Sound insulation performance of composites developed using waste carbonaceous materials

Sunali 1

Automotive Health Monitoring Laboratory, Centre for Automotive Research &Tribology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India

Jonty Mago 2

Automotive Health Monitoring Laboratory, Centre for Automotive Research &Tribology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India

Ashutosh Negi 3 School of Interdisciplinary Research, Indian Institute of Technology Delhi, Hauz Khas, New Delhi- 110016, Indi a Automotive Health Monitoring Laboratory, Centre for Automotive Research & Tribology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India S. Fatima 4

Automotive Health Monitoring Laboratory, Centre for Automotive Research &Tribology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi-110016, India

ABSTRACT

Vibration and noise mitigation in a system has many benefits associated with them. Reducing unwanted vibrations could lead to improved performance, lower noise emission, and enhanced system lifespan. Therefore, it is necessary to eliminate mechanical vibration and noise through appropriate measures. State-of-the-art techniques utilize sustainable carbonaceous resources to develop sound insulating materials to reduce the environmental externalities of synthetic materials. It is noteworthy to mention that carbonaceous resource like biochar assists in atmospheric carbon sequestration (capturing and storing CO 2 ) and limits CO 2 concentration in the environment. In the present work, biochar obtained from biomass waste was utilized as a filler with a natural rubber matrix to develop sound insulating materials. Furthermore, the physical, mechanical, and acoustical properties of developed composites were studied. The sound transmission loss of the composites was measured as per ASTM E2611-17 using a four-microphone impedance tube. Noticeably, significant improvement in the measured properties has been observed after adding biochar to the natural rubber matrix.

1. INTRODUCTION

During the last few decades, the rapid growth of industrialization and urbanization have presented severe noise and vibration issues across the globe [1]. Considering the importance of controlling noise

1 sunali013@gmail.com 2 jontymago@gmail.com 3 negi.ashutosh90@gmail.com 4 fatima@iitd.ac.in

pollution, researchers are coming up with various noise control methods, which are broadly classified into two groups: active and passive noise control methods [2]. Passive noise control involves the use of acoustic materials that absorb, dissipate, and reflect the sound wave energy. Sound insulating/absorbing materials help to manipulate sound waves by blocking or absorption [3,4].

In recent years, numerous studies have been carried out to develop sound-insulating composites such as wooden boards [5,6], metals [7], fibers [8], rubbers [9], and polymer composites [8]. Among these, polymer composites have gained more attention due to their exclusive properties like lightweight, mass production, and easy design. On the contrary, rubber composites have gained significant interest among researchers due to their low-cost availability and good performance for sound insulating applications. Carbon black (CB) plays an important role as a reinforcement filler among the rubber-based composite, leading to improved performance. However, CB is mainly produced from non-renewable petrochemical materials, which limits it’s utilizability due to volatile petroleum market [10].

In this context, there is a need to identify sustainable biobased fillers for rubber-based composites that provide comparable efficacy in sound insulating applications. Interestingly, biochar obtained from biomass pyrolysis is gaining popularity in composite filler applications due to its renewability and low cost. It can also be considered a potential candidate for the replacement of CB as it contains elemental carbon and other constituents such as ash, which is generally found in conventionally used CB [11]. So, from the perspective of sustainable and green chemistry, biochar can be used in rubber composites to replace conventionally used CB. This paper presents the use of bamboo biochar (BB) as a reinforcing agent in natural rubber (NR). Two different NR composites with and without reinforcing agents were prepared according to the ASTM D3182-21. Furthermore, their physical, mechanical, and acoustical properties were investigated.

2. EXPERIMENTAL DETAILS

2.1. Raw Materials

The natural rubber (Type RS4), bamboo biochar (BB), zinc oxide (ZnO), stearic acid, 6-PPD [N-(1,3- Dimethyl butyl)-N-phenyl-P-Phenylenediamine], paraffin oil, TBBS (N-tert-butyl-2-benzothiazole sulphonamide) and sulphur were purchased from local suppliers.

2.2. Preparation of NR-BB Composites

Two different composites were prepared, the first one without BB-filler (NR composite) and the second one with 30 phr of BB-filler (NR/BB30 composite). The compound was developed according to the ASTM D3182-21 standard. 100 phr (parts per hundred of rubber) of NR was first mixed with compounding ingredients like stearic acid (2 phr), ZnO (5 phr), 6-PPD (1.5 phr) with 50% BB on a two-roll mill at 60-80°C,15-20 rpm for 20-25 minutes. Afterward, the remaining 50% BB and paraffin oil was added to the pre-mixture and subsequently blended for 10 minutes. After 24 hours, sulphur (2.5 phr) and TBBS (1 phr) were added to the prepared compound and mixed for 10 minutes. Finally, the compound was hot-pressed at 150-160°C for 20 min under the pressure of 1.0-1.5 MPa to convert into sheets.

3. CHARACTERIZATION OF COMPOSITES

3.1. Physical Properties

The density of developed NR and NR/BB30 composites was measured as per ASTM D792-20 on a Mettler Toledo weighing balance as per Equation 1.

ρ liquid ×W air W air −W liquid (1)

ρ material =

where  material (in kg/m 3 ) is the density of material (NR and NR/BB30 composites),  liquid is the density of the liquid (acetone was used in the present,  acetone = 784 kg/m 3 ), W air is the weight of material in the air, W liquid is the weight of material fully submerged in the liquid, i.e., acetone.

3.2. Mechanical Properties

The tensile strength, elongation at break, and young's modulus of developed NR and NR/BB30 composite were determined using a 10 kN universal testing machine (Shimadzu, Japan), as shown in Figure 1(a). The samples were first prepared into a dumbbell specimen, as shown in Figure 1(b). The samples were tested under a constant displacement rate of 500 mm/min and a gauge length of 33 mm. Tensile strength was calculated according to ASTM D412-16. Moreover, the hardness of developed NR and NR/BB30 composites was measured using a Durometer (Model: KR-12KA; Make: Kori Seiki) as per ASTM D2240-15. The 30 mm diameter and 13 mm thickness samples were prepared with compression molding.

Figure 1: (a) Tensile test setup for measuring tensile properties, (b) NR and NR/BB30 composites

specimen for tensile test

3.3. Sound Transmission Loss

Four-microphone impedance tube (Model: Type 4206-T; Make: B & K) was used to determine the sound transmission loss (STL) of NR and NR/BB30 composites. The schematic of four microphone impedance tube is shown in Figure 2. The equipment is based on ASTM E2611-17 Samples of 100 mm and 29 mm diameter (thickness 2 mm) was inserted in the middle of the test tube and tested in the frequency range of 50 Hz-1.6 kHz and 500 Hz-5.0 kHz, respectively, at 20°C and 50% RH. The measured STL results were filtered (1/3 octave filter) and calculated in pulse lab shop software using Equation 2.

Figure 2: (a) Schematic of four microphone impedance tube setup (b) NR and NR/BB30 composites

specimen STL measurement

𝑤 𝑖 𝑤 𝑡 ) = 10 𝑙𝑜𝑔 10 (

1

𝜏 ) (2)

STL = 10 𝑙𝑜𝑔 10 (

where, STL = Sound transmission loss (dB), w i = Incident sound power (W), w t = Transmitted sound power (W), 𝜏= (

𝑤 𝑖 𝑤 𝑡 ) = Sound transmission coefficient.

4. RESULTS AND DISCUSSION

4.1. Density The density values of developed NR and NR/BB30 composites are listed in Table 1. It was observed that the density value of NR/BB30 composite (1050 kg/m 3 ) was increased by 7.91% compared with NR composite (973 kg/m 3 ). This is due to the formation of cross-linkages between the polymer, filler, and reinforcing agent during vulcanization.

Table 1: Density values of developed NR and NR/BB30 composites

S No. Composites Density (kg/m 3 ) 1 NR 973 2 NR/BB30 Composite (with 30 phr BB) 1050

4.2. Mechanical Properties

Figure 3(a) shows the typical stress vs. strain curve for developed NR and NR/BB30 composites. The mechanical properties of the developed NR/BB30 composite improved with the addition of filler. It can be observed from Figure 3 (b) that adding 30 phr of BB in the NR matrix, improvement in hardness (24.47%), tensile strength (233.6%), elongation at break (45.37), and young’s modulus (123.52%) was found. The increasing trend in tensile strength value, % of elongation value, and young’s modulus value are due to the formation of restriction in polymer chain mobility with the addition of BB content [12].

sapeaeaanaaetmeemrceeneaammanes —

Figure 3: (a) Stress vs. strain curve of NR, and NR/BB30 composites, (b) Hardness, Tensile

strength, % elongation at break, and young’s modulus of NR and NR/BB30 composites

4.3. Sound Transmission Loss A strong correlation exists between the sound-insulating effect and frequencies of the sound wave. The same material can exhibit different STL values when different sound wave frequencies are applied [5]. In this study, 0-5000 Hz frequencies range were selected to investigate the sound insulating characteristic of NR and NR/BB30 composites. Figure 4 (a) illustrates the STL as a function of frequency for developed NR and NR/BB30 composites. It can be observed from Figure 4 (a) that the value of STL is gradually increasing with increasing frequency and reached the maximum at 3300 Hz for both types of developed composites. Moreover, NR and NR/BB30 composites exhibit a similar trend of STL with increasing frequency.

Figure 4: (a) Sound transmission loss as a function of the frequency for developed NR and NR/BB30 composites (b) Average sound transmission loss of developed NR and NR/BB30

composites

Figure 4 (b) shows the average STL for developed NR and NR/BB30 composites. According to the mass law of acoustics, the composites having a high-density value will deliver better sound insulating properties [5]. Moreover, from the molecular structural point of view, the NR matrix consists of a long, flexible chain-like structure that can freely rotate about its backbone bonds. Initially, NR composite had a density value of 973 kg/m 3 , while the addition of 30 phr of BB in NR composite led to an increase in the density value to 1050 kg/m 3 . This is because the addition of filler in the NR matrix resists the polymer chain's motion, thereby enhancing the composite's stiffness and ultimately increasing the STL value of the composite. It is noteworthy to mention that with the addition of BB content in the NR matrix, the sound insulating property of the developed composite is improved by 8.04%.

5. CONCLUSIONS

This study introduces BB as an eco-friendly, sustainable, and low-cost filler in the natural rubber matrix. Two different composites were prepared, the first one without BB-filler (NR composite) and the second one with 30 phr of BB-filler (NR/BB30 composite). The physical, mechanical, and acoustical properties of developed composites have been measured. It was observed that adding 30 phr of BB in the NR matrix leads to significant improvement in the abovementioned properties. It could be concluded that BB can be used as a replacement for conventionally used CB.

6. ACKNOWLEDGEMENT

The authors would like to acknowledge the Department of Mechanical Engineering and Department of Material Science and Engineering, IIT Delhi, for mechanical characterizations.

7. FUNDING

This study is financially supported by the foundation for Innovation and Technology Transfer (FITT) of the Indian Institute of Technology Delhi, under the project titled, 'Development of Vibration and Sound Dampening Materials from Biochar Obtained from Waste Lignocellulosic Biomass' [Grant Number: MI02077] and Delhi Research Implementation and Innovation (DRIIV) Cluster.

8. REFERENCES

1. Fang, W., Fei, Y., Lu, H., Jin, J., Zhong, M., Fan, P., Yang, J., Fei, Z., Chen, F., & Kuang, T.

Enhanced sound insulation and mechanical properties based on inorganic fillers/thermoplastic elastomer composites. Journal of Thermoplastic Composite Materials , 32 (7), 936–950 (2019). 2. Rao, M. D. Recent Applications of Viscoelastic Damping for Noise Control in Automobiles and

Commercial Airplanes. Journal of Sound and Vibration, 262, 457–474 (2003). 3. Mohanty, A. R., & Fatima, S. (n.d.). An overview of automobile noise and vibration control . 10–

19. 4. Fatima, S., & Mohanty, A. R. Acoustical and fire-retardant properties of jute composite materials.

Applied Acoustics , 72 (2–3), 108–114 (2011). 5. Zhao, J., Wang, X. M., Chang, J. M., Yao, Y., & Cui, Q. Sound insulation property of wood-

waste tire rubber composite. Composites Science and Technology, 70(14), 2033–2038 (2010). 6. Liu, M., Peng, L., Fan, Z., & Wang, D. Sound insulation and mechanical properties of wood

damping composites. Wood Research , 64 (4), 743–758 (2019). 7. Bo, Z., & Tianning, C. Calculation of sound absorption characteristics of porous sintered fiber

metal. Applied Acoustics , 70 (2), 337–346 (2009). 8. Munde, Y. S., Ingle, R. B., & Siva, I. Vibration damping and acoustic characteristics of sisal

fibre–reinforced polypropylene composite. Noise and Vibration Worldwide , 50 (1), 13–21 (2019). 9. Messiry, M. El, & Ayman, Y. Investigation of sound transmission loss of natural fiber / rubber

crumbs composite panels. 0(0), 1–23 (2021). 10. Fan, Y., Fowler, G. D., & Zhao, M. The past, present and future of carbon black as a rubber

reinforcing filler–A review. Journal of Cleaner Production, 247, 119115 (2020). 11. Peterson, S. C. Evaluating corn starch and corn stover biochar as renewable filler in carboxylated

styrene–butadiene rubber composites. Journal of Elastomers & Plastics, 44(1), 43-54 (2012). 12. Visakh, P. M., Thomas, S., Oksman, K., & Mathew, A. P. Crosslinked natural rubber

nanocomposites reinforced with cellulose whiskers isolated from bamboo waste: Processing and mechanical/thermal properties. Composites Part A: Applied Science and Manufacturing, 43(4), 735-741 (2012).