Browsing by Author "Dr. Pam Banks-Lee, Committee Chair"

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    Acoustical Absorptive Properties of Nonwovens
    (2005-08-09) Allampalayam Jayaraman, Kannan; Dr. Michelle Jones, Committee Member; Dr. Behnam Pourdeyhimi, Committee Co-Chair; Dr. Pam Banks-Lee, Committee Chair
    Today much importance is given to the acoustical environment. Noise control and its principles play an important role in creating an acoustically pleasing environment. This can be achieved when the intensity of sound is brought down to a level that is not harmful to human ears. Achieving a pleasing environment can be obtained by using various techniques that employ different materials. One such technique is by absorbing the sound and converting it to thermal energy. Fibrous, porous and other kinds of materials have been widely accepted as sound absorptive materials. A literature scan [19, 20, 53, 76] showed nonwovens could be considered to be a prospective candidate for sound absorption. The impetus for this study stemmed from the drawbacks associated with the existing sound absorbing materials like felts made from glass, asbestos and rock wool and foams. Some of these drawbacks include the fact that the materials are unsuitable for molding, non-recyclable, difficult to handle and install, dust accumulating and in the case of foams are high in density. These drawbacks are forcing the acoustical product manufacturers to look into natural, biodegradable raw materials. To assist in that effort, the research presented here studies the feasibility of using kenaf fibers blended with reclaim polyester fibers and other fiber blends as sound absorptive materials. Products from kenaf/reclaim fiber blends will have the benefit of low raw materials and manufacturing cost, at the same time providing a suitable end use for reclaim polyester fibers. Early work in noise control has shown the importance of understanding micro- structural and other physical parameters in designing high performance acoustic materials. As a final objective, this research describes how the physical elements of nonwoven sound absorbent system like fiber type, fiber size, fiber cross section, material thickness, density, airflow resistance and porosity can change the absorption behavior of nonwovens. Influence of fire retardant treatment, surface impedance, air gap, compression, manufacturing methods and attachment of film on sound absorption behavior of nonwovens were also considered.
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    Thermal Barrier Properties of Flame Resistant Nonwovens
    (2005-08-10) Vallabh, Rahul; Dr. Pam Banks-Lee, Committee Chair
    Heat flux through nonwovens takes place by conduction through air and fibers, infrared radiation and also by convection. Radiation heat transfer is found to be the dominant mode of heat transfer at temperatures higher than 400-500K [18]. Convection heat transfer is negligible in nonwovens due to the small size of the pores and tortuous nature of air channels. Therefore, for optically thick nonwoven material, effective thermal conductivity is given by the sum of its conduction and radiation components. In this research two methods were identified to determine radiative thermal conductivity. In the first method, effective (total) thermal conductivity of needlepunched samples made from Nomex fibers was determined by using a Guarded Hot Plate instrument, while the conduction component was calculated by employing equations developed by Stark and Fricke (15). The radiative thermal conductivity (radiation component of effective thermal conductivity) was then determined by subtracting the conduction component from the effective thermal conductivity. In the second method radiation component of effective thermal conductivity was calculated using the extinction coefficient of samples. The extinction coefficient was determined by using direct transmission measurements made using a Fourier Transform InfraRed (FTIR) spectrometer. Results showed that while radiation was the dominant mode of heat transfer at temperatures higher than 530 K, the conduction component of effective thermal conductivity did not change much in the range of densities tested. Empirical models were developed for predicting the temperature difference across thickness of the fabric and the radiative thermal conductivity with R-square values of 0.94 and 0.88 respectively. Fabric density, fabric thickness, fiber fineness, fiber length, mean pore size and applied temperature were found to have significant effect on the effective thermal conductivity and its radiation component of needlepunched nonwoven samples. A high correlation between the results of Method 1 (Guarded Hot Plate) and Method 2 (FTIR) was not seen. However, the absorbance measurements made using the FTIR spectrometer were found to have significant effect on the radiative thermal conductivity.