Pulp and Paper 



3099 



Figure 25-9. — Scanning electron micrograph of sweetgum after removal of most of the 

 lignin by a pulping reagent, but before disturbing the matrix of different cell types. 

 Individual fibers (f), vessel elements (ve), and ray parenchyma cells (rp) are distin- 

 guishable. (Photo from Cote 1980.) 



Strength, lower tensile and burst strength, decrease apparent density and folding 

 endurance, and increase resistance to beating, with decreased printability. 



Horn (1978) also investigated the influence on paper strength of morphology 

 of hardwood fibers pulped by the kraft process (a very alkaline system using 

 sodium hydroxide plus sodium sulfide). He observed unbeaten, unbleached pulp 

 fibers of five southern hardwoods and five other North American hardwoods 

 (table 25-6). He found a range in pulp-fiber length from 0.85 mm in sugar maple 



