92 THE PLANT CELL WALL 



cells run 6-70 mm in length and 15-20^. in diameter, but the cells 

 overlap giving a toal fiber length of 1-3 ft. Hemp cells are similar 

 in dimensions, but give fiber lengths of 4-6 ft. Jute fiber bundles 

 may be even longer, giving lengths of up to 8 ft. 



The fibers of these plants are obtained from the bast by a de- 

 corticating fermentation process known as "retting". 



Ramie fibers can be prepared in a highly crystalline state by 

 simple washing procedures. The cells range from 50 to 250 mm in 

 length and 17-64jx in diameter. Total fiber lengths are short and 

 variable, 0.5-20 in. 



Leaf fiber products included manila hemp (Musa textilis, 

 Musaceae) and sisal hemp (Agave sisa/ina, Liliaceae). They are 

 coarse and strong as indicated by their consumption in cordage 

 and rope. 



Although native celluloses have retained much of their tradi- 

 tional importance as fibers, recent technological advances have 

 led to cellulose derivatives including viscose and cuprammonium 

 regenerates, esters, and ethers. Tn the fiber industry, regenerated 

 celluloses provide rayons. Viscose rayon is prepared by treating 

 a-cellulose with 17 per cent NaOH, aging the soda cellulose under 

 controlled conditions and converting it to sodium cellulose dithio- 

 carbonate (xanthate) by treatment with carbon disulfide. The 

 xanthate in alkaline solution is allowed to ripen (undergoing partial 

 decomposition), then extruded through spinnerets into a sulfuric 

 acid bath containing sodium and zinc salts. The xanthate is decom- 

 posed, the cellulose regenerated. In the cuprammonium process, 

 cellulose dissolved in cuprammonium hydroxide is extruded into an 

 aqueous regenerating bath. If the fine spinnerets are replaced 

 with a slit-shaped orifice, the extrusion product is a film, Cello- 

 phane for example. 



The viscose process, developed between 1892 and 1900, is signif- 

 icant in textile technology since it was the first time a fiber had 

 been produced by chemical procedures. Although ordinary viscose 

 rayons are lower in tensile strengths (23-30 kg/mm 2 ) than cotton 

 (25-80 kg/mm 2 ), flax (50-100 kg/mm 2 ), or ramie (90-95 kg/mm 2 ), 

 modern high tenacity rayons are stronger, ranging as high as 

 80 kg/mm 2 . 



