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Bamboo potential as a worldwide source of fibres for composite applications

Bamboo has manifested itself as a viable alternative to slow growing hardwood. The reason is that bamboo grows really fast, is strong and abundantly present. But not only bamboo 'wood' is interesting from a materials point of view. The bamboo fibres have a Young’s modulus that is up to three times higher than that of the bamboo culm itself, and because they are light, their specific properties can rival with glass fibres. During previous research at KU Leuven, a purely mechanical extraction procedure was developed, focussing on the Guadua angustifolia Kunth, the most important bamboo species of South America. This enabled the extraction of high quality bamboo fibres. In search of new insights, this doctoral thesis gives an answer to the following research questions:

Bamboo has manifested itself as a viable alternative to slow growing hardwood. The reason is that bamboo grows really fast, is strong and abundantly present. But not only bamboo 'wood' is interesting from a materials point of view. The bamboo fibres have a Young’s modulus that is up to three times higher than that of the bamboo culm itself, and because they are light, their specific properties can rival with glass fibres. During previous research at KU Leuven, a purely mechanical extraction procedure was developed, focussing on the Guadua angustifolia Kunth, the most important bamboo species of South America. This enabled the extraction of high quality bamboo fibres. In search of new insights, this doctoral thesis gives an answer to the following research questions:

- Which bamboo fibres are most suitable for use in composites and how should they be selected?

- What are the unique selling points of bamboo fibres for composites?

- How can we most optimally utilize the bamboo plant for applications in composite materials?

This research has shown that the technical fibre’s Young’s modulus of all evaluated species is quite comparable. The strength however is 16 – 44 % lower for species grown in Europe. For species grown in Europe, the season of harvesting showed to play a role as well, and autumn or winter harvest is recommended, since this resulted in the highest extraction yield and mechanical properties of the fibres. This is likely related to the moisture content of the material. One key selling point of bamboo fibres, is their ability to withstand moist environments. The hygroscopic behaviour of bamboo fibre reinforced composites was studied both for static and cyclic moisture conditioning. Static conditioning revealed that bamboo fibre reinforced composites retain a high Young’s modulus in moist conditions and even increase in tensile strength: a drop of 25 % in Young’s modulus at 30 °C and 80 % relative humidity was found compared to the fully dried state (dry fibre Young’s modulus ~55 GPa). In comparison, flax fibre reinforced composites, showed a decrease of 55 – 60 % in Young’s modulus under the same conditions. This different behaviour is linked to the chemical composition of the fibres, which consists out of different constituents that each react differently to moisture. This was investigated by studying the glass transition temperature of the composites. It was demonstrated that fibres containing a high lignin content (like bamboo) show no change in glass transition temperature when exposed to a moist environment. Lignin a 3D polymer holds the structure together and limits the plasticisation due to water. Cyclic conditioning showed that the cleanliness of the extracted fibre (remaining parenchyma tissue) plays a role in the long term behaviour of the composite. It is concluded that bamboo fibres are interesting to consider when designing natural fibre composites that need to withstand moist environments, though care should be taken in extracting and cleaning the fibres.

Which bamboo fibres are most suitable for use in composites and how should they be selected?

What are the unique selling points of bamboo fibres for composites?

How can we most optimally utilize the bamboo plant for applications in composite materials?

This research has shown that the technical fibre’s Young’s modulus of all evaluated species is quite comparable. The strength however is 16 – 44 % lower for species grown in Europe. For species grown in Europe, the season of harvesting showed to play a role as well, and autumn or winter harvest is recommended, since this resulted in the highest extraction yield and mechanical properties of the fibres. This is likely related to the moisture content of the material. One key selling point of bamboo fibres, is their ability to withstand moist environments. The hygroscopic behaviour of bamboo fibre reinforced composites was studied both for static and cyclic moisture conditioning. Static conditioning revealed that bamboo fibre reinforced composites retain a high Young’s modulus in moist conditions and even increase in tensile strength: a drop of 25 % in Young’s modulus at 30 °C and 80 % relative humidity was found compared to the fully dried state (dry fibre Young’s modulus ~55 GPa). In comparison, flax fibre reinforced composites, showed a decrease of 55 – 60 % in Young’s modulus under the same conditions. This different behaviour is linked to the chemical composition of the fibres, which consists out of different constituents that each react differently to moisture. This was investigated by studying the glass transition temperature of the composites. It was demonstrated that fibres containing a high lignin content (like bamboo) show no change in glass transition temperature when exposed to a moist environment. Lignin a 3D polymer holds the structure together and limits the plasticisation due to water. Cyclic conditioning showed that the cleanliness of the extracted fibre (remaining parenchyma tissue) plays a role in the long term behaviour of the composite. It is concluded that bamboo fibres are interesting to consider when designing natural fibre composites that need to withstand moist environments, though care should be taken in extracting and cleaning the fibres.

Date:1 Oct 2014  →  19 Dec 2018
Keywords:natural fibres, composite, durability, bamboo
Disciplines:Ceramic and glass materials, Materials science and engineering, Semiconductor materials, Other materials engineering
Project type:PhD project