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A Study on a New 3D Porous Polymer Printing Based on EPP Beads Containing CO2 Gas
Available online at www.sciencedirect.com
ScienceDirect Procedia Engineering 184 (2017) 10 – 15
Advances in Material & Processing Technologies Conference
A Study on a New 3D Porous Polymer Printing Based on EPP Beads Containing CO2 Gas C. J. Yoo1, B. S. Shin2,3,*, B. S. Kang1, C. Y. Gwak1, C. Park2, Y. W. Ma2, and S. M. Hong3 1
Engineering Research Center for Net Shape and Die Manufacturing, Pusan National University, Pusan 609-735, Korea 2 Department of Cogno-mechatronics Engineering, Pusan National University, Pusan 609-735, Korea 3 Convergence Research Center of 3D Laser-Aided Innovative Manufacturing Technology, Pusan National University, Pusan 609-735, Korea
Abstract We propose a new CO2 gas-based 3D PPP (Porous Polymer Printing) developed based on the Fused Deposition Modeling scheme of Additive Manufacturing. The 3D porous polymer structure was stacked layer by layer, which was a rapid single step manufacturing technique for a multilayer product in single device. A hybrid filament of diameter 1.75 mm was introduced with EPP (Expanded Polypropylene) beads containing CO2 gas. EPP beads, which have several desirable characteristics such as light weight, shock absorption, thermal insulation, heat resistance, weather resistance, oil resistance, and chemical resistance, were also subject to various process conditions such as EPP type, laminate thickness, printing speed and nozzle temperature. In this paper, three types of EPP beads with expansion ratios of 15, 30 and 40 % were investigated. We found the experimentally optimal process conditions of a new CO2 gas-based 3D PPP method and finally demonstrated a simple 3D structure. In the future, a faster production and the mechanical shock absorption effect will be studied and tested for application in the automobile industry © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of the Advances in Material & Processing Technologies (http://creativecommons.org/licenses/by-nc-nd/4.0/). Conference.under responsibility of the organizing committee of the Urban Transitions Conference Peer-review Keywords: 3D PPP (Porous Polymer Printing), Micro Porous Structure, Hybrid Filament Manufacturing, AM (Additive Manufacturing), EPP (Expanded Polypropylene)
* Corresponding author. Tel.: +82-51-510-2787; fax: +82-51-512-1722. E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the Urban Transitions Conference
doi:10.1016/j.proeng.2017.04.064
C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
Nomenclature Vf Pf P N0 M A
Void fraction of the extruded foam Density of sample in the water Density of sample in the air Original unfoamed polymer Magnification factor of the micrograph Area of micrograph
1. Introduction During the past few years, interest has grown in porous polymers involved in several fields of application because of the advantages of the porous structure. Compared to the existing polymer, the porous polymer has improved properties such as energy absorption, fracture toughness, fracture strength, sound absorption, thermal insulation and fatigue life [1-2]. Various products apply a porous structure and mostly need to be light weight. Currently, the method of forming a porous polymer is used for several processes such as the deposition of aerosol nanoparticles, nanoimprinting, batch foaming processes, and etc. [3-5]. However, these processes have the disadvantages of complexity, cost and time. Therefore, a new three-dimensional porous polymer stacking technology that simplifies processing and requires less expense and time is necessary. Recently, due to the advantages of AM(additive manufacturing), the application to fields such as food, medicine, and industry has spread rapidly. AM is suitable for small production, and easy for making individually customized products. AM encompasses a variety of methods such as FDM (Fused Deposition Modeling), SLS (Selective Laser Sintering), SLA (Stereo Lithography Apparatus), 3DP (3 Dimensional Printing), DLP (Digital Light Processing), LOM (Laminated Object Manufacturing), etc. [6]. Among them, FDM is the method of stacking while melting a thermoplastic in the nozzle. Compared to the existing method, it has the characteristics of simple structure and is inexpensive [7]. At this time, the required materials (thermoplastic polymers such as PVC, ABS, PLA, PVA, etc.) are in common use. However, the formation of a porous polymer using these materials is very difficult. Therefore, it is necessary that we use material made of a porous polymer structure. In this paper, we suggest a new 3D printing technique—CO2 gas-based 3D PPP (Porous Polymer Printing)— using EPP beads containing CO2 and investigated the simple 3D structure of the porous polymer based on the EPP foam ratios. 2. 3D PPP(Porous Polymer Printing) 2.1. 3D PPP process The process that we used in this paper is a CO2 gas-based 3D PPP process. 3D PPP refers to a technique that can manufacture a porous structure having a three-dimensional shape using 3D printing. In other words, it generates gas bubbles (N2, CO2, etc.) during the injection molding and extrusion molding processes, and the product is manufactured with air bubbles dispersed in the polymer resin. The purpose of this process can be to reduce weight and material cost because the volume consists of air bubbles. The mechanical properties can be adjusted to produce a superior product [8]. A CBA (Chemical Blowing Agent) hybrid filament was formed by mixing PP and CBA and extruded to a diameter of 1.75 mm. Using the CBA hybrid filament, the pores can be formed inside the shape during the thermal decomposition reaction of the CBA [9]. This porous structure was studied in the CO2 gas- based 3D PPP process to increase porosity. In summary, after the EPP beads were passed through the extruder, the CO2 hybrid filament was manufactured. The porous polymer structure of three-dimensional shape can be manufactured using the CO2 hybrid filament.
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C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
2.2. Shape of porous structure The shape of the porous structure is generally classified as opened cell or closed cell. An opened cell structure is one where the majority of pores are combined, such as in a sponge. On the other hand, the structure of a closed cell has different shapes for the pores, such as Styrofoam. Opened cell has better resilience than closed cell, and closed cell has better thermal insulation than opened cell [10-11]. The closed cell has the advantages of strength, high Rvalue, and high resistance to leakage of air or vapor. However, it is more expensive because it requires a dense structure. The porous structure has a greater elasticity modulus, when the height ratio (ratio of the size of pores to width of pores) is large. In other words, it deforms satisfactorily and has superior relief of mechanical shock. 2.3. Pore density After foaming, the mass densities of samples, “P” and “Pf”, were measured in air and in distilled water. “A” is the area of the micrograph and “n” is the number of pores in the optical micrograph within “A”. “M” is the magnification factor of the micrograph. The void fraction of the extruded foam (Vf) and the pore density per unit volume of the foamed polymer (N0) were determined from the optical micrograph using the equations (1) and (2) [12].
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· ڍª ڌº ¸ « ¸ » ڱ ڌ ¼ ہ ¹ ¬
(2)
3. Experiment 3.1. Material preparation Generally, EPS (Expandable Polystyrene) is a bead blowing agent that has been most widely used as packaging. The requirement of advanced and enhanced safety has been increased in product packaging. Thus, alternative materials have been developed to reinforcing the physical vulnerability of EPS. Initially, EPE (Expanded Polyethylene) has been developed with cross-linking having superior property. However, it has a complex manufacturing process, is recyclable, and increases production costs. Finally, by simplifying the process, EPP (Expanded Polypropylene) has been developed. It can be recyclable, and it is non-crosslinked. EPP has superior properties such as brittleness, repeated shock absorption, ductility, chemical resistance, etc., because it is based on PP [13-16]. Therefore, EPP beads with expansion ratios of 15, 30 and 40 % were used in this experiment, and were developed by Hanwha Advanced Materials. These are referred to as 15B, 30B and 40B, respectively. 3.2. Equipment The following is an explanation of the equipment used in this experiment. Fig. 1(a) is the extruder (Filabot Wee). With this equipment, it is possible to manufacture CO2 hybrid filaments using EPP beads. Since conventional temperature control devices have a large error range due to the large input power, we used a TPR electric controller (Korea Control Electric, Fig. 1(b)). It is possible to precisely control the temperature by controlling the input voltage. Fig. 1(c) is the 3D printing equipment (FDM scheme; Willyboy MS) used to create the three-dimensional shapes. Using these devices in a single step in a single device simplifies the 3D PPP process to save time and cost.
C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
Fig. 1. Equipment used in the experiment (a) Extruder; (b) TPR electric controller; (c) 3D printing based on FDM.
3.3. Experimental procedure Fig. 2 is the overall schematic of the experiment. Using the EPP bead (15, 30, 40 %), a hybrid filament containing CO2 was manufactured through the extruder (a). At this time, the diameter of the filament was 1.75 mm, and the temperature of the extruder was controlled at the optimized of temperature, 153 . Using the manufactured filaments, the 3D printing equipment based on the FDM scheme was used to manufacture the three-dimensional structure (b). Similarly, the temperature of the nozzle was controlled at 153 .
Fig. 2. Manufacturing process of (a) CO2 hybrid filament; (b) Three-dimensional structure.
4. Results and Discussion Fig. 3 is a photograph showing a cross-section of EPP beads. The number 15, 30, or 40 provides the rate of foaming; accordingly, the figure confirms the difference of CO2 gas compressed at internally.
Fig. 3. EPP beads observed by optical microscopy (a) 15B; (b) 30B; (c) 40B.
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C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
The following showed the inner cross-section of the CO2 hybrid filament. The pores generated internally were confirmed as different in accordance with the EPP beads. It is confirmed that as the rate of foaming increases the samples have more pores, as shown in Fig. 4. According to the foaming ratio increase, the number of pores tends to increase. Similarly, it confirmed that the size of pores is independent of the foaming ratio.
Fig. 4. CO2 hybrid filament observed by optical microscopy (a) 15B; (b) 30B; (c) 40B.
Fig. 5 showed the result of modifying the temperature during filament manufacture. The CO2 hybrid filament could not be manufactured at temperatures below 150 . The pores of the filament do not form because of leakage of the compressed CO2 gas, at 160 ͑ (a). In order to form the most pores, the optimal temperature was 153 ͑ ͙between 150 and 160 ͚.
Fig. 5. Filament inner cross-sections at different manufacturing temperatures (a) 160; and (b) 153.
The following showed the relationship between the number of pore per unit volume and the foaming ratio. The pore density was calculated using equations (1) and (2). The EPP beads (15B, 30B, 40B) have a porosity of 2.5ం107, 3.8ం107, and 5.4ం107 pores/cm3, respectively. The CO2 hybrid filaments have a porosity of 1.7ం106, 2.6ం106, and 4.8ం106 pores/cm3, respectively, as shown in Fig. 6.
Fig. 6. Number of pores with respect to the foaming ratios in (a) EPP beads; and (b) CO2 hybrid filament.
C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
5. Conclusion In this paper, we propose a new CO 2 gas-based 3D PPP, and manufactured a porous structure having a simple three-dimensional shape. From these experiments, we obtained the following results: x The optimal process temperature for the CO2 hybrid filament was 153 , which provided excellent pore shape inside the filament and protected from gas leakage. x Increasing the foaming ratio increased the number of pores and the porosity in the filament formed, which enhanced pore density. x The size of pores was not affected by the foaming ratio of EPP beads, which were measured approximately 110 ፗ for all three foaming ratios. In the future, a faster production and the mechanical shock absorption effect will be studied and tested for application to the automobile industry. Acknowledgements This work was supported by the National Research Foundation of Korea(NRF) Grant funded by the Korean Government(MSIP) (No.2015R1A5A7036513) and by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2015R1D1A3A01016057) References [1] D. W. Jung, J. H. Jeong, C. B. Park, and B. S. Shin, UV Laser Aided Micro-cell Opening of EPP Foam for Improvement of Sound Absorption, Int. J. Precis. Eng. Manuf. Vol. 15 No. 7 (2013) 1127-1131. [2] C. Park, B. S. Shin, M. S. Kang, Y. W. Ma, J. Y. Oh, and S. M. Hong, Experimental Study on Micro-porous Patterning Using UV Pulse Laser Hybrid Process with Chemical Foaming Agent, Int. J. Precis. Eng. Manuf. Vol. 16 No. 7 (2015) 1385-1390. [3] M. Kubo, Y. Ishihara, Y. Mantani, and M. Shimada, Evaluation of the Factors that Influence the Fabrication of Porous Thin Films by Deposition of Aerosol Nanoparticles, Int. Chemical Engineering Journal Vol. 232 (2013) 221-227. [4] T. Sun, Z. Xu, W. Zhao, W. Wu, S. Liu, S. Wang, W. Liu, S. Liu, and J. Peng, Fabrication of the Similar Porous Alumina Silicon Template for Soft UV Nanoimprint Lithography, Int. Applied Surface Science Vol. 276 (2013) 363-368. [5] J. I. Velasco, M. Antunes, V. Realinho, and M. Ardanuy, Characterization of Rigid Polypropylene-Based Microcellular Foams Produced by Batch Foaming Processes, Int. Polymer Engineering & Science Vol. 51 No. 11 (2011) 2120-2128. [6] S. K. Goo, Automobile Industry’s Future with 3D Printing Technologies, Auto Journal Vol. 37 No. 2 (2015) 35-37. [7] S. H. Paek, Introduction of 3D Printing Technology & Applications, KIC News Vol. 18 No. 1 (2015) 2-10. [8] B. S. Shin, C. J. Yoo, C. Park, and S. M. Hong, Apparatus for Printing 3D Porous Polymer Structure And Method for Printing 3D Porous Polymer Structure Using the Same, 10-2016-0064765 (2016). [9] C. J. Yoo, H. S. Kim, J. H. Park, D. H. Yun, J. K. Shin, and B. S. Shin, Study of Optimal Process Conditions of 3D Porous Polymer Printing for Personal Safety Products, J. of KSPE Vol. 33 No. 5 (2016) 333-339. [10] A. P. Roberts, and E. J. Garboczi, Elastic Moduli of Model Random Three-Dimensional Closed-Cell Cellular Solids, Int. Acta Materialia Vol. 49 No. 2 (2001) 189-197. [11] Kathryn A. Dannemann, and James Lankford Jr., High Strain Rate Compression of Closed-Cell Aluminium Foams, Int. Materials Science and Engineering Vol. 293 No. 1-2 (2000) 157-164. [12] L. M. Matuana, C. B. Park, and J. J. Balatinecz, Processing and Cell Morphology Relationships for Microcellular Foamed PVC/Wood-Fiber Composites, Int. Polymer Engineering and Science Vol. 37 No. 7 (1997) 1137-1147. [13] P. Guo, Y. Liu, Y. Xu, M. Lu, S. Zhang, and T. Liu, Effects of saturation temperature/pressure on melting behavior and cell structure of expanded polypropylene bead, Journal of Cellular Plastics Vol. 50 No. 4 (2014) 321-335. [14] W. Zhai, Y. W. Kim, and C. B. Park, Steam-Chest Molding of Expanded Polypropylene Foams. 1. DSC Simulation of Bead Foam Processing, Ind. Eng. Chem. Res. Vol. 49 No. 20 (2010) 9822-9829. [15] W. Zhai, Y. W. Kim, D. W. Jung, and C. B. Park, Steam-Chest Molding of Expanded Polypropylene Foams. 2. Mechanism of Interbead Bonding, Ind. Eng. Chem. Res. Vol. 50 No. 9 (2011) 5523-5531. [16] M. Nofar, Y. Guo, and C. B. Park, Double Crystal Melting Peak Generation for Expanded Polypropylene Bead Foam Manufacturing, Ind. Eng. Chem. Res. Vol. 52 No. 6 (2013) 2297-2303.
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ScienceDirect Procedia Engineering 184 (2017) 10 – 15
Advances in Material & Processing Technologies Conference
A Study on a New 3D Porous Polymer Printing Based on EPP Beads Containing CO2 Gas C. J. Yoo1, B. S. Shin2,3,*, B. S. Kang1, C. Y. Gwak1, C. Park2, Y. W. Ma2, and S. M. Hong3 1
Engineering Research Center for Net Shape and Die Manufacturing, Pusan National University, Pusan 609-735, Korea 2 Department of Cogno-mechatronics Engineering, Pusan National University, Pusan 609-735, Korea 3 Convergence Research Center of 3D Laser-Aided Innovative Manufacturing Technology, Pusan National University, Pusan 609-735, Korea
Abstract We propose a new CO2 gas-based 3D PPP (Porous Polymer Printing) developed based on the Fused Deposition Modeling scheme of Additive Manufacturing. The 3D porous polymer structure was stacked layer by layer, which was a rapid single step manufacturing technique for a multilayer product in single device. A hybrid filament of diameter 1.75 mm was introduced with EPP (Expanded Polypropylene) beads containing CO2 gas. EPP beads, which have several desirable characteristics such as light weight, shock absorption, thermal insulation, heat resistance, weather resistance, oil resistance, and chemical resistance, were also subject to various process conditions such as EPP type, laminate thickness, printing speed and nozzle temperature. In this paper, three types of EPP beads with expansion ratios of 15, 30 and 40 % were investigated. We found the experimentally optimal process conditions of a new CO2 gas-based 3D PPP method and finally demonstrated a simple 3D structure. In the future, a faster production and the mechanical shock absorption effect will be studied and tested for application in the automobile industry © 2017 The Authors. Published by Elsevier Ltd. © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license Peer-review under responsibility of the organizing committee of the Advances in Material & Processing Technologies (http://creativecommons.org/licenses/by-nc-nd/4.0/). Conference.under responsibility of the organizing committee of the Urban Transitions Conference Peer-review Keywords: 3D PPP (Porous Polymer Printing), Micro Porous Structure, Hybrid Filament Manufacturing, AM (Additive Manufacturing), EPP (Expanded Polypropylene)
* Corresponding author. Tel.: +82-51-510-2787; fax: +82-51-512-1722. E-mail address: [email protected]
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of the Urban Transitions Conference
doi:10.1016/j.proeng.2017.04.064
C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
Nomenclature Vf Pf P N0 M A
Void fraction of the extruded foam Density of sample in the water Density of sample in the air Original unfoamed polymer Magnification factor of the micrograph Area of micrograph
1. Introduction During the past few years, interest has grown in porous polymers involved in several fields of application because of the advantages of the porous structure. Compared to the existing polymer, the porous polymer has improved properties such as energy absorption, fracture toughness, fracture strength, sound absorption, thermal insulation and fatigue life [1-2]. Various products apply a porous structure and mostly need to be light weight. Currently, the method of forming a porous polymer is used for several processes such as the deposition of aerosol nanoparticles, nanoimprinting, batch foaming processes, and etc. [3-5]. However, these processes have the disadvantages of complexity, cost and time. Therefore, a new three-dimensional porous polymer stacking technology that simplifies processing and requires less expense and time is necessary. Recently, due to the advantages of AM(additive manufacturing), the application to fields such as food, medicine, and industry has spread rapidly. AM is suitable for small production, and easy for making individually customized products. AM encompasses a variety of methods such as FDM (Fused Deposition Modeling), SLS (Selective Laser Sintering), SLA (Stereo Lithography Apparatus), 3DP (3 Dimensional Printing), DLP (Digital Light Processing), LOM (Laminated Object Manufacturing), etc. [6]. Among them, FDM is the method of stacking while melting a thermoplastic in the nozzle. Compared to the existing method, it has the characteristics of simple structure and is inexpensive [7]. At this time, the required materials (thermoplastic polymers such as PVC, ABS, PLA, PVA, etc.) are in common use. However, the formation of a porous polymer using these materials is very difficult. Therefore, it is necessary that we use material made of a porous polymer structure. In this paper, we suggest a new 3D printing technique—CO2 gas-based 3D PPP (Porous Polymer Printing)— using EPP beads containing CO2 and investigated the simple 3D structure of the porous polymer based on the EPP foam ratios. 2. 3D PPP(Porous Polymer Printing) 2.1. 3D PPP process The process that we used in this paper is a CO2 gas-based 3D PPP process. 3D PPP refers to a technique that can manufacture a porous structure having a three-dimensional shape using 3D printing. In other words, it generates gas bubbles (N2, CO2, etc.) during the injection molding and extrusion molding processes, and the product is manufactured with air bubbles dispersed in the polymer resin. The purpose of this process can be to reduce weight and material cost because the volume consists of air bubbles. The mechanical properties can be adjusted to produce a superior product [8]. A CBA (Chemical Blowing Agent) hybrid filament was formed by mixing PP and CBA and extruded to a diameter of 1.75 mm. Using the CBA hybrid filament, the pores can be formed inside the shape during the thermal decomposition reaction of the CBA [9]. This porous structure was studied in the CO2 gas- based 3D PPP process to increase porosity. In summary, after the EPP beads were passed through the extruder, the CO2 hybrid filament was manufactured. The porous polymer structure of three-dimensional shape can be manufactured using the CO2 hybrid filament.
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C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
2.2. Shape of porous structure The shape of the porous structure is generally classified as opened cell or closed cell. An opened cell structure is one where the majority of pores are combined, such as in a sponge. On the other hand, the structure of a closed cell has different shapes for the pores, such as Styrofoam. Opened cell has better resilience than closed cell, and closed cell has better thermal insulation than opened cell [10-11]. The closed cell has the advantages of strength, high Rvalue, and high resistance to leakage of air or vapor. However, it is more expensive because it requires a dense structure. The porous structure has a greater elasticity modulus, when the height ratio (ratio of the size of pores to width of pores) is large. In other words, it deforms satisfactorily and has superior relief of mechanical shock. 2.3. Pore density After foaming, the mass densities of samples, “P” and “Pf”, were measured in air and in distilled water. “A” is the area of the micrograph and “n” is the number of pores in the optical micrograph within “A”. “M” is the magnification factor of the micrograph. The void fraction of the extruded foam (Vf) and the pore density per unit volume of the foamed polymer (N0) were determined from the optical micrograph using the equations (1) and (2) [12].
ڌ
ہڱ
ک
ڋ
ہګ ګ
§ ڨۉ ¨ ¨ ڜ ©
(1) ڎ
ڍ
· ڍª ڌº ¸ « ¸ » ڱ ڌ ¼ ہ ¹ ¬
(2)
3. Experiment 3.1. Material preparation Generally, EPS (Expandable Polystyrene) is a bead blowing agent that has been most widely used as packaging. The requirement of advanced and enhanced safety has been increased in product packaging. Thus, alternative materials have been developed to reinforcing the physical vulnerability of EPS. Initially, EPE (Expanded Polyethylene) has been developed with cross-linking having superior property. However, it has a complex manufacturing process, is recyclable, and increases production costs. Finally, by simplifying the process, EPP (Expanded Polypropylene) has been developed. It can be recyclable, and it is non-crosslinked. EPP has superior properties such as brittleness, repeated shock absorption, ductility, chemical resistance, etc., because it is based on PP [13-16]. Therefore, EPP beads with expansion ratios of 15, 30 and 40 % were used in this experiment, and were developed by Hanwha Advanced Materials. These are referred to as 15B, 30B and 40B, respectively. 3.2. Equipment The following is an explanation of the equipment used in this experiment. Fig. 1(a) is the extruder (Filabot Wee). With this equipment, it is possible to manufacture CO2 hybrid filaments using EPP beads. Since conventional temperature control devices have a large error range due to the large input power, we used a TPR electric controller (Korea Control Electric, Fig. 1(b)). It is possible to precisely control the temperature by controlling the input voltage. Fig. 1(c) is the 3D printing equipment (FDM scheme; Willyboy MS) used to create the three-dimensional shapes. Using these devices in a single step in a single device simplifies the 3D PPP process to save time and cost.
C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
Fig. 1. Equipment used in the experiment (a) Extruder; (b) TPR electric controller; (c) 3D printing based on FDM.
3.3. Experimental procedure Fig. 2 is the overall schematic of the experiment. Using the EPP bead (15, 30, 40 %), a hybrid filament containing CO2 was manufactured through the extruder (a). At this time, the diameter of the filament was 1.75 mm, and the temperature of the extruder was controlled at the optimized of temperature, 153 . Using the manufactured filaments, the 3D printing equipment based on the FDM scheme was used to manufacture the three-dimensional structure (b). Similarly, the temperature of the nozzle was controlled at 153 .
Fig. 2. Manufacturing process of (a) CO2 hybrid filament; (b) Three-dimensional structure.
4. Results and Discussion Fig. 3 is a photograph showing a cross-section of EPP beads. The number 15, 30, or 40 provides the rate of foaming; accordingly, the figure confirms the difference of CO2 gas compressed at internally.
Fig. 3. EPP beads observed by optical microscopy (a) 15B; (b) 30B; (c) 40B.
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C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
The following showed the inner cross-section of the CO2 hybrid filament. The pores generated internally were confirmed as different in accordance with the EPP beads. It is confirmed that as the rate of foaming increases the samples have more pores, as shown in Fig. 4. According to the foaming ratio increase, the number of pores tends to increase. Similarly, it confirmed that the size of pores is independent of the foaming ratio.
Fig. 4. CO2 hybrid filament observed by optical microscopy (a) 15B; (b) 30B; (c) 40B.
Fig. 5 showed the result of modifying the temperature during filament manufacture. The CO2 hybrid filament could not be manufactured at temperatures below 150 . The pores of the filament do not form because of leakage of the compressed CO2 gas, at 160 ͑ (a). In order to form the most pores, the optimal temperature was 153 ͑ ͙between 150 and 160 ͚.
Fig. 5. Filament inner cross-sections at different manufacturing temperatures (a) 160; and (b) 153.
The following showed the relationship between the number of pore per unit volume and the foaming ratio. The pore density was calculated using equations (1) and (2). The EPP beads (15B, 30B, 40B) have a porosity of 2.5ం107, 3.8ం107, and 5.4ం107 pores/cm3, respectively. The CO2 hybrid filaments have a porosity of 1.7ం106, 2.6ం106, and 4.8ం106 pores/cm3, respectively, as shown in Fig. 6.
Fig. 6. Number of pores with respect to the foaming ratios in (a) EPP beads; and (b) CO2 hybrid filament.
C.J. Yoo et al. / Procedia Engineering 184 (2017) 10 – 15
5. Conclusion In this paper, we propose a new CO 2 gas-based 3D PPP, and manufactured a porous structure having a simple three-dimensional shape. From these experiments, we obtained the following results: x The optimal process temperature for the CO2 hybrid filament was 153 , which provided excellent pore shape inside the filament and protected from gas leakage. x Increasing the foaming ratio increased the number of pores and the porosity in the filament formed, which enhanced pore density. x The size of pores was not affected by the foaming ratio of EPP beads, which were measured approximately 110 ፗ for all three foaming ratios. In the future, a faster production and the mechanical shock absorption effect will be studied and tested for application to the automobile industry. Acknowledgements This work was supported by the National Research Foundation of Korea(NRF) Grant funded by the Korean Government(MSIP) (No.2015R1A5A7036513) and by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2015R1D1A3A01016057) References [1] D. W. Jung, J. H. Jeong, C. B. Park, and B. S. Shin, UV Laser Aided Micro-cell Opening of EPP Foam for Improvement of Sound Absorption, Int. J. Precis. Eng. Manuf. Vol. 15 No. 7 (2013) 1127-1131. [2] C. Park, B. S. Shin, M. S. Kang, Y. W. Ma, J. Y. Oh, and S. M. Hong, Experimental Study on Micro-porous Patterning Using UV Pulse Laser Hybrid Process with Chemical Foaming Agent, Int. J. Precis. Eng. Manuf. Vol. 16 No. 7 (2015) 1385-1390. [3] M. Kubo, Y. Ishihara, Y. Mantani, and M. Shimada, Evaluation of the Factors that Influence the Fabrication of Porous Thin Films by Deposition of Aerosol Nanoparticles, Int. Chemical Engineering Journal Vol. 232 (2013) 221-227. [4] T. Sun, Z. Xu, W. Zhao, W. Wu, S. Liu, S. Wang, W. Liu, S. Liu, and J. Peng, Fabrication of the Similar Porous Alumina Silicon Template for Soft UV Nanoimprint Lithography, Int. Applied Surface Science Vol. 276 (2013) 363-368. [5] J. I. Velasco, M. Antunes, V. Realinho, and M. Ardanuy, Characterization of Rigid Polypropylene-Based Microcellular Foams Produced by Batch Foaming Processes, Int. Polymer Engineering & Science Vol. 51 No. 11 (2011) 2120-2128. [6] S. K. Goo, Automobile Industry’s Future with 3D Printing Technologies, Auto Journal Vol. 37 No. 2 (2015) 35-37. [7] S. H. Paek, Introduction of 3D Printing Technology & Applications, KIC News Vol. 18 No. 1 (2015) 2-10. [8] B. S. Shin, C. J. Yoo, C. Park, and S. M. Hong, Apparatus for Printing 3D Porous Polymer Structure And Method for Printing 3D Porous Polymer Structure Using the Same, 10-2016-0064765 (2016). [9] C. J. Yoo, H. S. Kim, J. H. Park, D. H. Yun, J. K. Shin, and B. S. Shin, Study of Optimal Process Conditions of 3D Porous Polymer Printing for Personal Safety Products, J. of KSPE Vol. 33 No. 5 (2016) 333-339. [10] A. P. Roberts, and E. J. Garboczi, Elastic Moduli of Model Random Three-Dimensional Closed-Cell Cellular Solids, Int. Acta Materialia Vol. 49 No. 2 (2001) 189-197. [11] Kathryn A. Dannemann, and James Lankford Jr., High Strain Rate Compression of Closed-Cell Aluminium Foams, Int. Materials Science and Engineering Vol. 293 No. 1-2 (2000) 157-164. [12] L. M. Matuana, C. B. Park, and J. J. Balatinecz, Processing and Cell Morphology Relationships for Microcellular Foamed PVC/Wood-Fiber Composites, Int. Polymer Engineering and Science Vol. 37 No. 7 (1997) 1137-1147. [13] P. Guo, Y. Liu, Y. Xu, M. Lu, S. Zhang, and T. Liu, Effects of saturation temperature/pressure on melting behavior and cell structure of expanded polypropylene bead, Journal of Cellular Plastics Vol. 50 No. 4 (2014) 321-335. [14] W. Zhai, Y. W. Kim, and C. B. Park, Steam-Chest Molding of Expanded Polypropylene Foams. 1. DSC Simulation of Bead Foam Processing, Ind. Eng. Chem. Res. Vol. 49 No. 20 (2010) 9822-9829. [15] W. Zhai, Y. W. Kim, D. W. Jung, and C. B. Park, Steam-Chest Molding of Expanded Polypropylene Foams. 2. Mechanism of Interbead Bonding, Ind. Eng. Chem. Res. Vol. 50 No. 9 (2011) 5523-5531. [16] M. Nofar, Y. Guo, and C. B. Park, Double Crystal Melting Peak Generation for Expanded Polypropylene Bead Foam Manufacturing, Ind. Eng. Chem. Res. Vol. 52 No. 6 (2013) 2297-2303.
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