Next Article in Journal
Quantifying the Annual Cycle of Water Use Efficiency, Energy and CO2 Fluxes Using Micrometeorological and Physiological Techniques for a Coffee Field in Costa Rica
Next Article in Special Issue
Professionals’ Feedback on the PEFC Fair Supply Chain Project Activated in Italy after the “Vaia” Windstorm
Previous Article in Journal
Seasonal Shifts in Cold Tolerance and the Composition of the Gut Microbiome of Dendroctonus valens LeConte Occur Concurrently
Previous Article in Special Issue
Optimization and Mechanical Properties of Fabricated 2D Wood Pyramid Lattice Sandwich Structure
 
 
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Acoustic Properties of Larch Bark Panels

1
Forest Products Technology and Timber Construction Department, Salzburg University of Applied Sciences, Markt 136a, 5431 Kuchl, Austria
2
Faculty of Furniture Design and Wood Engineering, Transilvania University of Brasov, B-Dul. Eroilor Nr. 29, 500036 Brasov, Romania
3
Faculty of Wood Sciences and Technology, Technical University in Zvolen, 96001 Zvolen, Slovakia
4
National Forest Centre, Forest Research Institute, 96001 Zvolen, Slovakia
*
Author to whom correspondence should be addressed.
Submission received: 10 June 2021 / Revised: 4 July 2021 / Accepted: 6 July 2021 / Published: 7 July 2021
(This article belongs to the Special Issue Wood Production and Promotion)

Abstract

:
The potential of tree bark, a by-product of the woodworking industry, has been studied for more than seven decades. Bark, as a sustainable raw material, can replace wood or other resources in numerous applications in construction. In this study, the acoustic properties of bark-based panels were analyzed. The roles of the particle size (4–11 mm and 10–30 mm), particle orientation (parallel and perpendicular) and density (350–700 kg/m3) of samples with 30 mm and 60 mm thicknesses were studied at frequencies ranging from 50 to 6400 Hz. Bark-based boards with fine-grained particles have been shown to be better in terms of sound absorption coefficient values compared with coarse-grained particles. Bark composites mixed with popcorn bonded with UF did not return the expected results, and it is not possible to recommend this solution. The best density of bark boards to obtain the best sound absorption coefficients is about 350 kg/m3. These lightweight panels achieved better sound-absorbing properties (especially at lower frequencies) at higher thicknesses. The noise reduction coefficient of 0.5 obtained a sample with fine particles with a parallel orientation and a density of around 360 kg/m3.

1. Introduction

The negative effects of chronic exposure to noise are, nowadays, an important issue [1]. The outdoor noise levels directly influence housing market prices, which can decrease by 0.3 to 3% in areas with noise pollution [2]. The noise level in a building is influenced by a variety of factors such as location [3], city planning [4], building design [5], vegetation [6], façade elements [7], construction features and material selection [8,9,10]. A proper selection of materials improves the noise control in buildings to a great extent. It facilitates minimizing many costly techniques of noise control in buildings.
The use of natural insulation materials with minimal production processing is an emerging trend in construction. The use of sustainable and recyclable materials is an important aspect to warrant a healthy environment. Many studies scrutinized the environmental and technical benefits of using sustainable materials (natural or recycled) as basic elements to produce commonly used as well as new porous materials (granular or fibrous) [11,12,13,14,15,16,17,18] such as rice husk, cotton stalk, jute fiber, straws of wheat, hemp, flax, coconut fibers, stalks of maize and sheep’s wool [19,20,21,22,23,24,25]. These lignocellulosic materials, when used appropriately, can provide thermal and acoustic insulation performance comparable with the most used insulation materials, but with excellent environmental properties [26].
The sound absorption coefficient is the measure for the acoustical effectiveness of a material and is defined as the fraction of the energy of incident sound waves absorbed by the material [27]. The sound absorption coefficient can range between 0 (no absorption) and 1 (complete absorption) [28].
The acoustic performance of insulation materials made of lignocellulosic materials was examined in various studies [29,30,31,32]. Plenty of natural products were investigated and tested for acoustic applications [33] such as kenaf, coir fiber, reeds, sisal, flax, bamboo fibers and corn husk [34,35,36]. These materials are becoming increasingly popular because they are nonabrasive, renewable and cheap and have lower health risks during processing [37,38]. These materials are susceptible to absorbing a large amount of moisture [39]. In addition, they are affected by heat, have low anti-fungal/bacteria activity and are prone to decomposition [40]. Chemical treatment of the surface of materials made from natural products can reduce these disadvantages [41].
Bark can contribute to the modern construction philosophy: to use materials with a low environmental impact and a high proportion of recycled materials while maintaining the parameters of a healthy building [42,43]. Besides showing advantageous properties such as a low density, a high resistance against microorganisms and fire, a low thermal conductivity and excellent thermal diffusivity [44,45], bark also presents a high heat storage capacity [46,47,48]. Bark also acts as an excellent formaldehyde scavenger [49,50,51,52]. From an economic point of view, bark as a by-product of timber manufacturing is available at low prices [53,54,55]. Previous research shows that the best acoustic properties of bark-based boards as thermal insulation panels are achieved at densities of around 350 kg/m3 [56,57] and reported on the possibilities of bark insulation panel utilization as a means of absorbing formaldehyde emissions in the indoor environment of buildings. The sound absorption coefficient of spruce and larch bark-based boards was the tested parameter when using selected frequencies between 125 and 4000 Hz [8]. The density of spruce bark-based boards ranged from 400 to 500 kg/m3, and that for larch bark-based boards ranged from 500 to 700 kg/m3. The analysis of the results showed that such bark panels have comparable values of the sound absorption coefficient to lignocellulosic insulation materials, and it is possible to describe them as a material with the potential to meet the acoustic functions in boundary structures [58,59].
The aim of this work is to compare the frequency-dependent flow of sound absorption coefficients of different types of larch bark-based boards, to study if these values are comparable with other industrial established sound absorption materials and then to determine the potential of bark-based boards as an element used in boundary structures which would also fulfill the acoustic function.

2. Materials and Methods

The larch bark (Larix decidua Mill.) was sourced from the Graggaber sawmill in Unternberg, Salzburg, Austria, specialized in larch processing. The bark was dried by means of a vacuum kiln dryer (Brunner–Hildebrand High VAC-S, HV-S1, Hannover, Germany) from 100% to 9% moisture content. The drying temperature was 60 °C at a pressure of 200–250 mbar. The bark was subsequently crushed in a 4-spindle shredder (RS40) at Untha Co. in Kuchl, Austria, and repeatedly screened to obtain different distributions of the particle size: 4–11 mm, 10–30 mm and 10–45 mm. One board was manufactured with a mixture of 10–45 mm larch bark particles and 50 wt-% (based on the dry mass) of pre-expanded industrial corn (Balanceboard, Pfleiderer, Neumarkt, Germany) in order to lower the density.
Urea formaldehyde (UF) type Prefere 10F102 (Metadynea, Krems, Austria) was used as an adhesive. The resination factor (solid content), according to Table 1 and Table 2, was calculated based on the dry mass of bark and mixed with the particles in a plough share mixer ENT type WHB-75.
The panels with a size of (320 × 320 × 30) mm were pressed in a Höfer HLOP 280 (Taiskirchen, Austria) hydraulic laboratory press at a plate temperature of 180 °C and a press factor of 20 s/mm (significantly higher than in an industrial application). After pressing, the panels were stored in a climate room (temperature 20 °C/relative humidity (RH) 65%) until a constant mass was achieved. Afterwards, the samples were cut according to EN 326-1 [60].
The dependence of the sound absorption coefficient on the frequency was determined on nine types of bark-based boards. The individual larch bark panels differ from one to another in particle size, density, thickness and resination factor (Table 1 and Table 2).
The sound absorption coefficient of the bark-based boards was compared with commercially available insulating materials (Table 3 and Table 4). These samples were also stored in a climate room (20 °C/65% relative humidity (RH)) until a constant mass was achieved.
For the acoustic measurements, samples with 30 mm and 100 mm diameters and thicknesses of 30 and 60 mm were used.
The measurement of the sound absorption coefficient was performed in accordance with EN ISO 10534-2 [68]. It is a two-microphone method of measuring acoustic absorption which is based on the decomposition of a broadband random signal into a signal from a source and a reflected signal. The complex acoustic transfer function is calculated from the obtained values of the complex acoustic pressure. It is possible to determine the coefficients of sound absorption and reflectivity from it for selected frequencies [9,69].
The measuring device consisted of an impedance (Kundt) tube Brüel & Kjær type 4206, a PULSE 14 system, the only module LAN-XI Brüel & Kjær type 3050 with two active inputs and CPB (constant percentage band—constant percentage width of the frequency band) analysis, sound generator signals from two identical microphones and a computer to display and store the measured data (Figure 1).
The measurement of the sound absorption coefficient was performed in the frequency range of 20 to 1600 Hz using a Kundt tube with a diameter of 100 mm and in the frequency range of 1600 to 6400 Hz using a Kundt tube with a diameter of 30 mm. When measuring the sound absorption coefficient, the test specimens had a corresponding circular cross-section with a thickness of 30 and 60 mm. Four test specimens were created from each type of sample [9]. The noise reduction coefficient (NRC) is used as an evaluation parameter in the frequency range of the spoken word. It is a single number rating which represents the average of sound absorption coefficients of a material at specific mid-range frequencies (tested at 250, 500, 1000 and 2000 Hz octaves) rounded to the nearest 0.05. This value is influenced by the thickness and density of the material. Based on this parameter, the samples were assessed in sound absorption classes, which are weighed by A–E, where absorption class A is the best, calculated according to EN ISO 11654:2017 [70].

3. Results and Discussion

3.1. Sound Absorption Coefficient

All tested specimens were examined by the method of the sound absorption coefficient by the impedance tube method. The measurement results are shown in Figure 2, Figure 3, Figure 4 and Figure 5. To ensure the clarity, the graphs of the dependence of the sound absorption coefficient on the frequency are combined into two pairs of graphs. The displayed frequency range is from 50 to 6400 Hz. Figure 2 and Figure 3 show the sound absorption coefficient for test specimens with a 30 mm thickness, and Figure 4 and Figure 5 show the sound absorption coefficient for the 60 mm samples. The distribution parameter was the grain size (the first of the pair—the graph for the fraction 4 to 11 mm, and the second of the pair—the graph for the fraction 10 to 30 mm).
The graph for panel type 3 is not depicted in Figure 2 and Figure 3, due to its formulation as a board manufactured with a mixture of larch bark particles and popcorn. This combination proved to be problematic in the determination of the sound absorption coefficient by the transformation function method. The results for type 3 of the bark popcorn board can be described as inconclusive due to the large air gaps between the individual board elements. This did not ensure the condition of repeatability of the measurement. This board would probably also appear unstable in a real structure.
The sound absorption coefficient as a function of the frequency of the selected tested specimens with a thickness of 60 mm is shown in Figure 4 and Figure 5. In comparison with Figure 2 and Figure 3, there is a significantly changed course of the curves. In the case of the 60 mm samples, more peaks are formed, and the first maxima are shifted to shorter wavelengths, which is a very desirable phenomenon for noise reduction in both cases (4–11 mm and 10–30 mm). The graph can even be interpreted in the sense that the absorption capacity increases with the increasing thickness at low frequencies at the same time. This result is consistent with previous studies of porous materials that revealed that low-frequency sound absorption has a direct relationship with the thickness [71,72,73]. An increase in the thickness also provides a better absorption of the wave [74]. This improvement in properties was best seen on types 2 and 8 of the test specimens. The other test specimens showed better acoustic properties at important lower frequencies as well. Only the tested specimens types 1 and 5 showed a different course. This is due to their solid structure (high density and low porosity), and, with sufficient thickness, they behave as reflective materials. These results are consistent with those of [75] that suggest a denser and less open structure absorbs worse sound of lower frequencies. On the contrary, a lower density is connected to a much higher porosity. As it can be seen from the results, a lower density and a higher porosity allow the sound to enter the matrix more easily, for dissipation, which contributed to greater sound energy absorption, thus a better acoustic absorption property [76]. This theory also explains differences due to the resin content. As it can be seen from Figure 3 and Figure 5, the sound absorption coefficient increases with the increasing resin content. This is in agreement with the fact that, with the increasing resin content, smaller pores are formed, which in turn results in increasing the flow resistivity [77]. The results about the density, porosity, board thickness and reflectivity influence on sound absorption are also confirmed by [8,78,79].
The results show that the sound absorption is better with fine-grained particles (4 to 11 mm) and lower densities (in this case, it showed a critical value of 500 kg/m3) than with the tested specimens with coarse-grained particles (10 to 30 mm). The increase in the sound absorption is mainly due to the different pore structures. When the sound wave reaches pores containing air molecules, they will vibrate and cause the sound energy to be converted to heat under the action of the air viscosity [80,81]. On the other hand, there is a sufficient energy transfer with an acceptable range of porosity, which means that open pores with continuous channels prevail with better sound absorption due to the multiple reactions between the sound wave and the walls of the pores. That is why test specimens with coarse-grained particles absorbed more sound at lower frequencies. Results showing better absorption with shorter elements were also confirmed in research by [82,83] in the case of bamboo panels, where a higher sound absorption coefficient was obtained with the smaller particle size. The results are also in accordance with the findings of [73]. The authors investigated the dependence of the sound absorption coefficient for redwood classes (chips and sawdust). They found that the sound absorption coefficient increases regularly over the entire frequency range as the particle size decreases (particle sizes were from 1.25 to more than 16 mm).
The effect of the particle orientation on the sound absorption of testing specimens made of coarse-grained particles was also analyzed. This phenomenon was mostly visible in the case of samples 6 and 7 at a thickness of 30 mm, which differed only in the orientation of particles. It was shown that, when the particles were oriented perpendicular to the panel’s plane, maxima were reached at frequencies of 2060 Hz (board type 6) and 2560 Hz (board type 7). This result is in agreement with the results of [84] on the influence of the particle orientation on the sound absorption coefficient.

3.2. The Noise Reduction Coefficient

The calculated values of the noise reduction coefficient (NRC) for the tested bark boards are shown in Table 5. The values displayed in Table 5 show that these materials achieved the highest sound absorption class, E, at a thickness of 30 mm, except for type 6 of the test specimen, which reaches class D. When doubling the thickness for types 2, 4, 6, 7, 8 and 9 of the test specimens, the NRC value also reaches class D. The best results were obtained with types 2, 7 and 8 of the bark-based board with a thickness of 60 mm in terms of the absolute value of the NRC parameter (0.4, 0.4 and 0.50, respectively).
The noise reduction coefficient (NRC) is used as an evaluation parameter in the frequency range of the spoken word. It is calculated as the arithmetic mean of the sound absorption coefficient values for frequencies of 250 Hz, 500 Hz, 1000 Hz and 2000 Hz. The calculated values for bark boards are shown in Table 5.
The bark-based boards were compared with other panels commercially used in boundary structures to express their potential as an element where they perform a thermal insulation and acoustic function. The calculated NRC value shown as a function of the density of the tested material is a parameter to be compared (Figure 6).
From Figure 6, it can be observed that polystyrene-based materials (extruded, white and graphite polystyrene), which are grouped in area A, have a very low density (25 to 35 kg/m3), and their NRC values range from 0.1 to 0.3. Area B contains typical sound-insulating materials (very soft fiberboard, recycled textiles, mineral wool) with a density from 60 to 120 kg/m3, whose NRC values range from 0.65 to 0.75. Area C belongs to natural cellulose-based insulations (cork, slightly harder fiberboard and straw) with a density ranging from 250 to 280 kg/m3, and their NRC values range from 0.25 to 0.35.
Most conventional insulation materials (such as polystyrene, polyurethane foams, mineral wool) and their processing offer many different options with easy installation and have excellent thermal properties. On the other hand, these materials are derived from petrochemical substances and are environment-impairing [85].
The tested bark-based boards formed a separate group D which contains natural insulations based on raw materials similar to group C. Their density is slightly higher (around 350 kg/m3), and they have better sound insulation properties (NRC is in the range from 0.40 to 0.50). From group C, lignocellulosic materials straw and cork, together with bark sample types 2, 7 and 8 (group D), have in common good thermal insulation properties, no harmful effects on health and being available in large quantities, often as a waste product of other production cycles. The same problem occurs with low-density fiberboard (group B), which also has a poor mechanical property [86,87]. This is not the case of bark, which naturally has excellent resistance against microorganisms and very good fire-resistant properties [45,88].
The NRC is a commonly used value for classifying materials into absorption classes, although for materials with a fluctuating sound absorption coefficient, for a more accurate comparison, it is necessary to analyze the whole frequency spectrum. Figure 7 shows a more accurate comparison of the sound absorption coefficients of bark-based boards with selected commercially available materials (cereal straw, polystyrene graphite, fiberboard). These materials were selected to include material from each of groups A, B and C (Figure 7). As it can be seen from Figure 7, the NRC proves to be relatively inaccurate for materials that have a very fluctuating sound absorption coefficient. Bark-based board type 8 was selected from group D because it showed the best acoustic properties (sound absorption coefficient of 0.9 at 2250 Hz and 3575 Hz). The compared specimens had a thickness of 60 mm, and the frequency dependence of the sound absorption coefficient is, again, shown in the range from 50 to 6400 Hz.
The bark composite type 8 shows a slightly better value of the sound absorption coefficient than straw at frequencies up to 1 kHz. This result is consistent with research by [89,90,91]. Cereal straw is a better sound absorber at frequencies higher than 3 kHz due to the structure of the composite [92]. Graphite polystyrene shows no significant acoustic property, and it achieves lower values of this parameter comparing to bark board type 8 at all frequencies due to its very low density and closed porosity. The course of the dependence curve is very similar, typically for the materials with a granular structure with closed porosity [93]. Bark achieves a slightly lower value of the sound absorption coefficient in the whole frequency spectrum when comparing the type 8 bark with a low-density fiberboard, where the difference is more visible at frequencies higher than 3575 Hz.

4. Conclusions

The best density of bark-based boards is around 350 kg/m3 for performing the acoustic functions in a structure. This density coincides with the density of the bark-based boards for the correct performance of thermal insulation functions in boundary structures. The critical upper density limit is 500 kg/m3. At densities over 500 kg/m3, due to their solid structure (high density and low porosity), and with a sufficient thickness, bark-based boards behave as reflective materials. Mixing bark with popcorn resinated with UF did not return the expected results, and it is not possible to recommend this solution.
Bark-based boards with fine-grained particles have been shown to be better in terms of sound absorption coefficient values compared with coarse-grained particles.
The key finding is that the bark-based panels can be better evaluated in terms of the parameter of the sound absorption coefficient compared to cereal straw, fiberboard with a slightly higher density and cork, despite their higher density.
The results show that the sound absorption is better for fine-grained particles (4 to 11 mm) and lower densities than for the tested samples with coarse-grained particles (10 to 30 mm). A board manufactured with a mixture of larch bark particles and popcorn is problematic in the determination of the sound absorption coefficient by the transformation function method due to the large air gaps between the individual board elements.
In the case of the 60 mm samples, more peaks were formed, and the first maxima were shifted to shorter wavelengths than in the case of the 30 mm samples. The most significant improvement in sound absorption occurred in the case of boards 2 and 8. From the NRC’s point of view, the same boards with board number 7 are the best. These reached sound absorption class D at a thickness of 60 mm.
The sound absorption coefficient for the best samples, 2 and 8, ranged from 0.5 to 1 at frequencies higher than 750 Hz and at a thickness of 60 mm. Sample 2 obtained an NRC value of 0.4, and sample 8 even obtained an NRC value of 0.5. An NRC value of 0.4 was achieved by sample 7. It can be seen from this sample that the NRC value does not describe the completely correct properties of materials with a fluctuating course sound absorption coefficient.
Bark boards achieve relatively good absorption properties compared to polystyrene-based materials and similar properties to straw. However, they are much worse sound absorbers than fiberboards or textile materials.
The potential of bark-based composites in applications such as insulation layers with increased requirements for the mechanical stability of roofs, floors or façades should be further studied. New applications could encompass boundary structures where it is necessary to maintain the defined basis weight of the structure and, at the same time, to maintain airborne soundproofing.
Bark-based panels can contribute to the modern building philosophy: to use materials with a low density, low thermal conductivity, excellent thermal diffusivity, high heat storage capacity and high natural resistance against microorganisms and fire.
It is necessary to consider bark boards with a thickness higher than 50 mm as a material with the potential to perform an acoustic function in boundary structures. At thicknesses of less than 50 mm, the individual layers of the bark elements are not overlapped, and such a panel has large air gaps and therefore cannot act as an effective sound absorber.

Author Contributions

Conceptualization, E.M.T. and G.K.; methodology, M.C.B., T.G. and M.N.; validation, M.N.; formal analysis, L.K.; investigation, T.G.; resources, G.K.; data curation, M.N. and T.G.; writing—original draft preparation, E.M.T. and L.K.; writing—review and editing, L.K. and M.N.; supervision, M.C.B. and R.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by the Slovak Research and Development Agency under contracts No. APVV-18-0378, APVV-19-0269, VEGA1/0717/19 and VEGA1/0714/21.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Zalejska-Jonsson, A. Perceived Acoustic Quality and Effect on Occupants’ Satisfaction in Green and Conventional Residential Buildings. Buildings 2019, 9, 24. [Google Scholar] [CrossRef]
  2. Wilhelmsson, M. The Impact of Traffic Noise on the Values of Single-family Houses. J. Environ. Plan. Manag. 2000, 43, 799–815. [Google Scholar] [CrossRef]
  3. Camara, T.; Kamsu-Foguem, B.; Diourté, B.; Faye, J.P.; Hamadoun, O. Management of acoustic risks for buildings near airports. Ecol. Inform. 2018, 44, 43–56. [Google Scholar] [CrossRef]
  4. Mueller, N.; Rojas-Rueda, D.; Khreis, H.; Cirach, M.; Andrés, D.; Ballester, J.; Bartoll, X.; Daher, C.; Deluca, A.; Echave, C.; et al. Changing the urban design of cities for health: The superblock model. Environ. Int. 2020, 134, 105132. [Google Scholar] [CrossRef] [PubMed]
  5. Shield, B.; Conetta, R. A survey of acoustic conditions and noise levels in secondary school classrooms in England. J. Acoust. Soc. Am. 2015, 137, 177. [Google Scholar] [CrossRef]
  6. Azkorra, Z.; Pérez, G.; Coma, J.; Cabeza, L.F.; Bures, S.; Alvaro, J.E.; Erkoreka, A.; Urrestarazu, M. Evaluation of green walls as a passive acoustic insulation system for buildings. Appl. Acoust. 2015, 89, 46–56. [Google Scholar] [CrossRef]
  7. Gonzales, D.M.; Barrigon Morillas, J.M.; Godinho, L.; Amado-Mendes, P. Acoustic screening effect on building facades due to parking lines in urban environments. Effects in noise mapping. Appl. Acoust. 2018, 130, 1–14. [Google Scholar] [CrossRef]
  8. Tudor, E.M.; Dettendorfer, A.; Kain, G.; Barbu, M.C.; Réh, R.; Krišťák, Ľ. Sound-Absorption Coefficient of Bark-Based Insulation Panels. Polymers 2020, 12, 1012. [Google Scholar] [CrossRef] [PubMed]
  9. Danihelová, A.; Němec, M.; Gergeľ, T.; Gejdoš, M.; Gordanová, J.; Sčensný, P. Usage of Recycled Technical Textiles as Thermal Insulation and an Acoustic Absorber. Sustainaility 2019, 11, 2968. [Google Scholar] [CrossRef]
  10. Čulík, M.; Danihelová, A.; Ondrejka, V.; Aláč, P. Sound Absorption on Board Construction Materials Used in Wood Buildings. Akustika 2020, 37, 51–57. [Google Scholar] [CrossRef]
  11. Silva, D.A.L.; Lahr, F.A.R.; Garcia, R.P.; Freire, F.M.C.S.; Ometto, A.R. Life cycle assessment of medium density particleboard (MDP) produced in Brazil. Int. J. Life Cycle Assess. 2013, 18, 1404–1411. [Google Scholar] [CrossRef]
  12. Branowski, B.; Zabłocki, M.; Sydor, M. The Material Indices Method in the Sustainable Engineering Design Process: A Review. Sustainaility 2019, 11, 5465. [Google Scholar] [CrossRef]
  13. Novák, I.; Krupa, I.; Sedliačik, J.; Žigo, O.; Jurkovič, P.; Matyašovský, J. Investigation into mechanical, surface and adhesive properties of date palm wood-polyolefin micro composites. Acta Fac. Xylologiae Zvolen 2020, 62, 27–34. [Google Scholar]
  14. Souza, A.M.; Nascimento, M.F.; Almeida, D.H.; Lopes Silva, D.A.; Almeida, T.H.; Christoforo, A.L.; Lahr, F.A.R. Wood-based composite made of wood waste and epoxy based ink-waste as adhesive: A cleaner production alternative. J. Clean. Prod. 2018, 193, 549–562. [Google Scholar] [CrossRef]
  15. Antov, P.; Mantanis, G.I.; Savov, V. Development of Wood Composites from Recycled Fibres Bonded with Magnesium Lignosulfonate. Forests 2020, 11, 613. [Google Scholar] [CrossRef]
  16. Savov, V.; Antov, P. Engineering the Properties of Eco-Friendly Medium Density Fibreboards Bonded with Lignosulfonate Adhesive. Drv. Ind. 2020, 71, 157–162. [Google Scholar] [CrossRef]
  17. Vanova, R.; Vlcko, M.; Stefko, J. Life Cycle Impact Assessment of Load-Bearing Straw Bale Residential Building. Materials 2021, 14, 3064. [Google Scholar] [CrossRef]
  18. Moresova, M.; Sedliacikova, M.; Stefko, J.; Bencikova, D. Perception of wooden houses in the Slovak Republic. Acta Fac. Xylologiae Zvolen 2019, 61, 121–135. [Google Scholar]
  19. Dukarska, D.; Pędzik, M.; Rogozińska, W.; Rogoziński, T.; Czarnecki, R. Characteristics of straw particles of selected grain species purposed for the production of lignocellulose particleboards. Part. Sci. Technol. 2021, 39, 213–222. [Google Scholar] [CrossRef]
  20. Aristri, M.A.; Lubis, M.A.R.; Yadav, S.M.; Antov, P.; Papadopoulos, A.N.; Pizzi, A.; Fatriasari, W.; Ismayati, M.; Iswanto, A.H. Recent Developments in Lignin- and Tannin-Based Non-Isocyanate Polyurethane Resins for Wood Adhesives—A Review. Appl. Sci. 2021, 11, 4242. [Google Scholar] [CrossRef]
  21. dos Santos, M.F.N.; Battistelle, R.A.G.; Bezerra, B.S.; Varum, H.S.A. Comparative study of the life cycle assessment of particleboards made of residues from sugarcane bagasse (Saccharum spp.) and pine wood shavings (Pinus elliottii). J. Clean. Prod. 2014, 64, 345–355. [Google Scholar] [CrossRef]
  22. Battistelle, R.A.G.; Fujino, D.M.; Silva, A.L.C.; Bezerra, B.S.; Valarelli, I.D. Physical and mechanical characterization of sugarcane bagasse particleboards for civil construction. J. Sustain. Dev. Energy Water Environ. Syst. 2016, 4, 408–417. [Google Scholar] [CrossRef]
  23. Hejna, A.; Barczewski, M.; Skórczewska, K.; Szulc, J.; Chmielnicki, B.; Korol, J.; Formela, K. Sustainable upcycling of brewers’ spent grain by thermo-mechanical treatment in twin-screw extruder. J. Clean. Prod. 2021, 285, 124839. [Google Scholar] [CrossRef]
  24. Liuzzi, S.; Rubino, C.H.; Stefanizzi, P.; Martellotta, F. Performance Characterization of Broad Band Sustainable Sound Absorbers Made of Almond Skins. Materials 2020, 13, 5474. [Google Scholar] [CrossRef] [PubMed]
  25. Rammou, E.; Mitani, A.; Ntalos, G.; Koutsianitis, D.; Taghiyari, H.R.; Papadopoulos, A.N. The Potential Use of Seaweed (Posidonia oceanica) as an Alternative Lignocellulosic Raw Material for Wood Composites Manufacture. Coatings 2021, 11, 69. [Google Scholar] [CrossRef]
  26. Potkány, M.; Gejdoš, M.; Debnár, M. Sustainable Innovation Approach for Wood Quality Evaluation in Green Business. Sustainability 2018, 10, 2984. [Google Scholar] [CrossRef]
  27. Bohatkiewicz, J. Noise Control Plans in Cities–Selected Issues and Necessary Changes in Approach to Measures and Methods of Protectin. Transp. Res. Procedia 2016, 14, 2744–2753. [Google Scholar] [CrossRef]
  28. Peng, L. Sound absorption and insulation functional composites. In Advanced High Strength Natural Fibre Composites in Construction; Woodhead Publishing: Cambridge, UK, 2017; pp. 333–373. [Google Scholar]
  29. Asdrubali, F.; Ferracuti, B.; Lombardi, L.; Guattari, C.; Evangelisti, L.; Grazieschi, G. A review of structural, thermo-physical, acoustical, and environmental properties of wooden materials for building applications. Build. Environ. 2017, 114, 307–332. [Google Scholar] [CrossRef]
  30. Desarnaulds, V.; Costanzo, E.; Carvalho, A.; Aurlaud, B. Sustainability of acoustic materials and acoustic characterization of sustainable materials. In Proceedings of the 12th International Congress on Sound and Vibration (ICSV12), Lisbon, Portugal, 11–14 July 2005. [Google Scholar]
  31. Pedroso, M.; de Brito, J.; Silvestre, J. Characterization of eco-efficient acoustic insulation materials (traditional and innovative). Constr. Build. Mater. 2017, 140, 221–228. [Google Scholar] [CrossRef]
  32. Jensen, M.S.; Alfieri, P.V. Design and manufacture of insulation panels based on recycled lignocellulosic waste. Clean. Eng. Technol. 2021, 3, 100111. [Google Scholar] [CrossRef]
  33. Asdrubali, F.; Schiavoni, S.; Horoshenkov, K.V. A Review of Sustainable Materials for Acoustic Applications. Build. Acoust. 2012, 19, 283–311. [Google Scholar] [CrossRef]
  34. D’Alessandro, F.; Pispola, G. Sound absorption properties of sustainable fibrous materials in an enhanced reverberation room. In Proceedings of the Internoise 2005, Rio de Janeiro, Brazil, 7–10 August 2005. [Google Scholar]
  35. Fouladi, M.H.; Ayub, M.; Nor, M.J.M. Analysis of coir fiber acoustical characteristics. Appl. Acoust. 2011, 72, 35–42. [Google Scholar] [CrossRef]
  36. Oldham, D.J.; Egan, C.A.; Cookson, R.D. Sustainable acoustic absorbers from the biomass. Appl. Acoust. 2011, 72, 350–363. [Google Scholar] [CrossRef]
  37. Jiang, W.; Adamopoulos, S.; Hosseinpourpia, R.; Žigon, J.; Petrič, M.; Šernek, M.; Medved, S. Utilization of Partially Liquefied Bark for Production of Particleboards. Appl. Sci. 2020, 10, 5253. [Google Scholar] [CrossRef]
  38. Fatima, S.; Mohanty, A.R. Acoustical and fire-retardant properties of jute composite materials. Appl. Acoust. 2011, 72, 108–114. [Google Scholar] [CrossRef]
  39. Sari, N.H.; Wardana, I.N.G.; Irawan, Y.S.; Siswanto, E.P. Physical and Acoustical Properties of Corn Husk Fiber Panels. Adv. Acoust. Vib. 2016, 2016, 5971814. [Google Scholar] [CrossRef]
  40. Salit, M.S. Tropical natural fibres and their properties. In Tropical Natural Fibre Composites. Engineering Materials; Springer: Singapore, 2014; pp. 15–38. [Google Scholar]
  41. Saha, P.; Manna, S.; Chowdhury, R.; Sen, R.; Roy, D.; Adhikari, B. Enhancement of tensile strength of lignocellulosic jute fibers by alkali-steam treatment. Bioresour. Technol. 2010, 101, 3182–3187. [Google Scholar] [CrossRef]
  42. Kairytė, A.; Kremensas, A.; Balčiūnas, G.; Matulaitiene, I.; Członka, S.; Sienkiewicz, N. Evaluation of self-thermally treated wood plastic composites from wood bark and rapeseed oil-based binder. Constr. Build. Mater. 2020, 250, 118842. [Google Scholar] [CrossRef]
  43. Abilleira, F.; Varela, P.; Cancela, A.; Alvarez, X.; Sanchez, A.; Valero, E. Tannins extraction from Pinus pinaster and Acacia dealbata bark with applications in the industry. Ind. Crop. Prod. 2021, 164, 113394. [Google Scholar] [CrossRef]
  44. Kain, G.; Tudor, E.M.; Barbu, M.-C. Bark Thermal Insulation Panels: An Explorative Study on the Effects of Bark Species. Polymers 2020, 12, 2140. [Google Scholar] [CrossRef]
  45. Tudor, E.M.; Scheriau, C.; Barbu, M.C.; Réh, R.; Krišťák, Ľ.; Schnabel, T. Enhanced Resistance to Fire of the Bark-Based Panels Bonded with Clay. Appl. Sci. 2020, 10, 5594. [Google Scholar] [CrossRef]
  46. Martin, R.E. Thermal properties of bark. For. Prod. J. 1963, 13, 419–426. [Google Scholar]
  47. Kain, G.; Lienbacher, B.; Barbu, M.-C.; Plank, B.; Richter, K.; Petutschnigg, A. Evaluation of relationships between particle orientation and thermal conductivity in bark insulation board by means of CT and discrete modeling. Case Stud. Nondestruct. Test. Eval. 2016, 6, 21–29. [Google Scholar] [CrossRef]
  48. Busquets-Ferrer, M.; Czabany, I.; Vay, O.; Gindl-Altmutter, W.; Hansmann, C. Alkali-extracted tree bark for efficient bio-based thermal insulation. Constr. Build. Mater. 2021, 271, 121577. [Google Scholar] [CrossRef]
  49. Réh, R.; Igaz, R.; Krišťák, Ľ.; Ružiak, I.; Gajtanska, M.; Božíková, M.; Kučerka, M. Functionality of Beech Bark in Adhesive Mixtures Used in Plywood and Its Effect on the Stability Associated with Material Systems. Materials 2019, 12, 1298. [Google Scholar] [CrossRef]
  50. Tudor, E.M.; Barbu, M.C.; Petutschnigg, A.; Réh, R.; Krišťák, Ľ. Analysis of Larch-Bark Capacity for Formaldehyde Removal in Wood Adhesives. Int. J. Environ. Res. Public Health 2020, 17, 764. [Google Scholar] [CrossRef]
  51. Réh, R.; Krišťák, Ľ.; Sedliačik, J.; Bekhta, P.; Božiková, M.; Kunecová, D.; Vozárová, V.; Tudor, E.; Antov, P.; Savov, V. Utilization of Birch Bark as an Eco-Friendly Filler in Urea-Formaldehyde Adhesives for Plywood Manufacturing. Polymers 2021, 13, 511. [Google Scholar] [CrossRef] [PubMed]
  52. Barbu, M.C.; Lohninger, Y.; Hofmann, S.; Kain, G.; Petutschnigg, A.; Tudor, E.M. Larch Bark as a Formaldehyde Scavenger in Thermal Insulation Panels. Polymers 2020, 12, 2632. [Google Scholar] [CrossRef] [PubMed]
  53. Kain, G.; Barbu, M.-C.; Teischinger, A.; Musso, M.; Petutschnigg, A. Substantial Bark Use as Insulation Material. For. Prod. J. 2012, 62, 480–487. [Google Scholar] [CrossRef]
  54. Tudor, E.M.; Zwickl, C.; Eichinger, C.; Petutschnigg, A.; Barbu, M.C. Performance of softwood bark comminution technologies for determinantion of targeted particle size in further upcycling applications. J. Clean. Prod. 2020, 269, 122412. [Google Scholar] [CrossRef]
  55. Tudor, E.M.; Barbu, M.C. Cost analysis of larch bark coatings for flooring tiles. ProLigno 2020, 16, 46–51. [Google Scholar]
  56. Pásztory, Z.; Börcsök, Z.; Tsalagkas, D. Density optimization for the manufacturing of bark-based thermal insulation panels. In IOP Conference Series: Earth and Environmental Science, Proceedings of the 5th International Conference on Environment and Renewable Energy, Ho Chi Minh City, Vietnam, 25–28 February 2019; IOP Publishing Ltd.: Bristol, UK, 2019; Volume 307. [Google Scholar]
  57. Tsalagkas, D.; Börcsök, Z.; Pásztory, Z. Thermal, physical and mechanical properties of surface overlaid bark-based insulation panels. Eur. J. Wood Prod. 2019, 77, 721–730. [Google Scholar] [CrossRef]
  58. Taban, E.; Mirzaei, R.; Faridan, M.; Samaei, E.; Salimi, F.; Tajpoor, A.; Ghalenoei, M. Morphological, acoustical, mechanical and thermal properties of sustainable green Yucca (Y. gloriosa) fibers: An exploratory investigation. J. Environ. Health Sci. Eng. 2020, 18, 883–896. [Google Scholar] [CrossRef]
  59. Smardzewski, J.; Batko, W.; Kamisiński, T.; Flach, A.; Pilch, A.; Dziurka, D.; Mirski, R.; Roszyk, E.; Majewski, A. Experimental study of wood acoustic absorption characteristics. Holzforschung 2013, 68, 160. [Google Scholar] [CrossRef]
  60. European Committee for Standardization. EN 326-1:2005 Wood Based Panels—Sampling, Cutting and Inspection—Part 1: Sampling and Cutting of Test Pieces and Expression of Test Results; European Committee for Standardization: Brussels, Belgium, 2005. [Google Scholar]
  61. Graphite Polystyren, Isover EPS Greywall. Available online: https://www.isover.sk/sites/isover.sk/files/assets/documents/isover-sk_technicky-list_isover-eps_greywall.pdf (accessed on 1 June 2021).
  62. White Polystyrene—Polyform EPS 200S. Available online: https://www.isover.sk/sites/isover.sk/files/assets/documents/isover-sk_technicky-list_isover-eps_200s.pdf (accessed on 1 June 2021).
  63. Extruded Polystyrene—Isover. Available online: https://www.isover.sk/sites/isover.sk/files/assets/documents/isover-sk_isover-styrodur_3000_cs_technicky_list.pdf (accessed on 1 June 2021).
  64. Fiberboard—Steico Flex 036. Available online: https://tepore.sk/wp-content/uploads/2018/03/STEICO-Flex-036_CZ.pdf (accessed on 1 June 2021).
  65. Mineral Wool—Isover TF Thermo. Available online: https://www.isover.sk/sites/isover.sk/files/assets/documents/isover-sk_isover_tf_thermo_epd_en.pdf (accessed on 1 June 2021).
  66. Masonite Board—Steico Protect. Available online: https://www.jafholz.sk/action/shop/pdf?product=1351400 (accessed on 1 June 2021).
  67. Cork Boards. Available online: https://www.korok.sk/data/files/jcg_insulation-cataloque-eng_43.pdf (accessed on 1 June 2021).
  68. EN ISO 10534-2. Acoustics—Determination of Sound Absorption Coefficient and Impedance in Impedance Tubes—Part 2: Transfer-Function Method; European Committee for Standardization (CEN): Brüssel, Belgium, 2002. [Google Scholar]
  69. Morgans, R.C.; Li, X.; Zander, A.C.; Hansen, C.H. Statistics and the Two Microphone Method for the Measurement of Sound Absorption Coefficient. Proc. Acoust. 2004, 15, 3–5. [Google Scholar]
  70. EN ISO 11654. Acoustics—Sound Absorbers—Rating of Sound Absorption Coefficients; European Committee for Standardization (CEN): Brüssel, Belgium, 2017. [Google Scholar]
  71. Nordin, M.N.A.A.; Wan, L.M.; Zainulabidin, M.H.; Kassim, A.S.M.; Aripin, A.M. Research finding in natural fibers sound absorbing material. ARPN J. Eng. Appl. Sci. 2016, 11, 8579–8584. [Google Scholar]
  72. Echeverria, C.A.; Pahlevani, F.; Handoko, W.; Jiang, C.; Doolan, C.; Sahajwalla, V. Engineered hybrid fibre reinforced composites for sound absorption building applications. Resour. Conserv. Recycl. 2019, 143, 1–14. [Google Scholar] [CrossRef]
  73. Boubel, A.; Garoum, M.; Bousshine, S.; Bybi, A. Investigation of loose wood chips and sawdust as alternative sustainable sound absorber materials. Appl. Acoust. 2021, 172, 107639. [Google Scholar] [CrossRef]
  74. Limited, K. Acoustic Performance Guide; Kingspan Limited: Holywell, UK, 2005. [Google Scholar]
  75. Koizumi, T.; Tsujiuchi, N.; Adachi, A. The development of sound absorbing materials using natural bamboo fibers. WIT Trans. Built Environ. 2002, 59, 157–166. [Google Scholar]
  76. Arenas, J.P.; Asdrubali, F. Eco-Materials with Noise Reduction Properties. In Handbook of Ecomaterials; Martinez, L.M.T., Kharissova, O.V., Kharisov, B.I., Eds.; Springer International Publishing AG: New York, NY, USA, 2018. [Google Scholar]
  77. Hassani, P.; Soltani, P.; Ghane, M.; Zarrebini, M. Porous resin-bonded recycled denim composite as an efficient sound-absorbing material. Appl. Acoust. 2021, 173, 107710. [Google Scholar] [CrossRef]
  78. Arenas, J.P.; Crocker, M.J. Recent Trends in Porous Sound-Absorbing Materials. Sound Vib. 2010, 44, 12–18. [Google Scholar]
  79. Akay, A. Acoustics of friction. J. Acoust. Soc. Am. 2002, 111, 1525–1548. [Google Scholar] [CrossRef]
  80. Amares, S.; Sujatmika, E.; Hong, T.W.; Durairaj, R.; Hamid, H.S.H.B. A Review: Characteristics of Noise Absorption Material. J. Phys. Conf. Ser. 2017, 908, 012005. [Google Scholar] [CrossRef]
  81. Soltani, P.; Zerrebini, M. The analysis of acoustical characteristics and sound absorption coefficient of woven fabrics. Text. Res. J. 2012, 82, 875–882. [Google Scholar] [CrossRef]
  82. Karlinasari, L.; Hermawan, D.; Maddu, A.; Bagus, M.; Lucky, I.K.; Nugroho, N.; Hadi, Y.S. Acoustical Properties of Particleboards Made from Betung Bamboo (Dendrocalamus asper) as Building Construction Material. Bioresources 2012, 7, 5700–5709. [Google Scholar] [CrossRef]
  83. Karlinasari, L.; Hermawan, D.; Maddu, A.; Martiandi, B.; Hadi, Y.S. Development of particleboard from tropical fast-growing Species for acoustic panel. J. Trop. For. Sci. 2012, 24, 64–69. [Google Scholar]
  84. Luu, H.T.; Perrot, C.; Panneton, R. Influence of porosity, fiber radius and fiber orientation on the transport and acoustic properites of random fiber structures. Acta Acust. United Acust. 2017, 103, 1050–1063. [Google Scholar] [CrossRef]
  85. Aditya, L.; Mahlia, T.M.I.; Rismanchi, B.; Ng, H.M.; Hasan, M.H.; Metselaar, H.S.C.; Muraza, O.; Aditiya, H.B. A review on insulation materials for energy conservation in buildings. Renew. Sustain. Energy Rev. 2017, 73, 1352–1365. [Google Scholar] [CrossRef]
  86. Niu, M.; Hagman, O.; Wang, X.; Xie, Y.; Karlsson, O.; Cai, L. Effect of Si-Al Compounds on Fire Properties of Ultra-low Density Fiberboard. Bioresources 2014, 9, 2415–2430. [Google Scholar] [CrossRef]
  87. Chen, T.; Liu, J.; Wu, Z.; Wang, W.; Niu, M.; Wang, X.; Xie, Y. Evaluating the Effectiveness of Comples Fire-Retardants on the Fire Properties of Ultra-low Density Fiberboard (ULDF). Bioresources 2016, 11, 1796–1807. [Google Scholar]
  88. Pausas, J.G. Bark thickness and fire regime. Funct. Ecol. 2014, 29, 315–327. [Google Scholar] [CrossRef]
  89. D’Alessandro, F.; Schiavoni, S.; Bianchi, F. Straw as an acoustic material. In Proceedings of the 24th International Congress on Sound and Vibration, London, UK, 23–27 July 2017. [Google Scholar]
  90. Dalmeijer, R. Straw bale sound insulation and acoustics. Last Straw. Int. J. Straw Bale Nat. Buid. 2006, 53. Available online: http://www.thelaststraw.org/strawbale-sound-isolation-acoustics/ (accessed on 1 July 2013).
  91. Deverell, R.; Goodhew, S.; Griffiths, R.; De Wilde, P. The noise insulation properties of non-food-crop walling for schools and colleges: A case study. J. Build. Apprais. 2009, 5, 29–40. [Google Scholar] [CrossRef]
  92. Dance, S.; Herwin, P. Straw bale sound insulation: Blowing awy the chaff. In Proceedings of the Meerings on Acoustics ICA 2013, Montreal, QC, Canada, 2–7 June 2013. [Google Scholar]
  93. Schiavoni, S.; D’Alessandro, F.; Bianchi, F.; Asdrubali, F. Insulation materials for the building sector: A review and comparative analysis. Renew. Sustain. Energy Rev. 2016, 62, 988–1011. [Google Scholar] [CrossRef]
Figure 1. Scheme of the apparatus for measuring the sound absorption coefficient.
Figure 1. Scheme of the apparatus for measuring the sound absorption coefficient.
Forests 12 00887 g001
Figure 2. Sound absorption coefficient as a function of frequency of tested specimens of bark panels 1, 2, 5 and 8 with a thickness of 30 mm and a particle size of 4 to 11 mm.
Figure 2. Sound absorption coefficient as a function of frequency of tested specimens of bark panels 1, 2, 5 and 8 with a thickness of 30 mm and a particle size of 4 to 11 mm.
Forests 12 00887 g002
Figure 3. Sound absorption coefficient as a function of frequency of tested specimens of bark panels 1, 2, 5 and 8 with a thickness of 30 mm and a particle size of 4 to 11 mm.
Figure 3. Sound absorption coefficient as a function of frequency of tested specimens of bark panels 1, 2, 5 and 8 with a thickness of 30 mm and a particle size of 4 to 11 mm.
Forests 12 00887 g003
Figure 4. Sound absorption coefficient as a function of frequency of tested specimens of bark panels 4, 6, 7 and 9 with a thickness of 30 mm and a grain fraction of 10 to 30 mm.
Figure 4. Sound absorption coefficient as a function of frequency of tested specimens of bark panels 4, 6, 7 and 9 with a thickness of 30 mm and a grain fraction of 10 to 30 mm.
Forests 12 00887 g004
Figure 5. Sound absorption coefficient as a function of frequency of tested specimens of bark panels 4, 6, 7 and 9 with a thickness of 30 mm and a grain fraction of 10 to 30 mm.
Figure 5. Sound absorption coefficient as a function of frequency of tested specimens of bark panels 4, 6, 7 and 9 with a thickness of 30 mm and a grain fraction of 10 to 30 mm.
Forests 12 00887 g005
Figure 6. The NRC value of selected materials depending on the density of the tested material (A–polystyrene based materials, B–typical sound-insulating materials, C–cellulose-based insulations, D–bark-based boards).
Figure 6. The NRC value of selected materials depending on the density of the tested material (A–polystyrene based materials, B–typical sound-insulating materials, C–cellulose-based insulations, D–bark-based boards).
Forests 12 00887 g006
Figure 7. Comparison of frequency dependence of the sound absorption coefficient of straw, graphite polystyrene, fiberboard and bark type 8.
Figure 7. Comparison of frequency dependence of the sound absorption coefficient of straw, graphite polystyrene, fiberboard and bark type 8.
Forests 12 00887 g007
Table 1. Overview of parameters of tested specimens made of bark-based boards.
Table 1. Overview of parameters of tested specimens made of bark-based boards.
Panel Nr.12345
ImageForests 12 00887 i001Forests 12 00887 i002Forests 12 00887 i003Forests 12 00887 i004Forests 12 00887 i005
Particle size (mm)4–114–1110–45
(with popcorn)
10–304–11
Orientationparallelperpendicularparallelparallelparallel
Density (kg/m3)688 ± 14344 ± 7308 ± 8477 ± 25536 ± 11
Resination factor (%)1010201010
Table 2. Overview of parameters of tested specimens made of bark-based boards.
Table 2. Overview of parameters of tested specimens made of bark-based boards.
Panel Nr.6789
ImageForests 12 00887 i006Forests 12 00887 i007Forests 12 00887 i008Forests 12 00887 i009
Particle size (mm)10–3010–304–1110–30
Orientationperpendicularparallelparallelperpendicular
Density (kg/m3)354 ± 8369 ± 12362 ± 9470 ± 6
Resination factor (%)20201010
Table 3. Overview of parameters of tested commercially available insulating materials.
Table 3. Overview of parameters of tested commercially available insulating materials.
PanelGraphite
Polystyrene [61]
White
Polystyrene [62]
Extruded
Polystyrene [63]
Fiberboard [64]Recycled Textile [9]
ImageForests 12 00887 i010Forests 12 00887 i011Forests 12 00887 i012Forests 12 00887 i013Forests 12 00887 i014
Density (kg/m3)30 ± 1.925.2 ± 0.235.1 ± 0.559.9 ± 1.259.8 ± 1.09
Table 4. Overview of parameters of tested commercially available insulating materials.
Table 4. Overview of parameters of tested commercially available insulating materials.
PanelMineral Wool [65]Masonite Board [66]Cereal StrawCork [67]
ImageForests 12 00887 i015Forests 12 00887 i016Forests 12 00887 i017Forests 12 00887 i018
Density (kg/m3)100 ± 15265 ± 21250 ± 23280 ± 1
Table 5. Noise reduction coefficient (NRC) for the tested bark boards (* sample 3 is scored-out due to inconsistent results).
Table 5. Noise reduction coefficient (NRC) for the tested bark boards (* sample 3 is scored-out due to inconsistent results).
SampleNRC for 30 mmNRC for 60 mm
10.100.15
20.100.40
3**
40.100.35
50.200.25
60.300.30
70.200.40
80.150.50
90.150.35
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Tudor, E.M.; Kristak, L.; Barbu, M.C.; Gergeľ, T.; Němec, M.; Kain, G.; Réh, R. Acoustic Properties of Larch Bark Panels. Forests 2021, 12, 887. https://0-doi-org.brum.beds.ac.uk/10.3390/f12070887

AMA Style

Tudor EM, Kristak L, Barbu MC, Gergeľ T, Němec M, Kain G, Réh R. Acoustic Properties of Larch Bark Panels. Forests. 2021; 12(7):887. https://0-doi-org.brum.beds.ac.uk/10.3390/f12070887

Chicago/Turabian Style

Tudor, Eugenia Mariana, Lubos Kristak, Marius Catalin Barbu, Tomáš Gergeľ, Miroslav Němec, Günther Kain, and Roman Réh. 2021. "Acoustic Properties of Larch Bark Panels" Forests 12, no. 7: 887. https://0-doi-org.brum.beds.ac.uk/10.3390/f12070887

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop