Production of NSSC Cellulosic Pulp Fibers from Eucalyptus Cameldulensis- Juniper Publishers
JUNIPER PUBLISHERS- ACADEMIC JOURNAL OF POLYMER SCIENCE
Abstract
This study has aimed to investigate production of
neutral sulfite semi-chemical (NSSC) pulping from eucalyptus
camaldulensis in Zabol, Sistan & Balouchestan, Iran. Chemical
composition including cellulose, lignin, extractive and ash were
measured (48.33%), (28.49%), (5.94%) & (0.65%) respectively, while
dimension of fibers including length (0.935mm), diameter (19.13μm),
lumen cavity (8.89μm) & cell wall thickness (5.12μm). Cooking
conditions were consist of three levels of chemical charge (10, 14 &
18% on O.D weight), constant time of 90min, constant temperature of 170
°C & liquor to wood ratio of 7:1. The pulps were refined to
400±25mL, CSF & 127gm-2 hand sheets were made. Finally, strength
properties of the pulps were compared and evaluated with that of
Mazandaran Wood and Paper Industries (MWPI), Iran. The results showed
that pulp yield decreases with increase of chemical charge. Analysis of
the mechanical properties indicated that the paper from NSSC of
eucalyptus at various cooking levels has preference of NSSC pulp of
hardwoods produced in MWPI for all strength indices.
Keywords: Eucalyptus camaldulensis; Chemical charge; Pulp; NSSC
Introduction
The use of fast-growing species, such as tagasaste,
leucaena, paulownia [1-3]. The fast-growing commercial plantations of
Eucalyptus species have nowadays an important role in the fulfillment of
the worldwide increasing demand for pulpwood [4]. By 2008, the total
area of Eucalyptus plantations, mainly distributed in about one dozen
countries spread worldwide, [5] exceeded 19 x 106ha [1]. In fact, the
Eucalyptus species are the most important fiber sources for pulp and
paper production in South-West Europe (Portugal and Spain), South
America (Brazil and Chile), South Africa, Japan, Iran and other
countries [6].
Nowadays researchers are engaged in applying those
pulping processes which needs less chemical for the production process
due to environmental concerns. In this regard, NSSC process, as one of
the production processes which observes environmental issues, requires
further investigations to optimize the production method along with
economic and ecological objectives for reducing the chemical charge and
application of the proper species [7]. Neutral Sulfite Semi-Chemical
process briefly called NSSC is mainly used to produce high-yield pulps
from
hardwoods. Sodium sulfite cooking liquor is used in this process to
neutralize organic acids released from lignocelluloses materials during
cooking with small amounts of sodium carbonate, sodium hydroxide or
sodium bicarbonate [8]. These materials are utilized for initial
treatment while separation of the fibers is finally accomplished by
mechanical processes. On the other hand, limitations in utilization of
wood from forests in northern part of Iran, entails looking for
alternative sources from various parts of the country. Eucalyptus,
especially camaldulensis are of quick growing species which is expected
to be consistent with ecological conditions of Iran. Eucalyptus has
special value and importance considering the continental conditions of
Iran with large arid areas [9]. Based on global research and experiences
in making pulping from eucalyptus wood species [9-14] the purpose of
this research was to investigate chemical composition and biometrical
properties of the fibers from eucalyptus camaldulensis, production of
NSSC pulp from it and finally, comparison of the mechanical properties
of the handsheet papers with those samples made in MWPI.
Experimental
Materials
Three eucalyptus camaldulensis trees from agriculture
researches station of Zabol were selected randomly and cut
down. Logs of Breast height were cut and prepared from each
tree. This region has hot and dry climate such that its yearly
maximum temperature reaches 45 °C. Meanwhile, annual
precipitation of this region is 41mm and so-called 120-days
wind of Sistan is of the dominant phenomena in this region.
Measurement of chemical composition
Measuring percentage of cellulose was done through
nitric acid method [15], while percentage of lignin, extractives
soluble in acetone, and ash content were measured according to
TAPPI test methods T222-om-98, T204-om-97 & T211-om-93,
respectively.
Measurement of fibers dimensions
Franklin’s technique (1954) was used to prepare the
samples. Dimensions of the fibers including length and diameter,
Lumen width and thickness of cell wall were measured by
LeicaQ5000MC Image analyzer apparatus and biometric ratios
and coefficient being calculated from the following equations:
Slenderness Ratio = L/d ………(1) [16]
Flexibility coefficient = (c/d)*100....(2) [17]
Runkel Ratio(tear strength of fiber)=(2p/c)*100....(3)[18]
Experimental Pulping
Three amounts of chemicals of sodium sulfite (Na2SO3) and
sodium bicarbonate (Na2CO3) (10%, 14%, & 18%, on the basis of
oven dry mass of eucalyptus) and constant pulping time of 90min
were used. For each combination of variables, 3 replica pulp
samples were made. A pulping temperature of 170 °C was kept
constant. The cooking liquor to eucalyptus (L/W) was at a 7-1
ratio. The cooking trials were performed using an experimental
rotating digester (HATTO), with 500 grams of eucalyptus in each
trial. Pulping time was measured after reaching 170°C. The time
to reach the cooking temperature was adjusted at 30 minutes. At
the end of each cooking, the content of the cooking cylinder was
discharged on a 200-mesh screen, and the cooked material was
washed using hot water. The remaining liquor was separated by
hand-pressing the cooked material. Digester yield was measured
by weighing the washed material on top of the screen without
defibration. The cooked material was defibrated using a 25cm
laboratory single-disc refiner, and then pulp was screened using
a set of 2 screens, a 12-mesh screen on top of a 200-mesh screen.
The material remaining on the 12-mesh screen was considered
as reject (shives), and the fibers that passed the 12-mesh screen
but remained on the 200-mesh screen were considered as
accept. To estimate the required refining, initial freeness was
determined according to TAPPI 227 om-92, and then the pulp
was refined to 400±25 mL CSF according to TAPPI 248 om-88,
with a PFI Mill. Hand sheets (with basis weight of 127gm-2)
were made according to TAPPI 205 om-88. Hand sheets were
kept in a conditioning chamber at 23 °C & 50% RH for 24 hours.
Then, basic weight, caliper, Corrugating Medium Test (CMT),
Ring Crush Test (RCT), stiffness and tensile strength index,
tear strength index, and the burst strength index of the hand
sheets were determined according to TAPPI T410 om-98, T411
om-89, T809-om-99, T818-om-87, T240 om-92, SCAN P11:73,
T403 om-91, and T403 om-91 test methods, respectively. Oneway
Variance Analysis test was used to analyze differences in
strength properties of the hand sheets due to change in chemical
charge of cooking liquor at confidence level of 95%. Meanwhile,
average values of the properties were classified using Duncan
multiple range testing.
Results and Discussion
Chemical composition and fiber dimensions
The percentage of cellulose, lignin, extractives soluble in
alcohol-acetone, and ash are summarized in Table 1. Fiber
dimensions and biometrical coefficient of eucalyptus are
summarized in Table 2. The cellulose content of eucalyptus was
found to be 48.3%, which is in the satisfactory range for pulp
production. The cellulose content of eucalyptus is more than rice
straw (41.20%) [19]and wheat straw (38.20%) [20]. The lignin
content of eucalyptus was found to be higher than rice straw
(21.90) and Egyptian cotton stalks (22.50) [21]. The Extractives
soluble in alcohol-acetone content of eucalyptus was found to be
almost similar to rice straw but higher than aspen (2.50%), and
lower than wheat straw (7.80%). The ash content of eucalyptus
was also low.
Chemical composition of the raw material is one of the most
important factors in pulp and paper production. Therefore,
identification of chemical composition of eucalyptus has
significant importance for predicting properties of the paper
made. Cellulose is the most important component of cell wall
in pulping process. Strength properties of paper increase with
greater percentage of cellulose. Lignin is another component of
cell wall which is responsible for connection of fibers to each
other. Removing lignin is known as one major objective for any
pulping process since once lignin has been solved and removed,
cellulose fibers can establish more intermolecular bonds which
will lead to higher strength of the paper produced [22].
Fibers were classified into three groups. The first group was
considered short fibers with lengths of less than 0.9mm such as
hardwood. The second group had an average length between
0.9-1.9mm. The results showed that the average fiber length of
eucalyptus was 0.935mm. The third group included fibers longer
than 1.9mm [23]. Eucalyptus fibers are shorter than wheat straw
(1.73mm) [24]. On the other hand, the cell walls of eucalyptus
fibers are thicker than those of aspen (1.93μm) (Law and Jiang
2001) [25] and cotton stalks (3.40μm) [26]. The calculated
Runkel ratio for eucalyptus fibers (115.19%) is higher than
that of cotton stalks (84%), aspen (23%), and date palm rachis
fibers (80%). The slenderness ratio of eucalyptus fibers is 48.88
and is higher than that of cotton stalks (42.35) and aspen fibers
(46.15), but the flexibility coefficient of eucalyptus fibers is less
than both cotton stalks (65.31) and aspen (81.44). This indicates
good sheet forming potential from these fibers.
Dimensions including Length, diameter, lumen width and
cell wall thickness have great effects on physical and mechanical
properties of papers. In this regard, length of fibers has a very
distinct role on improving strength indices of paper. Generally
speaking, an acceptable amount for slenderness ratio for pulping
is believed to be higher than 33 [27] such that eucalyptus fibers
will be stand at this range.
Pulping and pulp evaluation
Pulp yield after cooking is one important characteristic which
must be measured after pulping process. The results show that a
higher chemical charge reduced digester yield. The yield of these
pulps varied between the highest values of 74.18% to the lowest
value of 67.1%. Statistical analysis indicated that the effect of
chemical charge as well as the combined effect of the variables
on digester yield was statistically significant at 95% (Table 3).
Therefore, to compare the averages, the Duncan multiple range
test was used, and the results are shown in each figure using
lower case letters. An increase of chemical charge resulted in a
decrease of the pulping yield because of lignin and carbohydrate
dissolution, especially hemicelluloses (under the influence of
sodium sulphite and sodium bicarbonate). Generally, charging
10% chemical led to the greatest yield, and the lowest yield was
related to 18% chemical charge as expected [23].
Intensity of chemical reactions and delignification is increased
with greater amount of chemicals used and the raw material
becomes much softer. Thus, fibers will be separated more
simply and there would be a better refining. Deniz I et al. [20]
have reported that the effect of utilized chemical charge on properties
of pulp is very crucial as the pulp yield is reduced with
higher amounts of chemicals in the cooking liquor.
Furthermore, results of freeness distinguished that by increasing
the percentage of chemical charge, treatment will be intensified,
lignin dissolution will be increased, and water passing
through pulps will be decreased due to more bonds between fibers.
Moreover, greater amounts of chemical will intensify chemical
reaction; encourage penetration of chemical into fiber structures;
and increase their swelling which will lead to improve
refining of the fibers. As a result, needed rotations of the refiner
for meeting the desired freeness will be decreased.
The impact of chemical charge on strength properties, including
tensile strength index, burst strength index, and tear
strength index, was statistically significant at 95% (Table 3). The
results showed that a higher chemical charge increased pulp
strength property.
Even though the influence of chemical charge on strength
indices revealed that higher chemical charges improved the
strength values of the pulps, CMT, RCT, tensile index, Stiffness,
tear index, and burst index, increased to 217.33KNm-1, 1.95KNm-
1, 54.79Nmg-1, 770.22KNm-1, 7.43mNm2g-1 & 3.86kPam2g-1,
respectively. While the lowest value is related to the paper
produced from pulp of MWPI, due to elimination of more lignin.
The most effective factors on mechanical properties are
quality and quantity of bonds among fibers, fibers strength
and length of fibers [28]. Among these factors, “bonds between
fibers” is more important than others. Refining of the pulps
introduces a positive effect on strength properties of the papers
produced. Comparison of the sample (NSSC pulp of MWPI)
(Figure 1) with the papers made from eucalyptus wood shows
that the later were refined with higher rotations. Further
refinement increases the quality and quantity of bonds between
fibers, improves flexibility and thus, more fiber fibrillation
than before. So enhanced mechanical properties of the papers
made from eucalyptus can be partially attributed to the further
refinement of its resultant pulps.
Higher tear index of the eucalyptus paper can be explained
by better biometrics coefficients which cause better refinement
of the fibers and leads to improved bond of papers prepared
from eucalyptus, as the most effective factor on the tear strength
index is length of fibers. Increased length of the fibers improves
tear strength, since in this case greater force would be required
to cut the fibers [29]. In fact, length of fibers, slenderness ratio
and Runkel ratio of eucalyptus fibers are almost the same as
hardwoods of forests in northern Iran and even its Runkel ratio
(115.19μm) is far better than many industrial hardwood species
which itself can improve tear index additionally.
Two factors are effective on burst strength properties,
namely length of fibers and bonds between fibers. Although
increased length of fibers may lead to higher burst index, this
characteristic is more dependent on the bonding between fibers.
Increased rotations of refiner will also enhance burst strength to
some extent, while additional removing of lignin from pulp and
formation of stronger bonds within pulp will also improve burst
strength characteristics. The above-mentioned reasons can
explain higher burst strength index for the samples produced
from eucalyptus at various cooking conditions.
Figures 2-7 show the effects on pulp strength properties
under the influence of chemical. The maximum amount of
strength indices observed in the NSSC pulp produced by 18
% chemical charge while the minimum amount of them was
observed in the NSSC pulp made in MWPI. It can be observed
that all average values of resultant papers are categorized in four
distinct groups (Figures 2-7).
Conclusion
a) The result of chemical content of eucalyptus is in the
satisfactory range for pulp production.
b) The results showed that pulp yield decreases with
increase of chemical charge.
c) Analysis of the mechanical properties indicated that
the paper from NSSC eucalyptus at various cooking levels
has preference to NSSC pulp of hardwoods produced in
MWPI for all strength indices.
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