Pulp and Paper 



3105 



Bursting and tensile strengths. — Horn (1978) found that, as in softwood 

 pulps, bursting and tensile strengths of hardwood pulps are highly dependent on 

 fiber-to-fiber bond strengths. In unbeaten pulps, bursting strength was most 

 highly correlated with fiber length (fig. 25-12 left), with L/T ratio (ratio of fiber 

 length to cell wall thickness) a secondary influence (r = 0.709); tensile strength 

 of unbeaten pulps was mostly closely correlated with L/T ratios (r = 0.796). 



Horn (1978) found that after beating, L/T ratio was the dominant factor for 

 both bursting strength (fig. 25-12 right) and tensile strength (fig. 25-13). Burst- 

 ing and tensile strengths of handsheets made of white oak kraft pulp fibers were 

 increased by removal of fine material, chiefly parenchyma cells (table 25-8). 

 The presence or absence of vessel elements from handsheets had little influence 

 on the tensile strength of handsheets made from either unbeaten or beaten white 

 oak kraft pulp fibers; the white oak pulp contained 1 .9 percent vessel elements 

 by weight (Horn 1978). 



§ 



I 



i 



20 



16 



12 - 



400 ml CSF 



Y = 5400+ 23.68(X) 

 r =0.833 

 r2=0.694 



100 



200 



300 



400 



500 



L/T RATIO 



M 145 678 

 Figure 25-13. — Relationship of tensile strength to L/T ratio (fiber length to cell wall 

 thickness) for pulp sheets made from unbleached hardwood kraft fiber beaten to 

 Canadian Standard Freeness of 400 ml. (Drawing after Horn 1978.) 



