**4. Experimental part**

Today, while studies on new sound insulating materials continue intensively, the usage of recycled products in this area is also increasing. Recycling technology provides environmental, social, and economic benefits. With environmental awareness and increased sensitivity to sustainability, recycled materials provide significant advantages for sound insulation.

In this study, nonwoven materials produced from conventional polyester (PES), mechanically recycled polyester (rm-PES), recycled polyester (r-PET), polypropylene (PP), and recycled polypropylene (r-PP) were compared with each other in terms of their sound absorption characteristics [47]. In **Figure 5**, photographs of the samples are given.

Supplying the raw materials and producing the nonwoven fabrics were carried out in a Turkish company working especially on recycled products. The processes

**Figure 5.** *Photographs of the samples used in experimental.*

applied for the mechanically recycled polyester and polypropylene fibers were as follows: the collected waste fabrics were cut with guillotine cutting machine and then shredded into pieces with particles of a suitable size. Then, the pieces were weighted on an electronic balance and blended in a vertical mixing blender. Carding process was applied to break down the big fiber bundle to the small size. Two-time carding process was applied to get uniform web formation, and then, the fine opener was used.

r-PET fibers provided by using r-PET flakes gained from PET bottles were used in this study. The common method of fiber production is as follows: at first, PET bottle wastes are separated from the other wastes; then, they are broken into flakes, washed, and dried before the spinning process of the fiber. In this method, r-PET fibers are acquired by transforming PET chips by the melt fiber drawing method [17].

The nonwoven fabric samples were produced by needle-punching technology. The webs were fed to a needling loom to produce nonwoven surfaces. Softness, bulkiness, conformability, fibrousness, and high strength characteristic without binder usage make the needle-punched nonwoven fabrics unique among the other nonwovens.

Before the physical tests, nonwoven samples were conditioned in standard atmospheric conditions (20 ± 2°C temperature, 65 ± 4% relative humidity). The mass per unit area was determined in accordance with the ISO 9073-1 standard, and thickness measurements of the materials were carried out according to the ISO 9073-2 standard using SDL Atlas fabric thickness gauge. Air permeability test was conducted according to the EN ISO 9237 standard by using Textest FX 3300 air permeability meter at 200 Pa pressure difference and 20 cm2 measurement areas.

Two methods were applied to measure sound absorption properties of the samples: alpha cabinet and impedance tube methods. Nonwoven textile products supplied within the scope of the study were tested by using alpha cabinet according to the Renault D49-1977-B standard. The cabinet volume was 6.44 m3 , and the total surface area was 22.2 m<sup>2</sup> . The surface area of the test specimens was 1.12 m<sup>2</sup> ; the

**97**

**Table 1.**

*Investigation of Sound Absorption Characteristics of Textile Materials Produced from Recycled…*

height of the microphone from the ground was 0.88 m; and the height of the sound source was 0.20 m. The frequency measurement range was set at 400–10,000 Hz.

Impedance tube method was also used to measure the sound absorption coefficients of the samples according to the EN ISO 10534-2 method. The frequency was set from 100 to 1600 Hz. The test was carried out by three test samples randomly

The structural properties and air permeability values of five different nonwoven

The test results obtained from the impedance tube method are given in **Figure 6**.

Compared to conventional polypropylene, r-PP indicates better sound absorption characteristics for all frequencies. It is associated with the micro voids in the

The acoustic absorption test results of the textile surfaces according to the alpha

**100% r-PET**

Mean (**X**¯) <sup>550</sup> <sup>596</sup> <sup>519</sup> <sup>509</sup> <sup>500</sup>

CV (%) 1.48 2.03 5.25 2.15 0.96

CV (%) 3.93 2.89 9.46 2.67 2.28

Mean (**X**¯) <sup>1136</sup> <sup>1270</sup> <sup>600</sup> <sup>875</sup> <sup>1536</sup>

CV (%) 5.08 9.17 18.66 17.01 4.50

Mean (**X**¯) 0.136 0.202 0.164 0.141 0.110

**100% rm-PES**

8.14 12.10 27.27 10.92 4.81

0.16 0.09 0.30 0.10 0.10

57.71 116.40 112.13 148.66 69.14

**100% PP**

**100% r-PP**

**PES**

Thickness (mm) Mean (**X**¯) 4.04 2.95 3.17 3.60 4.55

As air permeability results of nonwoven fabrics are examined, the surface produced from r-PP material has the highest air permeability, whereas the lowest air

According to the results, at low frequencies between 100 and 400 Hz, it can be clearly seen that r-PP, rm-PES, and r-PET surfaces have higher sound absorption coefficient values than the conventional PES and PP fabrics. This is an important point that recycled textile surfaces can be suggestible as sound insulation materials in low frequency band gap (100–400 Hz) as an alternative to the conventional fibers. In addition to this, r-PP material has the highest sound absorption coefficient (over 0.50) among the other recycled products since its lower density and porous structure create a higher friction surface. As the performance at the mid frequencies (400–1600 Hz) is analyzed, only PP, r-PP, and rm-PES fabrics have sound absorption coefficient over 0.50. Therefore, these surfaces can be suggested for sound

permeability value belongs to mechanically recycled polyester surface.

*DOI: http://dx.doi.org/10.5772/intechopen.92792*

surfaces used in the study are given in **Table 1**.

insulation materials to be used at mid frequencies.

recycled material caused by the inhomogeneity [48].

cabinet method are given in **Figure 7**.

Mass per unit area (g/m2 )

Air permeability

Fabric density (g/cm3 )

(l/m2 s)

**Measured parameter 100%** 

Standard deviation (SD)

Standard deviation (SD)

Standard deviation (SD)

*Properties of nonwoven fabrics used in the study.*

taken from nonwoven fabrics.

Three Brüel and Kjaer 2669 model microphones were used.

## *Investigation of Sound Absorption Characteristics of Textile Materials Produced from Recycled… DOI: http://dx.doi.org/10.5772/intechopen.92792*

height of the microphone from the ground was 0.88 m; and the height of the sound source was 0.20 m. The frequency measurement range was set at 400–10,000 Hz. Three Brüel and Kjaer 2669 model microphones were used.

Impedance tube method was also used to measure the sound absorption coefficients of the samples according to the EN ISO 10534-2 method. The frequency was set from 100 to 1600 Hz. The test was carried out by three test samples randomly taken from nonwoven fabrics.

The structural properties and air permeability values of five different nonwoven surfaces used in the study are given in **Table 1**.

As air permeability results of nonwoven fabrics are examined, the surface produced from r-PP material has the highest air permeability, whereas the lowest air permeability value belongs to mechanically recycled polyester surface.

The test results obtained from the impedance tube method are given in **Figure 6**. According to the results, at low frequencies between 100 and 400 Hz, it can be clearly seen that r-PP, rm-PES, and r-PET surfaces have higher sound absorption coefficient values than the conventional PES and PP fabrics. This is an important point that recycled textile surfaces can be suggestible as sound insulation materials in low frequency band gap (100–400 Hz) as an alternative to the conventional fibers. In addition to this, r-PP material has the highest sound absorption coefficient (over 0.50) among the other recycled products since its lower density and porous structure create a higher friction surface. As the performance at the mid frequencies (400–1600 Hz) is analyzed, only PP, r-PP, and rm-PES fabrics have sound absorption coefficient over 0.50. Therefore, these surfaces can be suggested for sound insulation materials to be used at mid frequencies.

Compared to conventional polypropylene, r-PP indicates better sound absorption characteristics for all frequencies. It is associated with the micro voids in the recycled material caused by the inhomogeneity [48].

The acoustic absorption test results of the textile surfaces according to the alpha cabinet method are given in **Figure 7**.


#### **Table 1.**

*Properties of nonwoven fabrics used in the study.*

*Waste in Textile and Leather Sectors*

applied for the mechanically recycled polyester and polypropylene fibers were as follows: the collected waste fabrics were cut with guillotine cutting machine and then shredded into pieces with particles of a suitable size. Then, the pieces were weighted on an electronic balance and blended in a vertical mixing blender. Carding process was applied to break down the big fiber bundle to the small size. Two-time carding process was applied to get uniform web formation, and then, the fine

r-PET fibers provided by using r-PET flakes gained from PET bottles were used in this study. The common method of fiber production is as follows: at first, PET bottle wastes are separated from the other wastes; then, they are broken into flakes, washed, and dried before the spinning process of the fiber. In this method, r-PET fibers are acquired by transforming PET chips by the melt fiber drawing

The nonwoven fabric samples were produced by needle-punching technology. The webs were fed to a needling loom to produce nonwoven surfaces. Softness, bulkiness, conformability, fibrousness, and high strength characteristic without binder usage make the needle-punched nonwoven fabrics unique among the other

Before the physical tests, nonwoven samples were conditioned in standard atmospheric conditions (20 ± 2°C temperature, 65 ± 4% relative humidity). The mass per unit area was determined in accordance with the ISO 9073-1 standard, and thickness measurements of the materials were carried out according to the ISO 9073-2 standard using SDL Atlas fabric thickness gauge. Air permeability test was conducted according to the EN ISO 9237 standard by using Textest FX 3300 air

Two methods were applied to measure sound absorption properties of the samples: alpha cabinet and impedance tube methods. Nonwoven textile products supplied within the scope of the study were tested by using alpha cabinet according

. The surface area of the test specimens was 1.12 m<sup>2</sup>

measurement areas.

, and the total

; the

permeability meter at 200 Pa pressure difference and 20 cm2

to the Renault D49-1977-B standard. The cabinet volume was 6.44 m3

**96**

surface area was 22.2 m<sup>2</sup>

opener was used.

*Photographs of the samples used in experimental.*

**Figure 5.**

method [17].

nonwovens.

**Figure 6.** *Sound absorption coefficients based on the impedance tube method.*

#### **Figure 7.**

*Sound absorption coefficients based on alpha cabinet method.*

Materials can be tested at a wide frequency band in case of their sound absorption properties. In this study, the tested frequency range is 400–10,000 Hz. According to **Figure 7**, between 400 and 1600 Hz, sound absorption coefficients of all nonwoven

**99**

**Acknowledgements**

*Investigation of Sound Absorption Characteristics of Textile Materials Produced from Recycled…*

surfaces are close to each other and are lower than 0.35. Over 2500 Hz frequency, which is a high frequency level, sound absorption coefficients of the nonwovens are over 0.5, which supply a better sound insulation property and can be an alternating

In this study, acoustic absorption coefficients were measured according to two different sound measurement methods. The results obtained from the alpha cabinet and the impedance tube methods complement each other and give the idea for the performance and comparability of the materials at different sound frequencies. For obtaining the required results, the choice of the appropriate method is crucial. The impedance tube method is mostly suitable in order to develop new materials, while a reverberation room test is more relevant to design acoustic adjustments of the space [49]. Moreover, reverberation rooms are often preferred since they give closer results to the actual working conditions of the material by means of the random incidence excitation. However, the tests in impedance tube allow obtaining the additional information about the characteristic acoustic impedance of the sample [50].

Along with the growing population, noise has become one of the major problems of everyday life, affecting our quality of lives and, in some cases, our health. As the studies on reducing the noise generation continue, new solutions are being searched on systems that allow absorbing more quantities of the present disturbing noise. Within this scope, many different technical textile materials are produced, which are closely related to building construction, automotive, and machinery industries. The use of these high-performance products is becoming increasingly widespread in terms of technical specifications. However, in today's competitive conditions, products that can compete in terms of cost are more preferred in the market. Recycled surfaces are one of these preferred products. In addition to the price advantage, waste materials are transformed into usable products by recycling, which is completely an environmentally friendly production that provides sustainability.

In this study, characteristics of conventional polyester and polypropylene nonwoven insulation materials commonly used in the market and the nonwoven fabrics produced from recycled materials were compared. When the test results were examined, it was concluded that the recycled materials used in sound insulation area had very successful competitive performance when compared with the conventional materials. They had the qualifications supplying the expectations in terms of sound

Insulation materials are used, especially in areas where sound insulation is desired (e.g., children's houses, hospitals, entertainment places, and automotive sector) and in civil engineering area. In addition, it is a good application area for recycled materials to supply a sustainable world, to increase the environment friendly approach, and to evaluate the waste materials in a technical field. By the year 2019, price of PP fiber in the market is about 3.2 \$/kg, 1.6 \$/kg for r-PP fiber, about 1.6 \$/kg for 100% PES and r-PET fibers, and 1.2 \$/kg for rm-PES fibers. In the scope of economy, it can be foreseen that recycling materials will provide an

This study was supported by the Ege University Scientific Research Projects Coordination Unit (Project Number: 15-MÜH-078). The authors would also like

insulation when produced in enough thickness value.

important advantage for both producers and consumers.

*DOI: http://dx.doi.org/10.5772/intechopen.92792*

insulation material for the industry.

**5. Conclusion**

*Investigation of Sound Absorption Characteristics of Textile Materials Produced from Recycled… DOI: http://dx.doi.org/10.5772/intechopen.92792*

surfaces are close to each other and are lower than 0.35. Over 2500 Hz frequency, which is a high frequency level, sound absorption coefficients of the nonwovens are over 0.5, which supply a better sound insulation property and can be an alternating insulation material for the industry.

In this study, acoustic absorption coefficients were measured according to two different sound measurement methods. The results obtained from the alpha cabinet and the impedance tube methods complement each other and give the idea for the performance and comparability of the materials at different sound frequencies. For obtaining the required results, the choice of the appropriate method is crucial. The impedance tube method is mostly suitable in order to develop new materials, while a reverberation room test is more relevant to design acoustic adjustments of the space [49]. Moreover, reverberation rooms are often preferred since they give closer results to the actual working conditions of the material by means of the random incidence excitation. However, the tests in impedance tube allow obtaining the additional information about the characteristic acoustic impedance of the sample [50].
