Textile waste as thermal insulation material thermal conductivity

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Thermo physical characterization of
sustainable insulation materials made from
textile waste
Article in Journal of Building Engineering · June 2017
DOI: 10.1016/j.jobe.2017.06.008
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2. Contents lists available at ScienceDirect
Journal of Building Engineering
journal homepage: www.elsevier.com/locate/jobe
Thermo physical characterization of sustainable insulation materials made
from textile waste
Mohamed El Waznaa,b,⁎
, Mohamed El Fatihib
, Abdeslam El Bouaria
, Omar Cherkaouib
a
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
A R T I C L E I N F O
Keywords:
Textile waste
Building insulation
Energy efficiency
Needle punching technique
A B S T R A C T
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 prop-
erties. 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 950–1033 L/(m2
s) for wool samples. The de-
pendency 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 in-
creasing 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.
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 t of oil equivalent per capita, increases of 4.3%
each year. Regarding electricity, a Moroccan consumes 781 kW h an-
nually, which increases by 7.8% annually [1]. The building sector used
approximately 115 EJ globally, accounting for 32% of global final en-
ergy demand (24% for residential and 8% for commercial) and 30% of
energy-related CO2 emissions [2]. Also, it is responsible for approxi-
mately 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 com-
position. 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 eco-
logical considerations (energy and environmental issues) [6].
For this purpose, the textile wastes are proposed as thermal in-
sulation 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 re-
source 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-Sa 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
http://dx.doi.org/10.1016/j.jobe.2017.06.008
Received 30 January 2017; Received in revised form 7 June 2017; Accepted 7 June 2017
⁎
Corresponding author at: Laboratory REMTEX, Higher School of Textile and Clothing Industries, Km 8, Route d’EL JADIDA, Casablanca, Morocco.
E-mail address: elwazna-mohamed@hotmail.fr (M. El Wazna).
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
Journal of Building Engineering 12 (2017) 196–201
Available online 09 June 2017
2352-7102/ © 2017 Elsevier Ltd. All rights reserved.
MARK

3. this practice. Patnaik et al. [9], developed insulation nonwoven mate-
rial from wool and recycled polyester and studied their thermal,
acoustic properties and also their biodegradation behavior. The devel-
oped 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.
2. Materials and methods
2.1. Nonwoven preparation
Nonwoven fabrics were prepared by using needle punching tech-
nique using a DILO DI-LOOM 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 me-
chanical 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 Benguerir
region, Morocco. It is then washed and treated at the MOCARI Com-
pany. 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% hu-
midity and 20 ± 2 °C temperature.
2.2. 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
Fig. 1. List of the commercial insulation materials.
Fig. 2. Illustrations of the needling loom. Fig. 3. Illustrations of nonwoven made from textile waste: (a) A1, (b) A2, (c) W2, (d) W1.
M. El Wazna et al. Journal of Building Engineering 12 (2017) 196–201
197

4. thickness and mass per unit area.
2.3. 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]:
=ρ
Ma
t (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 ca-
pacities of a nonwoven [13]. Porosity ε is defined by the following
equation:
= − × =
⎛
⎝
⎜ −
⎞
⎠
⎟ ×α
ρ
ρ
1 100 1 100ε ( )
f (2)
where: α = packing density, ρ = nonwoven density, ρf = fiber or
polymer density.
Sample compositions and their physical properties are given in
Table 1.
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 4×/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 tem-
perature gradient. The guarded hot plate apparatus λ-Meter 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 one-dimensional thermal conduction
as follows:
= =
Q t
S
U I t
S
λ
ΔT ΔT
.
.
. .
. (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 in-
nermost 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:
=R
t
λ
th
(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:
=k
Q
S t. (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. 4A. Consequently, the structure of the needle-pun-
ched 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. 4B. This unique structure often has special properties such as
thermal insulation.
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 di-
mensions 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)). De-
spite the fact that the analyzed textile wastes showed thermal insulation
ability, it may be concluded that the wool samples may be more in-
teresting 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
Table 1
Sample compositions and their physical properties.
Sample Source of waste Thickness d (mm) Area weight (g/m2
) Bulk density ρ (kg/m3
) Porosity ɛ (%)
A1 Spinning process 30 ( ± 0.8) 750 ( ± 20) 25 97.8
A2 knitting process 30 ( ± 0.7) 900 ( ± 15) 30 97.4
W1 Washed and treated raw wool 30 ( ± 0.5) 1860 ( ± 10) 62 95.2
W2 Carpet waste 30 ( ± 0.7) 1350 ( ± 15) 45 96.5
Values in the parenthesis indicate the standard deviation.
M. El Wazna et al. Journal of Building Engineering 12 (2017) 196–201
198

5. measured values of the thermal conductivity and thickness according to
the Eq. (4). The highest value is observed for the wool sample W2 (RW2
= 0.88 m2
K/W).
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. There-
fore, 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
25–30 kg/m3
for the acrylic samples respectively, and from 0.0339 to
0.0348 W/(m K) for densities of 45–62 kg/m3
for the wool sample re-
spectively. These results are explained by the inverse relationship be-
tween density and porosity. Therefore, density might not be an im-
portant parameter as it can be replaced by porosity.
Fig. 4. Horizontal sections of nonwoven fabric using optical micrographs.
Table 2
Thermal and physical properties of nonwoven fabric.
Sample Thermal conductivity
W/ (m K)
Thermal
resistance (m2
K)/
W
Air permeability L/
(m2
s)
A1 0.0350 0.85 600
A2 0.0355 0.84 616
W1 0.0348 0.86 1033
W2 0.0339 0.88 950
Table 3
The thermal properties of nonwoven fabric and other insulators.
Materials Bulk density ρ
(kg/m3
)
Thermal conductivity W/
(m K)
Normalized thermal conductivity
λ ρ/ × 10−3
10 °C 25 °C 10 °C 25 °C
Developed products 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
Conventional insulations materials
(Manufacturers declared value)
Glass wool (GW) 24 0.0350 – 1.45 –
Mineral wool (MW) 36 0.0370 – 1.02 –
Extruded expanded
polystyrene (XPS)
15 0.0380 – 2.53 –
Fig. 5. The dependency of the thermal conductivity λ and air permeability k on the
porosity ɛ.
M. El Wazna et al. Journal of Building Engineering 12 (2017) 196–201
199

6. 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 ac-
cording 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. Ac-
cording 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 in-
crease 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 va-
lues 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 and 0.0326 W/(m K) much lower than the conventional in-
sulation 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 in-
sulation 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 con-
ductivity 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 ob-
served for the XPS and GW samples because of their lower density,
contrary to the wool sample. For acrylic samples they showed sa-
tisfactory 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 ac-
rylic samples density is lower and λ value is higher. The best value in
terms of density and thermal conductivity values is attributed to XPS.
4. Conclusion
Thermal insulation is a key element in the building sector, it mini-
mizes 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 per-
formance. 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
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.
M. El Wazna et al. Journal of Building Engineering 12 (2017) 196–201
200

7. investigated, the anisotropic structure, the random distribution of the
fibers and the width, the shape and tortuosity of the conductive chan-
nels 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.
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M. El Wazna et al. Journal of Building Engineering 12 (2017) 196–201
201
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