Properties of Phenol Formaldehyde-Bonded Layered Laminated Woven Bamboo Mat Boards Made from Gigantochloa scortechinii

: Bamboo is suitable to be a material for the production of new products that can be used indoors and outdoors. Five-, seven-and nine-ply laminated woven bamboo mat boards from semantan bamboo, Gigantochloa scortechinii , were fabricated in this study. G. scortechinii has been used commercially in a structural application and is easily available in Malaysia. The present work investigated the physico-mechanical properties and flammability of the laminated bamboo mat boards as a function of the number of ply. Phenol-formaldehyde resin was used as a binder. The panels’ density, physical, mechanical properties, formaldehyde emission and flammability were evaluated. As the number of ply increased, the density of the laminated boards decreased. Similarly, the highest modulus of elasticity was found in 5-ply laminated boards. However, the lowest modulus of rupture was also measured in 5-ply laminated boards. Regarding shear strength, 5-ply and 7-ply laminated boards outperformed 9-ply laminated boards. Meanwhile, 7-ply laminated boards exhibited the highest dimensional stability, as evidenced by the lowest water absorption and thickness swelling. In terms of flammability, all composites are classified as V-0 because the burning stops within 10 s and no flaming drips are observed.


Introduction
It is only right and natural that we try to devise ways to utilize and process all the wood and non-wood lignocellulosic raw materials available on this planet. In the current period of reduced raw material resources, this issue is very topical [1,2]. Bamboo is the most important non-wood species, which grows abundantly in most of the tropical and subtropical zones. using strips of semantan bamboo (G. scortechinii) bonded with epoxy resin. The study shows that the effect of the number of layers on the mechanical properties of the laminated woven bamboo composites is significant. To the best of the author's knowledge, however, relevant studies are scarce. Therefore, in this study, five-, seven-, and nine-layer bamboo mat boards were made from woven semantan bamboo mats bonded with phenol formaldehyde resin. The physico-mechanical properties and flammability of the bamboo mat boards were evaluated.

Preparation of the Bamboo Strips and Woven Mat
Matured semantan bamboo (Gigantochloa scortechinii) was used in this study since it exists abundantly in Malaysia and is among the most popularly used bamboo species by the local manufacturers. Semantan bamboo culm, with a diameter ranging from 45 to 60 mm, was supplied from a mill in the northern part of Peninsular Malaysia (Kedah, Malaysia). The bamboo plant height was around 3 m tall and only the first 2 m above the ground of the bamboo stem were used. The bamboo culms were then split into lumber strips using a cleaver and a handsaw to a dimension of 1000 mm (L) × 20 mm (W) × 5-10 mm (T). The bamboo strips were then treated with 5% borax and boric acid before being air-dried. After being dried, bamboo green (a thin pliable layer) was removed from the strips manually using a knife. The removed bamboo green was then weaved manually into a herringbone pattern as shown in Figure 1. The width of each strip was around 18 mm. The woven mat's final size was around 500 mm wide × 500 mm long.
Bamboo mat board is a hot-pressed flat cross-laminated plywood-like panel made of woven bamboo mats in the face layers and stitched bamboo curtains in the inner layers [20]. It can also be made entirely of woven bamboo mats with multiple layers in some cases. The material used to make mats, the adhesive used for bonding, and the number of layers all significantly impact the bamboo mat board's physical and mechanical properties. Two-to six-layered laminated woven bamboo composites were produced by Rassiah et al. [21] using strips of semantan bamboo (G. scortechinii) bonded with epoxy resin. The study shows that the effect of the number of layers on the mechanical properties of the laminated woven bamboo composites is significant. To the best of the author's knowledge, however, relevant studies are scarce. Therefore, in this study, five-, seven-, and nine-layer bamboo mat boards were made from woven semantan bamboo mats bonded with phenol formaldehyde resin. The physico-mechanical properties and flammability of the bamboo mat boards were evaluated.

Preparation of the Bamboo Strips and Woven Mat
Matured semantan bamboo (Gigantochloa scortechinii) was used in this study since it exists abundantly in Malaysia and is among the most popularly used bamboo species by the local manufacturers. Semantan bamboo culm, with a diameter ranging from 45 to 60 mm, was supplied from a mill in the northern part of Peninsular Malaysia (Kedah, Malaysia). The bamboo plant height was around 3 m tall and only the first 2 m above the ground of the bamboo stem were used. The bamboo culms were then split into lumber strips using a cleaver and a handsaw to a dimension of 1000 mm (L) × 20 mm (W) × 5-10 mm (T). The bamboo strips were then treated with 5% borax and boric acid before being air-dried. After being dried, bamboo green (a thin pliable layer) was removed from the strips manually using a knife. The removed bamboo green was then weaved manually into a herringbone pattern as shown in Figure 1. The width of each strip was around 18 mm. The woven mat's final size was around 500 mm wide × 500 mm long.

Fabrication of Laminated Woven Bamboo Mat Board
The conventional hand lay-up technique was used to fabricate laminated woven bamboo mat boards with 5, 7, and 9 layers of woven bamboo mats. Commercial phenol formaldehyde (PF) resin purchased from Aica Malaysia Sdn. Bhd., Senawang, Selangor was used as binder in this study. PF resin was brushed on the woven mat in one direction

Fabrication of Laminated Woven Bamboo Mat Board
The conventional hand lay-up technique was used to fabricate laminated woven bamboo mat boards with 5, 7, and 9 layers of woven bamboo mats. Commercial phenol formaldehyde (PF) resin purchased from Aica Malaysia Sdn. Bhd., Senawang, Selangor was used as binder in this study. PF resin was brushed on the woven mat in one direction at a glue spread rate of 250 g/m 2 , single glueline. The woven mats were then stacked into 5, 7 and 9 layers and were hot pressed at a platen temperature of 150 • C for 10 min. The pressure was kept at 4 MPa. The final size of the panel after trimming was 450 mm (L) × 450 mm (W) × ply thickness (T).

Density
Five blocks of 10 mm × 30 mm × ply thickness were obtained from 5, 7, and 9 ply laminated woven mat bamboo for density evaluation. The initial weight of the blocks was recorded. Then, the blocks were oven-dried for 48 h at 103 ± 2 • C until they reached a consistent weight. The oven-dry weight was calculated by weighing the blocks. The density of the block was then expressed as mass over volume in kg/m 3 .

Static Bending
The static bending test was performed using JAS 233-2003 to determine the modulus of elasticity (MOE) and modulus of rupture (MOR) using a UTM Instron (50 kN, INSTRON, Norwood, MA, USA). The dimension of test specimen was 200 mm (L) × 50 mm (W) × ply thickness. The sample was supported at two ends, and the load was applied at the center of the sample at a loading rate of 10 mm/min. The MOE and MOR were calculated by using the following formulae: Modulus of elasticity (MOE) = pl 3 /4Dbh 3 Modulus of rupture (MOR) = 3p l 3 /2bh 2 where p is the maximum load (N), p is the applied load at the elastic limit (N), l is the span length of the test specimen (mm), D is the deflection at the elastic limit (mm), b is the breadth of the specimen (mm) and h is the height of specimen (mm).

Shear Strength
The shear strength of the samples was determined using the procedures outlined in ISO 12466-1. Prior to testing, the samples were subjected to pre-treatments. Dry shear strength is defined as samples that have not been pre-treated. Prior to testing for moisture resistance shear strength, the samples were soaked in water for 24 h. The boil-dry-boil pre-treatment cycle was used for water boiling proof shear strength. The samples were immersed in boiling water for 4 h, then dried in a ventilated drying oven for 16 to 20 h at 60 ± 3 • C, then immersed in boiling water for 4 h, followed by at least 1 h cooling in water less than 30 • C. The samples were then tested for shear strength using a Universal Testing Machine (UTM, Instron-3366, Norwood, MA, USA).

Delamination
Delamination tests in cold and hot water were conducted following JAS 234:2007. The cold water delamination test was performed by soaking the samples in water at a room temperature for 6 h before placing them in an oven at 40 ± 3 • C for 18 h. The specimens were examined for hot water delamination by boiling them in water (100 • C) for 4 h and then soaking them at a room temperature water for 1 h. After that, the samples were dried in an oven at 70 ± 3 • C for 18 h. The following formula was used to calculate the delamination ratio: Delamination Ratio: Sum of delaminated lengths of two cross − sections Sum of gluing lengths of two cross − sections × 100

Dimensional Stability
The dimensional stability of the bamboo was evaluated based on water absorption (WA) and thickness swelling (TS). Pre-weighed wood samples were cut into dimensions of 20 mm × 20 mm × ply thickness and were oven-dried at 103 ± 2 • C until constant weight. They were immersed in distilled water for 24 h. The samples were then removed from water and wiped with tissue paper to remove excess water. The TS and WA values were then calculated based on the difference before and after water soaking and expressed in percent (%).

Formaldehyde Emission
The formaldehyde emission for the laminated woven bamboo mat board was tested according to standard ISO 12460-5: wood based panels, assessment of formaldehyde emission using the Perforator method. The moisture content was assessed first according to EN 322: wood based panels, determination of MC. The size dimension of the sample for the testing was 25 × 25 mm and the thickness varies based on the thickness of ply.

Flammability Test
The woven laminated bamboo panel's flammability was tested per the UL-94 flammability test. The vertical burning test was chosen for the sample because no fire retardant treatments or coatings were applied. For the UL-94 test, the sample was dimensioned to 130 mm × 20 mm × ply thickness, resembling a strip or a stick. The sample was held vertically and fired for 10 s with a 20 mm high flame at one end. The burning time was recorded and calculated as the sample began to burn. The flame re-ignited for 10 s after the fire was extinguished. To determine the sample class, the combustion duration, the sample's dripping, and the burning state at fixing were investigated. The distance between the burner and the sample's targeted one end was 10 mm.

Statistical Analysis
All property evaluation tests were performed in ten replicates and analyzed using the statistical software IBM-SPSS. The analysis test of choice was one-way analysis of variance (ANOVA), which was further evaluated using Tukey's HSD test.

Density
Density values of the laminated woven bamboo mat boards are shown in Figure 2. The boards' density ranged from 784, 766 and 756 kg/m 3 for 5-, 7-, and 9-ply panels, respectively. The results showed no significant difference between 5-ply and 7-ply, as well as between 7ply and 9-ply. However, 5-ply laminated boards have significantly higher density than 9-ply laminated boards. The reason for the density value shown in Figure 2, is probably related to the number of ply. As the number of ply increases, the porosity increases, leading to air bubbles and spaces, which are contributed by each ply and increases as the ply increase, thus decreasing the density [22]. The formation of the 5-ply is more compact than 7-and 9-ply, due to the relation of the number of ply and porosity. Density has a linear correlation to porosity; the higher the density, the lower the porosity, resulting in a denser composite. The density profile of the laminated woven bamboo mat boards with various ply are shown in Figures 3-5. The thickness of 5-ply laminated boards was around 4.5 mm, while 7-ply was almost 8 mm thick and 9-ply has a thickness of around 10.5 mm. Dissimilar to the U-shape pattern found in particleboard and medium density fiberboard where the density of the core layer of the board are the lowest [23], laminated woven bamboo mat boards have a wavy density profile. This indicates that the density of boards varies strongly across the thickness of the boards. Such observation was due to the alternating arrangement of the woven bamboo mat and PF resin, in which PF resin has higher density than the woven bamboo mat [24]. The density profile of the laminated woven bamboo mat boards with various ply shown in Figures 3-5. The thickness of 5-ply laminated boards was around 4.5 mm, wh 7-ply was almost 8 mm thick and 9-ply has a thickness of around 10.5 mm. Dissimilar the U-shape pattern found in particleboard and medium density fiberboard where density of the core layer of the board are the lowest [23], laminated woven bamboo m boards have a wavy density profile. This indicates that the density of boards var strongly across the thickness of the boards. Such observation was due to the alternat arrangement of the woven bamboo mat and PF resin, in which PF resin has higher dens than the woven bamboo mat [24].

Static Bending
The static bending of the laminated woven bamboo mat boards is shown in Figu Five-ply laminated boards have the highest MOE value of 10,885 MPa, while 7-ply 10,705 MP and the lowest MOE value of 10,103 MPa was observed in 9-ply boards. N ply boards have significantly lower MOE compared to that of 5-ply boards. As for M the trend is in reverse order, where the highest MOR values were found in 9-ply boa (39.62 MPa), followed by 7-ply (34.42 MPa) and 5-ply (33.20 MPa). However, no signifi difference between these boards in terms of MOR was observed.

Static Bending
The static bending of the laminated woven bamboo mat boards is shown in Figure 6. Five-ply laminated boards have the highest MOE value of 10,885 MPa, while 7-ply has 10,705 MP and the lowest MOE value of 10,103 MPa was observed in 9-ply boards. Nineply boards have significantly lower MOE compared to that of 5-ply boards. As for MOR, the trend is in reverse order, where the highest MOR values were found in 9-ply boards (39.62 MPa), followed by 7-ply (34.42 MPa) and 5-ply (33.20 MPa). However, no significant difference between these boards in terms of MOR was observed.   Figure 7 illustrates the failure modes of the sample after the static bending test w conducted while Figure 8 shows the micrograph of the failure samples. When observ under the SEM, the deformation and breakage of the fiber can be clearly seen in Figure  When compared to the other ply, the 9-ply structure showed the most deformation. T failure of bamboo fiber to support the load transferred between the resin and woven ba boo layer is most likely the cause of this, which also relates to the low interfacial bondi between the bamboo as the number of ply increases [21]. The interfacial debonding caus large cracks and holes in the 9-ply sample when compared to the 5-and 7-ply sampl Further stress load propagation causes an increase in the crack area, resulting in def 10  When compared to the other ply, the 9-ply structure showed the most deformation. The failure of bamboo fiber to support the load transferred between the resin and woven bamboo layer is most likely the cause of this, which also relates to the low interfacial bonding between the bamboo as the number of ply increases [21]. The interfacial debonding causes large cracks and holes in the 9-ply sample when compared to the 5-and 7-ply samples. Further stress load propagation causes an increase in the crack area, resulting in deformation of the bamboo fiber.  Figure 7 illustrates the failure modes of the sample after the static bending test was conducted while Figure 8 shows the micrograph of the failure samples. When observed under the SEM, the deformation and breakage of the fiber can be clearly seen in Figure 8. When compared to the other ply, the 9-ply structure showed the most deformation. The failure of bamboo fiber to support the load transferred between the resin and woven bamboo layer is most likely the cause of this, which also relates to the low interfacial bonding between the bamboo as the number of ply increases [21]. The interfacial debonding causes large cracks and holes in the 9-ply sample when compared to the 5-and 7-ply samples. Further stress load propagation causes an increase in the crack area, resulting in deformation of the bamboo fiber.  The static bending test was conducted on all three ply to know the sample's MOE and MOR value. MOE is used to determine the value of wood stiffness. It measures the resistance of the composite to bending deformation. Based on Figure 6 above, the 5-ply laminated woven bamboo has the highest value of MOE (10,886 ± 838.44 MPa) compared The static bending test was conducted on all three ply to know the sample's MOE and MOR value. MOE is used to determine the value of wood stiffness. It measures the resistance of the composite to bending deformation. Based on Figure 6 above, the 5-ply laminated woven bamboo has the highest value of MOE (10,886 ± 838.44 MPa) compared to other numbers of ply, which correlates to the density of the composite, where 5-ply has the highest density. The MOE value showed a descending pattern as the number of ply increased.
The MOR is also called flexural strength, which is related to both tensile and compressive strength, which varies with the inter-laminar shear strength [25]. The MOR value showed a contrasting value pattern when compared to MOE, where 9-ply woven bamboo has the highest MOR value (39.62 ± 16.13 MPa). MOR value went ascending as the number of ply increases, whereas 5-ply woven bamboo with the lowest MOR value (33.20 ± 17.74 MPa) showed lower flexural strength than 7-and 9-ply. Nine-ply woven bamboo shows better flexural properties compared to other ply due to the increase of interlacing fiber. The increasing number of ply and arrangement of the fiber causes the movement of the woven bamboo to be constrained, so the pressure and stress applied during the MOR test lead to an even distribution of force, indirectly enhancing the woven bamboo withstand threshold [21]. Furthermore, an increase in the ply number is related to an increase in bamboo fiber, thus, a stiffer end-result with less elastic qualities when enforced with pressure. Table 1 shows laminated woven bamboo mat boards' internal bonding (IB) strength. Five-ply laminated boards had the highest dry IB strength of 0.89 N/mm 2 , while 9-ply laminated boards had the lowest dry IB strength (0.59 N/mm 2 ). When the ply number was increased from 5-ply to 9-ply, dry shear strength decreased by 33.7%. In terms of moisture resistance shear strength, after 24 h of immersion in water, laminated boards showed varying degrees of bonding quality degradation. Shear strength values of 0.51 N/mm 2 and 0.53 N/mm 2 were recorded in 5-and 7-ply samples, respectively. However, 9-ply samples had the most severe bonding degradation, with only 0.14 N/mm 2 recorded, a 76.3% reduction from its shear strength in dry state. Shear strength was severely reduced in all ply samples under cyclic boiling conditions, ranging from 0.11 to 0.16 N/mm 2 . Table 1. Shear strength of laminated woven bamboo mat boards of different ply.
In terms of shear strength, 5-ply and 7-ply laminated boards performed better than 9-ply laminated boards. This could be due to the thickness of the samples, which affects heat transfer to the board's core layer. According to Li et al. [9], the time required for the core layer of 5-, 7-, and 9-layer plywood to reach 100 • C was 80 s, 150 s, and 250 s, respectively. Simultaneously, the duration of the first constant temperature range, or moisture vaporization, increased from 360 s to 700 s to 1240 s for 5-, 7-, and 9-ply plywood, respectively. The 9-ply laminated board is very thick and has a negative effect on heat transfer efficiency. Furthermore, the 9-ply laminated board has more glue lines than the 5-ply and 7-ply laminated boards, so its moisture content is higher. The adhesive was unable to flow freely as the time for moisture vaporization increased, preventing effective adhesion. As a result, 9-ply laminated boards had lower bonding qualities than 5-and 7-ply laminated boards.

Delamination Test
The delamination test was conducted to assess the bonding quality of the laminated woven bamboo mat boards. The test was carried out through immersion of the samples in cold water and hot water. Figure 9 depicts the percentage delamination of laminated boards of different ply. In a cold water immersion test, the result showed that 9-ply has the lowest delamination, followed by 7-and 5-ply. Similarly, 9-ply showed the lowest in delamination when immersed in hot water with an average delamination value of 7%, with 5-ply having the highest delamination (17%). The result indicated that 9-ply fares better in hot and cold water tests. The ANOVA test conducted showed that the effects of ply number is insignificant.

Dimensional Stability
According to Table 2, when compared to 7-and 9-ply, 5-ply has the highest percentage of water absorption. Bamboo strips are a naturally porous fiber composite material, meaning that the number of woven ply increases would inevitably increase water absorption. However, in this laminated woven bamboo panel, 7-ply showed the lowest percentage of water absorption rather than 5-ply. Despite the fact that 5-ply is denser, the high water absorption was most likely due to the large surface area of porous tubular structures present in bamboo fiber, which increases water penetration, which was hindered for other ply by the increase in ply layer and the phenol-formaldehyde resin. A high water absorption rate will increase the composite's thickness and swelling. As shown in Table 2, the thickness swelling percentage corresponds to the water absorption rate, with 5-ply having the highest thickness swelling compared to 7 and 9-ply. Based on the analysis of both aspects, 7-ply is the optimum ply number for the laminated woven bamboo panel in terms of dimensional stability. The dimensional stability test has some correlation with the delamination results, with 5-ply having the most delamination and thus higher water absorption and thickness swelling. Meanwhile, 7-ply has lower water absorption and thickness swelling than 9-ply, but the difference is not statistically significant. Additionally, the delamination results of 7-ply and 9-ply was also relatively small. 37.73 ± 6.14 ab 11.13 ± 1.73 a Note: Mean follow by the same letters a, b is not significantly different at p ≤ 0.05.

Formaldehyde Emission
The perforator method was used to conduct the formaldehyde emission test. Table 3 shows no significant difference in the value of formaldehyde extracted for each number

Dimensional Stability
According to Table 2, when compared to 7-and 9-ply, 5-ply has the highest percentage of water absorption. Bamboo strips are a naturally porous fiber composite material, meaning that the number of woven ply increases would inevitably increase water absorption. However, in this laminated woven bamboo panel, 7-ply showed the lowest percentage of water absorption rather than 5-ply. Despite the fact that 5-ply is denser, the high water absorption was most likely due to the large surface area of porous tubular structures present in bamboo fiber, which increases water penetration, which was hindered for other ply by the increase in ply layer and the phenol-formaldehyde resin. A high water absorption rate will increase the composite's thickness and swelling. As shown in Table 2, the thickness swelling percentage corresponds to the water absorption rate, with 5-ply having the highest thickness swelling compared to 7 and 9-ply. Based on the analysis of both aspects, 7-ply is the optimum ply number for the laminated woven bamboo panel in terms of dimensional stability. The dimensional stability test has some correlation with the delamination results, with 5-ply having the most delamination and thus higher water absorption and thickness swelling. Meanwhile, 7-ply has lower water absorption and thickness swelling than 9-ply, but the difference is not statistically significant. Additionally, the delamination results of 7-ply and 9-ply was also relatively small. 37.73 ± 6.14 ab 11.13 ± 1.73 a Note: Mean follow by the same letters a, b is not significantly different at p ≤ 0.05.

Formaldehyde Emission
The perforator method was used to conduct the formaldehyde emission test. Table 3 shows no significant difference in the value of formaldehyde extracted for each number of ply, which also applied to the perforator value. The number of ply does not affect formaldehyde emission, and the formaldehyde content of 5, 7, and 9-ply woven laminated bamboo was almost the same. Table 3. Formaldehyde emission of laminated woven bamboo mat boards of different ply.

Flammability Test
A flammability test was performed on the sample to determine its burning behavior. Because the sample was not coated with any fire retardant, only the vertical flame test was chosen for the flammability test. After the initial flame application, the burning duration for 5-ply is the longest (3.7 s), and the shortest for 9-ply (2.9 s). The sample burning time did not change significantly after the second flame application. According to Table 4, 7-ply has the longest burning duration (1.4 s), while 9-ply has the shortest (1.2 s). The overall burning time for 5-ply is 5 s, followed by 4.6 s and 4.1 s for 7-ply and 9-ply, respectively. Figures 10 and 11 show char formation on the composite surfaces of 5-, 7-, and 9-ply woven bamboo panels during combustion, but not burning. There was no melt dripping from the composite samples. These characteristics allowed the composites to be classified as V-0 because the burning stopped within 10 s after two ten-second flame applications to the test bar. The number of ply had an effect on the flammability of the sample, which can be seen directly based on the duration of the burning time. Samples with higher numbers of ply have higher numbers of gluelines. For instance, 5-ply has four gluelines, 7-ply has six gluelines and 9-ply has eight gluelines. As PF resin is less flammable than the woven bamboo mat, therefore, the more gluelines, the lesser burning time of the samples.  Table 3. Formaldehyde emission of laminated woven bamboo mat boards of different ply.

Flammability Test
A flammability test was performed on the sample to determine its burning behavior. Because the sample was not coated with any fire retardant, only the vertical flame test was chosen for the flammability test. After the initial flame application, the burning duration for 5-ply is the longest (3.7 s), and the shortest for 9-ply (2.9 s). The sample burning time did not change significantly after the second flame application. According to Table 4, 7ply has the longest burning duration (1.4 s), while 9-ply has the shortest (1.2 s). The overall burning time for 5-ply is 5 s, followed by 4.6 s and 4.1 s for 7-ply and 9-ply, respectively. Figures 10 and 11 show char formation on the composite surfaces of 5-, 7-, and 9-ply woven bamboo panels during combustion, but not burning. There was no melt dripping from the composite samples. These characteristics allowed the composites to be classified as V-0 because the burning stopped within 10 s after two ten-second flame applications to the test bar. The number of ply had an effect on the flammability of the sample, which can be seen directly based on the duration of the burning time. Samples with higher numbers of ply have higher numbers of gluelines. For instance, 5-ply has four gluelines, 7-ply has six gluelines and 9-ply has eight gluelines. As PF resin is less flammable than the woven bamboo mat, therefore, the more gluelines, the lesser burning time of the samples.

Future Research Directions
In this study, laminated woven bamboo mat boards bonded with PF resin could be used for exterior applications. However, when exposed to the elements, bamboo-based products are easily attacked by molds, termites, and decaying fungi, reducing their strength. Furthermore, direct sunlight causes discoloration of the laminated woven bamboo mat boards, reducing their service life. Although PF resin can help improve board durability, it causes uneven sizing and poor continuity of the adhesive/bamboo interface due to its high surface tension and low permeability. As a result, thermal treatment of laminated woven bamboo mat boards could be an excellent option for improving the boards' weather resistance [26]. Wang et al. [27] discovered that bamboo treated at 180 °C under saturated steam has a significant impact on the physical, chemical, and mechanical properties of the bamboo. Some benefits include increased biological durability and dimensional stability of thermally treated bamboo. Unfortunately, there are some flaws associated with the thermal treatment, such as decreased wettability of the bamboo surface, which will inevitably affect the spreading of the PF resin during consolidation. Furthermore, thermally treated bamboo is weaker and more prone to cracking. As a result, Lou et al. [28] proposed another method for addressing the aforementioned issues through the use of nano-scaled inorganic materials. The nano-Fe3O4 decorated bamboo bundles were created by combining iron/alkali liquid impregnation, nanocrystalline in situ crystallization, and hot pressing at high temperatures. The nano-Fe3O4/bamboo bundles/phenolic resin-oriented recombination ternary composite boards demonstrated improved hydrophobicity, satisfactory compressive properties, dimensional stability, and mildew resistance. It is worth noting that the nano-Fe3O4 used in the study is only a member of the inorganic material family; thus, the potential of inorganic materials is still enormous and well worth investigating.
Bamboo flattening technology, on the other hand, could be used in conjunction with the bamboo recombination technique reported in this study to develop bamboo-based structural materials with improved performance. Bamboo flattening is a high-efficiency utilization technology that ensures a higher utilization rate of bamboo resources as well as reducing the amount of adhesive and increasing the added value of the bamboo [29]. Bakar et al. [7] also confirmed that flattening V-grooved bamboo has an astounding 82% recovery. Aside from that, flattened bamboo boards frequently have higher bending strength, which could be advantageous when converted into recombined bamboo-based products [30]. According to Yuan et al. [31], bamboo flattening technology enables the efficient and value-added utilization of bamboo in the manufacture of furniture and engineered composites. As a result, combining bamboo flattening technology with current Figure 11. The cross section of (A) 5-ply, (B) 7-ply and (C) 9-ply of laminated woven bamboo mat boards after flammability test.

Future Research Directions
In this study, laminated woven bamboo mat boards bonded with PF resin could be used for exterior applications. However, when exposed to the elements, bamboo-based products are easily attacked by molds, termites, and decaying fungi, reducing their strength. Furthermore, direct sunlight causes discoloration of the laminated woven bamboo mat boards, reducing their service life. Although PF resin can help improve board durability, it causes uneven sizing and poor continuity of the adhesive/bamboo interface due to its high surface tension and low permeability. As a result, thermal treatment of laminated woven bamboo mat boards could be an excellent option for improving the boards' weather resistance [26]. Wang et al. [27] discovered that bamboo treated at 180 • C under saturated steam has a significant impact on the physical, chemical, and mechanical properties of the bamboo. Some benefits include increased biological durability and dimensional stability of thermally treated bamboo. Unfortunately, there are some flaws associated with the thermal treatment, such as decreased wettability of the bamboo surface, which will inevitably affect the spreading of the PF resin during consolidation. Furthermore, thermally treated bamboo is weaker and more prone to cracking. As a result, Lou et al. [28] proposed another method for addressing the aforementioned issues through the use of nano-scaled inorganic materials. The nano-Fe 3 O 4 decorated bamboo bundles were created by combining iron/alkali liquid impregnation, nanocrystalline in situ crystallization, and hot pressing at high temperatures. The nano-Fe 3 O 4 /bamboo bundles/phenolic resin-oriented recombination ternary composite boards demonstrated improved hydrophobicity, satisfactory compressive properties, dimensional stability, and mildew resistance. It is worth noting that the nano-Fe 3 O 4 used in the study is only a member of the inorganic material family; thus, the potential of inorganic materials is still enormous and well worth investigating.
Bamboo flattening technology, on the other hand, could be used in conjunction with the bamboo recombination technique reported in this study to develop bamboo-based structural materials with improved performance. Bamboo flattening is a high-efficiency utilization technology that ensures a higher utilization rate of bamboo resources as well as reducing the amount of adhesive and increasing the added value of the bamboo [29]. Bakar et al. [7] also confirmed that flattening V-grooved bamboo has an astounding 82% recovery. Aside from that, flattened bamboo boards frequently have higher bending strength, which could be advantageous when converted into recombined bamboo-based products [30]. According to Yuan et al. [31], bamboo flattening technology enables the efficient and value-added utilization of bamboo in the manufacture of furniture and engineered composites. As a result, combining bamboo flattening technology with current bamboo recombination technology is a promising future direction that can increase bamboo utilization effectiveness.

Conclusions
Laminated woven bamboo mat boards were fabricated using semantan bamboo woven mats and bonded with phenol formaldehyde resin. The effects of the number of ply (5-, 7-and 9-ply) on the properties of the laminated boards were investigated. The density of the laminated boards decreased as the number of ply increased. Correspondingly, 5-ply laminated boards had the highest modulus of elasticity. However, lowest modulus of rupture was also recorded in 5-ply laminated boards. As for shear strength, both 5-ply and 7-ply laminated boards exhibited superior performance compared to that of 9-ply. Meanwhile, 7-ply laminated boards displayed the best dimensional stability as indicated by the lowest water absorption and thickness swelling. All laminated boards were classified as V-0 because the burning stopped within 10 s after two ten-second flame applications to the test bar.