
341Properties and Characterization of Natural Fiber
The cell wall of a ber is made up of a number of layers: the so-called primary
wall (the rst layer deposited during cell development) and the secondary wall
(S), which again is made up of three layers (S1, S2, and S3). In all lignocellulosic
bers these layers contain cellulose, hemicellulose, and lignin in varying amounts
(Table15.2). The individual bers are bonded together by a lignin-rich region known
as the middle lamella. Cellulose attains its highest concentration in the S2 layer
(about 50%), and lignin is most concentrated in the middle lamella (about 90%),
which, in principle, is ...