The use of synthetic  materials as acoustic absorbers is still applied 

extensively in building industry. These non-biodegradable materials do not only 

cause pollution to the environment, but also contribute significantly in increasing 

the CO2  causing the effect of global warming. Therefore researchers have now 

driven their attentions to find sustainable and eco-friendly materials to be an 

alternative sound absorber. This paper discusses the use of natural fibers from 

dried paddy straw as a fibrous acoustic material. Since this is one of common 

natural waste materials found across South East Asia, the usage will also 

minimize the production cost. A panel sound absorber from paddy straw is 

fabricated and its acoustic properties are investigated through experiment. Good 

acoustic performance is  obtained  and is comparable against that from the 

classical synthetic absorber

Putra, Azma

English

Universiti Teknikal Malaysia Melaka (UTeM) Repository

  Hari Penyelidikan 2011, Fakulti Kejuruteraan Mekanikal, Universiti Teknikal Malaysia Melaka,            20 Julai 2011  52  Dried Paddy Straw Fibers as an Acoustic Absorber:  A Preliminary Study   Yasseer Abdullah1, Azma Putra1, Hady Effendy2, Wan Mohd Farid2, Md Razali Ayob3   Abstract –The use of synthetic materials as acoustic absorbers is still applied extensively in building industry. These non-biodegradable materials do not only cause pollution to the environment, but also contribute significantly in increasing the CO2 causing the effect of global warming. Therefore researchers have now driven their attentions to find sustainable and eco-friendly materials to be an alternative sound absorber. This paper discusses the use of natural fibers from dried paddy straw as a fibrous acoustic material. Since this is one of common natural waste materials found across South East Asia, the usage will also minimize the production cost. A panel sound absorber from paddy straw is fabricated and its acoustic properties are investigated through experiment. Good acoustic performance is obtained and is comparable against that from the classical synthetic absorber.  Keywords: Synthetic materials, sustainable, acoustic performance, non-biodegradable   I. Introduction Acoustics control in building improves significantly with technology. As progress in technology has enhanced the control of sound quality in the room interior, it is important to balance the development of advanced materials with responsible environmental practices. Hence, researchers are becoming interested in natural or renewable materials instead of producing and using synthetic non-renewable materials. According to F. Asdrubali [1], these synthetic materials such as foamglass contributes much higher Global Warning Potential (GWP) kg CO2 equivalent compared to coconut fiber. Natural fibers are low-cost, lightweight and environmental friendly if compared to glass fiber and mineral based synthetic materials. Moreover, natural fibers are sustainable, i.e. a resource to keep produce for the needs of present without affecting the future needs [2]. In addition, these natural materials are bio-degradable, non-abrasive, abundance and having less health and safety risk while handling and processing [3]. Several works have been published to investigate the performance of natural fibers as the acoustic absorber. D’alessandro and Pispola [4] measure sound absorbing panels made of Kenaf and blankets of recycled polyester (PET) ibers. Both samples were tested in reverberation chamber, acoustic properties of both samples are good at frequency range between 1000 Hz to 5000Hz with the average of 0.8.  Lindawati et. al [5] studied the acoustic properties of Arenga Pinnata fiber. A 40 mm thick panel shows good absorption coefficient from 2000 Hz to 5000 Hz. Comparisons were also made with other natural fibers such as coir and palm oil. Arenga Pinnata shows good properties above 2000 Hz, better than that of coir fiber, but slightly lower than that of the palm oil fiber at the average of 0.7.  Ersoy and Kucuk [6] investigated sound absorption of tea-leaf fibers and compared it with woven textile cloth. It shows that sound absorption of six layers woven textile cloth are slightly equivalent to 1cm thick tea-leaf fiber at frequency range between 500 Hz to 3000 Hz.   Hari Penyelidikan 2011, Fakulti Kejuruteraan Mekanikal, Universiti Teknikal Malaysia Melaka,            20 Julai 2011  53  Zulkifli et. al [7] worked on the coconut coir fibers compressed into a panel. Coir fiber is found to be good acoustic absorber when the fibers were compressed into sheet. Single layer of coir sheet shows good absorption coefficient at mid and high frequencies. Low frequency performance improves when the panel consists of multiple layers [8]. M.H Fouladi et. al [9] then utilized the coir panel with perforated panel facing improved the performance at lower frequencies.  Non-fibrous materials from unmodified straw and reed have also been investigated for its acoustic properties. These natural materials are found to have a good absorption coefficient from 500 Hz to 5000 Hz [10].  H.S. Yang et al. [11] utilized rice straw to become insulation boards to overcome lacking of solid woods in wood-industry. The rice straw was mixed with commercial binder to have certain shape and strength. The absorption coefficient is found to be on the average 0.5 between 1000 Hz to 8000 Hz.      Paddy straw is one of the natural fibers that abundantly available in South East Asia. Since the last decade, it is commonly used for many applications such as for roof, rope, animal foods and also floor mat. However, sound absorption of dried paddy straw fiber as sound absorber panel has not yet been investigated. This paper discusses the potential of using dried paddy straw fiber as raw material for sound absorbing material.   II. Research Methodology A. Raw Material Preparation Construction into an absorber sample is divided into two stages, namely the pre-treatment stage and preparation stage. The flow chart of the process is shown in Fig. 1.  In the pre-treatment stage, raw material was cut into 1 to 3 mm length as shown in Fig. 2. It was then sundried for 1 week and again heated in the oven at 115ᵒC for 10 minutes.  In preparation stage, the raw material was mixed with different composition of binders, blowing agent and additives such as methylcellulose, gypsum, water, aluminium oxide and lime. The amount of ingredient was applied using trial and error process to gain optimum strength of bonding. Each ingredient was then scaled and noted for future references.  Then the mixture was compressed using hydraulic presser at 10 bars in specially fabricated mould to obtain a round shape. The shaped mixture was hardened by heating it in oven at 115ᵒC for 30 minutes. The sample constructed has 33 mm diameter as seen in Figure 4. In this experiment, two samples with different composition were tested. The amount of methylcellulose was varied while preparing these samples. Methylcellulose was acting as glue or binder for the fibers. The ratio of the methylcellulose between the samples is 1:1.6, respectively for sample 1 and sample 2. The effect of this binder is investigated in this report.  B. Sound Absorption Testing The test was performed using home-made impedance tube by applying two-microphone transfer function method according to ISO 10534-2:2001 international standards [12]. The acoustic microphones used are the ½” Prepolarized free-field microphones (GRAS 40AE) with ½” CCP pre-amplifier (GRAS 26CA).  Data acquisition system used was RT Pro Photon 6.34 analyzer with Dactron software. The signal processing of raw data was calculated using Matlab software. Fig. 3 shows the equipment used in the test and the setup. The sample was placed at the end of the impedance tube and backed by a rigid surface.    Hari Penyelidikan 2011, Fakulti Kejuruteraan Mekanikal, Universiti Teknikal Malaysia Melaka,            20 Julai 2011  54  Paddy Straw FiberSundried for 1 weekCut 1-3 mmSample FiberMixing with binder, additives and blowing agentCool press at 10 barOven Heat 115°C for 30 minsOven Heat 115°C for 10 minsSound Absorber PanelPretreatment StagePreparationStage  Fig. 1: Flow Chart of fiber pre-treatment and sample preparation process    Fig. 2: Paddy Straw Fibres    (a)    (b)  Fig. 3: (a) Equipment used in the experiment and (b) diagram of the measurement set-ups (adapted from Handbook of Noise and Vibration Control 2007)     Fig. 4: The constructed sound absorber sample from the paddy straw.     Un-processes 1-3mm lengths DAS Impedance tube Analyzer Amplifier Speaker Mic A Mic B   Hari Penyelidikan 2011, Fakulti Kejuruteraan Mekanikal, Universiti Teknikal Malaysia Melaka,            20 Julai 2011  55  III. Results & Discussion Fig. 5 shows the absorption coefficient for sample 1 and 2. It can be seen that larger amount of methylcellulose improves the absorption of sound energy at low frequencies (sample 2), but reduces it at high frequencies. The effect of the fiber, however, can be optimized with less methylcellulose and therefore increases the absorption at high frequencies (sample 1). This phenomenon can then be controlled to compromise between the strength of the panel and its sound absorption performance.    Fig. 5: Comparison of the absorption coefficient of the paddy straw with different composition of methylcellulose.    Fig. 6: Comparison of absorption coefficient, α from paddy straw sample with commercial glass wool.  Fig. 6 shows the comparison between the sample and the synthetic glass wool. It can be seen that the paddy absorber has comparable performance compared to the commercial glass wool absorber.   IV. Conclusion Samples of sound absorber have been constructed from dried paddy straw. The experiment shows that this natural fiber can be a good alternative sound absorber among many other natural fibers. The methylcellulose binder is also found to affect the absorption coefficient. The performance, especially at lower frequency can be improved by increasing the sample thickness or by coupling it with perforated panel facing. These will be investigated in the future work.  Acknowledgements The author is grateful for the financial support from Universiti Teknikal Malaysia Melaka (UTeM) under short-term grant PJP/2010/FKM (23B) S737.  References [1] OECD. Reducing Noise in OECD Countries, A report of the Ad-Hoc Group On Noise Abatement Policies. Paris.1975 [2] Bugliarello,G. et.al, The Impact of Noise Pollution. New York : Pergamon Press, 1976 [3] A. Putra. PHD Thesis 2008 [4] Hamidi Abdul Aziz. Pencemaran Bunyi: Teori, Sumber, Perundangan dan Kawalan. Universiti Sains Malaysia, Pulau Pinang. 2008 [5] F. Asdrubali. Green and Sustainable Materials for Noise Control in Buildings, 19th International Congress On Acoustics. 2007 [6] R. Zulkifli, Zulkarnain & M.J.M Nor. Noise Control Using Coconut Coir Fibre Sound Absorber with Porous Layer Backing and Perforated Panel. American Journal of Applied Sciences. Vol 7(2) pp 260-264,2010 [7] M.J.M Nor, N. Jamaluddin & F.M Tamiri. A preliminary study of sound absorption using multi-layer coconut coir fibres. Electronic Journal Technical Acoustic 2004. [8] Zulkifli, et al. Effect of Perforated Size and Air Gap Thickness on Acoustic Properties of Coir Fibre Sound Absorption. European Journal of Scientific Research. 2009 [9] M. H Fouladi et al. Utilization of Coir Fibre in Multilayer Acoustic Absorption Panel. Applied Acoustics.Vol 7 pp 241-249, 2010. [10] D.J Oldham, C. A Egan & R. D Cookson.  Sustainable acoustic absorbers from the biomass. Applied Acoustics. Vol 72 pp 350-363, 2011 [11] H.S. Yang, D.J. Kim, H.J Kim. Rice straw-wood particle composites for sound absorbing wooden construction materials. Bioresource Technology Vol 86 pp 117-121, 2003 [12] BS EN ISO 10534-2:2001. Acoustics -Determination of sound absorption coefficient and impedance in impedance tubes – Part 2: Transfer-function method; 2001.      Hari Penyelidikan 2011, Fakulti Kejuruteraan Mekanikal, Universiti Teknikal Malaysia Melaka,            20 Julai 2011  56  1Vibration and Acoustics Research Group, Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Malaysia. 2Advanced Material Research Group, Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Malaysia 3Energy Management Research Group, Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka, Malaysia                                   Wan Mohd Farid was born in Kelantan on 13rd May 1976. He received Master of Engineering (2001) from Universiti Sains Malaysia, Malaysia. His current interests are composite materials, metallurgy and ceramics engineering. He is currently a lecturer at Department of Structure & Materials, Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka.   Hady Efendy was born in Cimahi, Indonesia on 2nd December 1970. He received his Ph.D in 2008 from Bandung Institute of Technology, Indonesia. His current interests are material science such as ceramic and oxide materials. He is currently a senior lecturer at Department of Structure and Material, Universiti Teknikal Malaysia Melaka.   Azma Putra is a senior lecturer in Faculty of Mechanical Engineering, UTeM. He received his Ph.D in 2008 from Institute of Sound and Vibration Research (ISVR), University of Southampton, United Kingdom. His current interests are engineering acoustics and noise control, vibro-acoutics, vibration and structural dynamics. Yasseer Abdullah was born in Malacca on 24th July 1984. He received Bachelor of Mechanical Engineering (Aero) in 2007 from Universiti Teknologi Malaysia. He is currently a postgraduate student in Universiti Teknikal Malaysia Melaka .   Md. Razali Ayob received his PhD degree in United Kingdom. His current interests are air-conditioning and refrigeration, combustion and fuel engineering. He is currently the Dean of the Faculty of Mechanical Engineering, Universiti Teknikal Malaysia Melaka.   

Dried Paddy Straw Fibers as an Acoustic Absorber:  

A Preliminary Study

http://eprints.utem.edu.my/id/eprint/7677/1/Paddy_straw_FKM2011.pdf

Dried Paddy Straw Fibers as an Acoustic Absorber: A Preliminary Study

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