The work of Zach et al. [5] explains the necessity for the authors to study sheep wool as a bio-sourced material with good thermal properties in order to improve comfort in buildings and reduce carbon emissions. The work of Zach et al. [5] responded to the demand for increasing ecological materials by supporting research and publications on alternative materials in which they specify the thermal and acoustic properties of sheep wool and conclude that sheep wool has comparable characteristics with conventional materials. This work contributes to the same logic for authors to contribute to the valuation of alternative materials in construction, such as sheep wool, for the purpose of reducing pollution and improving the ambiance of buildings.

In addition, Tiza et al. [6] assessed the role of bamboo and sheep wool fiber on sustainability in construction in order to save energy and use those materials in the industry. The authors described the characteristics of bamboo in terms of species, mechanical, biological, and moisture aspects: it has a tensile strength of up to 370 N·mm⁻², production energy lower than steel, and energy 50 times lower than steel in its industrialization. By analyzing this work, we tried to study the traditional biological treatment of sheep wool and the moisture aspect of the bio-sourced material, sheep wool, to analyze its characteristics compared to other alternative materials. Ghermezgoli et al. [7] studied the thermal and acoustical properties of samples of wool fabrics. Results indicate that fabrics made from wool fiber show interesting properties compared to mineral wool with less impact on the environment, which pushes the authors of our work to study the thermal characterization and energy efficiency of sheep wool to compare its physical characteristics with other industrial materials. Meanwhile, Dénes et al. [8] assessed the properties of sheep wool in the reinforcement of concrete compared to materials such as polypropylene and polyacrylonitrile. Results indicate that the performance of wool fibers is less than that of polypropylene; however, it can replace hydrocarbon-based products, with wool yielding carbon between 16% and 25% after being treated, stabilized at 160°C for 10 min in the presence of air, and carbonized at 800°C in an atmosphere containing nitrogen. By analyzing this work, the authors of this paper confirm the necessity of studying the material sheep wool as an insulating building material that has similar properties as other industrial ones.

The work of Mounir et al. [9] studied the thermal characterization and thermal inertia of the composite clay-wool and revealed the important effect of wool combined with clay in terms of thermal inertia parameters: damping factor, delay of temperature, and heat flow. They also estimated the low carbon impact of the clay-wool on the environment. This work proves the utility of studying wool as an insulating building material that possesses good thermal inertia. Maaloufa et al. [10] also investigated the mechanical characteristics and the effect of insulating materials such as fiber on improving the flexure strength of composites. The work of Alyousef et al. [11] studied the management of wool waste as an element integrated with concrete as a cheap material. For this goal, the authors investigated the mechanical and microstructural properties of eight samples mixed with four kinds of concrete. Results indicated that the incorporation of wool fiber in concrete decreased the compressive strength; however, the tensile and flexural strength values of the concrete improved. Also, the microstructural characteristics of sheep wool fiber reinforced concrete were found to have good bonding and low voids. The work of Mounir et al. [9] and Alyoussef et al. [11] proves the excellent mechanical properties of sheep wool in improving flexural strength, not only in terms of thermal properties but also in terms of mechanical characteristics. The work of Parlato et al. [12] studied the possibility of valuing sheep wool as an insulation material by developing a chain product industry in Italy; they studied the correct scale required for sustainable production of sheep wool insulation products. Our work contributes to the same context of promoting the use of sheep wool in industry as an eco-friendly material with excellent thermal properties.

The use of fibers as additives with the main matrix improves the insulating properties of materials, as the research of Zormati et al. [13] analyzed the effect of using cellulose nanofibers as an admixture in cement mortars. The authors investigated the physical properties of the new composite as the thermal conductivity, and they found a value between 0.95 and 2.25 (W·m⁻¹·K⁻¹). This finding encourages the authors of this research to investigate the insulating properties of sheep wool as a fiber.

Management of waste is the only way to reduce pollution and obtain a clean environment, as the work of Alsamaraie et al. [14] assessed the benefit of using feather as an insulating material due to its low thermal conductivity ranges from 0.024 to 0.034 (W·m⁻¹·K⁻¹), its low density of 0.68 g.cm⁻³, and its chemical composition and microstructure of trap air, which produce a good barrier. According to those properties, the feather can be used as an effective thermal and acoustic insulation material even if its use presents some limitations, such as the restriction by the U.K. to use this material, its biodegradation decomposes, and the fire resistance of the thermal insulation, which is a crucial concern. The work of Aloulou et al. [15] investigated the influence of nanofiber wood as an industrial waste on the properties of fresh cement mortar. Results showed that the compressive strength increased by more than 50% and the thermal conductivity decreased by adding 1% of nanofiber wood. Those findings can be explained by the modification of the chemical composition of the cement mortar by reducing the quantity of water and minimizing the pores. Also, it is observed that the hydration of cement increased due to the introduction of nanofiber wood, which contains calcium silicate gel and portlandite. Abdulmunem et al. [16] assessed the role of adding palm oil as a sustainable and passive cooling material for lithium batteries because when the ion lithium battery temperature increases, the power produced decreases. Palm fatty acid distillate (PFEA) was chosen as a Phase Change Material (PCM) to contribute to the reduction of LIB cells temperature and the increase of cells’ electrical power. Abdulmunem et al. [17] revealed that feather waste can be used with phase change material as insulation because it delivers excellent thermal and acoustic insulation, and by doing so, the cooling load and the electricity cost decreased. The authors developed a new bio-composite material based on PCM and feather waste (WCF) within polyvinyl chloride panels. Results indicate that the integration of WCF by a ratio of 75% improved the acoustic insulation by 9%, reduced the cooling load by 20.3%, and increased by 22.5% the electricity cost savings for the testing room located in Baghdad city. According to those studies, the authors of this research tried to manage the waste of sheep wool as an insulating material in buildings due to the interesting properties of additives and the improvement of thermal and mechanical properties of materials.

The research gap and objectives of this study are to promote the use of sheep wool in rural and urban areas by proposing an ecological treatment using Silini Folgariss and Camphor. The results of this treatment were determined by the method of aerobic mesophilic flora. Also, this research gives a clear idea about the thermal properties of this material by determining the thermal conductivity, which shows the power of insulating buildings, and investigating the thermal diffusivity to give a clear idea about the thermal inertia behavior of this bio-sourced material. Moreover, this work assesses the hygrothermal behavior of sheep wool in different forms compacted and expanded in both winter and summer, which permits understanding the behavior of this material toward humidity. Furthermore, the research studied the energy efficiency of this material used in buildings by evaluating the thermal transmittance and cooling needs during a year in dry climates. Finally, the research contributes to the management of sheep wool waste by proposing to use it as an insulating material in buildings treated ecologically.

The method of treating sheep wool was described below:

Washing sheep wool with Silini Folgariss traditional material;

The wool used was taken from the sheep, as shown in Fig. 1, and treated with Silini Folgariss, as illustrated in Fig. 2 and camphor. The diameter of sheep wool studied is described in paragraph 3.6 before and after treatment; however, the length is between 3.5 and 6.5 cm. Sheep wool has important thermal and environmental characteristics. It has a low density of 20 kg.m⁻³. Its thermal performance was characterized, and Fig. 1 shows the sample studied.

The camphor studied as shown in Fig. 3 is a traditional composite, which is a solid bicyclic organic composite taken from the camphor tree; its natural aspect is shown in Fig. 3. Its chemical formula is C₆H₁₆O. It is found in many plants [18], such as in the wood of the camphor laurel (Cinnamomum camphora), a large evergreen tree found in Asia, and also in the unrelated Kapur tree, which is a tall timber tree from the same region. It also occurs in some other related trees in the laurel family, notably Ocotea usambarensis, and in the oil rosemary leaves. The mint family contains 10% to 20% camphor, while camphorweed (Heterotheca) only contains 5%. Camphor can also be synthetically produced from the oil of turpentine. Tables 1–3 show the chemical components of the materials, respectively, sheep wool, camphor, and silini folgariss.

Wool is continuously exposed to contamination by microorganisms of all kinds (pathogenic or not, as well as bacteria and fungi), which are able to multiply rapidly under favorable conditions (moisture). This leads to a loss of resistance or other forms of degradation in wool fibers. In order to use this natural material in construction, we tested a traditional treatment (Silini Folgariss and camphor) to eliminate these microorganisms.

The hot wire method was used to characterize the thermal conductivity of sheep wool [20–22], as illustrated in Fig. 6. Eqs. (1)–(10) describe the principle of this method.

(1) ∂2T∂r2+1r∂T∂xR=1a∂T∂t    

(2) T(x,0)=Ts(0)=Ti  

(3) T(∞,t)=Ti       

(4) h[Ts(t)−T(0,t)]=−λ∂T(0,t)∂r 

(5) φ0=mcdTsdt+hS[Ts(t)−T(0,t)]    

To determine the resolution of the heat in Eq. (1) based on the initial and limit conditions in Eqs. (2) and (3) of this system using the quadrupole method, we write the formula of the Laplace transform T_s(t) in this way, as represented in Eq. (6).(6) θS=φ0pA0+(A0Rc+B0)/ZC0+(C0Rc+D0)/Z     (7) While   A0=1;   B=12πλLqr0I0 (qr0)I(qr0)−1ρcsπr02Lp C0=ρcsπr02Lp   D0=qr02I0(qr0)I1(qr0) (8) 1Z=2πλLqrK1(qr0)K0(qr0)           

where

Θs is the Laplace transform of the difference T_s(t) − T_s(t = 0)

Θ is the Laplace transform of the difference T(t) − T(t = 0)

R_c the resistance of contact in the interface heating element/sample

C_S: heat capacity of thermocouple-resistance

λ: thermal conductivity of the sample

a: thermal diffusivity of the sample

P: Laplace variable

r₀: radius of hot wire element

L: Length of the hot wire

ϕ₀: dissipated power in the heating element

I₀, I₁, K₀, K₁: Bessel Functions

If we consider a thin wire (r₀ small) and if we are in the long time ( p→0) (we can use the limit development of Bessel functions near zero), we have:(9) K(x)=ln(x);K1(x)=1/x;I0(x)=1I1(x)=x/2 (10) Which lead A0=1 B0=0C0=ρCsπr02LpD0=11Z=2πλLln(qr0) (11) θs=φ0pZ+Rcmscsp(Rc+Z)+1=φ0p(Z+Rc)=φ0p(ln(r0pa)2πλL+Rc)=φ0P(−ln(p)4πλL−ln(r0a)4πλL+Rc)

Using Laplace transform inverse, we calculate the temperature T_s(t) in the length time as shown in Eq. (12).(12) Ts(t)−Ts(0)=φ04πλLln⁡(t)+Rcφ0−γφ04πλL−φ0ln(r0a)2πλL

where γ = 0.57721 is the constant of Euler.(13) T(t)−T(0)=φ04πλLln⁡(t)+φ0[Rc−ln(r0a)2πλL+γ4πλL]

The drawing function Ts (t) − Ts (0) in function of ln(t) is a linear curve of slope φ04πλL . When we determine this slope, we can calculate the thermal conductivity.

A simulation study concerning the cooling needs during a year has been done using the tool TRNSYS, which evaluates the cooling needs in each hour during the year. The building studied is a simple ground floor with 60 m² located in Marrakech, a city with arid weather. The building contains one floor composed of four double glazing windows built with full brick, whose characteristics are λ = 0.19 (W·m⁻¹·K⁻¹); C = 0.794 (KJ·K⁻¹); and ρ = 1700 (kg·m⁻³). The software TRNSYS permits the evaluation of cooling needs for each hour during a year.

By counting the microbial load of the wool, it is possible to establish the link between the presence and absence of microorganisms and the effect of washing with tighecht and camphor treatment. The results obtained are shown in Table 4.

According to Table 4, the authors observe that concerning the method of aerobic mesophilic flora, the raw wool contains 18.10⁵ (UFC·g⁻¹); however, by the treatment of Tighecht, this value decreased to 12.10⁴ (UFC·g⁻¹), which represents a decrease of 93%; nonetheless, using Tighecht and camphor, the value of microorganisms decreased to 8.10⁴ (UFC·g⁻¹), which represents a decrease of 95.5% compared to the raw materials. The study of the percentage of yeast and mildew in sheep wool indicates that the raw wool contains 38.10² (UFC·g⁻¹), but when the authors used the treatment Tighecht, this value decreased to 6.10² (UFC·g⁻¹), which represents a decrease of 84% of yeast and mildew, and finally, by adding Tighecht and camphor, this value decreased to 2.10² (UFC·g⁻¹) of yeast and mildew responsible for the degradation of wool, which represents a decrease of 94.73%. The analysis of those results proves the efficiency of this natural treatment to eliminate microorganisms from the sheep’s wool. The authors conclude that the studied treatment of wool facilitates the building sector’s use of a natural and ecological insulating material, sheep wool, in construction.

The analysis of the fluorescence method as illustrated in Tables 1–3 proves that sheep wool is composed of carbon and oxygen in the majority of elements as an organic material; however, camphor is composed of CaO and SO₃ as illustrated in Table 2, while silina folgariss is composed of oxygen, carbon, and a small percentage of calcium and silicon, which does not exceed 1%.

The plot of Ts(t) – Ts(t=0) in function of ln(t) is a linear curve with a slope φ04πλ L . By determining this value, the authors deduce the thermal conductivity of sheep’s wool.

λ = 0.05 W·m⁻¹· K⁻¹ ± 0.01

λ = 0.046 W·m⁻¹·K⁻¹ ± 0.01

Results of thermal conductivity were presented according to Figs. 8 and 9 using the hot wire method. The authors observe that the thermal conductivity for the first experiment, according to Fig. 8, is 0.05 (W·m⁻¹·K⁻¹); however, concerning the second experiment, Fig. 9, the authors remark that the value of thermal conductivity is 0.046 (W·m⁻¹·K⁻¹).

a (Degiovanni) = 1.25.10⁻⁰⁶ m²·s⁻¹

a (Parker) = 1.57.10⁻⁰⁶ m²·s⁻¹

a (Complete) = 1.55.10⁻⁰⁶ m²·s⁻¹ ± 0.02

The thermal diffusivity was evaluated using the complete model, and the authors found a value of 1.5580.10⁻⁰⁶ m².s⁻¹, which is confirmed by the Degiovanni and Parker models as shown in Fig. 10.

The results obtained were compared to the work of Zach et al. [5] and the work of Pennacchio et al. [2], the work of Jerman et al. [26] as represented in Table 5, which seems to be comparable to those works at an ambient temperature of 20°C.

Tables 6 and 7 represent the results of measuring humid sheep wool samples in the summer season. The temperature is 30°C, and the authors observe that the combed sheep wool sample loses humidity more quickly than the compacted sample; the total weight lost is 26 g over three days.

The authors observed, according to Figs. 11 and 12, that the combed sheep wool sample loses weight more quickly than the compacted sample in a total weight of both samples of 26 g, and the combed or expanded sheep wool always loses 1 g of water more than the compacted sheep wool in a period of three days during the summer.

Tables 8 and 9 represent the results of measuring humid sheep wool samples in the winter season, when the temperature is 18°C. The authors observe, according to Figs. 13 and 14, that the combed sheep wool sample loses humidity more quickly than the compacted one, and the total weight lost is 26 g during six days.

The authors studied the microstructure of the sheep wool fiber before and after treatment to see the effect of the treatment used on its diameter. Figs. 15 and 16 show the morphology of the fiber before and after treatment. According to Fig. 15, the diameter of sheep’s wool that is not treated is between 52.612 and 25.816 μm, and the length is between 3.5 and 6.5 cm. However, the diameter of sheep’s wool after treatment represented in Fig. 16 is between 30.479 and 18.963 μm, and the length is between 3.5 and 6.5 cm, which means that the ecological treatment used reduces the diameter of sheep’s wool because it eliminates the deposits of the lipid layer on the surface of the cortex. The results obtained have been confirmed by the literature concerning the work of Alyoussef et al. [27] and Moore et al. [28], which proves the efficiency of the ecological treatment used instead of the chemical treatments used by other researchers.