Effect of Microwave Treatment on Density of Gigantochloa Scortechinii (Semantan) Bamboo Strips K. Nordin1,2*, O. Sulaiman1, and M.A. Jamaludin2 1
School of Industrial Technology, Universiti Sains Malaysia (USM) 11800 USM, Pulau Pinang, Malaysia 2 Faculty of Applied Sciences, Universiti Teknologi MARA (UiTM) 40450 Shah Alam, Selangor, Malaysia *Email:
[email protected]
Abstract. This study evaluated the effect of microwave treatment on density of Gigantochloa scortechinii (Semantan) bamboo strips. Gigantochloa scortechinii bamboo specimens were subjected to microwave radiation with varying power intensities and durations. Six combinations of power intensities and time were used in this study. After the microwave treatment, oven-dry density of the bamboo specimens was determined in accordance with ASTM D 2395-93 and comparison was made with untreated specimens. The results in general showed that density increased when exposing bamboo to microwave fields of varying intensities. Microwave combinations of 500 watts and 6 minutes exposure time was found having the greatest effect on bamboo internodes with density increase of about 23.3%. At medium power intensity (430 watts), increasing exposure time from 6 minutes to 10 minutes generally increased bamboo internodes density by 11.6%. However, at medium-high power intensity (500 watts), increasing exposure time did not contribute to larger percentage of density increase. Keywords: Bamboo; Density; Microwave treatment PACS: N 87.85.J
1. INTRODUCTION In view of the depleting supply of quality timber coupled with price factors, utilization of bamboo as an alternative to timber has markedly gain interest nowadays among researchers and timber users in the world as well as in Malaysia. Bamboo utilizing industries in Malaysia generally comprise of small mills producing product such as chopstick, poultry cages, vegetable basket, and skewer where usage of low technology with labor intensive is prominent. Bamboo utilization for furniture making, on the other hand is restricted to solid bamboo in round form of limited design and with simple construction procedures due to lack of fundamental knowledge and information. In order to make bamboo a more versatile and value-added material for furniture and other products, its utilization in the form similar to lumber need to be promoted. Utilization of bamboo strips in glued-laminated form is seen to have great potential to supplement timber, hence reduce dependency on a particular timber species for furniture such as Malaysian CREDIT LINE (BELOW) TO BE INSERTED ON THE FIRST PAGE OF EACH PAPER oak (formerly known as rubberwood). CP1217, International Conference on Advancement of Materials and Nanotechnology 2007 (ICAMN 2007) edited by W. T. Wui, N. Kamarulzaman, R. Y. Subban, K. Noorsal, M. H. Saleh, R. Ibrahim, R. Idris, I. Zainol, and F. A. Zakaria © 2010 American Institute of Physics 978-0-7354-0760-2/10/$30.00
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Gigantochloa scortechinii, commonly known as Semantan bamboo, has high industrial usage potential and being the most promising alternative materials to supplement timber in Malaysia. The suitability of Gigantochloa scortechinii bamboo
for glued-laminated products will very much depend among others upon its physical properties. Density is an important factor that affects bamboo behavior, to a larger
extent the physical and mechanical properties of the culm.
Microwave treatment is often applied to some wood species to improve dimensional stability [1]. Emergent interest to apply novel technology such as microwave technology on Gigantochloa scortechinii has prompted this study to be initiated. It was the objective this study to investigate the effect of microwave treatment on density of G. scortechinii.
2. EXPERIMENTAL METHOD Thirty culms of 4-years old Gigantochloa scortechinii bamboo were harvested from Bentong, Pahang. In order to reduce variability on sampling and to concentrate more on the effect of microwave, only the bottom part of bamboo were selected for the study. The average pole length of the bottom part of the culms was 1.85 m with an average of 5.5 internodes per pole. The average internodes length, diameter, and culm wall thickness were 34.3 cm, 24.6 cm, and 9.72 mm respectively. The culms were split into eight and the skins were then removed. The culms were further trimmed into smaller sizes in order to fit specimens into domestic microwave oven. They were later planed on both sides to remove some fractions of the outer and inner layer and were left to air-dry until it reached moisture content of approximately 60%. Gigantochloa scortechinii bamboo specimens were subsequently subjected to microwave radiation using domestic microwave oven operating at a frequency of 2.45 GHz with varying power intensities and durations. Six combinations of power intensities and time (650watts for 3 minutes; 500 watts for 6 minutes; 500 watts for 10 minutes; 430 watts for 6 minutes; 430 watts for 10 minutes; 250 watts for 12 minutes) were used in this study. After the microwave treatment, specimens were cut into dimensions of 20 mm (width), 20 mm (length) and 5 mm (thickness). Ten specimens for relative density measurement were randomly taken from the internodes of each microwave treatment variant giving a total of seventy specimens. For comparison purposes, specimens from nodes were also taken. The specimens were then placed in the conditioning chamber at temperature of 200C and relative humidity of 65% for at least three weeks prior to density determination. The oven-dry density of the bamboo specimens were determined using method of water immersion as stipulated in the standard test methods for specific gravity of wood and woodbased materials ASTM D 2395-93 [2]. Comparison of the average density between the internodes and nodes of the specimens that were subjected to different microwave treatment were made as well as with the untreated specimens.
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3. RESULTS AND DISCUSSION The mean density of internodes and nodes of microwave modified Gigantochloa Figure 1 illustrated the effect of microwave treatment variant on density of internodes and nodes of Gigantochloa
scortechinii bamboo strips is given in Table 1. scortechinii bamboo strips.
The results in general showed that density increased when exposing bamboo to microwave fields of varying intensities regardless of internodes or nodes. However, for specimens with nodes that were subjected to microwave combinations of 650 watts and 3 minutes exposure time, exceptional result was encountered with a decreased in density of about 7.55% from the untreated specimens. The internodes density was observed to be in the range of 633 kg/m3 for untreated bamboo strips to 782 kg/m3 for the treated ones while the nodes density was measured to be in the range of 663 kg/m3 for the untreated bamboo strips to 742 kg/m3 for those that were microware treated. Microwave combinations of 500 watts and 6 minutes exposure time was found having the greatest effect on bamboo internodes with density increase of about 23.3%. This was followed by microwave combinations of 650 watts and 3 minutes exposure time with density increase of 17.3%. At medium power intensity (430 watts), increasing exposure time from 6 minutes to 10 minutes generally increased bamboo internodes density by 11.6%. However, at medium-high power intensity (500 watts), increasing exposure time did not contribute to larger percentage of density increase. TABLE 1. Mean density of internodes and nodes of microwave modified Gigantochloa scortechinii bamboo strips Microwave variant No MW MW1 MW2 MW3 MW4 MW5 MW6
Density (kg/m3) Internodes 633 (101) 742 (72) 782 (100) 655 (100) 661 (161) 726 (132) 719 (102)
% inc. / dec. n.a 17.28 23.58 3.48 4.50 14.68 13.69
Nodes 663 (98) 613 (110) 728 (101) 724 (65) 711 (70) 693 (102) 742 (53)
Note: Values in parentheses denote standard deviation n.a.- not applicable 231
% inc. /dec. n.a -7.55 9.81 9.24 7.22 4.61 12.02
900 800
Density (kg/m 3)
700 600 500
Internodes
400
Nodes
300 200 100 0 No MW MW4
MW5
MW2
MW3
MW6
MW1
Microw ave variant
FIGURE 1. Effect of different microwave treatment variant on the density of internodes and nodes of Gigantochloa scortechinii bamboo strips.
The trend for nodes specimens however was somewhat different. Microwave combinations with the lowest power (250 watts) but longer exposure time (12 minutes) were found giving the greatest effect with density increase of about 12.0% followed by microwave combinations of 500 watts and 6 minutes exposure time with density increase of 9.81%. For nodes, it was also observed that regardless of microwave power intensity being applied (430 watts or 500 watts), increasing exposure time from 6 minutes to 10 minutes, did not increase further the density of the Gigantochloa scortechinii bamboo strips. The occurrence of density increase of Gigantochloa scortechinii bamboo strips when subjected to microwave irradiations could be possibly be due to microwave energy generated during the microwave process that is converted into heat which is capable to create steam pressure in the bamboo cells. The pressure exerted towards the bamboo cells subsequently will force the cells wall to expand within the bamboo structure resulting in the increase in the volume of solid materials.
4. CONCLUSION In conclusion, this study has established that by exposing Gigantochloa scortechinii bamboo strips to microwave fields of varying intensities, the density of the bamboo strips could be increased regardless of internodes or nodes. Increase in density of the bamboo materials by novel technology such microwave technology could perhaps increase other properties as well. Further investigation on the effect of microwave treatment on other properties of such as dimensional stability, surface roughness, wettability, mechanical properties, and gluing properties are currently being undertaken to determine the optimum microwave treatment conditions for performance improvement. Thus, conclusive remarks can only be made once the entire project is completed. 232
REFERENCES 1. 2.
Anonymous “Wood Handbook—Wood as an engineering material”. Gen. Tech. Rep. FPL– GTR–113. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory, 1999. ASTM D 2395-93“Standard test methods for specific gravity of wood and wood-based materials”. American Society for Testing and Materials (ASTM). Philadelphia, PA, 1997.
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