Investigation of industrial tea-leaf-fibre waste material for its sound absorption properties

Abstract

The sound absorption of an industrial waste, developed during the processing of tea leaves has been investigated. Three different layers of tea-leaf-fibre waste materials with and without backing provided by a single layer of woven textile cloth were tested for their sound absorption properties. The experimental data indicate that a 1 cm thick tea-leaf-fibre waste material with backing, provides sound absorption which is almost equivalent to that provided by six layers of woven textile cloth. Twenty millimeters thick layers of rigidly backed tea-leaf-fibres and non-woven fibre materials exhibit almost equivalent sound absorption in the frequency range between 500 and 3200 Hz.

Introduction

Sound absorption constitutes one of the major requirements for human comfort today. Sound insulation requirements in automobiles, manufacturing environments, and equipment, generating higher sound pressure drive the need to develop more efficient and economical ways of producing sound absorption materials. Industrial applications of sound insulation, generally includes the use of materials such as glass wool, foam, mineral fibres and their composites. A porous laminated composite material manufactured by lamination, preheating and molding of premix, exhibits a very high sound absorption property in the frequency range 500–2000 Hz [1]. Two-stage compression molding of recycled polyolefin-based packaging wastes along with plastic-coated aluminum foils, expanded polystyrene and coir pith, offers sound absorption properties comparable to glass wool [2]. Combination of non-woven fabric and para-amid paper were studied and a sound absorption performance at frequencies higher than 2000 Hz was found to be better than that of glass wool [3]. Sintered Al fibre with a relative density of 0.6 and 10 mm thickness demonstrates a sound absorption coefficient of 0.7 for the frequency range of 800–2000 Hz. Similarly metal foam yields good sound absorption coefficient between 2000 and 4000 Hz [4]. Use of recycled rubber particles with perforated, polymer-material results comparable sound absorption properties. The sound absorption of the composite material is dominated by recycled rubber when the rubber particle size is small, whereas the property is influenced by polymer porous material when the rubber particle size is larger. A composite structure with a combination of perforated panel, rubber particle, porous material, polyurethane (PU) foam and glass wool, were found to demonstrate significant sound attenuation [5]. Usually, wasted rubber particles demonstrate lower sound absorption at higher frequencies. This is altered by matching with polypropylene particles and polystyrene particles, resulting a novel composite material with higher sound absorption for a wider frequency range [6]. Although these materials possess good heat and acoustical insulating properties, they cause environmental pollution and pose danger to human health.

Traditionally, economics has enforced research to focus on the industrial non-woven textile waste. Recently human hygiene and environmental protection has become another major requirement, resulting in more environmentally benign, natural materials to be used in such applications. Sound absorption characteristic values of rock wool were measured and found to be similar to glass fibre [7]. From the view of environmental protection, natural bamboo fibres were used for sound absorbing purposes. Impedance tube measurement of the bamboo fibre samples, reveal similar properties to that of glass wool. Bamboo material formed into a fibreboard, yields a superior sound absorption property when compared to plywood material of similar density [8]. Composite boards of random cut rice straws and wood particles, were found to demonstrate higher sound absorption coefficient than particleboard, fibreboard and plywood for the frequency range of 500–8000 Hz [9]. Coconut coir fibre compressed into bales and mattress sheet was found to demonstrate good sound absorption coefficient. When compared to a single layer, multi-layer coconut coir fibres with airspace layers increase the absorption coefficient of the material at lower frequencies [10]. Alternatively, as a natural and environmentally friendly material, tea-leaf-fibre (TLF) has been tested for its sound absorption properties. Tea-leaf-fibre is a waste product of tea-leave processing, extracted after drying and chopping of the leaves. Besides being a hygienic material, tea-leaf-fibre is a product of renewable bio-resources that makes it biodegradable.