* This paper was invited and presented for the International Conference "Challenges for Science and Engineering in the 21 st Century ( June 14-18, 2000 , Stockholm , Sweden ) organized by the International Network of Engineers and Scienctists for Global Responsibility (INES).
Abstract
In order to make full use of bamboo, a fast renewable lignio-cellulosic resource, to replace wood and its excellent mechanical properties, Southwest Forestry College of China has successfully developed a new structural bamboo-based panel composite, i.e. bamboo-based waferboard with its technology and special equipment. Results from the R. & D activities and pilot industrial trial showed that bamboo-based waferboard owns the advantages of high recovery from raw bamboo up to 93%, wide adaptation of almost all the structural species and all the part of the culm and lower cost than the other bamboo-based panel composites such as bamboo-based plywood. Its physical and mechanical properties are better than those wood-based waferboard or oriented strand board, esp. its stronger strength and high elasticity. Its technology and equipment at industrial level is suitable for either simple or fully modernized production, as could be accepted in either developing area,e.g. mountainous area full of bamboo-resources, or developed area, in either small or large scale.
Keywords: bamboo, waferboard, structural panel, technology, equipment
Introduction
Based on the understanding of the relationships among the special characteristics and properties of raw bamboo, the composite technology and the final quality of the panel expected, the R & D group in Southwest Forestry College of China has successfully developed bamboo-based waferboard with its technology and special equipment at industrial level.
▲ Top
1 Characteristics and properties of bamboo
1.1 The gross structure of bamboo
It is well know that the hollow culm with the wall of different thickness, green skin outside, yellow covering inside and knots but no ray across the wall are the notable appearance of the gross structure of bamboo.
The outer green skin is a hard layer with a wax on and in it. It is about 0.1~0.3 mm thick and consists mostly of the thick-wall cell with a little corky cell and silicon cell. The texture of the green skin is fine. The inner yellow covering is a loosen and frailty layer. It is about 0.3~1.0 mm thick and consists mainly of woody stone cell.
The grain along the culm is straight except that at the tangential knot.
All this gross characteristics makes the technology, as welt as the equipment, for bamboo-based waferboard different from that for wood-based one.
1.2 Inhomogeneity of the texture
By the results (Table 1 and Fig.l~Fig.6) from the studying of the texture and physio-mechanical properties of four typical species of thick-growing structural bamboos ( Dendrocalamus giganteus, Dendrocalamus brandisii, Dendrocalamus memhranaceus and Bambusa lapidea ) in Yunnan, density of vascular bundle, fiber coverage, density, moisture content, shrinkage- bending and pressing strength are varied from different species and different part of the culm. i.e. texture and physio-mechanical properties are varied from different species and within a species. For most species, the density of vascular bundle, fiber coverage, density and strength at the top culm are higher than those at the bottom. The tangential shrinkage near the outer skin is much higher than that near the inner skin, and the radial shrinkage is lower than the tangential shrinkage near the outer skin but higher than that near the inner skin. The longitudinal shrinkage is very little.
Compared with those of wood, in general, the strength and elasticity of bamboo is higher, and the density, moisture content and tangential shrinkage are similar. Anyhow, the radial shrinkage is higher than that of wood, because there is no radial cell across the culm wall.
All those texture characierisrics and physio-mechanical properties indicate that the appropriate dimension of the wafer and the inner structure of the board should be properly designed.
1.3 Chemical composition
Higher content of the extractions in bamboo (Table 2), compared with those in wood, makes the composites easy to be destroyed by insects, decay or mold.
2 Technology for bamboo-based waferhoard
2.1 Processing flow
Culm preparation à Wafering à Seasoning of wafer à Glue blending à
Mat forming à Hot pressing à Final trimming à (Sanding for surface treatment)
The above is the processing flow for bamboo-based waferboad, which seems similar with that for wood-based one.
However, since the gross structure and texture of bamboo are different from those of wood, the key technology in the processing line is the watering, which should ensure the proper dimension and quality of the wafer and the full use of the raw bamboo including knot and skin to limit the cost. For this, a set of efficient special equipment for watering has been designed by Southwest Forestry College .
It should be noted that the glue content in bamboo-based waferboard might be lower than that in wood-based ones, due to the lower capability of water absorption for bamboo than that for wood. In general, only 6% urea-formaldehyde resin (UF) or 2% phenol-formaldehyde resin (PF) is required respectively for the standard board internally or externally used.
To avoid the destroying, there are two ways, one is to use phenol formaldehyde resin, and the other is to employ the chemical additives to prevent from insects, epiphyte and mildew.
Since, there is enough strength and elasticity in bamboo, it is not necessary to make the mat orientedly formed, as makes the forming easy.
Taking advantage of thermal-plasticity of bamboo, higher density bamboo-based waferboard with much higher strength and stable dimension can be produced employing proper hot pressing technology.
Extra attention should be paid to the tool and cutting conditions for the silica inside the bamboo wall, esp. in the outer skin.
To meet a various users, waferboard from bamboo can be covered with the surface materials commonly used for wood-based composites, e.g. wood veneer, resin-immerged paper and etc.
▲ Top
2.2 Properties of the product
The final quality property of the bamboo-baaed waferboard from the pilot industrial trial, employing the above technology and using Yunnanese structural bamboo, whose breast-height diameter is about is about 8 cm, and the average thickness of the wall is about 6 mm, is showed in Table 3. From Table 3, we can see that the modulus of rupture (MOR), the modulus of elasticity (MOE) and the internal bonding strength (IB, with 7% UF and 3% PF) of the bamboo-based waferboard are higher than those of wood-based oriented strand board whose structure is similar with that of waferboard. The thickness swelling is lower, due to the original wax in the wall material, than that of wood OSB, which means the better dimension stability. And the screw holding power on both plane and side are much higher too, owing to the special texture and strong strength of the raw bamboo. All these show that the quality property of bamboo-based waferboard is better than wood- based one and it can be used everywhere esp. for construction, packages, vehicles and etc. There is no doubt that it is a good substitution for wood ones in order to save the timber resources.
3- Economy Analysis
Table 4 shows the cost and profit (in Chinese price system) from a factory whose designed annual output of bamboo-based waferboard is 10.000 M 3 . Obviously, the critical factors to influence the cost and profit are the cost for raw bamboo, resin and fixed assets. If the recovery of raw bamboo is only 50%, like that of bamboo-based plywood, the cost per cubic meter rises to 203.3 USD/M 3 .
In general, less than 800 kilogram of raw bamboo, whose moisture content should be below 20 %, can support 1 M 3 of the panel. Then, if 6.000 kilogram of bamboo comes out from 1 ha. Bamboo forest, only about 1,700 ha. bamboo forest is sufficient with the raw bamboo to supply a plant of 10,000 M 3 product.
Anyway, the scale of a factory should be chosen according to the bamboo resources around. Even a small scale of a factory, which is suitable for the area lacking of large resource or investment, with only 5,000 M 3 or less output a year, a sound profit still can be made. If the scale is large enough, for instance, up to 100,000 M 3 a year, there is a greater profit, of course, from per cubic meter of the panel.
▲ Top
4- Comparison with the other bamboo-based panel composites
There are bamboo-based plywood laminated with the woven-mat "veneer", flatten-wall "veneer", strip "veneer" or curtain "veneer one", bamboo-based laminated strip parquet and bamboo-based particleboard and fiberboard in the world, mainly in China. All these bamboo-based panel composites are made just simply employing the technology and equipment for wood-based ones, ignoring the special biological characteristics and original physio-mechanical properties of raw bamboo, so that the quality of the products is not stable and the cost is high. In fact, lacking of special and efficient equipment in set, most of the factories are still in under-developing stage.
The advantages of that bamboo-based plywood are the strong strength and high elasticity due to the original property of raw bamboo, so that they are good panels for structural uses to replace wood ones. But the disadvantages for them are the uneven surface as well as the inner structure and high cost due to the strict requiring of the pole size (i.e. the strict requiring of the species and part of the pole with only thick wall), low recovery of the raw bamboo (averagely below about 40%) and high consumption of the glue. The high cost makes the manufactures make little profit.
Bamboo-based particleboard and fiberboard overcome such shortcomings of bamboo-based plywood. However, they could not exploit the strong strength and high elasticity originally from raw bamboo, because the unit for composition, either particle or fiber is too small to exert the original excellence. They can not be used as structural panel composites. The only significance for them is, as a raw material, to replace part of wood.
Compared with those bamboo-based panel composites, bamboo-based waferboard owns the following advantages:
wide adaptability for varies structural bamboo species with the only requirement that
minimum wall thickness should be over 2 mm;
high recovery from the raw bamboo up to 93%;
simple technology and processing line, but suitable the special biological characteristics and the properties of bamboo;
full exploitation of the original strength and elasticity of raw bamboo;
better quality properties than those of wood-based ones;
adjustable physical and mechanical properties by adjusting the density of the board (Fig.7);
easy for small or large scale industrial production with lower cost than any other bamboo-based structural panel composite.
5- Summary and suggestions
What described above is the answer of "How does it work, bamboo-based waferboard". However, the active answer should be from a lot of active manufactures. Here, in China , esp. in Yunnan province where is full of bamboo resources, several plants are in the way, based on the pilot technology and equipment developed by Southwest Forestry College, Any cooperation, either in China or in the world, is welcome.
Let's make efforts to promote the industry of bamboo-based panel composite, which will benefit, there is no doubt, the whole world not only in economy but also in society and ecology.
▲ Top
6- Literature cited
1. Li Zhengli, Xin Zichen, 1961. Anatomical observation and comparison of 10 Chinese bamboo. Journal of Botany, 9(I):76~79
2. Fang Wei et al, 1989. Anatomical comparison and study on part of Chinese bamboo (Part 2). Collection of Bamboo Research,8(4): 1 11
3. Zhang Hong-Jian. Zhao Li, 1990. Study on the finishing technology of woven-mat bamboo plywood. Jour. Of Southwest Forestry College . 10(2): 215222
4. Xian Kejuan el al, l990.Microstructure and its relationship with the mechanical properties of bamboo. Collection of Bamboo Research, 9(3): 1023
5.Zhou Fangchun, 1991. Report of the constitution and properties of bamboo. Bamboo Research. 11(2):8
6. Hamdan Husain, Latif Mohmod, 1992. Effects of physico-anatomical characteristics on machining properties of Malaysian bamboos. Bamboo Journal ( Japan ). (10):56'66
7. Yao Xishen et al, 1992, Micro structure of the main species of bamboo in China . Dalian Publishing House
8. International Tropical Timber Organization and Chinese Academy of Forestry, 1992. Proceedings of International Symposium on Industrial Use of Bamboo, Beijing , pi99-209
9. Zhang Qisheng, 1995. Industrial utilization of bamboo in China . Publishing House of Chinese Forestry,27~46
10. Zhang Hong-Jian, 1995. Development of bamboo-based composites in the world. Proceedings of the Invited Papers for IUFRO 20th World Conference ( Finland ):397
11. Zhang Hongjian, Ye Xi, Li Jim. 1995. Research on main processing parameters of bamboo-based waferboard. Journal of Southwest Forestry College . 15(4):56~-60
12. Zhang Hongjian. Wang Wenjiu and Du Fan, 1998. Chemical composition of 4 typical thick-growing woody bamboos in Yunnan . Yunnan Forestry Science and Technology, (4):75~78
13. Zhang Hongjian, Zhang Fuxin and Yuan Yongsheng, 1998. Adaptability of bamboo-based waferboard to the biological characteristics and properties of bamboo. China Forestry Products Industry. 25(6):1~-4
14. Zhang Fuxing, Zhsng Zhifeng, Yuan Yongsheng and Zhang Hongjian, 1999. Watering Conditions for Bamboo- Based Wafer. China Wood Industry, 13(2): 10-12
15. Zhang Hong-Jian. Du Fan and Zhang Fuxin. 1999: Relationships between the texture and main physical and mechanical properties of four typical thick-growing structural Bamboos in Yunnan . Forestry Science, 35(4):66-~70
Corresponding address of the group lender
Hong-Jian Zhang,
Professor of the Faculty of Forest Industry
Director of Wood Products Research Institute
Southwest Forestry College
POB 126, Bai Long Si, Kunming , China , 650224
Tel: 86-871-3863014, 3862733
Fax:86-871-3863214
E-mail: hjzhang@public.km.yn.cn
Brief Introduction of the Inventor
Mr. Hong-Jian Zhang, born on September 6 of 1952 in Shanghai , master of engineering from Beijing Forestry University , is the director of Wood Products Research Institute (WPRI) and professor of the Faculty of Forest Engineering (FEE) of Southwest Forestry College (SWFC) of China . He is also the first-grade national and provincial leading fellow in science and technology, vice chairman of Forest Products Associate of Yunnan, member of Supervision Committee of Wood Industry of China Forestry Ministry, vice chairman of National Bamboo Processing Committee, council member of National Wood Industry Associate and the expert member of Expert Group of Renewable Resources Research ofUNEP Working Group on Suslainable Products.
He has being dealt with teaching and R & D work in the field of Wood Science and Technology, esp. of the technology of wood and non-wood based panel composites and their finishing as well as the equipment since 1976. He has lectured more than II of the causes, such as "Technology of Wood-Based Composites" and "Principle of Cutting and Knives for Wood". As a group leader or principal worker, he accomplished 7 technical innovations (such as an automatic saw sharpener), 4 feasibility research and design projects of wood- or bamboo-based composite plants, 4 patents about furniture, bamboo-based composites and their equipment, more than 10 R & D projects (e.g. "Finishing technology of woven-mat bamboo plywood", "Technology of PF-MDF and its finishing". "Technology of impregnated laminated veneer lumber ( Canada )", "Compression control of poplar LVL ( Canada )". "Study of the further utilization of bamboo resources in Yunnan", "Technology and special equipment of bamboo-based waferboard", "Technology of bamboo-based parallel strand lumber", "Bondability of accelerated weathered CCA treated southern pine (USA)", "Technology of reconstituted wood products reinforced with resin") and 4 research programs about high education including "Strategy of high education of forestry in market economic system of China". He has been awarded more than 10 times by the government for his excellent achievements in science and technology. As a visiting scientist or cooperator, he visited more than 20 countries to do collaborative R & D work, or to make technical visits or lectures. He has got more than 60 publications, in which over 10 were international-published.
▲ Download complete version of the paper including figures and tables. Click Here
