A Publication on World Pulp, Paper & Allied Industry

April-June'2001 - Vol. 5 Issue 3

Tech Watch

   

Physical Strength Properties of Standard test sheets made from bagasse and their Blends with Bamboo pulp
by Sushma Mahajan*, O. P Bhatt** and Rajiv Pandey***

 

In modern paper making mixed furnishes are being used to conserve long fibred and costly fibrous raw materials. Bamboo and eucalyptus are the major fibrous raw materials being used in big paper mills of Indian paper industry. In medium size paper mills furnishes containing bagasse, wheat straw , rice straw and waste paper are being mixed with bamboo pulp for smooth running of paper machines. In some paper mills bagasse chemical and semi chemical pulps are being mixed with bamboo chemical pulp/ imported waste paper/ hessain pulp for production of industrial and cultural grades of papers. Several workers have demonstrated the increased Wet Pressing results in improved strength properties of sheet(1-5)

Earlier investigations in the laboratory on wet pressing to study the effect of intensity of pressure during wet pressing on physical properties of standard test sheets made from bamboo (Dendrocalamus strictus), eucalyptus (Eucalyptus .hybrid) and mixed hardwoods from middle Andaman area revealed that, while using short fibred pulps, beating can be reduced by increasing the intensity of pressure during wet pressing of standard test sheets.(6) By reducing the level of beating followed by wet pressing a sheet of equal or even higher physical strength can be produced. Reduction in beating increases sheet porosity and significantly helps in removal of water from sheet during pressing and drying. Besides this, it was also investigated whether beating of pulps can be reduced and can be substituted by increasing intensities of pressure during wet pressing, so as to conserve energy during beating. Present study is carried out with bagasse pulp and its blend with bamboo pulp, to find out the effect of wet pressing on physical strength properties of the sheets made at higher freeness levels as compared to that of standard test sheets made at 3.5 kg/cm2 pressure, unbeaten (600ml/CSF), lightly beaten (450ml/CSF), well beaten (300ml/CSF) and over beaten (150ml/CSF).

EXPERIMENTAL:

Preparation of pulps:

Unbleached sulphate pulp of bamboo (D. strictus) and unbleached soda pulp of depithed bagasse were prepared in laboratory. The screened pulps were having the following characteristics

Characteristics Bamboo pulp
(D. strictus)
Bagasse  pulp

A. Kappa No.

22 16

B. Average Fiber Dimension

1. Fibre Length(mm) 1.65 1.38
2. Fibre diameter(mm) 0.012 0.018
 
 

Table 1 : Results of evaluation of standard test sheets prepared from pure bagasse pulp pressed at different intensities of pressure during wet pressing

 

Freeness m1 (CSF)

Pressure (kg/cm2)

2.04

6.14

12.27 18.41 24.55 30.68 36.82 42.96

Apparent Density
 gm/cm3

600
450
300
150

0.47
0.59
0.75
0.79

0.72
0.82
0.87
0.94

0.80
0.88
0.91
0.94

0.84
0.90
0.93
0.96

0.83
0.90
0.91
0.94

0.87
0.92
0.92
0.98

0.89
0.94
0.98
0.98

0.89
0.95
0.96
0.97

Tear Index 
mNm2/g

600
450
300
150

4.66
5.36
5.49
5.07
5.38
5.26
5.36
4.60
5.36
5.40
5.30
5.17
5.84
5.60
5.33
4.88
5.08
5.24
4.39
4.48
5.44
5.52
5.08
4.87
5.27
5.40
5.41
4.65

5.07
5.05
5.00
4.65

Tensile Index
Nm/g

600
450
300
150

10.75
28.11
36.23
40.69
24.53
36.98
35.30
39.33
29.33
43.19
45.94
49.18
33.37
47.40
52.65
54.90
44.17
59.31
60.18
63.40
35.01
47.65
51.71
47.08
30.98
35.47
36.26
39.61
35.19
47.14
49.71
50.81

Burst Index Kpam2/g

600
450
300
150

0.56
1.94
2.19
2.36
1.13
2.67
2.84
3.16
1.69
2.24
2.94
3.21
2.19
2.93
3.03
3.39
2.71
3.36
3.51
3.81
2.03
2.98
3.28
3.49
2.24
2.86
2.75
3.03
2.05
2.26
2.92
3.29

Solid Content %

600
450
300
150

36.08
36.60
31.27
29.82
48.72
50.24
46.42
33.95
57.71
52.54
52.16
51.01
62.54
59.59
56.50
56.42
61.21
61.70
64.26
59.81
61.16
69.57
65.43
57.46
67.31
67.35
63.00
60.83
66.11
64.40
64.18
61.77
 


The pulps were air dried and stored for further studies.

Beating of pulps and preparation of blends

Unbleached bamboo sulphate pulp and bagasse soda pulps were beaten in valley beater as per TAPPI standard T 200 t-61.

S.No Degree of beating Energy consumed Energy saved**(kwh) Percentage saving
1. Unbeaten ( disintegrated)600ml 0.05 - -
2. From 600 to 450 ml (CSF) 0.07 0.07 50
3. from 600 to 300 ml(CSF) 0.14 0.06 30
4. From 600 to 150 ml(CSF) 0.20 - -

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