Technical information & background

Abstract - 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 fibers have a Young’s modulus that is up to three times higher than the bamboo culm itself, and because they are light, their specific properties can rival with glass fibers. Bamboo is native to almost all continents, mostly tropical and sub-tropical climate regions, but some bamboo is native to temperate climate zones and can therefore adapt to grow in European regions. It is a very diverse plant, with over 1600 known species. These advantages give bamboo the potential to become a prominent fiber in the domain of natural fiber reinforced composites.  '

Delphine Depuydt KU Leuven 2018 '

 

USP: No chemicals are used. Optimal preservation mechanical properties

Bambooder fiber extraction method

Technical bamboo fiber

Introduction - In light of the growing awareness of environmental problems, especially the use of petroleum-based products, natural fiber composites are emerging as a viable alternative to synthetic fibers. The specific mechanical properties of natural fiber composites can rival those of traditional materials, especially glass fiber composites. 

Typical sttffness values (Young's modulus) for natural fibers compared to glass fibers, at standard environmental conditions.

Design

Fiber categories - The natural fibers can be divided into three categories: plant, animal and mineral fibers. The plant fibers are composed out of: straw (wheat, rice), grass (bamboo, bagasse), bast (flax, hemp, jute), fruit (coir, kapok), leaf (abaca, banana, sisal), seed fibers (cotton) and wood fibers. Bamboo belongs to the grass family Poaceae, where the tribes of the woody bamboos, Bambuseae and Arundinarieae, and more precise the ‘giant bamboos’ (that can grow to 30 m with a diameter of up to 30 cm are of special interest for composite applications. Bamboo genera that have been identified as potential source for fibre extraction due to their anatomical characteristics and their common use in traditional construction are: Bambusa, Dendrocalamus, Gigantochloa, Guadua and Phyllostachys. 

Bamboo has a few advantages over other natural fibers, beside the fact that it grows fast, for some species up to 21 cm a day, it is abundant and can help with the reforestation of degraded land. It is estimated that 15 million hectare of ‘giant bamboo’ is present, which can be used for fibre extraction. It is a very diverse plant, since over 1600 species are known and spread worldwide. Bamboo is native to all continents except for Antarctica and Europe. The natural distribution of the bamboo can mostly be found in the tropical and sub-tropical climate regions, but some bamboo is native to temperate climate zones and can Selection and caracterisation of bamboo fibers therefore adapt to grow in European regions.

 

INBAR compared the CO2 sequestration of Ma bamboo (Dendrocalamus latiflorus) and an Eucalyptus plantation and found that they have comparable carbon sequestration capacity as long as the bamboo forest is managed and that for both species valuable products are made that fixate the carbon. The accumulated carbon content after 10 years is 128 t C/ha for Ma bamboo and 115 t C/ha for Eucalyptus. 

Bambooder has developed a process to extract long bamboo fibers. This is a purely mechanical extraction technique which results in the extraction of long, largely undamaged fibers. The question raised how well fibers of other bamboo species are suited for composite applications. For flax and hemp fibers, a variation in mechanical properties is found depending on the species. For flax, Young’s moduli between 49 – 68 GPa are reported and for hemp between 20 – 45 GPa. 

The image above gives an exploded hierarchical view from culm to microfibril, demonstrating the multicomponent structure of a bamboo plant. The plant is optimized in order to withstand bending induced by external factors like wind, with a minimum of material. The hollow culm is reinforced by nodes, where the nodal diaphragm gives extra stiffness to the culm and helps to prevent buckling. The nodes appear with a certain regularity along the height of the culm. In the cross section of the culm, vascular bundles, containing the bamboo fibers, can be distinguished. The vascular bundles are longitudinally aligned in the culm and surrounded by a matrix of parenchyma tissue. In a vascular bundle the phloem, protoxylem and metaxylem, having the function of conducting tissue are present. 

Generally the metaxylem vessels are attached by four fiber sheaths (sclerenchyma sheaths), though some species have additionally isolated fiber strands that carry out the function of mechanical support. The concentration of the vascular bundles increases from the inner part to the outer part of the culm, making bamboo a functionally graded material, perfectly adapted to high specific bending stiffness and strength.

 

The image gives an overview of the 4 most common types. Differences can be found in the presence of additional isolated fibre strands. Both the fibre sheaths and the strands are referred to as technical fibers once extracted from the plant. Their length is equal to the inter-nodal length, since in the node, the longitudinal orientation of the fibers is lost as they get entangled. Typical length and diameter of the technical fibers is 20 – 35 cm and 90 – 280 μm respectively. 

Each technical fiber (or fiber bundle) consists out of a smaller building unit, named elementary fibers (a single plant cell). On a cross sectional view they are recognized by their hexagonal and pentagonal shapes, with a small hole, the lumen in the middle. In between the elementary fibers, the middle lamellae are found, the ‘intercellular glue’ that binds the cells together. The typical diameter and length for elementary fibers ranges from 10 – 40 μm and 1.0 – 4.3 mm respectively with lumen sizes in between 2 – 20 μm.

'Delphine Depuydt, KU Leuven 2018 '

Partners

Validation - Together with our partner Koninklijke Van Wijhe verf (Wydo) & KU Leuven we develop and validate our products.

Fire resistant / retarding - For our customers we develop products that requires their demands. In Automotive fire resistant or retarding is very important. Bambooder has developed a 100% biobased + fire resistant composite. 

Moist - Bamboo as a unique fiber for composites in moist environment.

Sorption behaviour of bamboo fiber reinforced composites, why do they retain their properties? 

The influence of moisture on the mechanical properties of bamboo fiber reinforced composites was assessed both for static and hygroscopic cyclic conditioning. Static conditioning revealed that bamboo fiber reinforced composites show a smaller decrease in Young’s modulus with moisture content than other natural fiber reinforced composites such as for example flax based composites. The behaviour is explained by the chemical composition of the fiber and demonstrated by dynamic mechanical analysis that illustrates how composites made with fibers of high lignin content retain their glass transition temperature in moist conditions. The influence of hygroscopic cycling was also assessed, with emphasis on the influence of the remaining parenchyma on the fiber. Clean fibers, are beneficial for the long term behaviour, with less deterioration in properties. Porosity analysis was performed via X-ray computed tomography to provide insight into the material structure of the composite and the effects of hygroscopic cycling. 

Adapted from ‘D. Depuydt, J. Soete, Y.D. Asfaw, M. Wevers, J. Ivens, A.W. van Vuure, “Sorption behaviour of bamboo fiber reinforced composites, why do they retain their properties?”, Submitted 2018’ 

Fiber competitionThe graphics show the stiffness (Young’s modulus) of different natural fibers compared to glass fibers. It can be seen that flax, bamboo, hemp and kenaf are amongst the stiffest fibers. When designing a structure it is common to compare the mechanical properties for an equal component weight.

Since natural fibers have a very low density (~1.4 g/cm³), they are competitive with other materials, which is shown in the figure where the specific properties of different cross-ply composites reinforced with carbon, glass, flax and bamboo fibre are compared to more traditional materials like steel and aluminium. It can be seen that regarding specific stiffness and strength, carbon fiber reinforced composites outperform all the other materials. From the same graph it is also noted that natural fibre reinforced composite can compete with glass fiber reinforced composites, stiffness wise, not strength wise. The specific stiffness for a plate bending load case is shown, where the influence of the low density of composite materials becomes even more clear. For this load case all composite materials, including the natural fibre reinforced composites, outperform steel and aluminium.

Specific stiffness E/ρ

Specific tensile strength σ/ρ

Specific longitudinal stiffness for a plate bending load case of different materials. Composite materials with cross-ply layup are assumed with a volume fraction of 40 % fibers and an epoxy matrix (E = 2.73 GPa, σ = 70 MPa). 'Delphine Depuydt, KU Leuven 2018'