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An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam
Materials Today: Proceedings xxx (xxxx) xxx
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam L. Yuvaraj, S. Jeyanthi ⇑, Nikhil S. Thomas, Vishnu Rajeev SMBS, Vellore Institute of Technology, Chennai 600127, India
a r t i c l e
i n f o
Article history: Received 6 August 2019 Accepted 17 September 2019 Available online xxxx Keywords: Energy absorption Silica gel Sound absorption coefficient Sustainable foam Porosity
a b s t r a c t Polyurethane foams (PU), are found in various industrial and domestic applications due to their high energy absorption and sound absorption properties, especially in shock absorbers and noise control problems. This study investigates the effect of silica gel as additive filler in castor oil-based PU foam and its mechanical and acoustical properties are evaluated. Three different loading of 5%, 10%, and 15% silica gel is used as filler. For mechanical properties, the compression test is carried out. As the percentage of filler increases, the rigidity of the foam increases. The acoustical properties of the sample are tested using the two-microphone impedance tube method. Raw PU foams are seen to exhibit a reasonable sound absorption only in higher frequencies. The results show that the sound absorption coefficient of 10% filler PU foam has comparatively better sound absorption capabilities throughout all frequencies, ranging from 200 Hz to 4000 Hz, that it is exposed to. This can be attributed to the optimum number of voids present, compared to the highest number in 15% (high porosity) and lowest in 5%. The results show that the addition of silica gel up to a certain extent enhances both, the mechanical as well as acoustic properties. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction Polymeric Foams are used invariably in household as well as industrial applications every day. Well recognized as a comfort material for furniture cushions, mattresses, packaging and automobile seating, foams play a prominent role in sound and energy absorption in automobiles, industrial and domestic shockproofing requirements. In today’s globalized world, pollution poses a strong threat to the existence of all resources and living things. Of all types, Sound pollution is one of the most common and complex categories of pollution. It is responsible for a list of health and safety issues residing in the society. With regard to the automobile industry and its applications related to mechanical properties, foams are widely used in automotive seats. The firmness of the polymer structure determines the overall safety, durability, and comfort to the passenger [1,2]. Therefore, the overall situation constantly demands a novel and efficient technique in dampening excess sound and impact energy. The need of the hour demands thin, lightweight; renewable materials that absorb sound waves
⇑ Corresponding author.
at wider frequency ranges and at the same time, exhibiting a considerable improvement in compressive strength. Few proposals in the market include fibrous, foam and granular materials, but for these, it is not easy to alter the microscale geometry to exhibit better performances or obtain specific absorption spectrum [3]. In addition to that, these materials are usually poor absorbers at low frequencies of sound and thereby making it a requirement to come up with open celled materials which are considered as good absorbers [4–8] (see Fig. 1). Among polymeric foams, Polyurethane foams have found a significant space due to its unique characteristics of visco-elasticity, relatively simple processing, lightweight, commercial availability [9–11]. This research work is based on the effects of acoustic insulation and mechanical properties of castor oil-based polyurethane foam, reinforced with silica gel. Various kinds of literature have evidenced the possibility of improvement of acoustic [12,13] and mechanical properties [14], using macro-sized reinforcement fibers and particles [15], accounting majorly to the pore size, number and porosity [16,17]. The utilization of PU foams in the market is expanding every day, leading to the waste accumulated from production and post-consumer products [18]. Therefore, proper disposal of waste is a serious need for the environment [19]. Castor
E-mail address: [email protected] (S. Jeyanthi). https://doi.org/10.1016/j.matpr.2019.09.115 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: L. Yuvaraj, S. Jeyanthi, N. S. Thomas et al., An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.115
2
L. Yuvaraj et al. / Materials Today: Proceedings xxx (xxxx) xxx
2.4. Acoustic properties
Fig. 1. Impedance tube setup.
oil polyol was chosen because of its biodegradable nature for semirigid and rigid foams. In order to produce a rigid PU foam the hydroxyl number is a crucial parameter, as the rigidity is proportional to the number of hydroxyl groups [20]. It also lowers the curing rate [21]. To encounter this, toluene diisocyanate was added. The addition of cross-linkers increases the count of hydroxyl, which enhances damping [22]. The main motivation of this paper is to obtain the influence of different loading percentile of silica gel doped as filler in polyurethane foam when it subjected to mechanical and acoustic testing, and morphological studies of foam sample are used to justify results as well (see Table 1).
The sound absorption capability of the PU foam samples was tested as per ISO 10534-2 standard in the two-microphone impedance tube method, wherein the test sample sizes were 33 mm and 98 mm in diameter for higher frequency and lower frequency, respectively. In this method, white noise was excited from a speaker and the signals of incident wave and reflected wave were captured by the microphones and data was acquired in M + P Vibpilot. Using MatlabÒ, the transfer function between the input signals gave the sound absorption coefficient at 1/3 octave signals of frequency range 220–4000 Hz. 2.5. Morphological investigation The nanostructures of the silica gel and cell structures of Polyurethane samples were evaluated by a SEM analyser (Model FEI Quanta FEG 200) at SAIF, IIT Madras. The samples were cut into 10 10 10 mm3 and tested at ambient temperature. 3. Results and discussion 3.1. Compression strength analysis
The natural based polyol was obtained from castor oils - Jagropol RGG, which was sourced from Jayant Agro-Organics Ltd (Mumbai, India). Polymeric MDI wannate 8018 was provided by Manali Petrochemicals Ltd. Silica gel crystals were supplied by Waxchem India Sarvodaya Chemical Corporation (Chennai, India). The composition and chemical ratio of the premixed polyol is given in the following table.
In multiple applications of PU foam for domestic, industrial and other commercial products, physical durability should be taken into account, for good material life. In this regard, the compression test carried out for the samples is summarized in Fig. 2. The sample with 15% silica gel shows a considerably larger intake of compression force with time, for a given stroke, compared to samples of 5% and 10%. It can be inferred that the silica gel filler becomes an additional physical crosslinker, which tends to enhance the modulus of the flexible segment in the polyurethane matrix. As the flexibility increases, the capacity of the foam to withstand compressive forces also increases. Thus, the highest percentage of filler reflects the highest compressive strength.
2.2. PU foam sample preparation
3.2. Acoustic behaviour
The PU foam was synthesized using the method of free rising, during which, the polyol was mixed with wannate 8018. The required ratio of polyol and isocyanate was weighed. Additionally, Polyol Jagropol-RGG, along with silica gel weight percentages of 5, 10 and 15 were mixed in 3 test samples respectively. To enhance the mixing, a stirrer was used at 2500 rpm for about 15 s, followed by which, it was poured into a rectangular mold. The mold was left undisturbed for a curing time of 300 s at room temperature. This was done to avoid collapsing of the foam.
When sound strikes a material, a part of it gets absorbed while the rest of it get reflected or transmitted. In order to quantify the amount of sound absorbed, the sample was placed in an impedance tube where only absorption and reflection occur. Sound
2. Experimental setup 2.1. Materials
2.3. Mechanical properties Uniaxial Compression test was carried out in Shimadzu Universal Testing Machine AG-X Plus 50kN at room temperature by using specimens of size 25 25 25 mm3. The readings were taken at a crosshead speed of 0.5 mm/sec with a maximum compressive strain of 50%.
Table 1 Natural Polyol formulation. Chemical
Chemical proportion (pbw)
Methylene Di-isocyanate Castor Polyol Water Surfactant Catalyst
165 100 3.5 1.75 1
Fig. 2. Compressive strength of PU foams with different Silica gel percentages.
Please cite this article as: L. Yuvaraj, S. Jeyanthi, N. S. Thomas et al., An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.115
L. Yuvaraj et al. / Materials Today: Proceedings xxx (xxxx) xxx
3
nance peak. All the filler doped samples exhibit the same drop in the mid frequency region because the resonance frequency cannot persist over the time. The gradual increase in the trend continues towards higher frequency region. Among the various samples tested, the 10% filler PU foam shows a consistently better sound absorption characteristics at lower frequency range. This can be attributed to the pore size, which varies with the filler percentage. When sound penetrates into the porous medium, the kinetic energy of the acoustic field decreases. The effectiveness of sound absorption rises with increasing porosity of the material. The influence of cell pore sizes on the acoustic insulation is shown in Fig. 2. As the pore size decreases due to compressive disturbance from the neighboring voids generated from filler, the sound absorption increases. Addition of fillers enhances the tortuosity. This explains why the silica gel-reinforced foams have better acoustic insulation than pure PU foam. However, excess amount of filler, as in the 15% sample creates large voids which favor sound reflection instead of absorption. The 10% sample, being moderately porous shows to be the better absorber of sound. 3.3. SEM analysis Fig. 3. Sound absorption measurements in foams with varied loading fraction of Silica gel.
absorption coefficient signifies the absorption capability of porous material. In this study, porous material is doped with silica gel which makes the foam even more porous. The sound absorption characteristics of porous materials highly depend on its cell size and structural form. In the low frequency range, the natural frequency of the material matches with that of the sound source in the impedance tube, which causes the reso-
The SEM micrographs, taken at uniform magnification and scale of the silica gel and PU foam cross section is shown in Fig. 3. With an increasing percentage of silica gel, the size of pores decreases. All the pores present in the foam are open cells, which are good sound absorbers. The sample with 5% silica gel shows maximum pore cell size. This subjects the foam structure to highest compression stress at a lesser force. On addition of fillers, the absorption capacity increases due to increased tortuosity and dissipation of sound waves accounted to the irregular crystal orientation. Hence, compared to pure PU foam, the addition of 5% silica gel increases the absorption coefficient. In the 10% sample, the pores are of aver-
Fig. 4. SEM images of Silica gel-reinforced PU foam – (a) Silica gel crystal (b) 5% Silica gel (c) 10% Silica gel (d) 15% Silica gel.
Please cite this article as: L. Yuvaraj, S. Jeyanthi, N. S. Thomas et al., An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.115
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L. Yuvaraj et al. / Materials Today: Proceedings xxx (xxxx) xxx
age size which gives it a moderately better compressive strength. But it proves to be the most effective sound absorber. This is because, the void size is maximum in the 15% sample, giving a low air resistance and higher sound reflection (see Fig. 4). 4. Conclusion In this study, the morphology of pore cells, mechanical properties and acoustic properties of Silica gel-reinforced PU foams have been investigated. As the loading fraction of silica gel increases, the porosity of the foam increases. This enhances the sound absorption to an extent as in the 10% sample, beyond which, the larger pores tend to allow more transmission of sound waves. The compressive strength is maximum for the 15% loaded sample. As the porosity keeps increasing, the wettability between silica gel and the foam decreases, thus reducing the stiffness and hence flexible segment. This makes it brittle if the filler exceeds 15%, which is not desired. Therefore, considering an overall scale, the 10% silica gel reinforced PU foam shows a comparatively good result and hence provides an effective and promising way for the required applications. Acknowledgements The authors are grateful to Department of Science and Technology (DST-SERB; File no: ECR/2015/000111) for providing the necessary facilities and funds for conducting this research. References [1] Bernard E. Obi, Applications of Polymeric foams in Automobiles and transportation, Polymeric Foams Structure Property Performance, A Design Guide (2018), Pages 341–366. [2] G. Sung, J.S. Kim, J.H. Kim, Sound absorption behavior of flexible polyurethane foams including high molecular-weight copolymer polyol, Polym. Adv. Technol. (2017) 1–8, https://doi.org/10.1002/pat.4195. [3] C. Zhang, J. Li, Z. Hu, F. Zhu, Y. Huang, Mater. Des. 41 (2012) 319, https://doi. org/10.1016/j.matdes.2012.04.031.
[4] Z.P. Lv, X.N. Li, X. Yu, The effect of chain extension method on the properties of polyurethane/SiO2 composites, Mater. Des. 35 (2012) 358–362. [5] I.O. Bakare, F.E. Okieimen, C. Pavithran, H.P.S. Abdul Khalil, M. Brahmakumar, Mechanical and thermal properties of sisal fiber-reinforced rubber seed oilbased polyurethane composites, Mater. Des. 31 (2010) 4274–4280. [6] F.M. Casati, B. Dawe, S. Fregni, Y. Miyazaki, Natural oil polyols-applications in module polyurethane foams, PU Mag. 5 (2008) 246–253. [7] X. Wang, J. Eisenbrey, M. Zeitz, J.Q. Sun, Multi-stage regression analysis of acoustical properties of polyurethane foams, J. Sound. Vib. 273 (2004) 1109– 1117. [8] R. Verdejo, R. Stampfli, M. Alvarez-Lainez, S. Mourad, M.A. Rodriguez-Perez, P. A. Brühwiler, et al., Enhanced acoustic damping in flexible polyurethane foams filled with carbon nanotubes, Compos. Sci. Technol. 69 (2009) 1564–1569. [9] Y. Imai, T. Asano, Studies of acoustical absorption of flexible polyurethane foam, J. Appl. Polym. Sci. 27 (1982) 183e195. [10] D. Lee, L. Chen, A. Sendijarevic, V. Sendijarevic, K. Frisch, D. Klempner, Effect of morphology on sound attenuation of flexible polymeric foams, J. Cell. Plast. 27 (1991) 135e142. [11] L.J. Lee, C. Zeng, X. Cao, X. Han, J. Shen, G. Xu, Polymer nanocomposite foams, Compos. Sci. Technol. 65 (2005) 2344–2363. [12] G. Sung et al., Fabrication of polyurethane composite foams with magnesium hydroxide filler for improved sound absorption, J. Ind. Eng. Chem. (2016), https://doi.org/10.1016/j.jiec.2016.08.014. [13] Y. Wang, C. Zhang, L. Ren, M. Ichchou, M.A. Galland, O. Bareille, Polym. Compos. 34 (2013) 1847. [14] A. Agrawal, R. Kaur, R.S. Walia, PU Foam derived from renewable sources: perspective on properties enhancement: an overview, Eur. Polym. J. (2017), https://doi.org/10.1016/j.eurpolymj.2017.08.022. [15] R. Gayathri, Sound absorption, thermal and mechanical behavior of polyurethane foam modified with nano silica, nano clay and crumb rubber fillers, Int. J. Sci. Eng. Res. 4 (5) (2013) 801–808. [16] Chunhua Zhang, Junqing Li, Hu. Zhen, Fenglei Zhu, Yudong Huang, Correlation between the acoustic and porous cell morphology of polyurethane foam: Effect of interconnected porosity, Mater. Des. 41 (2012) 319–325. [17] Bc. Tomáš Matoušek, Foams pore size estimation and their acoustic properties, Diplomová práce, UTB ve Zlíneˇ, Fakulta technologická, 2009. [18] W. Yang, Q. Dong, S. Liu, H. Xie, L. Liu, J. Li, Recycling and disposal methods for polyurethane foam wastes, Procedia Environ. Sci. 16 (2012) 167–175. [19] Polyurethane – PU Waste Recycling of Plastics: http://www.plastemart.com/ upload /literature /PUrecycling.asp. [20] Y. Li, X. Luo, S. Hu, Bio-based polyols and polyurethanes, Springer Briefs in Green Chemistry for Sustainability, 2015. [21] M. Carme Coll Ferrer et al., Characterisation of polyurethane networks based on vegetable derived polyol, Polymer 49 (2008) 3279–3287. [22] Zoran S. Petrovic, Polyurethanes from vegetable oils, Polym. Rev. 48 (1) (2008) 109–155, https://doi.org/10.1080/15583720701834224.
Please cite this article as: L. Yuvaraj, S. Jeyanthi, N. S. Thomas et al., An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.115
Contents lists available at ScienceDirect
Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr
An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam L. Yuvaraj, S. Jeyanthi ⇑, Nikhil S. Thomas, Vishnu Rajeev SMBS, Vellore Institute of Technology, Chennai 600127, India
a r t i c l e
i n f o
Article history: Received 6 August 2019 Accepted 17 September 2019 Available online xxxx Keywords: Energy absorption Silica gel Sound absorption coefficient Sustainable foam Porosity
a b s t r a c t Polyurethane foams (PU), are found in various industrial and domestic applications due to their high energy absorption and sound absorption properties, especially in shock absorbers and noise control problems. This study investigates the effect of silica gel as additive filler in castor oil-based PU foam and its mechanical and acoustical properties are evaluated. Three different loading of 5%, 10%, and 15% silica gel is used as filler. For mechanical properties, the compression test is carried out. As the percentage of filler increases, the rigidity of the foam increases. The acoustical properties of the sample are tested using the two-microphone impedance tube method. Raw PU foams are seen to exhibit a reasonable sound absorption only in higher frequencies. The results show that the sound absorption coefficient of 10% filler PU foam has comparatively better sound absorption capabilities throughout all frequencies, ranging from 200 Hz to 4000 Hz, that it is exposed to. This can be attributed to the optimum number of voids present, compared to the highest number in 15% (high porosity) and lowest in 5%. The results show that the addition of silica gel up to a certain extent enhances both, the mechanical as well as acoustic properties. Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
1. Introduction Polymeric Foams are used invariably in household as well as industrial applications every day. Well recognized as a comfort material for furniture cushions, mattresses, packaging and automobile seating, foams play a prominent role in sound and energy absorption in automobiles, industrial and domestic shockproofing requirements. In today’s globalized world, pollution poses a strong threat to the existence of all resources and living things. Of all types, Sound pollution is one of the most common and complex categories of pollution. It is responsible for a list of health and safety issues residing in the society. With regard to the automobile industry and its applications related to mechanical properties, foams are widely used in automotive seats. The firmness of the polymer structure determines the overall safety, durability, and comfort to the passenger [1,2]. Therefore, the overall situation constantly demands a novel and efficient technique in dampening excess sound and impact energy. The need of the hour demands thin, lightweight; renewable materials that absorb sound waves
⇑ Corresponding author.
at wider frequency ranges and at the same time, exhibiting a considerable improvement in compressive strength. Few proposals in the market include fibrous, foam and granular materials, but for these, it is not easy to alter the microscale geometry to exhibit better performances or obtain specific absorption spectrum [3]. In addition to that, these materials are usually poor absorbers at low frequencies of sound and thereby making it a requirement to come up with open celled materials which are considered as good absorbers [4–8] (see Fig. 1). Among polymeric foams, Polyurethane foams have found a significant space due to its unique characteristics of visco-elasticity, relatively simple processing, lightweight, commercial availability [9–11]. This research work is based on the effects of acoustic insulation and mechanical properties of castor oil-based polyurethane foam, reinforced with silica gel. Various kinds of literature have evidenced the possibility of improvement of acoustic [12,13] and mechanical properties [14], using macro-sized reinforcement fibers and particles [15], accounting majorly to the pore size, number and porosity [16,17]. The utilization of PU foams in the market is expanding every day, leading to the waste accumulated from production and post-consumer products [18]. Therefore, proper disposal of waste is a serious need for the environment [19]. Castor
E-mail address: [email protected] (S. Jeyanthi). https://doi.org/10.1016/j.matpr.2019.09.115 2214-7853/Ó 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International conference on Materials and Manufacturing Methods.
Please cite this article as: L. Yuvaraj, S. Jeyanthi, N. S. Thomas et al., An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.115
2
L. Yuvaraj et al. / Materials Today: Proceedings xxx (xxxx) xxx
2.4. Acoustic properties
Fig. 1. Impedance tube setup.
oil polyol was chosen because of its biodegradable nature for semirigid and rigid foams. In order to produce a rigid PU foam the hydroxyl number is a crucial parameter, as the rigidity is proportional to the number of hydroxyl groups [20]. It also lowers the curing rate [21]. To encounter this, toluene diisocyanate was added. The addition of cross-linkers increases the count of hydroxyl, which enhances damping [22]. The main motivation of this paper is to obtain the influence of different loading percentile of silica gel doped as filler in polyurethane foam when it subjected to mechanical and acoustic testing, and morphological studies of foam sample are used to justify results as well (see Table 1).
The sound absorption capability of the PU foam samples was tested as per ISO 10534-2 standard in the two-microphone impedance tube method, wherein the test sample sizes were 33 mm and 98 mm in diameter for higher frequency and lower frequency, respectively. In this method, white noise was excited from a speaker and the signals of incident wave and reflected wave were captured by the microphones and data was acquired in M + P Vibpilot. Using MatlabÒ, the transfer function between the input signals gave the sound absorption coefficient at 1/3 octave signals of frequency range 220–4000 Hz. 2.5. Morphological investigation The nanostructures of the silica gel and cell structures of Polyurethane samples were evaluated by a SEM analyser (Model FEI Quanta FEG 200) at SAIF, IIT Madras. The samples were cut into 10 10 10 mm3 and tested at ambient temperature. 3. Results and discussion 3.1. Compression strength analysis
The natural based polyol was obtained from castor oils - Jagropol RGG, which was sourced from Jayant Agro-Organics Ltd (Mumbai, India). Polymeric MDI wannate 8018 was provided by Manali Petrochemicals Ltd. Silica gel crystals were supplied by Waxchem India Sarvodaya Chemical Corporation (Chennai, India). The composition and chemical ratio of the premixed polyol is given in the following table.
In multiple applications of PU foam for domestic, industrial and other commercial products, physical durability should be taken into account, for good material life. In this regard, the compression test carried out for the samples is summarized in Fig. 2. The sample with 15% silica gel shows a considerably larger intake of compression force with time, for a given stroke, compared to samples of 5% and 10%. It can be inferred that the silica gel filler becomes an additional physical crosslinker, which tends to enhance the modulus of the flexible segment in the polyurethane matrix. As the flexibility increases, the capacity of the foam to withstand compressive forces also increases. Thus, the highest percentage of filler reflects the highest compressive strength.
2.2. PU foam sample preparation
3.2. Acoustic behaviour
The PU foam was synthesized using the method of free rising, during which, the polyol was mixed with wannate 8018. The required ratio of polyol and isocyanate was weighed. Additionally, Polyol Jagropol-RGG, along with silica gel weight percentages of 5, 10 and 15 were mixed in 3 test samples respectively. To enhance the mixing, a stirrer was used at 2500 rpm for about 15 s, followed by which, it was poured into a rectangular mold. The mold was left undisturbed for a curing time of 300 s at room temperature. This was done to avoid collapsing of the foam.
When sound strikes a material, a part of it gets absorbed while the rest of it get reflected or transmitted. In order to quantify the amount of sound absorbed, the sample was placed in an impedance tube where only absorption and reflection occur. Sound
2. Experimental setup 2.1. Materials
2.3. Mechanical properties Uniaxial Compression test was carried out in Shimadzu Universal Testing Machine AG-X Plus 50kN at room temperature by using specimens of size 25 25 25 mm3. The readings were taken at a crosshead speed of 0.5 mm/sec with a maximum compressive strain of 50%.
Table 1 Natural Polyol formulation. Chemical
Chemical proportion (pbw)
Methylene Di-isocyanate Castor Polyol Water Surfactant Catalyst
165 100 3.5 1.75 1
Fig. 2. Compressive strength of PU foams with different Silica gel percentages.
Please cite this article as: L. Yuvaraj, S. Jeyanthi, N. S. Thomas et al., An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.115
L. Yuvaraj et al. / Materials Today: Proceedings xxx (xxxx) xxx
3
nance peak. All the filler doped samples exhibit the same drop in the mid frequency region because the resonance frequency cannot persist over the time. The gradual increase in the trend continues towards higher frequency region. Among the various samples tested, the 10% filler PU foam shows a consistently better sound absorption characteristics at lower frequency range. This can be attributed to the pore size, which varies with the filler percentage. When sound penetrates into the porous medium, the kinetic energy of the acoustic field decreases. The effectiveness of sound absorption rises with increasing porosity of the material. The influence of cell pore sizes on the acoustic insulation is shown in Fig. 2. As the pore size decreases due to compressive disturbance from the neighboring voids generated from filler, the sound absorption increases. Addition of fillers enhances the tortuosity. This explains why the silica gel-reinforced foams have better acoustic insulation than pure PU foam. However, excess amount of filler, as in the 15% sample creates large voids which favor sound reflection instead of absorption. The 10% sample, being moderately porous shows to be the better absorber of sound. 3.3. SEM analysis Fig. 3. Sound absorption measurements in foams with varied loading fraction of Silica gel.
absorption coefficient signifies the absorption capability of porous material. In this study, porous material is doped with silica gel which makes the foam even more porous. The sound absorption characteristics of porous materials highly depend on its cell size and structural form. In the low frequency range, the natural frequency of the material matches with that of the sound source in the impedance tube, which causes the reso-
The SEM micrographs, taken at uniform magnification and scale of the silica gel and PU foam cross section is shown in Fig. 3. With an increasing percentage of silica gel, the size of pores decreases. All the pores present in the foam are open cells, which are good sound absorbers. The sample with 5% silica gel shows maximum pore cell size. This subjects the foam structure to highest compression stress at a lesser force. On addition of fillers, the absorption capacity increases due to increased tortuosity and dissipation of sound waves accounted to the irregular crystal orientation. Hence, compared to pure PU foam, the addition of 5% silica gel increases the absorption coefficient. In the 10% sample, the pores are of aver-
Fig. 4. SEM images of Silica gel-reinforced PU foam – (a) Silica gel crystal (b) 5% Silica gel (c) 10% Silica gel (d) 15% Silica gel.
Please cite this article as: L. Yuvaraj, S. Jeyanthi, N. S. Thomas et al., An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.115
4
L. Yuvaraj et al. / Materials Today: Proceedings xxx (xxxx) xxx
age size which gives it a moderately better compressive strength. But it proves to be the most effective sound absorber. This is because, the void size is maximum in the 15% sample, giving a low air resistance and higher sound reflection (see Fig. 4). 4. Conclusion In this study, the morphology of pore cells, mechanical properties and acoustic properties of Silica gel-reinforced PU foams have been investigated. As the loading fraction of silica gel increases, the porosity of the foam increases. This enhances the sound absorption to an extent as in the 10% sample, beyond which, the larger pores tend to allow more transmission of sound waves. The compressive strength is maximum for the 15% loaded sample. As the porosity keeps increasing, the wettability between silica gel and the foam decreases, thus reducing the stiffness and hence flexible segment. This makes it brittle if the filler exceeds 15%, which is not desired. Therefore, considering an overall scale, the 10% silica gel reinforced PU foam shows a comparatively good result and hence provides an effective and promising way for the required applications. Acknowledgements The authors are grateful to Department of Science and Technology (DST-SERB; File no: ECR/2015/000111) for providing the necessary facilities and funds for conducting this research. References [1] Bernard E. Obi, Applications of Polymeric foams in Automobiles and transportation, Polymeric Foams Structure Property Performance, A Design Guide (2018), Pages 341–366. [2] G. Sung, J.S. Kim, J.H. Kim, Sound absorption behavior of flexible polyurethane foams including high molecular-weight copolymer polyol, Polym. Adv. Technol. (2017) 1–8, https://doi.org/10.1002/pat.4195. [3] C. Zhang, J. Li, Z. Hu, F. Zhu, Y. Huang, Mater. Des. 41 (2012) 319, https://doi. org/10.1016/j.matdes.2012.04.031.
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Please cite this article as: L. Yuvaraj, S. Jeyanthi, N. S. Thomas et al., An experimental investigation on the mechanical and acoustic properties of silica gel reinforced sustainable foam, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2019.09.115