Effect of nanofiber spinning duration on the sound absorption capacity of nonwovens produced from recycled polyethylene terephthalate fibers

In this study, new sound-absorbing composite materials in the form of nanofiber web-reinforced nonwovens and sandwich structures were produced by incorporating polyurethane (PU) nanofibers of different durations to recycled polyethylene terephthalate (PET) bottle waste nonwovens in order to execute environmentally friendly noise control in the lower frequency region. Effect of nanofiber spinning duration on the prepared structures was examined and the results were compared to commercial sound absorbers. Nanofiber spinning period optimization studies were done by producing nanofibers from 15 wt% PU solution for several durations and 5, 20, 60 and 120 min were chosen as the nanofiber spinning durations. The bead free PU nanofibers of 509.9 nm diameter were spun on the 250, 500 and 750 g/m2 needle punched nonwovens for the selected durations in order to produce the nanofiber web-reinforced nonwovens, afterward sandwich structures were prepared by laminating them with another nonwoven of the same. Noise reduction coefficient (NRC) values of all samples were calculated after the sound absorption coefficients (SACs) have been measured using a two-microphone impedance tube. It was seen that as nanofiber production time increased, resonance frequencies decreased and thicker nanofiber webs provided more effective sound absorption in the lower frequency range. There were statistically significant differences between noise reduction coefficients (NRCs) of the composites depending on the nanofiber spinning duration. In particular, 1560 (nanofiber web produced for 60 min) added nonwovens had the highest NRCs of all durations. However, in sandwich structures, better sound absorption coefficient (SAC) values were not obtained as the nanofiber spinning time increased. Amogst all samples, H750-1520-H750 had the highest NRC value of 0.574 with a thickness of 8.471 mm. H250-1560 which was formed by spinning nanofibers on H250 for 60 min was also regarded as a good sound absorber with a thickness of 1.548 mm and 0.435 NRC. The produced materials may be referred to as potential environmentally friendly sound absorbers with a value added utilization area for recycled polyethylene terephthalate fibers.