Abstract
Using a vacuum pressure cylinder, Gigantochloa scortechinii was treated with boron and copper chrome boron (CCB) preservative at different concentrations of 2% and 3%. The treatability of untreated and treated bamboo, as well as its physical and mechanical properties, were investigated. Both preservatives showed a high level of penetration into the bamboo strips. Weight percent gain (WPG) and extent of retention of CCB-treated bamboo strips were higher than those of the boron-treated samples. Swelling and shrinkage were proportionately reduced with treatment, with a significant difference between radial and tangential dimensions. When compared to untreated bamboo, treated bamboo showed a greater reduction in radial swelling but a lower reduction in shrinkage. The mechanical properties of untreated and treated samples differed in modulus of elasticity (MOE) and compression. Untreated samples had the highest MOE of 26,100 N.mm-2, while boron and CCB had MOE values of 22,800 and 22,900 N.mm-2, respectively. Copper chrome boron samples had the highest compression value of 86.3 N.mm-2, while the boron and untreated samples had values of 84.0 and 78.3 N.mm-2, respectively.
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Effect of Preservative Treatment on Physical and Mechanical Properties of Bamboo (Gigantochloa scortechinii) Strips
Norhazaedawati Baharuddin,a,b Seng Hua Lee,b,* Mohd Khairun Anwar Uyup,b,c and Paridah Md Tahir c
Using a vacuum pressure cylinder, Gigantochloa scortechinii was treated with boron and copper chrome boron (CCB) preservative at different concentrations of 2% and 3%. The treatability of untreated and treated bamboo, as well as its physical and mechanical properties, were investigated. Both preservatives showed a high level of penetration into the bamboo strips. Weight percent gain (WPG) and extent of retention of CCB-treated bamboo strips were higher than those of the boron-treated samples. Swelling and shrinkage were proportionately reduced with treatment, with a significant difference between radial and tangential dimensions. When compared to untreated bamboo, treated bamboo showed a greater reduction in radial swelling but a lower reduction in shrinkage. The mechanical properties of untreated and treated samples differed in modulus of elasticity (MOE) and compression. Untreated samples had the highest MOE of 26,100 N.mm-2, while boron and CCB had MOE values of 22,800 and 22,900 N.mm-2, respectively. Copper chrome boron samples had the highest compression value of 86.3 N.mm-2, while the boron and untreated samples had values of 84.0 and 78.3 N.mm-2, respectively.
DOI: 10.15376/biores.17.3.5129-5145
Keywords: Malaysian bamboo; Preservative; Vacuum pressure; Physical properties; Mechanical properties
Contact information: a: Fibre and Biocomposite Centre, Malaysian Timber Industry Board, 42700 Banting, Selangor, Malaysia; b: Institute of Tropical Forestry and Forest Products, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia; c: Forest Products Division, Forest Research Institute Malaysia, 52109 Kepong, Selangor, Malaysia;
*Corresponding author: lee_seng@upm.edu.my
INTRODUCTION
Bamboo is one of the non-timber forest products that is abundant in the forest. Bamboo grows naturally in a variety of climates and is most commonly found in logging areas, riverbanks, and hillsides. It has been reported that there are 70 bamboo species in Malaysia, divided into 10 genera. Based on the utilisation of the industries, a total of 13 species have been classified as commercial species (Azmy and Baharuddin 2015; Abdullah Siam et al. 2019). Gigantochloa scortechinii has been identified as the most commonly used bamboo species due to its availability and strength properties (Zakikhani et al. 2017; Abdullah Siam et al. 2019), making it well-publicized in research.
Bamboo is one of the potential alternative raw materials to be used for a variety of applications, particularly as a structural material, due to its strong characteristics and durability (Sharma et al. 2015). Bamboo is frequently converted into strips or thin flat laminae to produce laminated products due to its hollow cylindrical features (Zaidon et al. 2016; Bakar et al. 2019). To ensure the long-term viability of the applications, bamboo must be preserved to protect it from harmful organisms and to extend its lifespan (Rabbi et al. 2015). Despite the availability of numerous preservatives, waterborne preservatives are frequently used in treatment due to their advantages and effectiveness (Smith 2020). Boron and copper chrome boron (CCB) are the most commonly used (Abdul Karim et al. 2020). Furthermore, these preservatives have been widely used by the bamboo industries in Asia and other bamboo regions for a variety of product applications, including structural purposes (Liese and Tang 2015; Kaminski et al. 2016; Jivkov et al. 2021).
The use of these preservatives, however, is still subject to the environmental conditions. Boron is an effective preservative in treated bamboo, but its use is limited to dry and interior applications because it can be leached out if exposed to rain (Liese and Tang 2015). In contrast, copper chrome boron is better suited for exterior applications due to its better fixation and thus weather resistance (Shanu et al. 2015; Gauss et al. 2020).
Similarly, the use of a suitable preservative for the environmental conditions must be evaluated by examining the impact on the strength properties. Several studies have found that boron-based preservative treatment improves physical properties by increasing density and dimensional stability (Gecer et al. 2015; Baraúna et al. 2021; Aristri et al. 2021). In terms of strength, boron-based preservatives have been reported to affect it to some extent (Kartal et al. 2008; De Souza Almeida et al. 2019). In contrast, some studies show that the strength increased proportionately with the treatment (Perçin et al. 2015; Daud et al. 2018).
The use of appropriate preservatives with promising strength values, particularly for structural purposes, has been highly desired. There have been very few studies on the treatment ability of boron and CCB on G. scortechinii bamboo strips, particularly for these purposes. The previous study by Gauss et al. (2019) focused on the quality assessment of boron-based treated moso bamboo poles and discovered that mechanical properties were not affected by treatment.
As a result, this current study investigated the physical and mechanical properties of G. scortechinii bamboo strips treated with boron and CCB at the manufacturer’s recommended concentrations. The performance of the bamboo was evaluated in terms of changes in moisture content, density, dimensional stability, and strength properties.
EXPERIMENTAL
Materials
Sample preparation
Twenty matured Gigantochloa scortechinii culms were cut at approximately 1 m above ground level in Hulu Langat, Selangor, Malaysia, and only 2.4 m length was taken. The culms were dried for 14 days before being processed into bamboo strips with a splitter machine (Chin Yung, Changhua, Taiwan) and thicknesser planner (SCM, Rimini, Italy) to the required size of 2400 x 20 x 5 mm3. The bamboo strips were then divided into two groups: control and treatment.
A 2% solution of boron (Celcure Chemical, Selangor, Malaysia) and 3% of CCB (Celcure Chemical, Selangor, Malaysia) were prepared. Boron was prepared by diluting 5 kg of boron in 250 litres of water to make a 2% solution concentration while CCB was prepared by diluting 75 litres of CCB in 250 litres of water to make a 3% solution concentration. The bamboo strips were then treated using the vacuum chamber method as follows:
- Initial vacuum: > 85 kPa for 30 min (to suck the air out of the bamboo)
- Applying pressure: > 1300 kPa for 60 min after the preservative solution was introduced into the treatment cylinder
- Final vacuum: > 85 kPa for 20 min (to remove the access preservative from the bamboo)
Treatability Evaluation of Bamboo
Retention and penetration
A total of 10 specimens for each treatment with the size of 300 mm x 20 mm x 5 mm were used in this test. All the specimens’ weights and dimensions were weighed and measured before treatment. After treatment, the excess solution was drained off and conditioned at 20 °C ± 3 °C and 65% relative humidity until constant weight was achieved.
The weight percent gain (WPG) and net dry salt retention (NDSR) were calculated using Eq. 1 and Eq. 2, respectively,
WPG (%) = [(Wt – Wu)/Wu] x 100 (1)
where Wt is the weight (g) of the treated specimen and W is the weight (g) of oven-dried of bamboo strips, and
NDSR (kg/m3) = [(Wt – Wu)/V] x treating solution concentration (2)
where Wt is the weight (g) of the treated specimen, Wu is the weight (g) of the initial specimen, and V is the volume (m3) of the treated specimen.
After specimens were dried, two replicates of each treatment were cut to 20 mm x 20 mm pieces to assess the penetration level using chemical reagents. The chemical reagents used were Azurol S (Celcure Chemical, Selangor, Malaysia) for copper detection in CCB preservative and Curcumin (Celcure Chemical, Selangor, Malaysia) for boron detection. Boron was tested using a curcumin solution composed of turmeric powder and ethyl alcohol (10% wt/vol alcohol). Meanwhile, the penetration of copper was analysed using the solution of Chrome Azurol S and sodium acetate mixed in water. The presence of boron was indicated by the red colour, while the blue colour indicates the presence of copper. The penetration pattern referred to MS 833 (1984) in Table 1.
Table 1. Visual Classification of Preservative Penetration
Fourier transform infrared (FTIR) analysis
From the same specimens, three specimens from each treatment were ground into 40- to 60-mesh particles using IKA Grinder (Wilmington, USA) and run for FTIR testing for chemical content analysis. The FTIR measurements were conducted using a Perkin Elmer FTIR instrument (Llantrisant, UK) (1 cm−1 resolution, 32 scans, KBr method) in a laboratory of the Fibre and Biocomposite Centre (FIDEC) located in Banting, Selangor, Malaysia.
Physical Properties Evaluation
The procedures used for the determination of moisture content and density were conducted following the Indian Standard of Method of Tests for split bamboo (IS 8242 (1976)) as described by Anwar Uyup et al. (2005). Of these, 10 specimens of each treatment were used in the determination of moisture content and density. The equation for moisture content (MC) and density were calculated according to Eqs. 3 and 4, respectively,
MC (%) = [(W’ – W)/W] x 100 (3)
where W’ is the initial weight of bamboo strips (g) and W is the weight of oven-dried bamboo strips (g), and
Density (kg/m3) = W/V (4)
where W is the weight after oven drying (g) and V is the volume of the sample (mm3).
For the determination of radial and tangential shrinkage and swelling, 20 specimens were used and conducted according to ISO 13061-13 (2017) and ISO 13061-15 (2017), respectively. The equation for the linear shrinkage and linear swelling of the samples were determined and calculated by Eq. 5 to Eq. 10,
Linear shrinkage
Radial shrinkage (%) = [(lr1 – lr2)/lr1] x 100 (5)
Tangential shrinkage (%) = [(lt1 – lt2)/lt1] x 100 (6)
Total volumetric shrinkage (%) = [[(lr1 x 1t1) – (lr2 x lt2)]/ (lr1 x lt1)] x 100 (7)
where lr1 and lt1 are the dimensions (mm) of the green or fully saturated test piece measured in the radial and tangential directions, respectively, while lr2 and lt2 are the dimensions (mm) of the test piece at oven-dry condition measured in the radial and tangential directions, respectively. The linear swelling was calculated according to Eqs. 8 to 10,
Linear swelling
Radial shrinkage (%) = [(lr2 – lr1)/lr1] x 100 (8)
Tangential shrinkage (%) = [(lt2 – lt1)/lt1] x 100 (9)
Total volumetric shrinkage (%) = [[(lr2 x 1t2) – (lr1 x lt1)]/ (lr1 x lt1)] x 100 (10)
where lr2 and lt2 are the dimensions (mm) of the fully saturated test piece measured in the radial and tangential directions, respectively, while lr1 and lt1 are the dimensions (mm) of the test piece at oven-dry condition, measured in the radial and tangential directions, respectively.
Mechanical Properties Evaluation
Static bending
For the static bending test, 30 specimens of each treatment were prepared and tested according to the procedure described by Anwar Uyup et al. (2009) in reference to IS 8242 (1976). The modulus of rupture (MOR) and the modulus of elasticity (MOE) were calculated using Eqs. 11 and 12 as follows,
MOR (N/mm2) = 3P’l/2bh2 (11)
MOE (N/mm2) = Pl2/4bh3d (12)
where P is the load (N) at the proportional limit, b is the width (mm) of the specimen, h is the depth (mm) of specimen, l is the span length (mm), P’ is the maximum load (N), and d is the deflection (mm) at proportional limit.
Compressive strength
To determine compressive strength, 30 samples from each treatment were tested in accordance with the procedure described by Anwar Uyup et al. (2009) in reference to IS 8242 (1976) using a 10 kN Shimadzu universal testing machine (Shimadzu, Kyoto, Japan). The determination of compressive strength was calculated using the equation as follows:
Compressive strength (N/mm2) = P/bh (13)
where P is the maximum crushing load, b is width of the specimen, and h is the thickness of the sample.
Statistical analysis
Analysis of variance (ANOVA) at 95% confidence level (p ≤ 0.05) was used to analyse the data by using statistical analysis software (SAS) (9.4, SAS Institute, Cary, NC). All mechanical properties were adjusted to 12% MC according to BS EN 408 (2010). Tukey’s honest significant difference (HSD) test was employed to analyse the significant level for the mean value of each treatment.
RESULTS AND DISCUSSION
Treatability of Bamboo Strips
Retention and penetration
Both retention and penetration are important criteria for determining the efficacy of a preservative treatment. Retention is typically expressed as the weight of chemicals absorbed in the wood, whereas penetration is used to detect the presence of preservatives in the substance (Gauss et al. 2020). In contrast, weight gain was indicated as a chemical load in the substance (Baysal et al. 2006).
Table 2 displays the WPG of boron- and CCB-treated bamboo. The WPG and NDSR of boron-treated bamboo strips were 18.4% and 2.63%, respectively. In terms of CCB, a significantly higher WPG and NDSR of 23.12% and 4.92%, respectively, were recorded.
Table 2. Weight Percent Gain of Treated Bamboo Strips
Several studies on the retention of boron and CCB in other bamboo species have been conducted. Baysal et al. (2016) found that the average retention of boron and CCB in Phyllostachys bambusoides was 4.63 to 4.88 kg.m-3, whereas Wahab et al. (2005) discovered that the average retention in Gigantochloa scortechinii bamboo was 4.41 to 6.30 kg.m-3. Furthermore, Gauss et al. (2019) discovered that the extent of retention for Dendrocalamus asper was 11.82 to 17.41 kg.m-3 using 5% and 8% boron concentrations. The retention values in Table 4 were in accordance with the retention value for waterborne preservatives stipulated by the America Wood Preservative Association (AWPA), with a value limit of 2.8 kg.m-3 for boron and 4 kg.m-3 for CCB for interior dry and exterior usage, respectively (Smith 2020).
The visual penetration assessment revealed that the preservative penetrated well into the treated bamboo strips (Fig. 1). The presence of test chemicals was determined by a change in the colour of the sample. Total penetration was determined by a blue colour for the presence of copper and a red colour for the presence of boron (Fig. 2). According to previous reports, the colour change during preservative penetration was caused by chemical treatment and atmospheric conditions (Bons and Dhawan 2013). The microscope images of the boron- and CCB-treated sample subjected to the test are shown in Fig. 2. Through the penetration test, one can see that the whole cross-section was fully absorbed with the preservative and turned into red (for boron treated sample) and blue (for CCB treated sample). According to MS 833 (1984), the samples were classified under grade 5 as completely penetrated with preservative.
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