irradiation of dissolving pulp by electron beams - Lenzing

6.5
IRRADIATION OF DISSOLVING PULP BY ELECTRON BEAMS
Different dissolving pulps were treated by
electron beams. The dose-DP relation was
invesugated by different accelerators. The
Parameters of the Sakurada equation differ
from pulp to pulp.
As a result of our examinations the DP
distribution inside a mini bale Shows a great
inhomogeneity of the viscosity. The strongest
degradation was observed at the edge
positions of Single pulp sheets in a Penetration
depth of 30 sheets. The uniformity of the DP
distribution, measured by GPC in
LiWDMAc, of the alkali cellulose (AC) before
xanthation was compared to conventional AC
for different pulps. In all these examinations
no significant differentes between pre-aged
and irradiated pulp was observed.
The Phase transition from cellulose 1 to
cellulose 11 depending on temperature and
steeping lye concentration, measured by FT-
IR-spectroscopy, takes place in the same
range of NaOH-concentration for irradiated
and untreated pulp samples.
The influence of CS2, cellulose content, and
alkali ratio (AR) was examined using
hemicellulose-free steeping lye in Order to
check the influence of irradiation on viscose
quality. In case of irradiated pulp the steeping
lye concentration was 16%. In these trials the
Introduction
There has been some correspondence among
several research groups claiming that irradiation
of dissolving pulps Prior to viscose production
could be beneficial in several ways:
. the caustic requirement for steeping will be
reduced because the conversion to the cellulose
11 statle could be achieved at a remarkably lower
caustic soda concentration;
l the degree of polymerization tan be easily
adjusted and, thus, the aging step after
alkalization could be omitted;
G. Kraft, N. Schelosky
Lenzing AG, A - 4860 Lenzing, Austria
viscosity of AC before xanthation was the
same for both types of pulp. In a wide range
of CIS2 input (36% to 26% calculated on a-
cellulose) and AR from 0.60 down to 0.47 no
differente between the irradiated samples and
the conventional pre-aged pulp was observed.
Increasing the cellulose content up to 15.7%
(relaLtive to Standard), no benefit was observed
by using irradiated pulp. Only in case of a
drastic reduction of the input chemicals down
to 22% CS2 and AR 0.5 the irradiated pulp
gives a better viscose quality than the
reference pulp under the same conditions. The
same trials performed in the 2kg lab plant did
not show any statistical differente between
irraldiated and conventional pre-aged pulp.
Reg:arding the fibre quality there was no
differente between irradiated and
conventional pre-aged pulp samples in terms
of elongation and tenacity. The fibres from the
irraldiated pulp showed a higher degree of
yellowing. The formation of H2S was not
increased according to by-product analyses.
The frequently published results of drastically
bettier viscose quality by using irradiated pulp
could not be confirmed in our study.
Keywords: viscose, irradiation, electron beam
l the xanthation will occur with substantially
reduced carbon disulfide input and, because of a
higber reactivity of pulp degradation, still give a
viscose with good filterability;
l less CS*-derived byproduct formation will
result in a reduced H2S-formation.
The objective of this study was the evaluation of
the potential of electron treatment of dissolving
pulps with a special focus on the feasibility of a
drastic reduction of CS* and NaOH charges in
the case of Solucell dissolving pulp.

Economical considerations. . The price of
irradiated of pulp is composed of high costs of
botlh investment and Operation, the latter one
mainly depending on expenses for electric
power. From this Point of view, the irradiation of
pulp would become an economically interesting
innovation only if it is possible to carry out the
viscose process with drastically reduced input
chemicals (22% CS*, AR: 0.5) without any
impairment of the fiber quality.
Experimental
For the experiments at lab plant and Pilot plant,
50 sheets (isostack) of Solucell 450 were
irraldiated at STUDER AG with a 1OMeV
Rhodotron TT300 accelerator built by IBA.
The viscose quality was evaluated by PVC and
KWP filter value (constant pressure) and particle
i
-
I
Irradiated Pulp fl2 kCy)
BA: 10 MeV
homogeneous nking of prllp chips
Steeping lye concentratioe: 16%
/ Viscose of the sanuz composition was prepared for irradiated and
-.
LAB PLANT
Viscose Quality
Viscose Rheology I
- -----.~-~~--~ _-_- - - ---~~_
66
count. The viscose was also characterized by
rheological investigations and analysis of
byproducts, see Table 1 and Figure 1.
No optimization of spinning conditions was done
for these experiments.
Table 1. Viscose composition for the experiments at lab
plant and Pilot plant.
Plant CS2 (%) AR Ce11 conc.
Lab 36 0.6
Lab 32 0.6
Lab’ 28 0.55
Lab 26 0.5
Lab 22 0.5
Lab 28 0.55
Lab
Pilot
Figure 1. Experimental setup.
--
28
22
0.475
0.5
Standard
Standard
Standard
Standard
Standard
Standard +
15.6%
Standard +
15.6%
Standard
Con~entionai Ageiag
Sieeping lye co~~~~~rati~a Standard
-.--I--~ --.x .._““

Viscosity [ml/g]
290 1 without aftertreatment
260-
Irrxhatwn Doiage: 12 kGy
250L 0 - I - I - I - . . 1
0 10 20 30 40 50
Sheet Numher
Figure :t. Intrinsic viscosity distribution within one mini
bale: homogeneity of irradiation at a dosage of 12 kGy.
In case of irradiated pulp the hemicellulose
concentration in press lye was higher than in the
conventional process (2.25 g/l versus 1.48 g/l).
67
Ball J?zLZ of viscose. As published, the ball fall of
viscose made from irradiated pulp should be
lowel than that of viscose made from
conventionally pre-aged pulp. Thus, it should be
possible to increase the production capacity by
using a higher content of irradiated cellulose
under retention of the same ball fall of the
viscose as before. However, only at high
celluliose content (115.6% of Standard) and very
low alkali content a lower ball fall seemed to
result from the use of irradiated pulp (Figure 3).
There is no benefit in ball fall by using irradiated
Pulp=
Polytlispersity of AC. No differente regarding
polydispersity between aging and electron beam
treatment could be observed in the respective
viscosity range (Figure 4).
100% [ca 100% [CS 100% [ca 100% 100% 115.6% [CS2z 115.6% [cs2:
360/0; ARZ 0.q 32v4 AR: 0.6) 280/0; AR: o.5.q [oi2:26%, AR [cs2:22%, AR BS, AR 0.55j 28%, AR:
O-Tl Wl 0.47Sj
2.6
Figure 3. Ball fall of various compositions of viscose prepared from irradiated and pre-aged pulp;
lab-plant trials. Ball fall corrected to target cellulose concentration.
1.6
400 300
Intrinsic viscosity [mYg]
Figure 4. Polydispersity vs. intrinsic viscosity of AC.

68
Phase transition Cellulose I - Cellulose II. The networks under extreme conditions (CS2
pha.se transition takes place in the same range of reduction, increase in cellulose) than reference
Na0H: concentration for irradiated and untreated pulp. It has a higher potential for savings from
pulp s amples . this Point of view.
Rheology of Viscose Spinning Dope. Under Viscose from irradiated pulp under saving
Standard conditions, irradiated pulp yields conditions is rheologically worse than one from
rheologically worse viscose than reference pulp. reference pulp under Standard conditions.
Under conditions of CS2 reduction and increase Quality of viscose. The often published results of
in cellulose, irradiated pulp yields rheologically drastically better viscose quality by using
better viscose than reference pulp. Irradiated irradiated pulp could not be confirmed in our
pulp seems to have a lower tendency of forming study of Solucell450.
800
700
0 600
L 500
2
P 400
5 300
-z
200
100
0
HFilter value [PVC] q Total particle volume[ppm]
Fignre 5. Viscose quality. Trials made at lab plant with Standard cellulose concentration (average +/- 95,4% conf. interval).
Filter value (higher is better) and total particle content at Standard cellulose content in viscose [CS,%/AR].
IFilter value [PVC] q Total particle volume [ppm]
pre aged - CS2: 28 % ; Irradiated - CS2: 28%; pre aged - CS2: 28%; Irradiated -CS2: 28%;
AR: 0.55 AR: 0.55 AR: 0.475 AR: 0.475
Figure 6. Viscose quality. Trials made at lab plant with Standard cellullose concentration (average +/- 95,4% conf. interval).
Filter value (higher is better) and total particle content at 15.6% higher cellulose content in viscose [C,‘$%/AR].
20
18

In a wide range of CS2 input (36% to 26%
calculated on a-cellulose) and AR from 0.60
down to 0.47 no significant differente in viscose
quality between the irradiated samples and the
conventionally pre-aged pulp was observed.
Upon increase of the cellulose content up to
115.7% of Standard, no benefit was observed by
using irradiated pulp. Only in case of a drastic
reduct-ion of the input chemicals down to 22%
CS; and AR 0.5 the irradiated pulp gave a better
viscose quality than the reference pulp under the
same conditions (Figures 5 and 6). The same
trials iperformed at the 2kg Pilot plant did not
show any statistical differente between irradiated
and conventionally pre-aged pulp (Table 2).
B~JW&KLS. There seems to be a slight tendency
to lower trithiocarbonate formation in the viscose
made from the irradiated pulp.
Fibre properties. Viscose of reduced CS2 content
showed good spinning properties, the spinning
conditions were not optimized. Tenacity and
elonga.tion were not significantly influenced by
the use of irradiated pulp, the tendency is slightly
better for aged pulp.
Tenacity and elongation were significantly
impaired by the reduction of CS2 Charge using
Standard spinning conditions (Figure 7).
69
Brightness and yellowing of fibres were
nega.tively influenced by both the use of
irrad.iated pulp and the reduction of CS2 Charge
(Figure 8).
Table 2. Results of trials at a Pilot plant [averagehange].
conventional irradiated
CS2 l%l Std. 22 Std. 22
Alkali ratio Std. 0.5 Std. 0.5
unfiltered viscose
Filter value, PVC 452 252 393 1156 335 /IO3
125 1167
Filter value, 77 144 230 117169 123 139
KWP 1230
Total particle 12.4 28.3 18.6/17.1 22.1 /3.2
volume [ppm] 17.8 140.0
Time for 43 78 60 70
filtration, min.
viscose spinning dope
Filter value, PVC 528 233 528 134 439 132
/186 /121
Filter value, 26112 47116 40115 43 145
KWP
Total particle 1.2 2.5 1.4 IO.5 1.3 IO.3
volume [ppm] IO.6 11.8
Ball fall [sec] 49 83 60 93
Ripening ind., “H 14.7 6.5 15.9 7.8
aged Standard irradiated aged 22% CS2; AR irradiated 22%
Standard 0.5 CS2; AR 0.5
Figure 7. Tenacity and elongation of fibers at standarcl spinning conditions (Pilot plant trials).

1
-
&Q
75
E 70
lQ5
-E
60
55
50
45
aged standard irradiated aged 22% CS2; AR irradiated 22%
Standarcl 0.5 (32; AR 0.5
Figve 8. Brightness of unbleached fibers at standard spinning conditions (pilot plant hi&).
Conclusion References
Electron beam treatment of pulp slightly
improves viscose filterability at a very low level
of CS2 charge (lab plant).
However, this improvement is not liirge enough
to justify the additional costs of electron beam
treatment. The higher hemicellulose conteat in
the steeping lye and the enhanced yellowing of
the fibers are further arguments against electron
beam treatment of dissolving pulp.
The often published results of drastically better
viscose quality by using irradiated pulp could not
be confirmed in our study of Solucell450.
[ 11 Fisher, K.; Goldberg, W.; Wilke, M. Lanz.
BeE 1985,59,32.
[Z] Rajagopal, S. et al. "Enhancement of
Cellulose Reactivity in Viscose Production
Using Electron F'rocessing Technology"'
Viscose Chemistry Seminat, Stockholm,
1994.
[3] Rajagopal, S. PETAS Seminar, Hamburg,
1995.
[4] Rajagopal, S. Cellulosic Man-Made Fibre
Summit, Singapore, 1997.
[5] Stavtsov, A.; Cassel, A. Cellulosic Man-
Made Fibre Sumit, Singapore, 1997.
[6]
Schleicher, H.; Bomneister, B.; Voges, M.
Cellulosic -Made Fibre Summit,
Singapore, 1997.