Study on Sound Absorption Properties of Natural Fiber and Its Composites

This research aimed to study the sound absorption properties of natural fibers and their reinforced composites. Sound absorption coefficients of three types of natural fibers, i.e., ramie, flax and jute fibers and their composites were measured by the two-microphone transfer function technique in the impedance tube. The results were compared with synthetic fibers and their composites. It was found that both natural fibers and their composites had superior capability of noise reduction. The multi-scale and hollow lumen structures of natural fibers contributed to the high sound absorption performance. Moreover, the sound absorption properties of these natural fibers were also calculated by the Delany-Bazley and Garai-Pompoli models.it also tells us how natural fiber reduces sound and as well as noise pollution. Eco-friendly green/ biocomposites were fabricated from chopped hemp fiber and cellulose ester biodegradable plastic through two process engineering approaches: powder impregnation through compression molding (process I) and extrusion followed by injection molding (process II). Cellulose ester, e.g. cellulose acetate (CA) plasticized with 30 wt% citrate plasticizer (CAP) was used as the matrix polymer for bio composite fabrication. Intimate mixing due to shear forces experienced in process II produced superior strength bio composites over their counterparts made using process I. Bio composite fabricated through process II containing 30 wt% hemp natural fiber showed an improvement of storage modulus by 150% over the virgin matrix polymer. The coefficient of thermal expansion of the said bio composite decreased from the CAP polymer by 60% whereas the heat deflection temperature improved by 30% versus the virgin bio plastic, indicating superior thermal behaviour of the bio composite. Plasticized cellulose acetate is proved to be much better matrix than non-polar polypropylene (PP) for hemp fiber (HF) reinforcements because of the better interaction of polar cellulose ester with the polar natural fiber. Fabricated through process II and with same content of hemp (30 wt%) the CAP-HF based bio composite exhibited flexural strength of 78 MPa and modulus of elasticity of 5.6 GPa as contrast to 55 MPa and 3.7 GPa for the corresponding PP-HF based composite. The experimental findings of tensile modulus of the bio composites are compared with the theoretical modulus using the rule of mixture. The fiber-matrix adhesion is evaluated through environmental scanning electron microscopy studies.