M Alimadadi

T Uesaka

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Exploring One-more 
Dimension of Paper: 
Properties of 3D-Orieneted 
Fiber Network 
 
 
M. Alimadadi and T. Uesaka 
 
Department of Chemical Engineering and FSCN 
Mid Sweden University  
Sundsvall, Sweden 
majid.alimadadi@miun.se, tetsu.uesaka@miun.se  
 
1 INTRODUCTION  
Fiber network is ubiquitous. It is seen not only in 
industrial materials (paper and nonwoven) but also 
in biological materials (such as plant cells, animal 
tissues, etc.). Nature intricately manipulates the 
network structures, such as density, aggregation, and 
fiber orientation, to create a variety of 
functionalities. In this paper, as inspired by nature, 
we explore 3D fiber network (3DFN) structures. 
Unlike typical paper where fibers are laid and 
oriented in-plane, 3DFN has a non-planar fiber 
orientation that may offer unique properties not seen 
in conventional papers, e.g. mechanical and 
mass/heat transport properties.  
The objective of this study is to create 3D network 
from pulp fibers using foam forming process, as 
recently highlighted by [1]. We have started 
investigating the properties and characteristics of 
such network structures. 
2 EXPERIMENTAL 
Foam (or bubble) as a suspending medium for solid 
materials is known for many years. It has been 
introduced to the paper industry since the mid 1960s. 
Initially the foam forming was utilized in paper 
industry to improve formation of long and fine fibers 
at higher consistencies, and then later to enhance 
bulk and softness characteristics. Efforts also has 
been made to produce three dimensional network 
structures, but such attempts largely failed because 
of the inherent tendency of fibers lying down on the 
plane [2-3].  
In this study a specially prepared foam suspension 
followed by controlled forming procedure made it 
possible to retain fibers orienting randomly in 3D 
space. Refined TMP-rejects with average fiber 
length of 0.98 mm were used to prepare the 
networks. Sodium dodecyl sulfate (SDS) with 98.5% 
purity from Sigma Aldrich was used as foaming 
agent. Foam generation was done in a home-made 
mixing container with rotational speed of 500-2000 
rpm. A home-made foam applicator was utilized for 
sheet-making. For comparison, normal handsheets 
were also prepared by means of Rapid-Köthen sheet 
making machine. Some of these normal handsheets 
were produced using water suspension and others 
were produced from foam suspension.  
The 3D structures of foam-formed sheets were 
evaluated using SEM microscope combined with an 
image analysis method. The aim was to measure the 
fiber orientation in the Z-axis direction (sheet 
thickness direction). To evaluate the fiber orientation 
we applied the concept developed in [4] with some 
modifications. The principle of this approach is 
shown in Figure 1, where the fiber orientation is 
determined by a pair of angles ( , ). Consider two 
fiber cross sections intersected by two parallel 
planes. The pair angles of fiber are calculated based 
on in-plane displacement of the cross section 
( ) and the distance between two 
intersecting planes ( ) by  
 , and  
 .  
 
Figure 1. Schematic graph which describes the 
fiber orientation with pair of angles ( , ) [4]. 
 
The in-plane displacement and the distance 
between parallel planes were obtained by controlled 
deep etching, followed by image analyses of SEM 
cross section. Distribution functions obtained from 
cross sections always contain a bias associated with 
the probability of a fiber cut by the cross section 
plane. We corrected this effect by applying the 
correction factor obtained in [5]. In-plane and out-
of-plane mechanical properties of the foam-formed 
sheets were determined by an MTS universal testing 
machine.  
3 RESULTS AND DISCUSSION 
Table 1 shows the basic physical properties of the 
3DFN. The same properties of the normal handsheet 
samples are also presented. At the same basis weight, 
there are significant differences in the density and 
bulk of the 3DFN as compared with normal 
handsheets. Particularly the density of 3DFN is only 
5 kg/m3, as compared with 400 kg/m3 (or more) for 
normal handsheets, and the corresponding bulk is 
190 cm3/g for 3DFN.  
Table 1. Physical properties of different samples: RKWF: handsheet of water suspended pulp produced with 
Rapid-Köthen machine; RKFF: handsheet of foam suspended pulp produced with Rapid-Köthen machine; and 
3DFN: 3D fiber network. CoV: Coefficient of Variation 
  Thickness (mm) Grammage (g/m2) Density (kg/m3) Bulk (cm3/g) 
Sample RKWF RKFF 3DFN RKWF RKFF 3DFN RKWF RKFF 3DFN RKWF RKFF 3DFN
Average 0.127 0.146 11.7 59.56 59.43 59.76 468 409 5 2 2 191 
CoV% 3.10 3.16 15.80 1.73 2.41 6.13 2.50 2.69 15.67 2,50 2.69 15.67
 
 
Figure 2 shows the tensile stiffness index values for 
3DFN and normal handsheet samples. As expected, 
3DFN showed extremely low stiffness (or high 
softness) as compared with the reference sheets. 
What is interesting is that the relationship between 
tensile stiffness and density clearly deviates from a 
linear relation in this very low density range. This 
suggests changes in the fundamental mechanism in 
stiffness development, such as 3D fiber orientation 
effect and percolation effect.  
We have also measured a spring-back tendency in 
ZD-compression of this network. The sample was 
compressed down to 10% of its initial thickness, 
retained for 30 seconds, unloaded, and after 10 
seconds, the residual deformation was measured. 
The result showed approximately 75% recovery of 
the applied deformation.  
 
 
Figure 2. Tensile stiffness index vs. density for 
3DFN and normal handsheets. 
 
To further understand the behavior of 3DFN under 
compression, the deformation process of 3DFN 
cross sections with 2 mm thickness was observed 
under the optical microscope (Figure 3). It was 
evident that there was no obvious failure of fiber-
fiber bondings during loading/unloading cycle in 
compression. Fibers seem to undergo a large elastic 
bending deformation. This may explain the large 
spring-back of compression deformation. 
The same figure also shows that a substantial 
number of fibers are oriented in out-of-plane (ZD), 
unlike typical paper sheets where fibers are layered 
and oriented preferentially in the in-plane direction.  
Figure 4 shows the probability density function of 
fiber angle in the Z-axis direction (θ). The angle θ
0 corresponds to ZD orientation of fibers and π/2 
corresponds to the in-plane orientation. It is clear 
that more fibers are oriented in the out-of-plane 
direction. 
 
 
Figure 3. 3DFN of 2 mm slice under compression: 
(a), (b), (c) loading sequence, and (d) unloading. 
 
In Figure 5, the in-plane (MD)/out-plane (ZD) ratio 
of tensile strength index of different samples are 
compared. The ratio for 3DFN drastically decreased; 
this also confirms the out-of-plane fiber orientation.  
 
 
Figure 4. Probability density function of the fiber 
orientation in 3DFN structure. Probability density 
function is not normalized.  
4 CONCLUSION 
The 3DFN has unique structures, which are not 
seen in normal sheets. Extreme high bulk and 3D 
fiber orientation may offer special mechanical 
properties and mass transport properties suited for a 
class of hygiene products and composite materials. 
For example, in the area of short-fiber-reinforced 
composites, dispersing individual fibers uniformly is 
the most challenging task in order to ensure the 
reinforcement effect of fibers. Pre-forms made of 
this 3DFN may be a way to make fiber-reinforced 
polymer composites without flocculating fibers 
within the composites. High spring-back property 
may offer additional comfort of, for example, bed 
cover and adult hygiene.  
 
 
Figure 5. MD/ZD tensile strength index ratio of 
3DFN and normal paper samples.  
ACKNOWLEDGEMENT 
The authors would like to thank Dr. Tuomo Hjelt 
from VTT Finland, for valuable discussions and 
information on foam forming process.  
REFERENCES 
 
[1] Poranen, J., et al., BREAKTHROUGH IN 
PAPERMAKING RESOURCE EFFICIENCY 
WITH FOAM FORMING, in TAPPI PaperCon 
2013. 2013, TAPPI: Atlanta, GA. 
[2] Gatward, A.P.J., Radvan, Bronislaw, 
METHOD AND APPARATUS FOR 
FORMING A NON-WOVEN FIBROUS WEB 
FROM A FOAMED FIBER FURNISH. 1973: 
United States. 
[3] Radvan, B. and A.P.J. Gatward, The Formation 
of Wet-Laid Webs by a Foaming Process. Tappi 
Journal, 1972. 55(5): p. 748-751. 
[4] Clarke, A., G. Archenhold, and N. Davidson, A 
novel technique for determining the 3D spatial 
distribution of glass fibres in polymer 
composites. Composites science and 
technology, 1995. 55(1): p. 75-91. 
[5] Zhu, Y., W. Blumenthal, and T. Lowe, 
Determination of non-symmetric 3-D fiber-
orientation distribution and average fiber length 
in short-fiber composites. Journal of composite 
materials, 1997. 31(13): p. 1287-1301. 
 
 


Exploring One-more Dimension of Paper: Properties of 3D-Orieneted Fiber Network

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Exploring One-more Dimension of Paper: Properties of 3D-Orieneted Fiber Network

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