Physical and chemical modification of the bamboo species Dendrocalamus asper
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2011
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Melbourne Authors
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Department of Forest and Ecosystem Science
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PhD thesis
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Sugiyanto, K. (2011). Physical and chemical modification of the bamboo species Dendrocalamus asper. PhD thesis, Department of Forest and Ecosystem Science, The University of Melbourne.
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© 2011 Dr. Krisdianto Sugiyanto
Abstract
In spite of its numerous beneficial properties, bamboo is dimensionally unstable and susceptible to attack by fungi and insects. Preservative treatment is therefore regarded as a necessity. Preservative treatment must provide sufficient uptake and even distribution in the culms for adequate protection. The treatability of bamboo, however, is generally poor.
Microwave technology was evaluated for improving wood permeability. Microwave surface modification of radiata pine peeler cores using the PC-1 applicator was studied in this thesis. The temperature distribution, preservative uptake and distribution, and macro-structure changes were evaluated. Results show that the PC-1 applicator allowed microwave energy to modify predominantly the surfaces of peeler cores and significantly improve permeability as a result of the modification.
The PC-1 applicator was suitable for bamboo culm because bamboo is hollow in the centre. The applicator allows microwave energy to heat the culm walls and not specifically heat the centre. The study of energy distribution in this thesis shows that the PC-1 applicator effectively distributed microwave energy onto the surface of the bamboo culm. Temperature distribution on bamboo culm surfaces was similar to those of the peeler cores.
Macro-structure changes to the bamboo culm after microwaving were different from those in radiata pine as the structure of bamboo is different from wood. There is no specific fracturing pattern in the bamboo culm as they contain no ray tissue. Surface treatment of bamboo nodes resulted in checking only occurring in the culm walls. These checks created pathways for liquid to penetrate into the culm walls without necessarily filling up the central hollow section. The use of the PC-1 applicator with microwave energy to modify bamboo nodes was found effective in improving liquid uptake.
Based upon successful chemical modification of wood, bamboo strips were subjected to two chemical modification processes (acetylation and furfurylation). Boiling bamboo strips with acetic anhydride achieved the highest weight percent gain compared to heating in a conventional oven. Bamboo strips boiled in acetic anhydride for an hour gained 16% weight compared to the conventional method (heating in an oven) that gave rise to a 3.5% weight gain after 24 hours of reaction time. Fourier transform spectra analysis confirmed an increase of the number of acetyl groups and a reduction in the number of hydroxyl groups in the acetylated bamboo strips.
For furfurylation of bamboo, soaking, vacuuming and combinations thereof were evaluated. Results demonstrated that soaking bamboo strips for two days after vacuum treatment achieved optimum uptake of furfuryl alcohol solutions and gave rise to an 80% weight gain. Catalyst addition during furfurylation did not increase the weight percent gain. Water was an effective solvent carrier for achieving higher weight gains.
The aim of chemical modification of bamboo strips was to reduce water sorption, improve dimensional stability and weathering performance and enhance natural durability. Results of the study suggest that water sorption of chemically modified bamboo strips was lower than non-modified strips, leading to dimensional stability enhancement. After undergoing accelerated weathering, acetylated and furfurylated specimens were still effectively protected from absorbing water. However, chemical modification did not reduce the greying process during weathering. Chemical modification was also effective in protecting bamboo stakes from decay in a soil bed test.
Side effects of chemical modification included alteration of the mechanical properties and colour changes. These were examined as a measure of the quality of the end product. The results of the analysis suggested that bending stiffness and bending strength of acetylated bamboo strips were slightly decreased. Furfurylated bamboo strips showed a slight decrease in bending stiffness and a slight improvement in bending strength. The colour of chemically modified bamboo was darker and redder than the natural colour of bamboo.
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bamboo, microwave, acetylation, fufurylation, dimensional stability, weathering, colour, strength, durability