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Silica from Geothermal Waste as Reinforcing Filler in Artificial
Leather MUH Wahyu Syabani1,a*, INA Amaliyana1,b , INDRI
Hermiyati1,c
and YAYAT Iman Supriyatna2,d 1 Department of Rubber and Plastic
Processing Technology, Politeknik ATK Yogyakarta, Jl Prof.
Dr. Wirdjono Prodjodikoro, Panggungharjo, Sewon, Bantul, DI
Yogyakarta, Indonesia 2 Research Unit for Mineral Technology,
Indonesian Institute of Sciences, Jl Ir Sutami Km 15
Tanjung Bintang, Lampung Selatan, Indonesia
[email protected], [email protected],
[email protected],
[email protected]
Keywords: Geothermal, Silica, Filler, Artificial Leather
Abstract. The main components of artificial leather were
polymer, plasticizer, stabilizer, and filler. Silica is one of the
commons reinforcing filler for many composites. Meanwhile,
amorphous silica is usually precipitate in geothermal power plants
and become solid waste in large amounts. The aim of this study is
to evaluate the mechanical properties of PVC-based artificial
leather by utilizing geothermal silica as reinforcing filler. The
plastisol was prepared by mixing the PVC, plasticizer,
co-plasticizer, stabilizer, and filler with the amount of 100, 60,
3, 0.5 and 25 phr respectively. Commercial-calcium carbonate and
geothermal-silica were used as filler for each sample formulation,
then the non-filler plastisol also prepared as a reference.
Artificial leather made by coating the release paper using the
plastisol then heated at 190oC. The mechanical properties were
investigated using a universal testing machine for the elongation,
tensile strength and separation force. The surface morphology of
each sample were analyzed using SEM. The results show us that the
geothermal silica filled artificial leather has better elongation,
tensile strength, and separation force compared to the calcium
carbonate since there are stronger filler-polymer bonds formed.
Therefore geothermal silica has high potential as filler for
artificial leather, thus gives an alternative solution for the
solid waste problem in geothermal power plant and also provide
low-cost source of reinforcing fillers for artificial leather
industries.
Introduction The demand for artificial leather has been
increased in recent years since it can be used in many
applications such as furniture, automotive, electronic
accessories, apparels and stationary [1–3]. The advantage of the
materials are cost-saving, various colors, easy processing,
consistent appearance, lightweight, and others [3]. The main
components of artificial leather were polymer, plasticizer,
stabilizer, and filler that called plastisol [4]. The plastisol
processing is one of the most efficient procedures since its
relatively easy processing and low equipment costs compared to
other method [5,6]. Artificial leather usually consists of topcoat,
middle coat, base coat, and backing cloth. The backing cloth is
covered with synthetic polymer coating layer [7] and the most
commonly used polymer is polyvinylchloride (PVC) [8].
Fillers are incorporated into almost all plastisol formulations
because of the properties modification and cost reduction [5]. Its
commons for artificial leather manufacturer using calcium carbonate
as filler because of low-cost and enhance color [9,10], but since
its inert filler, the mechanical properties of the leather tends to
decrease [10]. Silica is known as polymer reinforcing filler
because of its high thermal stability and better strength
properties of the composite products [11]. In general, amorphous
silica is preferred as filler, as the crystalline ones tend to
cause wear of compounding machinery and can causing fiber length
degradation [12]. Meanwhile, scaling that contains amorphous silica
is usually occurred in a geothermal power plant system [13,14].
During operation, a large amount of silica was extracted and
considered as solid waste [15]. This adds a real problem for the
power plants in waste management.
Key Engineering Materials Submitted: 2019-10-15ISSN: 1662-9795,
Vol. 849, pp 78-83 Revised: 2020-01-15© 2020 Trans Tech
Publications Ltd, Switzerland Accepted: 2020-01-15
Online: 2020-06-24
All rights reserved. No part of contents of this paper may be
reproduced or transmitted in any form or by any means without the
written permission of TransTech Publications Ltd,
www.scientific.net. (#538916974-27/04/20,16:30:51)
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There is some literature that studied the formulation of the
artificial leather [2,4,6,7,16] or the using of geothermal silica
[14,15,17] but there is still no exploration about utilizing
geothermal silica as an additive in artificial leather. In other
side, mechanical properties are an important factor in determining
the quality of artificial leather [3]. Therefore, the aim of this
study is to evaluate the mechanical properties of PVC-based
artificial leather by incorporate geothermal silica as reinforcing
filler.
Experimental Method Plastisol formulations applied are composed
of resin (PVC-E), plasticizer (dioctyl phthalate
(DOP) and 2,2,4-trimethyl-1,3-pentanediol diisobutyrate (TXIB)),
stabilizer (Lastab DP728), and filler as stated in table 1.
Commercial-calcium carbonate and geothermal-silica were used as
filler for each sample (CC and GS), then the non-filler plastisol
also prepared as a reference (REF) to studying the effect of
fillers addition. Geothermal silica is a by-product of power
generation by PT. Geodipa Energy unit Dieng, Indonesia.
Table 1. Artificial leather adhesive plastisol formulation
Material Sample, phr GS CC REF
Resin 100 100 100 Plasticizer
Co-plasticizer 60 3
60 3
60 3
Stabilizer 0.5 0.5 0.5 Calcium carbonate 0 25 0 Geothermal
silica 25 0 0
The formulations were prepared for application by mixing the
plasticizer and stabilizer together
for 20 seconds at 30 rpm. Then, adding filler into the mixture
and continuing mix for 2 minutes at 30 rpm. Afterward, PVC resin
was added and mixed for 7 minutes at 30 rpm. The plastisol ready
for coating processes.
The coating was carried out by heating the released paper at
170-180oC for 20 seconds, then the skin plastisol was coated and
heated at 190-200oC in 1-minute duration. The next step is coating
using adhesive plastisol and laminating using fabric, then dried at
190-200oC during 1 minute. Finally, the artificial leather was
cooled at room temperature.
The geothermal silica was characterize using X-Ray Fluorescence
(XRF) PANalytical Epsilon3XLE. The separation, tensile strength,
and elongation test was done using Universal Tensile Machine (UTM)
Gester GT-K02. The specimen is prepared carefully using the
standard methods for coated fabric ASTM D751-06. Two sets of three
specimens are cut at machine direction (MD) and also transverse
direction (TD). Sample surface morphology was studied using
Scanning Electron Microscope (SEM) SNE-4500M.
Results and Discussion Raw materials characterizations. The mass
percentage of components in the geothermal silica
was measured using XRF analysis. The analysis stated in table 2
shows that materials have 96.9% of SiO2.
Table 2. XRF analysis of geothermal silica Compound SiO2 P2O5
Fe2O3 K2O CaO
Conc unit, % 96.904 0.884 0.787 0.749 0.469 The percentage of
silicon dioxide (SiO2) in geothermal waste is suitable to be used
as filler in
commons polymer compound. Although, the impurities in mineral
fillers can be serious effects on the product, such as discoloring
products, lower strength, and oxidative stability [10].
Key Engineering Materials Vol. 849 79
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Surface morphology. It should emphasize that the redistribution
of the adhesive in the coating appears to be appreciably dependent
on the surface area of the filler [5]. Therefore the finer filler
particle size gives higher value of the mechanical properties [10].
In order to confirm the distribution of the filler to the matrix,
SEM was measured and the results are stated in Fig. 1.
(a) (b) (c)
Fig. 1. SEM micrograph of the sample surface at 35x
magnification (a) GS (b) CC and (c) REF
From the Fig. 1, we can conclude that the geothermal silica, as
well as the commercial calcium carbonate, is homogeneously
distributed into the coating plastisol. Greater distribution of the
fillers particle will increase the adhesive strength. The adhesive
strength depends on the distribution of adhesives between substrate
and filler surface [5]. Plasticizer type also influences the
dispersion because it can diffuse into the PVC core or placing
itself between polymer [6]. But, since the type and amount of the
plasticizer on the formulation were similar, the variable can be
neglected. It is also should be underlined, that the discoloring
artificial leather because of metal impurities in the geothermal
silica as mentioned before was not taken place. The non-coloring
effect of the filler in the product was important, so the
manufacturer can adding pigment additives without worried about the
color interferences.
Mechanical Properties. The artificial leather making processes
need heat treatment at the final stage, the fusion and gelation of
the PVC particles occurred at this stage. As a result, the
plastisols change into stronger material that the characteristics
are determined by their composition [5]. Therefore, any change in
the formulation, such as filler materials, would directly affect
the product properties. Mechanical properties were evaluated
Universal Testing Machine to analyze the separation force, tensile
strength, and elongation as shown in Fig. 2-4.
(a) Result for machine direction (MD) (b) Result for transverse
direction (TD)
Fig. 2. Separation test result
Separation tests are important to figure out whether the coating
is not easily released from the fabric. Fig. 2 shows the result of
applying the GS and CC as a filler in the artificial leather. The
separation force was evaluated in terms of machine direction (MD)
and transverse direction (TD)
80 Waste and Biomass Application
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due to the orthotropic behavior of the samples [1]. The result
of the MD gives that while the CC addition gives lower separation
force, the GS addition has no significant differences with the
references. Artificial leather with GS addition gives 25% higher
separation strength as compared to the CC addition. The value for
GS, CC, and REF in MD are 3.90, 2.90 and 3.83 respectively. The
separation strength of the sample also has a similar trend fo TD
with value for GS, CC, and REF are 3.13, 2.37 and 3.30
respectively. We can summarize that the addition of GS give
efficient products in terms of cost, but it can maintain product
adhesion performance. Similar papers also reported the effect of
silicon-containing chemical in improving the adhesion strength of
the synthetic leather [16]. The presence of silanol groups in the
silica particle surfaces disrupted the phase separation and caused
improved rheological, mechanical and adhesion properties [9]. In
opposite, the absence of surface functional groups in calcium
carbonate filler affected the lack of polymer-filler interaction
[9].
Fig. 3. Tensile strength Fig. 4. Elongation
The average tensile strength value in Fig. 3 for GS, CC, and REF
is 58.80, 33.97 and 44.43 respectively. It is shown that the
addition of calcium carbonate to the artificial leather gives 24%
lower tensile strength compared to the reference. It occurs because
the filler type is inert, that generally has weak filler-polymer
interaction [5]. However, when the geothermal silica added to the
formulation, the value of the tensile strength increased 32% than
the reference. Fine particle size silica can be very useful in
polymer compound and give enhancement in its properties [10]. The
phenomenon that gives better properties such as tensile strength,
modulus and hardness is known as reinforcement.
The average elongation in Fig. 4 for GS, CC and REF is 283.33,
200.00 and 323.33 respectively. Filler addition usually resulting
in higher plastisol viscosity [9] and the result was confirmed,
which is the GS and CC sample has lower elongation than the
references. But, it should be also noted that the sample using
geothermal silica has a 30% better elongation than the calcium
carbonate. Higher mechanical properties of the artificial leather
are generally preferred for its application.
Conclusions The results show us that the addition of calcium
carbonate gives lower separation force, tensile
strength dan elongation compared to the reference since
inert-filler has weak filler-polymer interaction. Meanwhile, the
geothermal silica filled artificial leather has better elongation,
tensile strength, and adhesion strength compared to the calcium
carbonate because there are stronger filler-polymer bonds formed.
But the addition of filler also gives higher viscosity to the
plastisol, thus make the elongation of the product lower when
compared with the reference. Therefore geothermal silica has high
potential as filler for artificial leather, thus gives an
alternative solution for solid
Key Engineering Materials Vol. 849 81
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waste handling in geothermal power plant and provide low-cost
source of reinforcing fillers for artificial leather
industries.
Acknowledgment The authors gratefully acknowledge the use of the
facilities at Politeknik ATK Yogyakarta and
PT. Sempurna Indah Multinusantara.
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