Natural Resources, 2011, 2, 125-129
doi:10.4236/nr.2011.22017 Published Online June 2011 (http://www.scirp.org/journal/nr)
125
Effect of Ultrasound and Xylanase Treatment on the
Physical-Mechanical Properties of Bleached Eucalyptus
Kraft Pulp
Larisse Ribas Batalha1, Juliana da Silva1, Carolina Jardim2, Rubens Oliveira1, Jorge Colodette1
1Federal University of Viçosa, Viçosa, Brazil; 2Suzano Celulose e Papel SA, Brazil
Received April 7th, 2011; revised April 18th, 2011; accepted April 25th, 2011.
ABSTRACT
The modification on the fiber structure of bleached eucalyptus kraft pulp is a very attractive alternative for improve-
ments in the properties of paper production. The enzymatic treatment by xylanases and ultrassonic treatments modify
the characteristics of the fibers, has been reported. Therefore, the purpose of this study was to evaluate the influence of
ultrasonic waves as a facilitator of the action of enzymes (hemicellulase) by modifying the physicochemical nature of
fiber eucalyptus Kraft pulp, in order to improve the physical and mechanical properties of the paper. But it was ob-
served the that idea of ultrasound acts as facilitator for action of enzymes can’t be affirmed, since in most properties
XA-1 and XA-2 were equal statistically. It may be noted that the junction of ultrasound and xylanase provided improves
on tensile index, specific elastic modulus and tensile energy absorption and a decrease of tear index on the mechanical
properties of handsheet and it increased the opacity when the ultrasound was applied before xylanase.
Keywords: Ultrasonic, Xylanases, Physical Properties, Mechanical Properties
1. Introduction
The modification on the fiber structure of bleached euca-
lyptus kraft pulp is a very attractive alternative for im-
provements in the properties of paper production. The
enzymatic treatment by xylanases modifies the character-
istics of fibers, improvement of hydration, internal fibril-
lation and delamination has been reported. The ultra-
sound promotes morphological changes, generating im-
provements in properties, without the increase of chemi-
cals demand or generation of toxic effluents.
The ultrasonic is defined with a sound of frequency
beyond response of human hearing, that is, higher than
16kHz (1600 cycles per second) [1]. This may produce
morphological changes in the fiber which can contribute
for a best conformability, flexibility and consolidation of
the fibers during paper formation [2]. The xylanases have
shown potential for modification of cellulose fibers,
promoting improvements in bleachability of kraft pulp
[3]. In the bleaching the enzyme acts degrading xylan
molecules precipitated (deposited in the fibers at the end
of cooking) and cleaving bonds lignin-carbohydrate [4].
Also, it is reported improvements in hydration (swelling),
internal fibrillation and delamination due to the enzy-
matic treatment of pulp, mediated by xylanases [5].
The effects of ultrasonic on the enzymes aren´t very
known and ccontradictory results are observed when they
are treated at high intensities. Only some enzymes are
inactivated by application of ultrasound systems at high
intensities, since the sonification doesn’t denature all
proteins, unlike heat denaturation, which could explain
the contradictions with respect to deactivation of the
enzymes by sonification [6]. The low intensities of ultra-
sonics in some cases may increase the activity of free
enzymes [7].
So, changes of eucalyptus fiber by ultrasonic and en-
zymatic treatment have considerable influence in the
paper production process and can improve the perform-
ance of fiber-fiber and fiber-water interactions. It also
contributes to the consolidation of product properties.
Therefore, the purpose of this study was to evaluate the
influence of ultrasonic waves as a facilitator of the action
of enzymes (hemicellulase) by modifying the physico-
chemical nature of fiber eucalyptus Kraft pulp, in order
to improve the physical and mechanical properties of the
paper.

126 Effect of Ultrasound and Xylanase Treatment on the Physical-Mechanical Properties of Bleached Eucalyptus Kraft Pulp
2. Experimental
2.1. Material
The equipment used to generate ultrasonic waves in this
work was the model VIRSONIC 475 with a frequency of
20 kHz using the maximum power of the equipment (190
W). The dosage of xylanases used was 5000 U/kg.
2.2. Methods
Three treatments were performed: I) treatment of euca-
lyptus kraft pulp by ultrasound and subsequent xylanase;
II) treatment of eucalyptus kraft pulp by xylanase and
subsequent ultrasound treatment; III) treatment of euca-
lyptus kraft pulp by xylanase only. In the three treat-
ments it was used pulp with consistency of 3% and pH
range of 7 to 7.5 After the treatments, the cellulose pulps
were refined in PFI mill laboratory. For the realization of
physico-mechanical and optical tests it was formed labo-
ratory sheets, which are stored in an environment with
relative humidity of 50  2% and 23  1˚C temperature.
All procedures and tests were realized according to
TAPPI procedures [8]. The treatments were compared
statistically.
The adjusted equations were compared by F test, using
the models identity test and adopting a significance level
of up to 5% probability according to the methodology
presented by [9] for linear models. The equations were
compared in order to check equality between them. If so,
the equations were reduced to a single equation. If it had
confirmed a significant difference between the equations,
it was not tested which differed. The tested hypotheses
were: H0: all equations are equal and they may be repre-
sented by a common reduced equation, and H1: the equa-
tions are different statistically and they can’t be reduced
to a common equation.
3. Results and Discussion
3.1. Nomenclature of Treatments
XA-1: treatment of eucalyptus kraft pulp by ultrasound
and subsequent xylanase;
XA-2: treatment of eucalyptus kraft pulp by xylanase
and subsequent ultrasound;
XA-3: treatment of eucalyptus kraft pulp by xylanase
only.
3.2. Refining PFI
The choice of the number of revolutions is indicated by
the degree of drainability of an aqueous suspension of
fibers [10]. The equipment used in the Pulp and Paper
Laboratory for measuring the degree of drainability is the
Schopper-Riegler. This expresses the degree of refining
as Schopper-Riegler degree (˚SR).
Four points of refining were made. In order to obtain a
curve to analyze how the properties of paper formed
“react” to refining, trying to achieve a value close to 50
˚SR. The maximum degree Schopper used was 60 ˚SR.
These values are used because many companies that
produce paper derived from bleached Kraft pulp employ
them. During the refining it is also obtained the energy
needed to refine the pulp. In a company the consumption
is very important, because it is directly tied to production
costs. To study the effect of enzyme treatment and ul-
trassonification on the consumption energy a graphic was
done which relates this with the degree Schopper-Riegler
(Figure 1).
Based on the F test, the hypothesis of equality between
equations relating at XA-1 and XA-2 in function of en-
ergy consumption was accepted (P < 0.05), and these can
be represented by the common model estimated, repre-
sented in Figure 1. Therefore XA-1 and XA-2 are statis-
tically equal, thus the order of application of ultrasound
and enzyme on pulp didn’t provide difference on the
energy consumption. However, it can see that the addi-
tion of the ultrasonic treatment and enzymatic treatments
didn’t provide energy consumption when compared to
treatment with only the enzyme. This is because when
ultrasound is applied before the xylanase promotes fibril-
lation and leaves the xylans more exposed and thus the
xylan are hydrolyzed more easily. The low xylans con-
tent affect the pulp hydration decreasing it, thus hinder-
ing the refining and increasing the energy consumption.
In the case of II treatment in which the xylanase is ap-
plied before the ultrasound have that the xylanase hydro-
lyzes xylans chains and the ultrasound removes xylan
deposited on the surface layer of the fiber. So content of
xylans also will be lower, therefore, becoming the refin-
ing difficult.
REF: ,
32
ˆ0.00030.02820.1211 24yxxx 2100R
XA-1 and XA-2: y (commonmodel),
2
ˆ0.006 0.279716.4 x
298.98R
XA-3: ,
2
ˆ0.013330.4898 17313yxx
299.77R
Figure 1. Schopper-Riegler (˚SR) versus energy consump-
tion. Below the estimated equations for each treatment.

Effect of Ultrasound and Xylanase Treatment on the Physical-Mechanical Properties of Bleached Eucalyptus Kraft Pulp 127
If loss of hemicelluloses occur the hydration of the pulp
becomes smaller, thus to achieve determined higher
Schopper-Riegler degree it would be necessary to inten-
sify the refining, this it may be observed in the treated
pulp with xylanase (XA-3) when it is considered the
enzyme effect (zero point of the refining), Schopper-
Riegler degree found was lower than the reference.
3.3. Physical and Mechanical Properties
3.3.1. Tensile Index
The tensile strength is related to the durability and utility
of the paper, for example, packaging papers are subject
to direct tension forces. This is favored by intensity of
interfibrillar links occurred during the formation of the
paper, the external fibrillation and the collapse of the
fibers [10].
For the F test, the hypothesis of equality between
equations relating at XA-1 and XA-2 in function of en-
ergy consumption was accepted (P < 0.05), and these can
be represented by the common model estimated, repre-
sented in Figure 2.
The xylanase removes superficial hemicelluloses
which decrease the interfibers links, consequently, the
tensile index, since this favored by intensity of interfi-
brillar links. Therefore, the treatment III has a tensile
index lower than the reference.
XA-1 and XA-2 were statistically equal. This shows
that the ultrasound acts superficially increasing the ex-
tern fibrillation, hence, raises the tensile index.
During the tensile tests force-deformation relations are
produced and through these relations the properties of
specific elastic modulus (MOE) and tensile energy ab-
sorption (TEA) will be derived. MOE is an important
property because they represent the capacity of the mate-
Figure 2. Tensile index versus energy consumption. Below
the estimated equations for each treatment.
rial to absorb force without, however, suffering substan-
tial deformation. The TEA represents the durability of
paper when subjected to repetitive use, under conditions
of tensile or impact. In this work it was observed that the
joint of enzymatic and ultrasonic treatment resulted in
additional properties MOE and TEA in relation to initial
pulp. It was found an increase of 48.0% and 12.1% for
TEA and MOE, respectively.
3.3.2. Tear Index
The tear resistance measures the work required to tear
the paper. The length of the fiber and the link between
them are factors that may affect the resistance for the
tearing [10].
The F test showed that the hypothesis of equality be-
tween equations relating at XA-1 and XA-2 in function
of energy consumption is accepted (P < 0.05), and these
can be represented by the common model estimated,
represented in the Figure 3.
It was observed the treatment of pulp with xylanase
only decreases the tear index. This fact may be explained
by action of xylanase that reduces the intrinsic fibrillar
resistance due to removal of superficial hemicelluloses.
It also noted that the ultrasound doesn’t compromise the
fibrillar wall, and the increase observed in relation to the
reference reinforces the idea of fibrillation.
3.4. Optical Property
3.4.1. Opacity
Opacity is an optical property that is related to the
amount of light transmitted through the paper [10], there-
fore, with phenomena of refraction, dispersion and ab-
sorption. Thus, the greater the amount of void spaces, the
greater the amount of surface refraction, dispersion and
absorption, and the lower the amount of light transmitted
to the opposite side of the paper and the greater the opac-
REF:
2
ˆ0.03072.1988 16.24yxx 2
R=99.4
XA-1 and XA-2: (common model),
2
ˆ0.01681.7655 21.527yxx 
2
R =99.16
XA-3: ,
2
ˆ0.00810.43493.5466yxx2 R=99.93
REF:
2
ˆ0.01140.5217 4.7284yxx 2
R=84.23
XA-1 and XA-2: (common
model),
2
ˆ0.00420.3116 5.4956yxx 
2
R =89.40
2 2
XA-3: ,
ˆ0.00810.43493.5466yxxR=99.4
Figure 3. Tear index versus energy consumption. Below the
estimated equations for each treatment.

128 Effect of Ultrasound and Xylanase Treatment on the Physical-Mechanical Properties of Bleached Eucalyptus Kraft Pulp
ity of the paper.
By F test applied to treatments it was found that the
hypothesis of equality between equations relating to REF
and XA-3 in function of energy consumption is accepted
(P <0.05), and these can be represented by the common
model estimated, represented in Figure 4.
It was observed that the xylanase didn’t act to the
point of causing alteration significant in the opacity. The
hydrolyzed xylan by enzyme and removed by ultrasound
(XA-2) caused an increase on bulk, which reflected in
rising of opacity (in relation to REF) provides higher
strength to light transmission. The figure of apparent
specific volume is represented in Figure 5.
The ultrasound due to direct effect in of resonance
loosens the fibrillar wall, and consequently, reduces
Figure 4. Opacity versus energy consumption. Beside the
estimated equations for each treatment.
Figure 5. Opacity versus energy consumption. Beside the
estimated equations for each treatment.
density of fibers [11]. The subsequent action of xylanase
causes stiffness due to loss of xylans, which during the
refining process result in a greater formation of thins and
these to take up spaces interfibrillar increase the opacity
of the paper formed.
4. Conclusions
The purpose of this study was to evaluate the influence
of ultrasonic waves as a facilitator of the action of en-
zymes (hemicellulases) by modifying the physicochemi-
cal nature of fiber eucalyptus Kraft pulp, in order to
improve the physical and mechanical properties of the
paper. But it was observed that the idea of ultrasound
acts as facilitator of action of enzymes can’t be affirmed,
since in most properties of XA-1 and XA-2 were equals
statistically. But, it was noticed that the junction of ultra-
sound and xylanase provided improves on tensile tensile
index, specific elastic modulus and tensile energy ab-
sorption and a decrease of tear index on the mechanical
properties of handsheet and increased the opacity when
the ultrasound was applied before xylanase.
REF and XA-3: , (common model),
2
ˆ0.00060.2352 80.657yx x
2
R =95.27
XA-1: ,
2
ˆ0.00110.19480.70yxx 2
R =99.10
XA-2: ,
ˆ0.141579.66yx 2
R =99.84
5. Acknowledgements
Financial support provided by the Minas Gerais State
Research Foundation (Fapemig) is greatly appreciated
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