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13 C CP–MAS NMR spectra of tropical hardwoods
Author(s) -
Sosanwo Olumide A.,
Fawcett Allan H.,
Apperley David
Publication year - 1995
Publication title -
polymer international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.592
H-Index - 105
eISSN - 1097-0126
pISSN - 0959-8103
DOI - 10.1002/pi.1995.210360304
Subject(s) - gmelina , khaya , lignin , deciduous , botany , chemistry , forestry , biology , geography
The carbon‐13 cross‐polarisation and magic angle spinning nuclear magnetic resonance spectroscopy studies of more than 20 tropical hardwoods are presented. Because of their productivity and area, the tropical evergreen forests are the location of more than one‐third of the net primary production of the terrestrial biosphere, a product which is currently of the order of 5.1 × 10 16 g of carbon per year. Samples are mainly from Nigeria, predominantly timberwoods such as Diospyros mespiliformis (ebony), Tectona grandis (teak), Nauclea diderichii (opepe), Chlorophora excelsa (iroko), Khaya ivorensis (lagos mahogany), Khaya senegalensis (sapele mahogany), Daniellia oliveri (ojia), Sterculia oblonga (aye), Brachystegia kennedyi (okwen), and Mitragyna cilliata (abura); also included are Hevea braziliensis (rubber tree) and Gmelina arborea , a source of paper pulp. Assignments of the various peaks of the spectra are given to the main components, lignin and holocellulose, and to other minor structures. The holocellulose features are those of cellulose, hemicellulose being masked, at least in woods in which it is known to be present. The signals from the holocellulose component indicate that about 35% of the material is cellulose in a recognisable crystalline form, presumably located at the centre of fiberes, but the type of crystal structure could not be identified because of interference from the rest of the holocellulose signals. The aromatic lignin signals were distinct, and were perceived to fall within a pattern of a smooth transition from the wood of aye, based upon a syringyl type of residue, to the woods of omo and mpingo, based on guaiacyl residues, the exceptions being the Khayas , ebony, teak and opepe, which contained a third structure. The proportion of lignin, according to the area of the aromatic region and the O—Me signals, was highest in mpingo (50%), a savanna wood; within the woods from the Nigerian rain forest, the population ranged from 22% for iroko to 44% for teak, a reasonable allowance being made for the extra lignin in the aliphatic network.