however this is overcome by drying of the culm strands, causing shrinking of the parenchyma and bringing the fibre strands closer together.
The distribution of fibrovascular bundles varies in the rind and core regions throughout the culm (Table 1). In general the strength of each fibrovascular bundle is determined by its R/T ratio. A high R/T ratio is indicative of strength and has been reported earlier in monocots like bamboo and sugarcane (Sekar 1992; Saravanan 1996).
C. pangorei fibres, as observed in light and electron microscopic studies, are multicellular and polylamellated. Such polylamellated fibres are also known to occur in bamboo and sorghum (Parameswaran and Leise 1975; Manimekalai et al. 2002) and are known to impart strength to finished products.
C. pangorei fibres are rich in their chemical composition. The holocellulose content of fibres was 83%. The combination of hemicellulose and celluloses are called holocelluloses and account for 65-70% of plant dry weight, and the alpha cellulose content is 41.79% in C. pangorei, which is similar to that of hemp and reeds such as Phragmites communis (43 %) (Hurter 2006). Plant materials with 34% and over of alpha cellulose content are characterized as promising for pulp and paper manufacture. Cellulose imparts strength and makes the culm strand liable to synthetic and natural dye fitness and binding. This property has a significant role in the strength and dye binding properties of the silk mats. Hemicellulose is responsible for the water absorption by plant fibres and serves to reduce inter-fibrillar cohesion and to relieve internal fibre stress (Baley 2002).
The lignin content in the culm strand is 13.28%, which is greater than that of pineapple leaf fibres (10.5 %) (Khalil et al. 2006), is similar to hemp stalk fibres (9- 13%), and less than kenaf, wheat, bamboo, grass, and reed fibres (Hurter 2006). Generally the high lignin content makes the fibre tougher and stiffer, thereby giving strength to mats, as reported in coir (Khalil et al. 2006). Lignin also imparts brittleness to the fibre, and hence the percent elongation of culm in this study is low. Partial removal of lignin will cause the other components such as cellulose to become more compact and thereby increase the strength and flexibility, as reported in areca nut fibres (Rajan et al. 2005). The flexibility of culm strands of C. pangorei during mat weaving may be attributed to the nature of fibres and fibrous sheath.
The moisture content in C. pangorei culm strands is 9.2%. The moisture content is directly related to strength and extension of fibres, besides dye absorption. Low moisture content enhances drying (Fathima and Balasubramaniam 2006). The moisture content of C. pangorei is similar to that of jute fiber (9.9 %), however less than that of pennywort (18.3 %) (Rowell et al. 2000) and therefore may influence better performance of the culms used in silk mats. Moisture content at a given relative humidity can have a great effect on biological performance of materials made of fibres, as they are more prone to decay.
From the maceration studies, four different types of fibres were recognized based on the relative thickness of the cell walls viz. very thick walled (vtkf), thick walled (tkf), thin walled (tnf), and very thin walled (vtnf). Fibre wall thickness is an important feature in imparting stiffness to the mats. Wall thickness increases from the pith towards the periphery; i.e. the rind fibres are very thick walled as compared to the core fibres. Similar observations were made relative to fibres of grasses like bamboo and sugarcane (Sekar
Benazir et al. (2010). “Sedge fibers and strands,” BioResources 5(2), 951-967.