Akustik uygulamalar için nanolifli resonant membran

Environmental noise from sources such as traffic, industries, construction, and public work, as well as noise from indoor sources like ventilation systems, office machines and white goods is an ever growing problem to human health. Fibrous textile materials are widely used for acoustic purposes applications such white goods. However, the absorption of lower-frequency sound is problematic with fibrous materials made up of coarser fibers. For this reason, sound absorption materials that perform effectively at low frequencies are required. Nanofibrous layers can perform as membranes that vibrate easily at low frequencies. This property is obtained by nano dimensions of the fibers as well as the interfiber areas. Sound waves incident on the acoustic resonance membrane make the membrane oscillate, and the maximum amplitude occurs in the case of resonance. This thesis aims at developing a nanofibrous resonant membrane based material in order to decrease the noise generated by white goods. The studies conducted were designed with reference to the detailed literature review, have novelty in research, and have produced remarkable as well as original results. The thesis study starts with the development/production of nanofibrous membranes having different mass per unit area, fiber diameter and polymer types. The process and polymer parameters used during the production of the nanofibrous membrane were set in the light of the information gathered from the literature survey regarding the acoustic characteristics of nanofibrous layers, the polymer properties for electrospinning and, electrospinning process and its variable parameters. The second part of the thesis involves the development of a novel optical method for determining the resonance frequency of the produced nanofibrous membranes. In order to determine the resonance frequency, a frequency range of 0–1500 Hz was studied by taking measurements at every 20 Hz, to obtain a rough estimate of the resonance frequency. The deflection size of the samples at a frequency range of 0-1500 Hz was measured using four different experimental settings such as; setting 1: open tube (one end of the tube is open), setting 2: closed tube (the tube closed with a rigid plate), setting 3: open tube with a 0.5387 g weight hung on the sample, and then immediately removed to create a radial tension on the sample while one end of the tube remained open and, setting 4: closed tube with a 0.5387 g weight hung on the sample, and then immediately removed to create a radial tension on the sample while the tube was closed with a rigid plate. Resonance frequency of the nanofibrous membranes was determined according to the optical method developed and effect of mass per unit area and fiber diameter on resonance frequency were analyzed. The results of the study showed that the resonance frequency of the polyvinyl alcohol (PVA) nanofibrous membrane decreased with the increase in mass per unit area and decrease in average nanofiber diameter. Moreover, a study on comparison of the resonance frequency of the produced membranes with that of a homogenous membrane, namely foil was conducted. It was found that both nanofibrous membrane and foil exhibit the same resonance frequency characteristic although nanofibrous membrane showed higher deflection than that of the foil at lower frequency ranges. Additionally, the resonance frequency of both the nanofibrous membrane and the foil increased in the setting involving the closed tube while the amplitude increased when radial tension was applied to the sample in the closed tube. Furthermore, resonance frequencies of different homogenous membranes in addition to foil and comparison of their properties with those of the nanofibrous membranes were conducted. The results indicated that nanofibrous membrane and low-density polyethylene (LDPE) stretch film had different frequency values at which the maximum deflections occur. Polymer types used for the production of nanofibrous membranes were also diversified. The results showed that a change in polymer type caused a shift in resonance frequency. The thesis continues with the third part in which the nanofibrous resonant membranes developed were tested to determine their sound absorption characteristics and transmission loss values. Moreover, special structures were developed by combining the produced nanofibrous membranes and spacer knitted fabrics and the acoustic behavior of the developed structures was analyzed. It was observed that the use of nanofibrous membrane had a significant impact on the acoustic performance of spacer knitted fabric. Furthermore, the use of nanofibrous membrane with porous structures provided a better sound absorption at larger frequency bandwidth. Finally, a novel nanofibrous membrane based combined (layered) structure was developed in which commercial nonwoven fabric (felt) was used as substrate material whereas spunbond (S)/meltblown (M) structures and their combinations were used as covering layer. Nonwoven technology was used in terms of surface technology considering cost and ease of manufacturing besides the sound absorption performance. The combined (layered) structures acoustic performance was also tested on domestic washing machines.The insulating material used in such application areas should be applied easily and exhibit satisfactory dimensional and structural characteristic besides good acoustic performance. In this context, nanofibrous membrane based combined structures developed were enhanced for the application area. It was observed that the addition of covering material to the layered structure made a positive contribution to the sound absorption property. The structures with multilayered nonwoven coverings tended to demonstrate better acoustic performance than those with single layer coverings. Moreover, the joining of the special structure (covering layer + nanofibrous membrane) to the felt, which is commercially used in washing machines, provided an about 1,6 dBA improvement in sound power level. This 1,6 dBA decrease corresponds to a 30% decrease in sound power level. In addition to that, multiple criteria decision making (MCDM) was applied to the study. Technique for order preference by similarity to ideal solution (TOPSIS) together with analytic hierarchy process (AHP) was employed not only to determine the best performed nonwoven as a covering layer, but also to find out the optimized solution among the combined structures developed, so far as the acoustic behaviour was concerned. In conclusion, when the thesis study is evaluated as a whole, it is predicted that it has an important and unique contribution to the existing knowledge for the topics such as the design of the novel material and innovative measurement methods. It also has a potential as forming a basis for new fields of related studies. Therefore, the results of this study will produce unique scientific and technologic results both in national and international arenas. The innovative product that was developed within the thesis will form a basis to develop other unique projects since the studies carried out during the thesis will provide a collection of technical knowledge that can be used in developing and improving similar innovative materials. Finally, this study has a unique value in both repeatability of producing acoustic materials and in potential mass production processes with the help of the presented technical knowledge.