Crossed cellulose fibre structure

Flax is stained blue by zinc chloride-iodine reagent (see Section 8.5.6), as are all other cellulose fibres. In addition the typical V- and X-shaped transverse structures can be seen more clearly. Differentiation from hemp can be made by means of a cross-sectional sample. Flax shows clearly visible irregular polygons with lumen, hemp shows relatively indistinct and often conglomerate structures. 

Figure I /./ (a) Cross-section through sisal fibres (after Nutman [7]) (b) structure of the cellulose fibre cells (after lllston et al. [8]). 

The fracture work (in-plane tear) of a medium consisting of small particles only, such as filler and nanofibrillated cellulose, is low. It can be considerably enhanced by adding reinforcement pulp fibres. Any particle crossing the rupture path must be released from the paper structure by bond failure, or it must be inactivated by fibre... 

The early history of polymers is really the conversion of natural polymers into useful materials. Examples include the vulcanization of rubber (Goodyear, 1839), celluloid (which is plasticized cellulose nitrate—Hyatt, 1868), and cellulose-derived fibres, e.g. cuprammonia rayon (Despeisses, 1890) and viscose rayon (Cross, Bevan and Beadle, 1892). The first truly synthetic polymer, that is, one made from laboratory chemicals, was Bakelite (Bakeland, 1907). This was made from phenol and formaldehyde. Bakeland probably did not know the chemical structure of the Bakelite, but he did realize that organic chemicals containing multiple functionality yielded insoluble materials. The various phenol-formaldehyde resins (PF), e.g. Bakelite and novolacs, were thus obtained in an empirical manner. 

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