corresponding author: rudihartono@usu.ac.id
GRAPHICAL ABSTRACT
INTRODUCTION
Bamboo is the most-produced non-timber forest product in Indonesia (Wardana et al. 2022). The Central Bureau of Statistics (2020) estimated that the country produced about 25,900 tons of bamboo. This forest product is a non-timber material with significant basic qualities, short rotation cycles, fast-growing species (3 to 5 years), and high productivity, reaching 20 to 40 tons/ha/year (Artiningsih 2012; Febrianto et al. 2015; Siswanto et al. 2022). In recent years, the demand for bamboo has increased due to a decrease in the quantity and quality of raw wood products (Febrianto et al. 2015). The widespread application as a building material compared to wood is attributed to high modulus elasticity (Sinarta et al. 2020; Yadav and Mathur 2021; Andriani and Putra 2022).
Among several species, belangke bamboo (Gigantochloa pruriens) is a potential building material. It is a native species of North Sumatra, which has expanded to the districts of Karo and Gayo (Iswanto et al. 2022). According to the previous study, belangke bamboo was found to have a density of 580 to 610 kg/m3 and high strength (Iswanto et al. 2020). Furthermore, belangke bamboo is superior to others due to longer fibers (Darwis et al. 2020), showing potential for application in the development of composite board (Belatrix et al. 2022; Hartono et al. 2022; Iswanto et al. 2022).
Particleboard and laminated board (LB) are composite boards made from bamboo. According to Iswanto et al. (2022), belangke bamboo particleboard has excellent mechanical qualities, with the ability to improve quality of wood particleboard when applied as a surface coating (Savov et al. 2023). A previous study reported that lamina bamboo had a modulus of rupture and elasticity ranging from 60 to 68 MPa and 73 to 83 MPa, respectively (Nurmalasari and Goestav 2020). This showed that the mechanical qualities of the raw bamboo used in LB were good (Hartono et al. 2022; Wulandari et al. 2022). Despite the significant potential, the disadvantages of using bamboo as a raw material for LB included high susceptibility to attack by harmful organisms, showing the need for modification (Iswanto and Togatorop 2019; Mahawan Sumawa et al. 2019).
In this context, polystyrene, citric, and boric acid modification has been shown to be effective in enhancing the quality of bamboo as a raw material for LB. Compared to LB modified with citric and boric acid, modification using polystyrene has a higher modulus of rupture, elasticity, density, and shear strength, alongside less delamination (Hartono et al. 2024). LB modified with a 6-h immersion in polystyrene met JAS 234 (2003) standards regarding density, moisture content (MC), delamination, modulus of rupture, and elasticity (Hartono et al. 2024). Despite the significant results, the resistance of LB against termite and decay attacks remains unknown. Therefore, this study aimed to determine the resistance of bamboo LB modified with polystyrene, citric, and boric acid against termite and decay attacks.
EXPERIMENTAL
Raw Material Preparation
Concentrations of 20% citric acid and 5% boric acid were dissolved in water (Basri et al. 2022; Priadi et al. 2022). Subsequently, the catalyst potassium peroxy-disulfate was combined with 100% polystyrene at a ratio of 1:0.01 v/v (Hadi et al. 2021a). Belangke bamboo base was divided into lamina pieces of 30 cm x 2 cm x 0.5 cm (length x width x thickness). This was followed by drying lamina in an oven set at 60 °C for 24 h, or until MC dropped to 10%. For 6 h, bamboo lamina was immersed in several solutions, covered in aluminum foil (polymerization process), and dried for 24 h at 60 °C (Hadi et al. 2021a, 2022).
Manufacturing of Laminated Board (LB)
The double adhesive spread method and isocyanate adhesive with a spread level of 280 g/m2 was used to construct the bamboo lamina into three layers of LB, each measuring 30 cm x 15 cm x 1.5 cm (length x width x thickness) (Hartono et al. 2024; Komariah et al. 2015; Hadi et al. 2022). The isocyanates to hardener ratio used to prepare the isocyanate adhesives was 85:15 (w/w%). LB was cold pressed for 24 h with clamps on all sides and conditioned for 10 days at room temperature, with the steps shown in Fig. 1.
Fig. 1. Manufacturing of laminated board (LB)
MC and density were measured following JAS 234 (2003).
Termite Test
Testing for termite resistance in LB was performed following the JIS K 1571 (2010) standard, as shown in Fig. 2. Parameters calculated after testing for termite with JIS standards consist of weight loss and mortality. Using a plaster bottom (5 mm high), sample blocks (20 x 20 x 10 mm3) were placed in an acrylic cylinder (65 mm in diameter and 60 mm in height). From a laboratory colony at the National Research and Innovation Agency, 150 laborers and 15 soldiers of Coptotermes gestroi were acquired and fed on the sample blocks. During this process, 3 weeks were spent keeping the testing containers dark, between 25 and 30 °C, as well as 80% and 90% relative humidity. For every type of board, 3 replicates were examined, and test samples were cleaned after termite examination and baked for 48 h at 60 °C. Weight loss (WL) and mortality of samples after being fed to termite was calculated based on the following Eqs. 1 and 2,
where W2 is the mass following testing (g), W1 is the mass before testing (g), D is the number of dead laborers termite (per piece), and n is the number of laborers termite in the test (150).
Fig. 2. Termite test on LB
Decay (Trametes versicolor and Fomitopsis palustris) Test
Based on JIS K 1571 (2010) standards, LB was evaluated against wood-rot decay (T. versicolor and F. palustris), as shown in Fig. 3. An infection was created in a 100-mL aliquot of liquid medium containing 0.3% peptone, 1.5% malt extract, and 4% glucose using a stock culture of F. palustris or T. versicolor. The inoculated liquid medium was incubated for 10 days at 26 °C using a shaker set to 120 rpm. A 250 g medium of sea sand was soaked with 80 to 85 mL of a nutrition solution containing 1.5% malt extract, 0.3% peptone, and 4% glucose for T. versicolor in a glass container. For F. palustris, approximately half of each component was used for analysis. The jars were inoculated with these liquid fungal stock cultures using 3 to 5 mL. Specimens were layered on top of the growing mycelium after spreading to cover the medium in the glass jars.
The 20 × 20 × 5 mm3 wood blocks from Hevea brasiliensis were used as the control. The parameter found was WL% following 48 h of the sample being in an oven at 60 °C after the decay was assessed using JIS K 1571 (2010) standards. Before testing, the mass of LB was obtained through weighing (W1). The sample was placed in a tightly closed test container to prevent contamination from other decaying objects, and the medium was covered with rotting decay. After 12 weeks, the sample was cleaned and air-dried in an oven at 60 °C for 48 h (W2). A total of 3 replicates were examined for every board and the value of weight loss (WL) was calculated using the formula below,
where W2 is the mass following testing (g) and W1 is the mass before testing (g).
Fig. 3. Decay test on LB
The type of solution (polystyrene, boric, and citric acids) was one of the variables included in the non-factorial completely randomized design (CRD) method. Analysis of variance (ANOVA) was used for statistical analysis (IBM SPSS Statistics 23, Armonk, NY, USA). The result was considered to have a substantial impact when the significance value of ANOVA was less than 0.05. Therefore, Duncan Multiple Range Test (DMRT) was conducted at a 95% confidence interval.
RESULTS AND DISCUSSION
Compared to LB modified with citric acid (7.00%) and boric acid (3.00%), polystyrene (7.67%) samples had a higher weight percent gain (WPG), as shown in Table 1. LB with polystyrene immersion experienced an increase in weight due to the ability of the cell walls in the bamboo to bind water. Nurhanifah et al. (2020) reported that polystyrene impregnation affected WPG of glulam. According to Hadi et al. (2021), the impregnation caused the lamina to have a certain amount of polymer loading and weight percent gain. The density increment of polystyrene glulam reached 10.7% compared with untreated glulam. Polystyrene would penetrate the empty pores and polymerize in the anatomical structure of the wood (Hadi et al. 2021).
Table 1. Weight Percent Gain, Density, and MC of LB
Note: The same letters in a column mean that those conditions did not result in significant differences (p≤0.05), Values in parentheses are standard deviations.
Regarding bamboo strips treated with a 5% boric acid solution, Gigantochloa levis had WPG value of 3.6%, Dendrocalamus asper was 1.47%, while Bambusa vulgaris and Gigantochloa scortechinii had 2.9% and 2.0%, respectively (Yusof et al. 2023). Each layer of WPG bamboo was subjected to the deposition of boric acid in the cell wall and lumen (Colakoglu et al. 2003). Wood modified with citric acid had a WPG of 7% (Feng et al. 2014), while those with 20% and 40% produced 25% and 28% WPG, respectively (Basri et al. 2022). The results showed that wood modified with citric acid could have higher WPG values and more termite resistance (Treu et al. 2020). Table 1 shows that the average density of LB ranged from 0.79 to 0.84, and MC from 10.44 to 12.48%. LB modified with polystyrene, boric, and citric acids had a smaller MC than the untreated LB (p < 0.05).
Termite mortality in LB ranged from 16.89% to 100%, as shown in Fig. 4. The mortality of LB modified with polystyrene, boric, and citric acids was higher than control and untreated, showing that termite used was healthy. Figure 4 shows termite WL after a 3-week exposure, which varied between 5.8% and 28.3%. After modification, the results showed that WL was reduced compared to the control wood, indicating the healthy condition of termites. Compared to the untreated, the modified LB had a lower WL by termite (p < 0.05) due to the influence of MC. As shown in Table 1, MC of LB modified was lower than untreated samples, which increased the resistance to termite attacks (Hadi et al. 2021b). The data analysis also showed that termite WL was significantly influenced by the type of solution used. In comparison, LB treated with boric acid showed lower activity against attacks than polystyrene and citric acid, as presented in Fig. 5.
Fig. 4. Weight loss and mortality of LB after exposure to termite
Fig. 5. LB after testing with termite: (a) control, (b) untreated, (c) modified with citric acid, (d) modified with boric acid, and (e) modified with polystyrene
Figure 6 shows WL of LB ranging from 12.3 to 43.8% after 12 weeks of decay by T. versicolor and F. palustris. In this study, WL of LB treated with polystyrene, boric, and citric acids was lower compared to the control and untreated (p < 0.05). Similarly, this phenomenon was impacted by MC, as strand bamboo was the least resistant to attacks by subterranean termite and decay (Iswanto et al. 2017). High-starch bamboo was also less resistant to termite than wood (De Melo et al. 2015; Maulana et al. 2022), as shown in Figs. 7 and 8.
Fig. 6. Weight loss of LB after exposure to decay brown rot and white rot
Fig. 7. LB after testing with brown rot: (a) control, (b) untreated, (c) modified with citric acid, (d) modified with boric acid, and (e) modified with polystyrene
Fig. 8. LB after testing with white rot: (a) control, (b) untreated, (c) modified with citric acid, (d) modified with boric acid, and (e) modified with polystyrene
The effect of citric acid on termite and decay attacks had been explored in various contexts, showing potential benefits in enhancing resistance. Citric acid was found to alter surface morphology in treated materials, leading to reduced debris and bacterial presence, which could contribute to decay resistance (Tanaka et al. 1989). In periodontal studies, the application led to a demineralized zone that exposed collagen fibrils, potentially enhancing the material’s structural integrity against decay (Garrett et al. 1978). Additionally, the role of citric acid in altering material properties could indirectly impact termite behavior. The degradation of termiticides was influenced by the chemical environment, which could be modified by citric acid (Saran and Kamble 2008). This interaction with other compounds potentially enhanced the effectiveness of existing termite treatments.
Boric acid is recognized for its effectiveness as a wood preservative against termite and decay attacks. These unique properties allow enhancement of wood durability while being environmentally friendly. Boric acid also interacts with wood components, forming complexes that reduce leaching and enhance preservative action. The mechanism of interaction allows boron to remain active against pests and reduce environmental impact (Pizzi and Baecker 1996). The combination of boric acid with proteins, such as albumin, leads to a durable, non-toxic wood preservative that significantly retards leaching (Thevenon et al. 1998). Treated wood shows resistance to decay fungi and termite, with studies reporting effectiveness after multiple weathering cycles (Yalinkilic et al. 1998). Boric acid’s antifungal properties are complemented by insecticidal effects, making it a broad-spectrum preservative (Thevenon et al. 1998).
The effect of polystyrene on termite and decay attacks is multifaceted, including both degradation processes and interaction with biological agents. Previous studies had shown that polystyrene was relatively resistant to decay, although degradation could be influenced by environmental factors and biological activity. Polystyrene experiences thermal degradation, mainly through pyrolysis, which produces volatile compounds such as styrene. This process is temperature-dependent, as higher temperatures lead to increased styrene emissions (Gurman et al. 1987). Accelerated weathering studies show that polystyrene degrades in two stages, namely initial photooxidation followed by microcrack formation, enhancing fragmentation into microplastics (Strohriegl et al. 2021). Although polystyrene is not a natural food source for termites, the presence in the environment can affect termite behavior. The degradation products are also capable of altering the habitat, potentially attracting or repelling termites (Braun-Lüllemann et al. 1997). Studies on the degradation of styrene by fungi suggest that biological agents can metabolize styrene, showing potential for biological control in polystyrene-rich environments (Braun-Lüllemann et al. 1997).
CONCLUSIONS
In conclusion, this study successfully investigated the resistance of laminated board (LB) modified with polystyrene, citric, and boric acid against termite and decay attacks. The results obtained were as follows:
- LB modified with polystyrene, citric, boric and acids had a higher mortality and lower weight loss (WL) than untreated and control samples at termite attacks.
- The modification of LB using polystyrene citric, and boric acid had lower weight loss than untreated and control at brown-rot and white-rot decay attacks.
- The samples modified with polystyrene, citric, and boric acid slightly increased the resistance of LB from belangke bamboo against termite and decay attacks.
- LB modified with polystyrene had lower WL than other samples, indicating that the samples were more resistant to termite and decay attacks.
- Based on the results, LB modified with polystyrene was recommended to improve the quality of LB from belangke bamboo.
ACKNOWLEDGMENTS
The authors are grateful to the TALENTA Universitas Sumatera Utara (USU) Scheme Penelitian Kolaborasi Pemerintah (101/UN5.4.10.S/PPM/KP-TALENTA/ RB1/2024) for providing financial support.
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Article submitted: August 5, 2024; Peer review completed: September 14, 2024; Revised version received: October 6, 2024; Accepted: October 20, 2024; Published: November 15, 2024.
DOI: 10.15376/biores.20.1.426-437