Coir fibre is extracted from the husk of coconut and is used in products such as floor mats, door mats, brushes and mattresses and in many applications. Here coir fibres are used to make particle boards of densities 300, 400 and 500 kg/m 3 using UF resin to determine its efficiency for interior applications like acoustic and thermal properties and also tested for Indian standard 3129. Noise Reduction Coefficient (NRC) of all the boards decreases with an increase in density. Maximum sound absorption coefficient for all three densities was found in the frequency range of 2500 to 30,000 Hz. Among three densities, 300 kg/m 3 board shows the maximum absorption coefficient at frequency 3000 Hz. The thermal conductivity results of all three densities boards increase with an increase in density. Modulus of Rupture for all three densities were meeting the requirement of standard. Results reveal that particle board manufactured from coir fibre can be used for acoustic and thermal insulation applications.
From ancient time, natural fiber material is used for day to day applications and in the recent inventions, it is also noticed that fibre composite materials can be used in building & furniture applications also [
Flax board has less hygroscopicity than solid timber and wooden chipboard. Linear thickness swelling in water, however, with the density classes 0.60 g/cm3 and 0.65 g/cm3 as well as water absorption are a little greater than in the case of wooden chipboard [
In past decade there have been many efforts to develop composites to replace the petroleum and other non-decaying materials-based products. The abundant availability of natural fibre in India gives attention to the development of natural fibre composites primarily to explore value-added application avenues. Reinforcement with natural fibre in composites has recently gained attention due to low cost, easy availability, low density, acceptable specific properties, ease of separation, enhanced energy recovery, CO2 neutrality, biodegradability and recyclable in nature.
In the present scenario, technical progress in manufacturing the modern equipment, generating higher sound pressure, implies the need to search for new sound absorbing materials to improve the human comfort [
Agricultural wastes can be used to prepare fibre reinforced polymer composites for commercial use. Although glass and other synthetic fibre-reinforced plastics possess high specific strength, their fields of application are very limited because of their inherent higher cost of production. Large amount of agro wastes are produced annually world over. If left unattended, these wastes occupy fertile, useful lands and possess serious environmental and health problems like water contamination by leaching, bad odour, microbial growths etc. Generally, they are burned in the field itself resulting in increased amount of greenhouse gases. The use of sustainable materials is now becoming a common practice for the noise and heat transfer reduction in construction and civil engineering due to the increasing health risk concern associated with materials such as glass and mineral fibre [
India produces 1.60 Mt/yr of coconut husk and is largely used in manufacture of building boards, roofing sheets, insulation boards, building panels, as a lightweight aggregate, coir fibre reinforced composite, cement board, geo-textile, rubberized coir [
Coir was procured from coir board, Peenya has a specific gravity of 0.55 with a moisture content of 10%. Coir of length 2 - 3 mm available was used as it is for the manufacture of board. The particles were dried in Hot Air Oven at 62˚C ± 2˚C to get requisite moisture content of 3% to 4%. Melamine Urea formaldehyde resin (MUF) synthesized at in-house laboratory was used for preparation of low density coir particle board. MUF resin with 1:1 weight ratio of urea and melamine were synthesized at pH 8.5 and at 85˚C till getting water tolerance of 1:4. The properties of the resin used for the manufacture of particle board are as shown in
Sixteen sets of single layered Coir particle boards of dimension 300 mm × 300 mm × 12 mm for a targeted density of 300 kg/m3, 400 kg/m3 and 500 kg/m3 were manufactured using MUF resin adhesive. The adhesive formulation having Ammonium chloride hardener (0.4%) and wax emulsion (1%) on the liquid resin was made. The particles were blended with 10% MUF adhesive on dry solid basis. The glue blended particles were placed into a mat forming box with base dimensions of 330 mm × 330 mm. The formulations for the manufacturing of boards are as shown in
| SI No. | Particulars | Results |
|---|---|---|
| 1. | PH of resin | 8.5 - 8.83 |
| 2. | Flow time of resin in B4 cup | 18 seconds |
| 3. | Water tolerance | 1:2.5 |
| 4. | Solid content | 50.8% |
| 5. | Gelation time | 180 seconds |
| 6. | Shelf life | One month |
| 300 kg/m3 | 400 kg/m3 | 500 kg/m3 | |
|---|---|---|---|
| Particles (g) | 290 | 400 | 500 |
| Resin solids (g) | 29 | 40 | 50 |
maintained at 160˚C for particle board. Pressure of 20 kg/cm2 for compression cycle and 12 kg/cm2 for curing cycle with requisite curing time for respective resin systems were employed. The boards were kept for stabilization for about 24 - 48 hours to attain equilibrium moisture content and then trimmed. The trimmed boards were further dimensioned to required sizes and subjected for testing as per relevant specifications.
All the test specimens were exposed to an atmosphere maintained at a relative humidity of 65 ± 5 %t and at a temperature of 27˚C ± 2˚C until their masses are nearly constant. The test specimens were kept in this controlled atmosphere until they are required for testing.
Physical properties of the boards viz; Moisture content, swelling due to surface absorption & water absorption (2 h) were tested as per IS: 2380 (Methods of test for wood particle boards and boards from other lignocellulosic materials) and compared with values prescribed in IS: 3129 (Specification for Low Density Particle Boards).
Modulus of Rupture the mechanical property carried out in UTM (Universal testing machine) available at the in-house laboratory as per Indian Standard 2380 and compared with Indian Standard 3129.
Sound absorption coefficient was calculated by the method as per IS: 10420-1982 (Determination of sound absorption coefficient of timber by standing wave method) using acoustic Pulse tester available at in-house laboratory. Three sets of samples of diameters 100 mm and 30 mm were prepared for studying acoustic properties for frequencies ranging from 125 Hz to 1500 Hz and 1500 Hz to 5000 Hz respectively. The sound absorption coefficient of the samples was recorded. The average values of three sets were noted for all the three (300, 400 & 500 kg/m3) density samples. The noise reduction coefficient (NRC) was also calculated as the average of the absorption coefficients at 250, 500, 1000 and 2000 Hz frequencies.
Thermal conductivity of the samples was determined by the method specified in IS 3346 (Method of the determination of thermal conductivity of thermal insulation materials) using thermal conductivity apparatus in our own laboratory procured from M/s PRAVAK Cybernetics (P) Ltd. which works on the principle of guarded hot plate method and uses an absolute method for the determination of thermal conductivity. Considering the Indian extreme conditions at summer season, the temperature of hot plate and cold plate were set at 50˚C and 30˚C respectively for determining thermal conductivity of manufactured boards. Three sets of samples from all three densities (300, 400 & 500 kg/m3) of cross sectional area 300 × 300 mm were prepared to determine thermal conductivity. The thermal conductivity of samples was recorded after steady state condition was observed and the temperature differential between the guarded metered hot plate and the primary guard as well as the auxiliary cold plate was within 0.5˚C. Also, this difference was stable for four consecutive periods of half an hour each. During testing of samples, readings were taken only after steady state condition.
The thermal conductivity is computed by the equation as given below:
k = Q D { A ( Δ T ) } , in W/m-K
where:
Q is the heat supplied through a medium, in W.
A is the cross-section of the sample, in m2.
∆T is the temperature differential across the medium, in K.
D is the length of the medium through which heat flows (thickness of sample), in m.
k is the thermal conductivity of the medium, W/m-K.
The average density of the coir particle boards manufactured was found to be 299 kg/m3, 410 kg/m3 and 502 kg/m3 respectively. The Moisture content, MOR and thickness swelling due to surface absorption values are reflected in
| SI No | Properties | Prescribed Value as Per IS: 3129-1985 | A (300 kg/m3) | B (400 kg/m3) | C (500 kg/m3) |
|---|---|---|---|---|---|
| 1 | Moisture content, % | Max 16 | 7.01 | 6.87 | 6.91 |
| Standard Deviation | 0.18 | 0.2 | 0.3 | ||
| Coefficient of Variation | 2.38 | 2.81 | 2.17 | ||
| 2 | Modulus of rupture (N/mm2) | Min 1.5 | 2.54 | 6.97 | 13.9 |
| Standard Deviation | 0.5 | 0.2 | 0.9 | ||
| Coefficient of Variation | 20.6 | 2.2 | 5.5 | ||
| 3 | Swelling due to surface absorption (after 2 hours soaking) % | Max 5 | 6.84 | 4.88 | 4.01 |
| Standard Deviation | 1.213 | 0.316 | 0.818 | ||
| Coefficient of Variation | 11 | 3.82 | 4.65 | ||
| 4 | Water absorption | No Splitting/ No disintegration | No splitting at edges & No sign of disintegration | ||
The absorption coefficient is a common quantity used for measuring the sound absorption of a material and is known to be the function of the frequency of the incident wave. It is defined as the ratio of energy absorbed by a material to the energy incident upon its surface. Sound absorption coefficient of all three densities boards was measured till 5000 Hz.
Noise Reduction Coefficient (NRC) is an average rating of how much sound an acoustic board can absorb. It is the average values of absorption coefficients for a specific material at the octave band center frequencies of 250, 500, 1000 and 2000 Hz. Noise reduction coefficients (NRC) of three density boards calculated were 0.29, 0.26 and 0.24 all the three values are comparable with NRC values of wadding material (30 mm thick, 0.31), Fiber board (25 mm thick, 0.258) and wood wool building slab (25 mm thick, 0.3) [
As shown in
| SI No | Sample | Density (kg/m3) | Thermal Conductivity (W/m-K) | ||
|---|---|---|---|---|---|
| 300 (kg/m3) | 400 (kg/m3) | 500 (kg/m3) | |||
| 1 | Coir PB | Average | 0.120 | 0.138 | 0.169 |
| Standard Deviation | 0.006 | 0.004 | 0.005 | ||
| Coefficient of Variation | 0.051 | 0.032 | 0.027 | ||
increases as the density of the board increases and follows linear trend line relationship y = 0.0002x + 0.0436 with coefficient of determination 0.9785 (R2).
It is seen that the thermal conductivity values are directly related to the density of the board, the highest density boards having the least insulating effect. This is due to the fact that the low-density board contains a large number of voids filled with air, which is one of the poorest conductors [
Note that, materials with the thermal conductivity less than 0.25 W/mK are generally seen as thermal insulations [
Experiment illustrates that particle board made from coir fiber particles can be used in acoustic application as sound absorbent material. Density of board 400 kg/m3 conforms all requirements of IS-3129 with better MOR and indicates that it can also take loads as prescribed in Indian standard 3129 for low density application. Particle boards with densities 400 kg/m3 & 500 kg/m3 conform to the requirement of swelling due to surface absorption as per IS 3129. With an increase in density, thermal conductivity also increases and coir particle boards can also be used for heat sink applications. Still the scope of applications can be extended by mixing other agro residues waste with coir to know how best it performs as insulator for thermal and acoustic applications.
The authors would like to sincerely thank to Director, IPIRTI-Bangalore for providing necessary research facilities and timely support.
The authors declare no conflicts of interest regarding the publication of this paper.
Kiran, M.C., Mamatha, B.S., Anand, N., Prakash, V. and Murthy, N. (2019) Efficiency of Coir Particle Board for Acoustic & Thermal Applications. Open Journal of Acoustics, 9, 39-47. https://doi.org/10.4236/oja.2019.93004