2.3.2 Nanofibrous membrane spinning

A nanofibrous layer formed by electrostatic spinning of the polymer from a solution of a 16% polyvinyl alcohol with 40% glyoxal, 85% phosphoric acid, and distilled water was used to produce the membrane. For production of PA6 nanofibrous membrane, a needleless electrospinning method from a cord was employed (NanospiderTM, NS 1WS500U). In this method [22], there is a solution carriage-feeding liquid polymeric material around a moving stainless steel wire. The wire electrode is connected to high-voltage supplier, and on the top, there is a grounded counter electrode. When the applied voltage exceeds a critical value, Taylor cones are then created on the wire surface, oriented toward the counter electrode. PA6 solution jets move toward the collector, and as the solvent evaporates, the PA6 nanofibrous layer is collected on a moving substrate.

The basis weight of the nanofibrous layer is given by the takeoff speed of the backing strip in the electrostatic spinning process. Four basis weights of the nanofibrous layer, namely, 6 g m<sup>2</sup> (exact value 5.7 0.2 g m<sup>2</sup> ), were formed at a corresponding process rate of 0.04 m min<sup>1</sup> ,3gm<sup>2</sup> (exact value 2.6 0.15 g m<sup>2</sup> ) at a corresponding process rate of 0.09 m min<sup>1</sup> ,2gm<sup>2</sup> (exact value 2.2 0.03 g m<sup>2</sup> ) at a corresponding process rate of 0.14 m min<sup>1</sup> , and 1 g m<sup>2</sup> (exact value 1.7 0.01 g m<sup>2</sup> ) at a corresponding process rate of 0.18 m min<sup>1</sup> . During the spinning on the Nanospider laboratory, a constant temperature of 22.4° C and a relative humidity of 44% RH were maintained with the built-in air conditioner. The spinning process was 0.33–0.34 mA and 50 kV. The distance of electrodes was 150 mm. In Figures 5 and 6, the thickness of nanofiber layer of different basis weights was determined using scanning electron microscopy (SEM). A small section of the fiber mat was placed on the SEM sample holder and sputter coated with gold (Quorum Q150R rotary-pumped sputter coater). Carl Zeiss Ultra Plus Field Emission SEM using an accelerating voltage of 1.48 kV was employed to take the SEM photographs.

2.3.3 Sound absorption measurement

Figure 5.

Figure 6.

29

(on the right).

(on the right).

Two-microphone impedance measurement tube typ. 4206 was used to measure the absorption coefficient in the frequency ranges 50 Hz to 6.4 kHz (standard large tube setup for samples diameter 100 mm: 50 Hz to 16 kHz; standard small tube setup for samples diameter 29 mm: 500 Hz to 6.4 kHz). The test was made

SEM images of PVA nanofibers of basis weights 2 (2.2 0.03) g m<sup>2</sup> (on the left) and 1 (1.7 0.01) g m<sup>2</sup>

SEM images of PVA nanofibers of basis weights 6 (5.7 0.2) g m<sup>2</sup> (on the left) and 3 (2.6 0.15) g m<sup>2</sup>

Sound Absorbing Resonator Based on the Framed Nanofibrous Membrane

DOI: http://dx.doi.org/10.5772/intechopen.82615

according to standard ISO 10534-2. The analyzer (Aubion X.8) generates a random signal which is then amplified by a power amplifier (B&K Typ. 2670, Crown D-75A); frequency is weighted by the frequency weighting unit in the large tube and then applied to the loudspeaker. The analyzer finally measures the response of the two microphones (B&K Typ. 4187) and calculates the frequency response function between these two microphone channels, so the data can be obtained from Sound Absorbing Resonator Based on the Framed Nanofibrous Membrane DOI: http://dx.doi.org/10.5772/intechopen.82615

#### Figure 5.

2.3.2 Nanofibrous membrane spinning

Figure 4.

9.0 14.2 mm.

Acoustics of Materials

A nanofibrous layer formed by electrostatic spinning of the polymer from a solution of a 16% polyvinyl alcohol with 40% glyoxal, 85% phosphoric acid, and distilled water was used to produce the membrane. For production of PA6 nanofibrous membrane, a needleless electrospinning method from a cord was employed (NanospiderTM, NS 1WS500U). In this method [22], there is a solution carriage-feeding liquid polymeric material around a moving stainless steel wire. The wire electrode is connected to high-voltage supplier, and on the top, there is a grounded counter electrode. When the applied voltage exceeds a critical value, Taylor cones are then created on the wire surface, oriented toward the counter electrode. PA6 solution jets move toward the collector, and as the solvent evapo-

Photo of applied grids. Rectangle with different side dimensions: 4.1 4.3 mm; 9.4 4.1 mm; 9.0 9.4 mm;

The basis weight of the nanofibrous layer is given by the takeoff speed of the

) at a corresponding process rate of 0.14 m min<sup>1</sup>

During the spinning on the Nanospider laboratory, a constant temperature of 22.4° C and a relative humidity of 44% RH were maintained with the built-in air conditioner. The spinning process was 0.33–0.34 mA and 50 kV. The distance of electrodes was 150 mm. In Figures 5 and 6, the thickness of nanofiber layer of different basis weights was determined using scanning electron microscopy (SEM). A small section of the fiber mat was placed on the SEM sample holder and sputter coated with gold (Quorum Q150R rotary-pumped sputter coater). Carl Zeiss Ultra Plus Field Emission SEM using an accelerating voltage of 1.48 kV was employed to

), were formed at a

, and 1 g m<sup>2</sup>

)

.

,3gm<sup>2</sup> (exact value 2.6 0.15 g m<sup>2</sup>

,2gm<sup>2</sup> (exact value

) at a corresponding process rate of 0.18 m min<sup>1</sup>

backing strip in the electrostatic spinning process. Four basis weights of the

rates, the PA6 nanofibrous layer is collected on a moving substrate.

nanofibrous layer, namely, 6 g m<sup>2</sup> (exact value 5.7 0.2 g m<sup>2</sup>

corresponding process rate of 0.04 m min<sup>1</sup>

2.2 0.03 g m<sup>2</sup>

(exact value 1.7 0.01 g m<sup>2</sup>

take the SEM photographs.

28

at a corresponding process rate of 0.09 m min<sup>1</sup>

SEM images of PVA nanofibers of basis weights 6 (5.7 0.2) g m<sup>2</sup> (on the left) and 3 (2.6 0.15) g m<sup>2</sup> (on the right).

Figure 6.

SEM images of PVA nanofibers of basis weights 2 (2.2 0.03) g m<sup>2</sup> (on the left) and 1 (1.7 0.01) g m<sup>2</sup> (on the right).

#### 2.3.3 Sound absorption measurement

Two-microphone impedance measurement tube typ. 4206 was used to measure the absorption coefficient in the frequency ranges 50 Hz to 6.4 kHz (standard large tube setup for samples diameter 100 mm: 50 Hz to 16 kHz; standard small tube setup for samples diameter 29 mm: 500 Hz to 6.4 kHz). The test was made according to standard ISO 10534-2. The analyzer (Aubion X.8) generates a random signal which is then amplified by a power amplifier (B&K Typ. 2670, Crown D-75A); frequency is weighted by the frequency weighting unit in the large tube and then applied to the loudspeaker. The analyzer finally measures the response of the two microphones (B&K Typ. 4187) and calculates the frequency response function between these two microphone channels, so the data can be obtained from it. The amount of sound energy which is absorbed is described as the ratio of sound energy absorbed to the sound energy incident and is termed the sound absorption coefficient α. The average of the five measurements was shown. The nanofiber layer was set at a distance of 30 mm from the reflective wall so that the nanofibrous membrane was able to vibrate under the incident sound wave as it is demonstrated on Figure 7.
