This paper presents a new kind of composite produced with small-diameter bamboo (Phyllostachys glauca McClure) and extruded tubular particleboard. The mechanical properties of the composite are significantly affected by the properties of the bamboo. First, the compression strength of the bamboo was studied. It was found that the compression strength (fc, MPa) and the maximum force of compression (Fmax, kN) of the bamboo are strongly, linearly related to its outer diameter (D, mm): fc = -0.5D+79.37 and Fmax = 0.83D–0.59. The compression strength of the composite made with the bottom part of the bamboo was larger than that of composites made with the middle and top parts. In addition, its reliability was also the best of the three groups due to the variation of the outer diameter of the bamboo from the bottom to the top. The bottom part of the bamboo is the best choice for manufacturing bamboo-reinforced extruded particleboard (BREP).
Reliability of Compression Strength of Hennon Bamboo-reinforced Extruded Tubular Particleboard
Haiyang Zhang,* Hai Luo, and Xiaoning Lu*
This paper presents a new kind of composite produced with small-diameter bamboo (Phyllostachysglauca McClure) and extruded tubular particleboard. The mechanical properties of the composite are significantly affected by the properties of the bamboo. First, the compression strength of the bamboo was studied. It was found that the compression strength (fc, MPa) and the maximum force of compression (Fmax, kN) of the bamboo are strongly, linearly related to its outer diameter (D, mm): fc = -0.5D+79.37 and Fmax = 0.83D–0.59. The compression strength of the composite made with the bottom part of the bamboo was larger than that of composites made with the middle and top parts. In addition, its reliability was also the best of the three groups due to the variation of the outer diameter of the bamboo from the bottom to the top. The bottom part of the bamboo is the best choice for manufacturing bamboo-reinforced extruded particleboard (BREP).
Keywords: Hennon bamboo; Tubular particleboard; Compression strength; Reliability analysis; Distribution model
Contact information: College of Wood Science and Technology, Nanjing Forestry University, 159# Longpan Road, Nanjing, 210037, China; *Corresponding author: firstname.lastname@example.org (Haiyang Zhang); email@example.com (Xiaoning Lu)
Bamboo grows in most tropical and subtropical regions. People originally used bamboo as a hunting tool. Currently, it is used for paper, mat materials, plywood, particleboard, fiberboard, and so on (Tang 1998; Shen et al. 2002). More recently, several new kinds of composites, such as oriented strand board (OSB), parallel strip lumber (PSL), and oriented strand lumber (OSL) (Sumardi et al. 2006, 2007, 2013; Ahmad and Kamke 2011; Malanit et al. 2011; Febrianto et al. 2012), have been invented for structural use.
The bamboo industry is the backbone of many rural economies in China, especially in the Zhejiang, Anhui, and Fujian provinces. Studies in the past have focused on large- and middle-sized bamboos, especially Moso bamboo (Phyllostachys pubescens) (Yu et al. 2008; Abe and Yano 2010; Fu 2011). Bamboo can be divided into three groups, based on its outer diameter: large (greater than 8 cm), middle (between 4cm and 8 cm), and small (smaller than 4 cm).
There has been little research regarding the industrial use of small bamboo. It is typically used by farmers for fences (Zhang et al. 2013). The production of small-diameter bamboo is the second largest (Fu 2011), so finding efficient uses for it is essential. In this study, a new composite was developed using small-diameter bamboo-reinforced extruded particleboard (BREP). The reliability of BREP was also studied.
Extruded tubular particleboard manufactured with the wood of ginkgo (Ginkgo biloba L.), a widely cultivated tree in China, was used in all experiments. It was produced by Kaixuan Wood Co., Ltd. in Jiangsu province. Common particles with dimensions of (10 to 20 mm length)×(0.2 to 0.6 mm thickness)×(3 to 6 mm width) and UF were used to manufacture the tubular particleboard. The thickness of the tubular particleboard was 33 mm and the diameter of the tube was 22 mm. The web thickness was 5 mm. The moisture content of the panels was 11%. The solid density and the average density of the particleboard were (0.65±0.04)g/cm3 and (0.28±0.02)g/cm3, respectively. The static bending strength and internal bonding strength of the particleboard with E1 grade performance were 1500 MPa and 0.23 MPa, respectively.
Small-diameter bamboo (P. glauca McClure) of differing ages was harvested from a bamboo garden in Zhenjiang, in the Jiangsu province of China. The height of the bamboo was about 4 m, and the outer diameter was in the range of 10 mm to 25 mm. The bamboo was air dried to a moisture content of 12±1%.
Fig. 1. Distribution and microstructure of vascular bundles and parenchyma cells of hennon bamboo (P. glauca McClure)
One-component polyurethane adhesive (HB S309) manufactured by Purboand Co., Ltd., which reacts with moisture in the air, was used in this study. It is the adhesive used for the production of structural wood products. It has an assembly time of 30 min and a curing time of 75 min.
The outer and inner diameters of the bamboo were measured in two perpendicular directions, and then the average wall thickness was calculated. The longitude of the bamboo was divided into three parts measuring about 1.2 m: top part, middle part, and bottom part. A t-test carried out with the experimental results showed that neither of the outer diameters and the thickness of the bamboo changed after three years of age. Therefore, all the bamboo samples were divided into two groups, young bamboo up to two years old and old bamboo with three or more years of age. The compression strength of the bamboo was tested according to JG/T 199-2007. Before the mechanical tests, all the samples had been put in a testing chamber with 25 ℃ and 65% relative humidity for two weeks to reach a constant quality. The distribution of vascular bundles from the outer to the inner surface and the structure of parenchyma and vascular bundle are shown in Fig. 1.
In order to improve the bonding strength between the panel and the bamboo, the outer skin of the bamboo was removed using a sanding machine. The adhesive was liberally applied to the surface of the sanded bamboo with a specially designed gluing machine. The thickness of the glue layer was about 1 mm. Next, the glue-covered bamboo was inserted into the holes inside the extruded tubular particleboard panels. The panels were stacked horizontally to allow the adhesive to foam and cure. After the bonding, the assemblies were conditioned for 7 days in the standard atmosphere (20 ℃ and 65% relative humidity).
The compression strength of the small diameter bamboo-reinforced extruded tubular particleboard (BREP) was tested. Compression strength was tested because it is the most important property of BREP and it will be employed in the load-bearing component for axial compressive forces. A cross section of BREP is shown in Fig. 2. The length of the samples was 100 mm. The compression tests were conducted in a universal mechanical experiment machine at a pressing speed of 2 mm/min in order to reach failure between 30 s and 90 s. Then the compression strength were calculated by the maximum force divided by the transverse area of the samples without subtracting the hollow structure.
Fig. 2. Cross section of BREP for the compression strength test
RESULTS AND DISCUSSION
Properties of the bamboo
The outer diameters of the young bamboo and old bamboo were 12 to 21 mm and 17 to 24 mm, respectively. The wall thicknesses were 2.1 to 3.1 mm and 2.7 to 3.5 mm, respectively. There was a positive correlation between wall thickness and outer diameter.
Compression tests on the small-diameter bamboo were then conducted (Table 1). The bamboo failed via splitting and buckling of its outer wall. This kind of failure is similar to that of fiber-reinforced composites. When the maximum force was reached, cracks appeared and propagated along the bamboo fibers in the longitudinal direction, resulting in buckling and failure.
Table 1. Results of Outer Diameter, Wall Thickness, Compression Strength, and Maximum Force Testing of Hennon Bamboo (P. glauca McClure)
The most interesting discovery was that the compression strength of this type of small diameter bamboo decreased as the outside diameter increased. This was true for all data for both young and old bamboo, as shown in Fig. 3. In other words, the compression strength of the bottom of the bamboo was smaller than that of the upper parts. This result was unexpected.