ISSN ………… - International Network for Bamboo and Rattan

cent arabinose and 12.8 per cent uronic acid; the acetyl and methoxyl value being nil (Negi 1969 309 ;
1970) 310 . The hemicellulose of Bambusa bambos contains 78.8 per cent xylose, 11.6 per cent
arabinose and 1.8 per cent galactose (Guha and Pant 1967) 394 . Xylose (82-92% yield) was the main
constituent of the hemicelluloses isolated from Dendrocalamus strictus, D. hamiltonii and Melocanna
baccifera (Dhawan and Singh 1982) 278 . Glucose, arabinose, rhamnose and glucuronic acid were also
found to be present in small amounts in all the hemicellulose isolates. The yield of sugars was highest
in the case of D. strictus whereas pentosans and methoxyl content were the highest in the case of D.
hamiltoni, Melocanna baccifera had the lowest yield of sugars, pentosans and methoxyl content.
As pentosans constitute more than 85 per cent of the hemicelluloses, their effect on pulping
characteristics is important. The pentosans are reported to be retained in the cellulose pulps even after
a final stage of cold-alkali purification with 17.5per cent NaOH. This suggests that there are ‘alkali
resistant’ pentosans in close association with the cellulose proper (Negi 1970) 310 . A probable inter-
relation between cellulose, lignin and hemicellulose in Dendrocalamus strictus is described by
Mukherjea and Guha (1971) 307 in their studies on the methods for isolating cellulose from lignin and
pentosan components. Once the pentosans are rendered non-resistant, treatment with alkali before
chlorite treatment produces pulps with a high content of resistant pentosans whereas chlorite treatment
alone makes the pentosans non-resistant to alkali extraction (Guha and Negi 1972) 394 . Maximum
amount of alkali resistant pentosans are retained in chlorite pulp and minimum in the sulphate pulp of
Dendrocalamus strictus (Singh et al. 1974) 317 . Biyani et al. (1967) 378 obtained a pulp with low
pentosan content from Bambusa bambos by nitric acid pulping. Prehydrolysis /sulphate process may
be the only effective means of removing the pentosans from bamboo chips (at a cost of considerable
loss of alpha-cellulose) and thus enabling a dissolving-grade pulp to be obtained (Bawagan 1968) 268 .
The pentosans present and ash content of the various bamboos used in India for making rayon pulp
were reported by Saboo (1992) 482 .
Bamboo lignin is a typical grass lignin composed of mixed dehydrogenation polymers of coniferyl,
sinapyl and p-coumaryl alcohols. The unique feature of bamboo lignin is that it contains 5-10 per cent
ester of p-coumaric acid (Higuchi 1958 288 , Higuchi and Kaivamura 1966) 289 . Lignin of D. strictus is
found to be composed of two fractions, one carrying high methoxyl value (19%) and the other having
low value (2%) (Pant et al. 1975) 311 . The former is easily extractable under mild conditions whereas
the latter requires drastic conditions. Aldol type side chain (R-CH-(OH)-CH2-CHO) and presence of
bivanillyl structure with alpha-alpha linkage and 1-(4-hydroxy-3-methoxy)-3 hydroxy propane-1-one
have been suggested for the bamboo lignin. Vanillic acid, vanillin and syringaldehyde are present as
terminal moieties and are linked through beta-position of side chain of the main precursors via
carboxylic acid group (Bist et al. 1974 275 ; 1975 276 ; Sabharwal et al. 1962) 313 .
41