Thermo physical characterization of sustainable insulation materials made from textile waste

Author’s Accepted Manuscript Thermo physical characterization of sustainable insulation materials made from textile waste Mohamed El Wazna, Mohamed El Fatihi, Abdeslam El Bouari, Omar Cherkaoui www.elsevier.com/locate/jobe

PII: DOI: Reference:

S2352-7102(17)30062-1 http://dx.doi.org/10.1016/j.jobe.2017.06.008 JOBE284

To appear in: Journal of Building Engineering Received date: 30 January 2017 Revised date: 7 June 2017 Accepted date: 7 June 2017 Cite this article as: Mohamed El Wazna, Mohamed El Fatihi, Abdeslam El Bouari and Omar Cherkaoui, Thermo physical characterization of sustainable insulation materials made from textile waste, Journal of Building Engineering, http://dx.doi.org/10.1016/j.jobe.2017.06.008 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Thermo physical characterization of sustainable insulation materials made from textile waste Mohamed EL WAZNAa,b*, Mohamed EL FATIHIb, Abdeslam EL BOUARIa, Omar CHERKAOUIb Laboratory of physic-chemical of applied materials, Sciences Faculty of Ben M’sik , University Hassan II Casablanca Morocco b Laboratory REMTEX, Higher School of Textile and clothing Industries, Km 8, Route d’EL JADIDA, Casablanca Morocco * Corresponding author. [email protected] a

Abstract The aim of this work is to evaluate the potential of textile waste application in building insulation in the form of a nonwoven fabric, and also to investigate the effects of porosity and density on the properties of needle-punched non-woven fabrics. For this purpose, four nonwoven waste based on acrylic and wool, termed here as A1, A2, W1 and W2, were prepared using needle punched technique and tested in terms of physical-microstructural properties. The thermal conductivity of A1, A2, W1 and W2 were 0.0350 W/(m.K), 0.0335 W/(m.K), 0.0348 W/(m.K) and 0.0339 W/(m.K) respectively. In addition, air permeability was found satisfactory for all nonwoven fabrics with values ranging from 600 to 616 L/(m2.s) for acrylic and 950 to 1033 L/(m2.s) for wool samples. The dependency of the thermal conductivity λ and the air permeability k on the porosity and density was investigated. It is observed that the thermal conductivity and the air permeability of non-woven fabrics decreases with increasing porosity, and increases linearly with density. The measured properties showed that the nonwoven fabrics present good insulating properties compared to the traditional insulation materials (glass wool, mineral wool etc.). Therefore the non-woven textile waste insulation may provide a promising solution for building insulations.

Keywords: Textile waste, building insulation, energy efficiency, needle punching technique Abbreviations ρ, bulk density; Ma, mass per unit area; t, thickness; ε, porosity; ρf, fiber density; α, packing density, Rth, thermal resistance; λ, thermal conductivity; k, air permeability

1. Introduction

The interest for improving insulation was attracted by the evolution of construction methods, the need for a more appropriate thermal comfort and energy saving. In Morocco the annual energy consumption (from all sources) is 0.5 tons of oil equivalent per capita, increases of 4.3% each year. Regarding electricity, a Moroccan consumes 781KWh annually, which increases by 7.8% annually [1]. The building sector used approximately 115 EJ globally, accounting for 32% of global final energy demand (24% for residential and 8% for commercial) and 30% of energy-related CO2 emissions [2]. Also, it is responsible for approximately two-thirds of halocarbon and approximately 25–33% of black carbon emissions [2-3]. Improving energy efficiency in the building sector is therefore a priority area for progress. Thermal insulation is often the first step to reduce energy requirements in a building, it can both reduces the heating and/or air conditioning energy consumption and increases thermal comfort. There is a wide variety of insulation on the market that can be classified according to its form, use and composition. Insulators come in many forms be it rigid, mat, bulk, injected or foam [4]. Generally, this thermal insulators are organized into three categories according to the nature of the constituents (Fig.1) [5]. In addition, not all insulators have the same composition, and this will influence the health and environmental risks associated with their use. However, the choice of insulation materials cannot be based only on practical and economical considerations, but must also integrate ecological considerations (energy and environmental issues) [6]. For this purpose, the textile wastes are proposed as thermal insulation for their good thermal properties, as well as the huge amount of textile waste that are discarded each year in the environment. Despite that, a small amount is recycled or incinerated by charities or companies while the remaining waste is thus wasted [7]. The use of textile waste for building insulation would add value to this local resource as an interesting alternative to the conventional insulators (e.g. glass wool, stone wool, etc.). Recycling textile waste is not yet a widespread activity, but researchers suggest that it will be developed rapidly. Already, more large companies are integrating the situation and many are calling on specialized providers for the treatment of textile waste as thermal insulator. In the literature, Briga-Sá et al. [8] investigated the feasibility of fabric waste as an alternative solution for thermal insulation, and they found that applying these wastes as a possible thermal insulation material seems to be an adequate solution. Environmental, sustainable and economical advantages may result from this practice. Patnaik et al. [9], developed insulation nonwoven material from wool and recycled polyester and studied their thermal, acoustic properties and also their biodegradation behavior.

The developed insulation materials have shown good insulating properties. Some researchers focused on the reuse of some textile waste, like wool as a source for the production of thermal insulation especially due to their positive ecological and health properties [10]. The previous work does not give sufficient information on the parameters responsible on the obtained thermo-physical properties of the nonwoven insulators. The aim of the present study was to produce a new insulation material with a low heat transfer coefficient using waste textile. The second part of the paper examines the parameters responsible of the obtained thermo-physical properties.

Fig.1. List of the commercial insulation materials.

2. Materials and methods

2.1. Nonwoven preparation Nonwoven fabrics were prepared by using needle punching technique using a DILO DILOOM OD-II 10069/2012 machine, which aims to locks the fibers together mechanically by a physical entanglement. The needling machine is equipped with a board which the needles are inserted, feed and exit rolls, bed plate and stripper (Fig.2). The mechanical bonding is obtained by the alternative movements of barbed needle through a moving web of fiber. The acrylic fibers and the wool carpet fibers are obtained by a shredding waste from a Moroccan manufacture unit. While, the raw wool is recovered from Bengrir region, Morocco. It is then washed and treated at the MOCARI Company. Acrylic and wool fibers of different origins were cut into small portion of 40-50 mm of length, and carded to ensure the opening of the fibers. The carded webs are transported directly to the bonding stage where they are repeatedly punctured by a battery of needles. In our case, we have reduced the striking speed, the needle barb depth and also the number of needles, to obtain a nonwoven with high porosity. Four samples were produced by needle punching process. A1 and A2 are both 100% acrylic materials, W2 and W1 are both 100% sheep wool. Photographs of the samples are shown in (Fig.3). The needle-punching parameters were kept same for all samples. All manufactured nonwoven were conditioned for 24 h prior to testing in a standard testing atmosphere maintained at 65 ± 4% humidity and 20 ± 2°C temperature.

Fig.2. Illustrations of the needling loom Fig.3. Illustrations of nonwoven made from textile waste: (a) A1, (b) A2, (c) W2, (d) W1

2.1. Thickness and mass per unit area The thickness (t) of sample was measured according to standard ISO 9073-2 [11]. The mass per unit area of the samples were measured according to standard EN 12127 [12] using an Adventure Pro AV 264C electronic balance. Five samples of 100 cm2 were taken by using a cutting dispositive. Five random readings were taken for measuring thickness and mass per unit area.

2.2. Bulk density and porosity Bulk density ρ [kg/m3] is defined as the ratio of the mass per unit area Ma [kg/m2] and thickness [m]: (1)

The porosity is defined as the set of voids of a nonwoven material. This is a physical quantity that determines the flow and retention capacities of a nonwoven [13]. Porosity ε is defined by the following equation: (

)

(

)

(2)

Where: α = packing density, ρ = nonwoven density, ρf = fiber or polymer density Sample compositions and their physical properties are given in Table 1. Table.1. Sample compositions and their physical properties Bulk density ρ(kg/m3)

Porosity ɛ (%)

750 (±20)

25

97.8

30 (±0.7)

900(±15)

30

97.4

30 (±0.5)

1860(±10)

62

95.2

Sample

Source of waste

thickness (mm)

A1

Spinning process

30 (±0.8)

A2

knitting process

W1

Washed and treated raw

d area weight (g/m2)

wool W2

Carpet waste

30 (±0.7)

1350 (±15)

45

96.5

Values in the parenthesis indicate the standard deviation.

2.4. Material structure The structure of nonwoven fabrics were determined using optical microscope (the Leica DME). The objective lens used was a 506226 Hi plan 4x/0.1.

2.5. Thermal conductivity and thermal resistance : The thermal conductivity λ of a material is defined as the amount of heat crossing a unit area of the material per unit time per unit temperature gradient. The guarded hot plate apparatus λMeter EP500e was used for measuring the thermal conductivity as per the EN 12667 [14]. The thermal conductivity test tool λ-Meter EP500e is based on the steady state heat transfer between a warm and a cold plate. It measures the sample thickness t [m] of the inserted sample, the temperature difference ΔT [K] over the sample and the heat flux Q [W/m2] which is equivalent to the electrical power of the measuring heating. The thermal conductivity λ W/(m.K) is determined based on the defined measurement area S [m2] and the onedimensional thermal conduction as follows: (3) The samples were placed between two plates with dimensions 500 mm ×500 mm. The upper plate is lowered with a pressure of 50 Pa until the pressure set point is reached. The measuring area is the innermost square of dimensions 200 mm × 200 mm, and the rest is a frame which should be made of a highly insulating material. In this study, the measuring temperature was 25°C. Moreover, the temperature difference between the hot plate and the cold plate is set at 15°C in all measurements. The thermal resistance is expressed by the following relationship: (4)

2.6. Air permeability Air permeability describes the rate of flow of a fluid through a porous material [15]. The mathematical expression is given by: (5) Where k is rate of flow L/(m2.s), Q is volume of flow of fluid through the sample [L], t is time [s] and S is the cross-sectional area [m2]. Air-Tronic instrument was used to determine the air permeability of textile waste nonwoven as per the ASTM D737, which measures the air flow passing vertically through a surface of 10 cm2 under pressure of 200 Pa.

3. Experimental results and discussion 3.1. Microscopic analysis

On a microstructural scale, the needle-punched fabrics consist of at least two different regions. The first one is the area marked by the needle. It contains fibers that are oriented out of the plane of fabric. The second zone is situated between the impacts regions that are associated with the striking of the needles. This zone is not directly perturbed by the needles and retains a structure similar to the carded original tape. This rearrangement of the fibers leads to a structural anisotropy which is observed in Fig.4-A. Consequently, the structure of the needle-punched fabrics is not homogeneous and can be assimilated to a two-phase system consisting of a skeleton of dense fibers and pores, as it is shown in Fig.4-B. This unique structure often has special properties such as thermal insulation.

Fig.4. Horizontal sections of nonwoven fabric using optical micrographs.

3.2. Analysis of the thermal conductivity of manufactured nonwoven 3.2.1. Measure of thermal conductivity The thermal conductivity λ W/(m.K) of the nonwoven fabric was determined using the guarded hot plate apparatus λ-Meter EP500e based on EN 12667. Samples were prepared from the mats with dimensions of (200 mm× 200 mm× samples thickness), and tested at a temperature of 25°C. The thermal conductivities of samples are shown in table 2. All

developed non-woven show an excellent insulation performance with λ< 0.040 W/(m.K) better than the existing product (table 3). The conductivity values observed for the samples A1 and A2 are rather the same with a slight difference of 0.005 W/(m.K). Wool sample W1 and W2 provided the best insulation properties. The lowest value of λ was observed for W2 (λW2=0.0339 W/(m.K)). These results show that wool samples have a better thermal insulation capacity than the acrylic samples (i.e. 0.0339 W/(m.K) against 0.035 W/(m.K)). Despite the fact that the analyzed textile wastes showed thermal insulation ability, it may be concluded that the wool samples may be more interesting for a building thermal insulation perspective. This finding is in accordance with the results found by Patnaik et Al., who studied the thermal properties of nonwoven material from wool and recycled polyester. The developed nonwoven showed comparable values of thermal conductivity found in the current study [9]. The thermal resistances shown in table 2 were obtained from the measured values of the thermal conductivity and thickness according to the equation (4). The highest value is observed for the wool sample W2 (RW2= 0.88 m2.K/W).

Table.2. Thermal and physical properties of nonwoven fabric. Thermal conductivity W/(m.K)

Thermal resistance Air permeability L/(m2.s) (m2.K)/W

A1

0.0350

0.85

600

A2

0.0355

0.84

616

W1

0.0348

0.86

1033

W2

0.0339

0.88

950

Sample

3.2.2. Effect of structural parameters on thermal conductivity

The dependency of the thermal conductivity λ on the porosity ɛ is shown in Fig.5. The thermal conductivity of non-woven is inversely proportional to the porosity of the nonwoven fabric, it decreases with increasing porosity. Physical entanglement of fibers during manufacture process created a unique structure, particular direction and also very high porosity (95.2 % < ɛ < 97.8 %). Nonwovens can be assimilated to a two-phase system consisting of a skeleton of the dense fibers and air (Fig.4). Moreover, thermal conductivity is related to the presence of pores [16], their types (open or

closed), their sizes and also their tortuosity. Small-pore have smaller thermal conductivity compared to wide pores. Trapped air in pores gives a better thermal conductivity coefficient. Better tortuosity also leads to a reduced free path of heat flux. Therefore, the conductivity will be reduced due to increased forward and backward reflection of the radiation component [17]. The dependency of the thermal conductivity λ on the density ρ is shown in Fig.6. The thermal conductivity increases linearly with density, it varies from 0.0350 to 0.0335 W/(m.K) for densities of 25 to 30 kg/m3 for the acrylic samples respectively, and from 0.0339 to 0.0348 W/(m.K) for densities of 45 to 62 kg/m3 for the wool sample respectively. These results are explained by the inverse relationship between density and porosity. Therefore, density might not be an important parameter as it can be replaced by porosity.

Fig.5. The dependency of the thermal conductivity λ and air permeability k on the porosity ɛ. Fig.6. The dependency of the thermal conductivity λ and air permeability k on the bulk density.

3.3. Analysis of the air permeability of the manufactured nonwoven fabric

3.3.1. Measure of the air permeability

The air permeability was determined by using AIR-TRONIC according to the ASTM D737. According to the literature the value of air permeability of the nonwoven shown in table 1, are satisfactory [18]. The air permeability values observed for the samples A1, A2, W1 and W2 are 600, 616, 1033 and 950 L/(m2.s) respectively.

3.3.2. Effect of structural parameters on the air permeability The dependency of the air permeability k on the porosity ɛ is shown in Fig.5. The air permeability decreases with increasing porosity. According to the literature [19], there is no simple correlation between air permeability and porosity because of the strong dependence of flow rate on the width, shape, and tortuosity of the conducting channels. Tortuosity, the ratio

of effective channel length and sample thickness, is an important factor in determining flow through nonwoven materials [17-20]. The dependency of the air permeability k on the density ρ is shown in Fig.6. It is clear that the air permeability of nonwoven fabric increase with the increase of density, these results are explained by the inverse relationship between porosity and density. The variation of the air permeability with the thermal conductivity is shown in Fig.5, as seen air permeability decrease with the decrease in thermal conductivity. This variation can be explained by the two following hypothesis: - The tortuosity is important which leads to the delay of heat flow and the air flow, consequently, both the conductivity λ and the air permeability decrease. - Existing pores mostly closed block the transfer of the heat and the air.

3.4. Comparison of properties of manufactured nonwoven with conventional insulators Table 3 shows the values of thermal conductivities of manufactured nonwoven and different thermal insulation materials. At 25°C the values of λA1 and λA2 are approximated to the λ value of glass wool, however the values of λW1 and λW2 are better. With the decrease in temperature, thermal conductivity decreases for all samples with an average of 0.0025 W/(m.K). At 10 ° C, the manufactured nonwoven has better insulating properties with a thermal conductivity between 0.0311-0.0326 W/(m.K) much lower than the conventional insulation

shown

in

Table

3.

This

result

leads

to

the

conclusion

that

the

manufactured nonwovens present a significant insulating property compared to the conventional insulating material (GW, MW and XPS). The Fig.7 shows the value of the thermal conductivity of samples and their density, it can be seen that even the wool samples had better insulation properties but their density remains higher, nevertheless the density factor is not important in view of the environmental benefits of wool. Besides, wool is a natural, renewable and durable material and it does not cause any kind of irritation or danger to human health.

Wool can absorb and desorb moisture without reducing thermal

performance, making it a perfect insulating material, moreover, it does not support combustion and is extinguished in case of fire [21]. For acrylic samples, the density is lower and λ value is higher, the best value in terms of density and thermal conductivity values is

attributed to XPS. The effect of density on the properties of a product varied from one insulating material to another, in order to eliminate this effect, the thermal conductivity λ was divided by the density ρ. The ratio λ/ρ provides a better means for comparison of thermal properties of non-woven materials by excluding variation in density [22]. Normalized thermal conductivity (λ /ρ) of the samples was compared to the conventional insulation materials and the results are shown in table 3. The best value is observed for the XPS and GW samples because of their lower density, contrary to the wool sample. For acrylic samples they showed satisfactory results. The Fig.8 shows the value of the thermal conductivity of samples and their density, we can see that even the wool samples had a better insulation properties but their density remains higher. For acrylic samples density is lower and λ value is higher. The best value in terms of density and thermal conductivity values is attributed to XPS.

Table.3. The thermal properties of nonwoven fabric and other insulators. Materials

Developed products

Conventional insulations materials (Manufacturers declared value)

Bulk density ρ (kg/m3)

Thermal conductivity W/(m.K)

Normalized thermal conductivity ⁄ ×103

10°C

25°C

10°C

25°C

A1

25

0.0326

0.0350

1.3

1.4

A2

30

0.0330

0.0355

1.1

1.18

W1

62

0.0321

0.0348

0.51

0.56

W2

45

0.0311

0.0339

0.69

0.75

Glass wool (GW)

24

0.0350

-----

1.45

-----

Mineral wool (MW)

36

0.0370

-----

1.02

-----

Extruded 15 expanded polystyrene (XPS)

0.0380

-----

2.53

-----

Fig.7. bulk density vs thermal conductivity of samples.

Fig.8. Normalized thermal conductivity of samples versus conventional insulation product.

Conclusion Thermal insulation is a key element in the building sector, it minimizes energy consumption and guarantees thermal comfort. Four nonwoven waste based on acrylic and wool, were made using needle punched technique and tested in terms of thermal conductivity and air permeability properties. The results of the experimental measurements show that all developed non-woven show an excellent insulation performance. The lowest value of thermal conductivity was observed for the nonwoven made from washed wool.

The developed

nonwoven showed comparable values of thermal conductivity and even better to the conventional insulating materials (GW, MW, XPS etc.). Furthermore, the dependency of the thermal conductivity λ and the air permeability k of nonwoven fabrics on the porosity and density was investigated, the anisotropic structure, the random distribution of the fibers and the width, the shape and tortuosity of the conductive channels are important factors in determining flow through nonwoven materials. Therefore, the determination of the correlation of these factors and the different measured properties remain complicated and will form the subject of further research.

References [1] http://www.aderee.ma/index.php/fr/expertise/efficacite-energetique/batiment consulted in 24/11/2016 [2] Ürge-Vorsatz, D., Cabeza, L. F., Serrano, S., Barreneche, C., & Petrichenko, K. (2015). Heating and cooling energy trends and drivers in buildings. Renewable and Sustainable Energy Reviews, 41, 85-98. [3] Lead, C., & LA, L. A. Energy End-Use: Buildings. [4] Pfundstein, M., Gellert, R., Spitzner, M., & Rudolphi, A. (2008). Insulating materials: principles, materials, applications. Walter de Gruyter. [5] Schiavoni, S., Bianchi, F., & Asdrubali, F. (2016). Insulation materials for the building sector: A review and comparative analysis. Renewable and Sustainable Energy Reviews, 62, 988-1011. [6] Oushabi, A., Sair, S., Abboud, Y., Tanane, O., & Bouari, A. E. L. (2015). Natural thermal-insulation materials composed of renewable resources: characterization of local date palm fibers (LDPF). J. Mater. Environ. Sci, 6(12), 3395-3402. [7] Newell, A. S. (2015). Textile Waste Resource Recovery: A Case Study Of New York State’S Textile Recycling System (Doctoral dissertation, Cornell University).

[8] Briga-Sa, A., Nascimento, D., Teixeira, N., Pinto, J., Caldeira, F., Varum, H., & Paiva, A. (2013). Textile waste as an alternative thermal insulation building material solution. Construction and Building Materials, 38, 155-160. [9] Patnaik, A., Mvubu, M., Muniyasamy, S., Botha, A., & Anandjiwala, R. D. (2015). Thermal and sound insulation materials from waste wool and recycled polyester fibers and their biodegradation studies. Energy and Buildings, 92, 161-169. [10] Zach, J., Korjenic, A., Petránek, V., Hroudová, J., & Bednar, T. (2012). Performance evaluation and research of alternative thermal insulations based on sheep wool. Energy and Buildings, 49, 246-253. [11] ISO 9073-2, Test methods for nonwovens. Part 2: Determination of thickness, 1995 [12] EN 12127, Determination of mass per unit area using small samples, British Standard, 1998 [13]Tsai, P. P., & Yan, Y. Y. (2010). The Influence of Fiber and Fabric Properties on Nonwoven Performance. Applications of Nonwovens in Technical Textiles, the Textile Institute, Woodhead Publishing Limited, ISBN978-1-84569-437, 1, 18-45. [14] EN 12667, Thermal performance of building materials and products-Determination of thermal resistance by means of guarded hot plate and heat flow meter methods. Products of high and medium thermal resistance, 2001. [15] Zhu, G., Kremenakova, D., Wang, Y., & Militky, J. (2015). Air permeability of polyester nonwoven fabrics. Autex Research Journal, 15(1), 8-12. [16] Kaviany, M. (2012). Principles of heat transfer in porous media. Springer Science & Business Media. [17] Maity, S., & Singha, K. (2012). Structure-property relationships of needle-punched nonwoven fabric. Frontiers in Science, 2(6), 226-234. [18] Kozłowski, R., Mieleniak, B., Muzyczek, M., & Mańkowski, J. (2008, July). Development of insulation composite based on FR bast fibers and wool. In International Conference on Flax and Other Bast Plants (pp.176-182). [19] Dullien, F. A. (2012). Porous media: fluid transport and pore structure. Academic press. [20] Mohammadi, M., & Banks-Lee, P. (2002). Air permeability of multilayered nonwoven fabrics: Comparison of experimental and theoretical results. Textile Research Journal, 72(7), 613-617. [21] Korjenic, A., Klarić, S., Hadžić, A., & Korjenic, S. (2015). Sheep wool as a construction material for energy efficiency improvement. Energies, 8(6), 5765-5781. [22] Sakthivel, S., & Ramachandran, T. (2012). Thermal conductivity of non-woven materials using reclaimed fibres. International Journal of Engineering Research and Applications (IJERA), 2(3), 2986.

Highlights  





Four nonwoven waste A1, A2, W1 and W2 were made using needle punched technique and tested in terms of physical-microstructural properties. The thermal conductivity λ of A1, A2, W1 and W2 were 0.035 W/m.K, 0.0335 W/m.K, 0.0348 W/m.K and 0.0339 W/m.K respectively, In addition, air permeability k was found satisfactory for all nonwoven fabrics with values ranging from 600 to 616 L.m-2.s-1 for acrylic and 950 to 1033 L.m-2.s-1 for wool samples. The dependency of the thermal conductivity λ and the air permeability k on the porosity and density was investigated, the thermal conductivity and the air permeability of non-woven fabrics decreases with increasing porosity and increases linearly with density. The non-woven textile waste insulation may provide a promising solution for building insulations.

Fig.1. List of the commercial insulation materials

Fig.2. Illustrations of the needling loom

(a)

(c)

(d)

Fig.3. Illustrations of nonwoven made from textile waste: (a) A1, (b) A2, (c) W2, (d) W1

Fig.4. Horizontal sections of nonwoven fabric using optical micrographs.

Fig.5. The dependency of the thermal conductivity λ and air permeability k on the porosity ɛ.

Fig.6. The dependency of the thermal conductivity λ and air permeability k on the bulk density.

Fig.7. Bulk density vs thermal conductivity of samples

( ⁄ )×10-3

Fig.8. Normalized thermal conductivity of samples versus conventional insulation product