Eliminating unwanted noise in passenger compartments of vehicles is important to automobile manufacturers. The ability to reduce noise inside the vehicle enhances the perceived value of the vehicle to the consumer, and offers a competitive advantage to the manufacturer. Several methods are presently employed to reduce noise and its sources, one of which uses sound-absorbing materials attached to various components such as floor-coverings, package trays, door panels, headliners and trunk liners. Natural fibers are noise-absorbing materials that are renewable and biodegradable, making them an effective choice for the automobile industry. Floor coverings using natural fibers (kenaf, jute, waste cotton, and flax) in blends with polypropylene (PP) and polyester (PET) were developed as carded needle-punched nonwovens. The acoustical absorption coefficients of these floor coverings, and of floor coverings in combination with an underpad (either a rebonded polyurethane foam, or a soft cotton nonwoven) were evaluated by ASTM E— 1050 in the frequency range of 100 to 3200 Hz. By stacking an underpad and a floor covering together, a floor covering system was created. The measurements demonstrated that each of the natural fiber-based nonwoven floor coverings contributed to noise reduction, e.g., coefficients = 0.54—0.81 at 3.2 kHz. Noise was significantly reduced with a floor covering system using either of the underpads. The most reduction occurred with a polyurethane pad; for example, for kenaf floor covering C20-1 the coefficients at 3.2 kHz were: 1.0 with polyurethane versus 0.81 with cotton pad.

Two types of nonwoven composites, uniform and sandwich structures, are produced using bagasse, kenaf, ramie, and polypropylene (PP) fibers. The experimental uniform composites include kenaf/PP (70/30), bagasse/PP (50/50), and ramie/PP (70/30). The experimental sandwich composites include kenaf/bagasse/kenaf and ramie/kenaf/ramie. A comparative study of these experimental composites is conducted in terms of mechanical properties, thermal properties, and wet properties. Composite tensile and flexural properties are measured using a desktop tensile tester. Composite thermal properties are characterized using dynamic mechanical analysis (DMA). Water absorption and thickness swelling of the composites are evaluated in accordance with an ASTM method. Scanning electron microscopy is used to examine the composite bonding structures. Statistical method of ANOVA is used for the comparative analysis. The study finds that the uniform structures have higher tensile strength and modulus, as well as higher flexural yielding stress and modulus than the sandwich structures. In terms of the wet properties, the uniform composites have less water absorption but higher swelling rate than the sandwich composites. The DMA results show that the uniform composites feature a higher softening temperature (140 C) and melting temperature (160 C), in contrast to the sandwich composites with the softening point 120 C and melting point 140 C. Within the uniform structure group or sandwich structure group, the composite thermal mechanical properties did not differentiate very much among the different natural fibers, indicating that the composite thermal mechanical strength was largely dependent upon the thermal property of the polypropylene bonding fiber.

Noise absorption is one method for noise reduction in engineering. The material acoustic property for noise absorption is principally based on the efficiency of material structures for damping sound wave reflections. In this paper, three non-woven composites with activated carbon fiber (rayon precursor) non-woven as a surface layer and cotton, ramie, and polypropylene fiber non-wovens as base layers were produced. Their noise absorption coefficients were measured using the Brüel and Kjær impedance tube instrument and compared to those of three glass-fiber-surfaced non-woven composites. Statistical significance of the differences between the activated carbon fiber composites and glass-fiber-surfaced composites was tested using the method of Duncan's grouping. The study concluded that the activated carbon fiber composites exhibited an exceptional ability to absorb normal incidence sound waves. The analysis also revealed that the activated carbon fiber composite with a cotton base layer would be 4.6 times lighter in weight, 14% higher in low-frequency absorption, and 7% higher in high-frequency absorption, in comparison with the composite having a glass fiber surface layer and a polypropylene fiber base layer.

Perpendicular-laid and cross-laid highloft nonwoven fabrics are constructed of cotton, polyester, and bicomponent co-polyester bonding fibers. Kawabata parameters describing the compressional resistance and recovery of these fabrics are measured with a comput erized Q-test instrument. Results are obtained from tests replicated by two independent operators in triplicate and on different dates. Compared to cross-laid fabrics, perpendic ular-laid fabrics show higher compressional resistance and superior elastic properties. These results confirm earlier findings on the compressional behavior of highlofts deter mined on a Gustin-Bacon thickness measurement instrument.

Noise can be reduced by sound barrier materials, and transmission loss (TL) measurements are used to determine the insulation performance of sound barriers. In this paper, TL of the non-woven composites with two surface layers and three base layers was measured and analyzed using Brüel and Kjær impedance tubes and Pulse software. The results show that non-woven composites with activated carbon fiber (ACF) non-woven as a surface layer had significantly higher values of average TL than glass fiber-surfaced composites in both the low frequency range (100—1600 Hz) and the high frequency range (1600—6400 Hz). Regarding the sound barrier performance, base non-wovens made of cotton and ramie were better than polypropylene-based non-wovens in the whole frequency range, while at the low frequencies, especially below 600 Hz, glass fiber-surfaced non-woven was better than ACF-surfaced non-woven. The composite with cotton non-woven as a base and ACF as a surface exhibited the highest average TL value of 8.56 dB and the lowest mass per unit area of 106 g/m2.