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 amw-syabani@kemenperin.go.id, binaamaliyana267@gmail.com, cindri_her@yahoo.co.id,

yayat_iman@yahoo.com

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)

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

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

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

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.

References [1] K. Pimapunsri, T. Wuttipornpun, D. Veeranant, A Study of the Factors Affecting the

Separation Force of Artificial Leather Laminating Process, Key Engineering Materials. 728 (2017) 307–312. https://doi.org/10.4028/www.scientific.net/KEM.728.307.

[2] C. Yang, J. Wang, L. Li, A novel approach for developing high thermal conductive artificial leather by utilizing smart electronic materials, Textile Research Journal. 87 (2017) 816–828. https://doi.org/10.1177/0040517516641356.

[3] E.K. Roh, K.W. Oh, S.H. Kim, Effect of raising cycles on mechanical, comfort, and hand properties of artificial suede, Textile Research Journal. 84 (2014) 1995–2005. https://doi.org/10.1177/0040517514528561.

[4] D. Gurera, B. Bhushan, Fabrication of bioinspired superliquiphobic synthetic leather with self-cleaning and low adhesion, Colloids and Surfaces A: Physicochemical and Engineering Aspects. 545 (2018) 130–137. https://doi.org/10.1016/j.colsurfa.2018.02.052.

[5] G.V. Rybachuk, I.I. Kozlova, V.B. Mozzhukhin, V.V. Guzeev, PVC plastisols: Preparation, properties, and application, Polym. Sci. Ser. C. 49 (2007) 6–12. https://doi.org/10.1134/S181123820701002X.

[6] A. Zadhoush, M.A. Alsharif, P.E. Alsharif, The Influence of K-Value and Plasticizer Type on the Rheological Behaviour of Plastisol Used in Coated Fabrics, Iranian Polymer Journal. 13 (2004) 371–379.

[7] I. Maia, J. Santos, M. Abreu, T. Miranda, N. Carneiro, G. Soares, PVC-based synthetic leather to provide more comfortable and sustainable vehicles, IOP Conf. Ser.: Mater. Sci. Eng. 254 (2017) 122006. https://doi.org/10.1088/1757-899X/254/12/122006.

[8] S. Joneydi, A. Khoddami, A. Zadhoush, Novel superhydrophobic top coating on surface modified PVC-coated fabric, Progress in Organic Coatings. 76 (2013) 821–826. https://doi.org/10.1016/j.porgcoat.2013.01.011.

[9] J. Donate-Robles, J.M. Martín-Martínez, Addition of precipitated calcium carbonate filler to thermoplastic polyurethane adhesives, International Journal of Adhesion and Adhesives. 31 (2011) 795–804. https://doi.org/10.1016/j.ijadhadh.2011.07.008.

[10] J.A. Brydson, Plastic Materials, 7th ed., Butterworth-Heinemann, Oxford, 1999. [11] Ł. Klapiszewski, F. Pawlak, J. Tomaszewska, T. Jesionowski, Preparation and Characterization

of Novel PVC/Silica–Lignin Composites, Polymers. 7 (2015) 1767–1788. https://doi.org/10.3390/polym7091482.

[12] R.N. Rothon, Particulate Fillers for Polymers, iSmithers Rapra Publishing, 2002. [13] D.B. van den Heuvel, E. Gunnlaugsson, I. Gunnarsson, T.M. Stawski, C.L. Peacock, L.G.

Benning, Understanding amorphous silica scaling under well-constrained conditions inside geothermal pipelines, Geothermics. 76 (2018) 231–241. https://doi.org/10.1016/j.geothermics.2018.07.006.

82 Waste and Biomass Application

[14] M. Olvianas, A. Widiyatmoko, H.T.B. Petrus, IR Spectral Similarity Studies of Geothermal SilicaBentonite Based Geopolymer, in: Green Construction and Engineering Education for Sustainable Future, 2017. https://doi.org/10.1063/1.5003498.

[15] J.A. Villarias, M.L.H. Yorro, M.-I.K.N. Galvan, L.J.L. Diaz, High Purity Silica Nanoparticles from Geothermal Waste Brine as Reinforcing Filler in Rubber Composite Material, Materials Science Forum. 894 (2017) 104-108. https://doi.org/10.4028/www.scientific.net/MSF.894.104.

[16] E.J. Kim, I.K. Paik, J.H. Park, Preparation and adhesion properties of waterborne polyurethane-coated resin for synthetic leather, in: California, USA, 2019: p. 030005. https://doi.org/10.1063/1.5094315.

[17] O.G.M. Sandoval, A.E.L. Orozco, S. Valenzuela, G.C.D. Trujillo, Modified amorphous silica from a geothermal central as a metal adsorption agent for the regeneration of wastewater, Water Resources and Industry. 21 (2019) 100–105. https://doi.org/10.1016/j.wri.2018.100105.

Key Engineering Materials Vol. 849 83