Naresworo Nugroho dan Naoto Ando

Development of structural composite products made from bamboo II: fundamental properties of laminated bamboo lumber

By   Naresworo Nugroho  dan  Naoto Ando 

Graduate School of Agricultural and Life Sciences, The University
of Tokyo, Tokyo 113-8657, Japan

Present address:
1Wood Engineering Laboratory, Department of Forest Products Technology,
Faculty of Forestry, Bogor Agricultural University, PO Box
168, Kampus Darmaga IPB, Bogor 16001, Indonesia
Tel. +62 251-621285; Fax +62-251-621256
e-mail: naresworo@yahoo.com

Part of this research was presented at the 49th Annual Meeting of the
Japan Wood Research Society, Tokyo, April 1999, and at the Pacific
Timber Engineering Conference, Rotorua, New Zealand, March 1999

J Wood Sci (2001) 47:237-242 ;  The Japan Wood Research Society 2001 

Download file:  b161 

Abstract

This experiment explored the technical feasibility of using bamboo zephyr mat with pre-hot-pressed treatment for the manufacture of laminated bamboo lumber (LBL), which is similar in construction to that of laminated veneer lumber (LVL). Six LBL boards (made from four-ply bamboo zephyr mats) with approximate dimensions of 2 • 42 x 42 cm were fabricated using resorcinol-based adhesive. The experimental design involved three combinations of layered structures (types I, II, and III) and two LBL loading positions (H-beam and V-beam) during the bending test. These materials were then compared to ordinary LVL. Results indicated that the bending properties (moduli of rupture and elasticity) of LBL were comparable to those of LVL, but there was no significant effect on the physical and mechanical properties among the three types of LBL beam. Interestingly, orienting the glue line to the vertical direction (V-beam) could maximize the ultimate strength of the LBL.

Key words Laminated bamboo lumber 9 Bamboo zephyr mat – Pre-hot-pressed. Bending properties

Introduction

Recently, the use of bamboo has been expanded to include its manufacture into various structural composite products.1-4 Previous studies showed that moso bamboo’s favorable stiffness and strength properties make it a promising material for the manufacture of various engineered composite products, such as bamboo zephyr board. 5

Elements in the composite product, such as a sheet/ mat, should be wide to facilitate handling during the manufacturing process; the elements should also be long along the grain to retain the strength of the fiber. Considering these two important conditions, it is concluded that the bamboo zephyr strand mat is suitable for constructing a new structural composite product. Zephyr is a sheet material of a fibrous net-like structure prepared similarly to scrimber, which was developed in Australia. 6,7 The process involves progressive crushing of materials through several sets of rollers until a continuous fibrous sheet is obtained, 8,9

Composite products composed of these zephyr-type elements and processed by hot pressing have a large amount of thickness swelling caused by water. Additionally, there is a large degree of unevenness of the surface of the board, especially thin boards, and many spaces among the elements, causing a weakening of the bonding strength between them and a poor appearance of the products. Considering these facts, the bamboo zephyr elements were pretreated by a hot-press method to reduce these problems. This study explored the technical feasibility of bamboo zephyr mats with pre-hot-pressing treatment for the manufacture of laminated bamboo lumber (LBL).

Materials and methods

Bamboo zephyr mat production with hot-pressed treatment

Mature moso bamboo culms (Phyllostachys pubescens Mazel), with an average base diameter of 13.7-18.4cm and a thickness of 9.8-12.3 ram, were collected from Kagoshima Prefecture, Japan. The density of the bamboo was about 0.74 g/cm 3. Each culm was split into quarters and was passed  through a roller press crusher five times to make a bamboo zephyr strand mat.

Pretreatment by hot pressing the bamboo zephyr mat was done by changing the condition of the temperature of the hot platens and the pressing time. For this study, bamboo zephyr in green condition (with approximate 30% moisture content) was hot-pressed for 6min at hot platen temperatures of 100 ~ 130 ~ 150 ~ and 180~ at a pressure of 60kgf/cm 2. The average initial thickness of the bamboo zephyr before it was hot-pressed was 11mm; five specimens were tested for each condition. Bamboo zephyr mat from moso bamboo after the pre-hot-pressed treatment is seen in Fig. 1.

Fig. 1. Bamboo zephyr mat from moso bamboo after pre-hot-pressed
treatment. From left to right: treatment at temperatures of 100 ° 130°
150° and 180° respectively

Based on the above result, the mats were then placed between platens of a 45 • 45 cm electrically heated hydraulic laboratory hot-press and flattened using a pressure of 60kg/cm 2 at 150~ for 6min. A distance bar was used to control the bamboo zephyr mat thickness at 6mm. All bamboo zephyr mats were passed through a planer to remove most of the inner and outer (epidermal) layers until a thickness of 5 mm was reached.

LBL production

Before this manufacturing process, a preliminary experiment was carried out on the glue bond made between the bamboo zephyr mats of LBL (two-ply) with varying application rates for the glue. This experiment involved two factors: three combinations of the layer structure (face-face, face-inner, and inner-inner layers) and three of glue spread rates (240, 300, and 360g/m 2 single glue line). Five 5 • 5cm specimens prepared from these products were then used for each treatment condition.

Six LBLs (four layers) with approximate dimensions of 2 • 42 • 42cm were fabricated using resorcinol-based adhesive (D-33; Oshika Shinko Co.) The experimental design involved three combinations of the layered structure (types I, II, and III), as illustrated in Fig. 2. The adhesive with a glue spread rate of 300g/m 2 was then applied to the bamboo zephyr mat by hand brushing. After glue spreading, four layers of bamboo zephyr mats were prepared and coldpressed at a pressure setting of 20kg/cm 2 at room temperature for 12h.

Fig. 2. Combination of layered structure on laminated bamboo lumber
(LBL). Light color, inner layer; dark color, face layer

Testing properties

The LBL specimens were conditioned at a controlled ~emperature of 25~ and 65% relative humidity ,~RH) for at least 2 weeks. All the boards were trimmed and cut into various test specimens as follows: 2 x 2 • 32cm for static bending tests: 5 • 5cm for internal bonding (IB) strength tests: 5 • 5 cm for thickness swelling (TS) and water absorption (WA) tests: and 5 x 10cm for linear expansion (LE) determination

The sample materials were tested for bending properties [modulus of rupture (MOR) and modulus of elasticity (MOE)], [B strength, and dimensional stability (WA, TS. and LE ). Tests were performed on the specimens in accordance with JIS A-59081 and JIS Z-2113. 11

For static bending the specimens were randomly separated into two groups with five replications for each treatment: one group for a load applied to the specimens with a horizontal glue-line (H-beam) and the other for load specimens with a vertical glue line (V-beam). Three test specimens were prepared by each treatment for the IB, TS. WA. and LE tests. For dimensional stability, the specimens were submerged horizontally under 25mm of distilled water. After 2-h and 24-h submersions the spemmens were suspended to drain for 10min to remove the excess water, and the weight and thickness of each specimen were determined immediately.

Results and discussion

Effect of the pre-hot-pressed treatment

Okuma and Dongn have done research on the effect of hot-pressing chopstick material. They found that a pressing

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