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The Effects of H2O2 Bleaching and DTPA Spraying on the
Brightness Stability of Hornbeam CMP Pulp Following
Accelerated Irradiation Aging
Ramin Vaysia and Sayed Aahmad Mirshokraieb
Hornbeam chips pulped under CMP conditions at the yield of 85%, then
pulps were bleached separately with DTPA and without DTPA, along
with hydrogen peroxide. Some of the pulps were bleached with sodium
dithionite. Then 60 gr/m2 handsheet were made. A solution of 0.5 % of
DTPA was sprayed over a number of handsheets. The handsheets
were irradiated for 10, 20, 30, or 40 minutes for optical aging. The results
of this study explored that complementary bleaching with sodium
dithionite improves optical behavior of the handsheets. Following DTPA
solution spraying on the surface of handsheets brightness, opacity and
yellowness in improved and K/S ratio and post-color number is
decreased. Among different samples and following optical aging, it was
found that in long-term aging, DTPA spray has considerable affect can
the stability of brightness and increasing it durability against optical
deterioration.
Key words; DTPA Spray; Brightness Stability; H2O2 Bleaching; Hornbeam; Optical Aging.
Contact information: a: Department of Wood and Paper Science, Islamic Azad University, Chalous
Branch, Mazandaran, Iran; Corresponding author: vaysi_r452@ yahoo.com. b: Professor, Department of
Chemistry, Payame -Noor University, Tehran, , Iran.
INTRODUCTION
High-yield mechanical and chemi-mechanical pulps are susceptible to photooxidative reactions, which cause the pulps to become discolored and brightness reversion.
Newsprint exposed to polychromatic radiation showed the largest amount of yellowing
when exposed to irradiation in the wavelength region of 330 to 385 nm (UV-A region);
such yellowing has been attributed to the formation of new phenolic and carboxylic
groups from quinines radicals during photo-yellowing and long-optical aging (Andrady
and Searle 1995). Several factors and structural elements have been proposed or
considered as initiators. The main cause of the yellowing in high-yield and mechanical
pulps are oxygen, -carbonyl structures, lignin double bond structures, singlet oxygen,
various radicals, phenolic groups (catechols), ortho-quinones, para- quinones such as
methoxy-p-benzoquinone, lignin -O-4 structures, hydroquinones, and stilbenes formed
from the phenylcoumaran-type entities. This phenomenon has been attributed to a lightinduced oxidation of the lignin present in the pulp. Extensive and comprehensive
Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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research, performed during the last decade, has given not only new information about the
photochemical reactions causing yellowing, but also information on potential photostabilizing methods. However, no single approach so far has become technically or
economically feasible to meet all the needs of the paper industry (Forsskahl 2000; Carter
1996). The quinone structures and quinone precursors such as hydroquinone and
catechols are important reactions in the photo-yellowing process in acetylated
groundwood pulps (Monica et al. 1992). Untreated and acetylated aspen CTMP exposed
to argon, ambient air, and oxygen atmospheres showed that the degree of photoyellowing of the untreated CTMP decreased when the air in the surrounding atmosphere
was replaced with oxygen-free argon, indicating that atmospheric oxygen is not of sole
importance for the light-induced discoloration or that trace amount of oxygen is
necessary to cause discoloration (Paulsson et al. 2001). In long-term aging, DTPA spray
has considerable affect on the stability of brightness, and has the potential to increase its
durability against optical deterioration in hornbeam CMP pulp following accelerated
irradiation aging (Vaysi et al. 2007). The catalytic activity of Mn+2 and Mn+3 decomposed
in hydrogen peroxide by DTPA as the only stabilizer. It was found that the addition of
DTPA to a Mn+2 containing system is more effective that if it is added to a Mn+3
containing system. To decrease the catalytic of Mn+3, sodium borohydride and DTPA
under an acidic condition were considered to reduce Mn+2 to Mn+3. The effect of pH on
using DTPA to decrease Mn induced peroxide decomposition is discussed (Qiu et al.
2003).
Fig.1. Photo-yellowing reactions are high- rich lignin pulps. Newsprint exposed to
polychromatic radiation showed the largest amount of yellowing when to irradiation in
the wavelength region of 330-385 nm (Searle1995).
Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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EXPERIMENTAL
Pulp
Hornbeam chips were chosen randomly from a chip pile at Mazandaran Wood
and Paper Mill (MWPM) and cooked under CMP conditions (l/w:7, SO2: 116 g/L,NO2:
106 g/L, sodium sulfite :20%, and for 60 minutes in 160 oC), and pulps were prepared at
a yield of 85% (Barzan and Soraki 2002; Vaysi et al. 2007).
Pulp Bleaching
One portion of pulp was bleached using hydrogen peroxide and DTPA as
chelating agent according to the method proposed under following conditions: Hydrogen
peroxide: 3%, sodium hydroxide on hydrogen peroxide ratio: 0.7% , DTPA charge: 0.3%,
Na2SiO3: 3%, pulp consistency: 12%, time: 1 hour, and temperature: 75 oC. Then, pulps
were refined to freeness of 300 mL (CSF) by PFI Mill. Some of the pulps were bleached
with sodium dithionite. Then 6o gr/m2 hand sheets were made from bleached and
unbleached pulp. Then DTPA 0.5% were sprayed on the hand sheets and hand sheet
optical properties were measured by standard TAPPI. And 6o gr/m2 hand sheets were
made from bleached and unbleached pulp according to TAPPI T 205 om-88 before
acetylating (Barzan and Soraki 2002; Vaysi et al. 2007).
Irradiation of Paper
TAPPI brightness and color change according to the CIELAB color scale
(L*,a*,b* values) were measured on 60 g/m2 paper sheets using a Technibrite Micro TB1C spectrophotometer and by using TAPPI Test Method T 224 om-94, respectively. The
paper sheets were subjected to accelerated light-induced aging in an apparatus (made by
Author) provided with 12 UV-fluorescent lamps ("black light" made by Phillips Co.).
The handsheets were irradiated for zero, 10, 20, 30, and 40 minutes for optical aging .
The optical characteristics of the handsheets were measured before and after optical
aging. Brightness, opacity, yellowness, and greenness were determined according to ISO
methods. The specific light scattering (s), light absorption (k) coefficient, k/s ratio, and
post-color (PC) number were calculated using the Kubelka-Munk theory. The k/s value
and PC number were calculated according to the following equations (Monica et al. 1992;
Paulsson et al. 2001; Vaysi et al. 2007),
k/s = (1-R  )2/ 2 R 
(1)
PC number = 100((k/s)t –(k/s)t=o )
(2)
where s is the light scattering coefficient, k is the light absorption coefficient, T is the
irradiation time, and R  is the reflectivity of an infinite pile of sheets.
Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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RESULTS AND DISCUSSION
The effects of accelerated irradiation treatments on the brightness stability of paper
sheets were investigated using bleaching, DTPA spraying and optical aging. The results
of this study showed that following accelerated irradiation aging up to 40 hours,
absorption coefficient, K/S ratio , opacity , yellowness , a* factor and post color(PC)
number were increased, and brightness and greenness were decreased .The post
color(PC) number is scale for paper aging, and that is zero for zero hour accelerated
aging .In that, the most of post color(PC) number and the least brightness stability were
observed in H2O2 bleaching and complementary bleaching with Sodium dithionite In the
following bleaching and DTPA spraying on the handsheets, brightness, greenness,
opacity improved and K/S ratio and post color(PC) number were decreased. Following
aging up to 40 hours, all optical Properties (except brightness) were increased. These
changes are more tangible up to 20 hours irradiation (table 1 and figures:2-7). Also
complementary bleaching with sodium dithionite improved optical behavior of the hand
sheets in short-term aging, but in Following long-aging, the least brightness stability and
most of optical deterioration were observed in unbleached paper and H2O2 bleaching
H2O2 bleaching and complementary bleaching with Sodium dithionite, too. It is because
the oxidizer H2O2 is reduced chromophores (quinones) to acid functional groups in
hydrogen peroxide bleaching. The quinone structures and quinine precursors such as
hydroquinones and catechols are important reactions in the photo-yellowing process in
acetylated ground wood pulps. The quinone structures and quinine precursors such as
hydroquinones and catechols are important reactions in the photo-yellowing process in
acetylated ground wood pulps.
70
65
Brightness%
60
55
50
45
40
35
30
25
20
0h
10 h
20 h
30 h
40 h
Irradiation
Unbleached
H2O2 bleached+DTPA Spray
H2O2 bleached
H2O2+Na2S2O4 bleached
Fig.3. Changes of brightness in handsheets of Hornbeam CMP pulp following accelerated
irradiation aging.
Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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PEER-REVIEWED ARTICLE
140
120
K/S*1000
100
80
60
40
20
0
0h
10 h
20 h
30 h
40 h
Irradiation
H2O2 bleached
H2O2+Na2S2O4 bleached
H2O2 bleached+DTPA Spray
Fig.3. Changes of K/S in handsheets of Horn beam CMP pulp following accelerated irradiation
aging.
110
Opacity%
100
90
80
70
60
50
0h
10 h
20 h
30 h
40 h
Irradiation
Unbleached
H2O2 bleached
H2O2 bleached+DTPA Spray
H2O2+Na2S2O4 bleached
Fig.3. Changes of opacity in handsheets of Horn beam CMP pulp following accelerated
irradiation aging.
Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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PEER-REVIEWED ARTICLE
33
Yellowness%
30
27
24
21
18
15
0h
10 h
20 h
30 h
40 h
Irradiation
Unbleached
H2O2 bleached+DTPA Spray
H2O2 bleached
H2O2+Na2S2O4 bleached
Fig.3. Changes of yellowness in handsheets of Hornbeam CMP pulp following accelerated
irradiation aging.
2.1
1.6
a* factor
1.1
0.6
0.1
-0.4
-0.9
-1.4
-1.9
0h
10 h
20 h
30 h
40 h
Irradiation
Unbleached
H2O2 bleached+DTPA Spray
H2O2 bleached
H2O2+Na2S2O4 bleached
Fig.3. Changes of a* factor in handsheets of Horn beam CMP pulp following accelerated
irradiation aging.
Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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PEER-REVIEWED ARTICLE
7
6
PC*100
5
4
3
2
1
0
0h
10 h
20 h
30 h
40 h
Irradiation
Unbleached
H2O2 bleached+DTPA Spray
H2O2 bleached
H2O2+Na2S2O4 bleached
Fig.3. Changes post color (PC) number in handsheets of Hornbeam CMP pulp following
accelerated irradiation aging.
Table 1: Changes in Optical Properties of Bleached Hornbeam CMP Pulp
Following Accelerated Irradiation Aging.
Treatment
Brightness%
Unbleached
Opacity %
L*
a*
b*
94.24
71.59
0.99
12.73
1.87
82.28
82.97
-0.45
13.96
0.5
1.79
85.02
87.92
-0.58
16.45
59.73
2.7
1.69
82.46
86.29
-0.55
15.13
87.63
1.94
2.56
84.13
-5.21
15.61
PC*100
38.73
K/S
*1000
232.1
2.4
absorption
coef.(m2/kg)
6.95
H2O2 bleached
53.84
69.29
2.2
H2O2+ DTPA
Spray
H2O2+ Na2S2O4
54.77
56.06
55.72
Optical Aging
51.15
85.21
The catalytic activity of Mn+2 and Mn+3 in hydrogen peroxide decomposed by using
DTPA as the only stabilizer. The addition of DTPA to a Mn+2 containing system is more
effective that if it is added to a Mn+3 containing system. To decrease the catalytic of
Mn+3, sodium borohydride and DTPA under an acidic condition were considered to
reduce Mn+2 to Mn+3. The effect of pH on using DTPA to decrease Mn induced peroxide
decomposition is discussed [Qiu et al.2005].However, phenolic and carboxylic news
groups formation from quinines radicals during photo-yellowing and long-optical aging .
This news groups could formation color groups with metallic ions. Those factors are
caused less optical properties and brightness reversion.
Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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Fig.8. Phenolic groups (catechols) from quinones of lignin in hydrogen peroxide and
sodium dithionite bleached pulps. The quinone structures and quinine precursors such as
hydroquinones and catechols are important reactions in the photo-yellowing process in
rich-lignin pulps [EK Monica 1992].
CONCLUSIONS
The following conclusions could be drawn from the results of the present study:
1. The results of this study showed that following irradiation up to 40 hours, yellowness,
opacity, absorption coefficient, K/S ratio and post color (PC) number increased and
brightness decreased
2. Following optical aging up to 40 hours, all optical Properties (except brightness) were
increased. The post color (PC) number is scale for paper aging, and that is zero for zero
for accelerated aging. These changes are more tangible up to 20 hours irradiation.
3. The DTPA treatment in long-term irradiation and the use sodium dithionite and
hydrogen peroxide in short-long aging have better brightness stability.
4. Following long-aging, the least brightness stability and most of optical deterioration
were observed in unbleached paper and H2O2 bleaching, too. It is because the oxidizer
H2O2 is reduced chromophores (quinones) to acid functional groups in hydrogen peroxide
bleaching.
5. Also complementary bleaching with sodium dithionite improved optical behavior of
the hand sheets in short-term aging, but in long-aging, the least brightness stability and
most of optical deterioration were observed in unbleached paper and H2O2 bleaching and
complementary bleaching with Sodium dithionite.
Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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PEER-REVIEWED ARTICLE
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6. Following DTPA solution spraying on the surface of hand sheets, brightness,
greenness, opacity improved and K/S ratio and post color (PC) number were decreased.
In long-term aging, DTPA spray has considerable affect on the stability of brightness and
increasing its durability against optical deterioration. DTPA spray has better brightness
stability and less brightness reversion and therefore better resistance towards optical
deterioration.
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Vaysi (2011)." The Effects of H2O2 Bleaching and DTPA Spraying on,”
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