**5. Formulation for textile thermoregulation**

In recent years, phase-change materials have generated particular interest in thermal energy storage. The advantage of using latent heat storage lies in the possibility of optimizing the thermal windows of use (or "activation") by the judicious choice of materials based on both temperatures and phase transformation enthalpies. The action of PCMs incorporated in textile composites is "temporary" or "transient," that is, it is effective as a barrier to thermal energy until all latent heat stabilizing the exchange temperature is absorbed or released during the phase change of the material. Thus, by choosing a PCM formulation adapted to exchanges, thermal energy can be stored or released, and can effectively be "recharged" by heat or cold source. Among the existing PCMs, we have chosen to work with paraffin, or n-alkanes, which are ideal candidates for latent heat thermal energy storage due to their thermal characteristics with phase change enthalpies in the order of 200 J g<sup>−</sup><sup>1</sup> and phase transition temperatures varying according to their number of carbon atoms in the molecules (**Table 1**).

The objective of this part is first to identify potential candidates from among all present n-alkanes likely to be suitable for textile thermoregulation, then to develop a formulation by binary mixing, by determining thermo-physical properties and by energy characterizations by differential enthalpy analyses.

#### **5.1 Choice of materials: enthalpy analysis of pure substances**

The thermal characteristics of the selected n-alkanes (n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, and n-eicosane) were studied by differential calorimetry using the computer-controlled TA Instrument type DSC 2920 apparatus using the TA Advantage control software. The analyses are carried out under nitrogen flow with a flow rate of 50 ml min<sup>−</sup><sup>1</sup> . The samples, with a mass of about 4.0 ± 0.1 mg, are placed in an aluminum crucible, closed by a cover on which two holes have been made to ensure the chemical inertia of the medium.

#### *5.1.1 The even n-alkanes*

The thermograms of n-hexadecane (**Figure 6**) and octadecane (**Figure 7**), during a fusion-crystallization cycle, are characterized by an endothermic peak during the heating and transition from triclinic to liquid structure and an exothermic peak during the cooling (liquid to triclinic).

The enthalpies and phase change temperatures measured are in accordance with those found in the literature. In both cases, it is also observed that the melting peak is always preceded by a slight deviation from the baseline a few degrees before the melting, due to the existence of pre-melting phenomena.

The case of n-eicosane is different. Although the 2°C min<sup>−</sup><sup>1</sup> cycles initially allowed us to measure enthalpies and phase change temperatures similar to those cited in the tables, the exothermic peak raised some questions. Indeed, the thermogram (**Figure 8(a)**) shows that this compound does not have any polymorphism during the temperature rise while the cooling presents a cluster of peaks that deconvolves into two distinct peaks during a cycle at 0.5°C min<sup>−</sup><sup>1</sup> (**Figure 8(b)**). We observe the liquid/a-Rotator II/triclinic transitions. The existence of this

**81**

**Figure 6.**

**Table 1.**

imposed on the sample.

*Heating and cooling curves of n-hexadecane (N2, 2°C min<sup>−</sup><sup>1</sup>*

rotating structure varies between 30 and 34°C, depending on the number of cycles

analyzed under the same conditions [39]. The existence of this phase was not observed when the temperature increased. To observe it, it would have been necessary to raise the temperature after crystallization and before the solid-solid phase

During his work, Espeau also noticed this type of variation for different samples

*).*

*Phase Change Materials for Textile Application DOI: http://dx.doi.org/10.5772/intechopen.85028*

**n-alkane Carbone atoms Melting point (°C)** n-octacosane 28 61.4 n-heptacosane 27 59.0 n-hexacosane 26 56.4 n-pentacosane 25 53.7 n-tetracosane 24 50.9 n-tricosane 23 47.6 n-docosane 22 44.4 n-heneicosane 21 40.5 n-eicosane 20 36.8 n-nonadecane 19 32.1 n-octadecane 18 28.2 n-heptadecane 17 22.0 n-hexadecane 16 18.2 n-pentadecane 15 10.0 n-tetradecane 14 5.9 n-tridecane 13 −5.5

*Change in the melting temperature of n-alkanes as a function of the number of carbon atoms.*


*Phase Change Materials for Textile Application DOI: http://dx.doi.org/10.5772/intechopen.85028*

#### **Table 1.**

*Textile Industry and Environment*

initial cost of the products.

atoms in the molecules (**Table 1**).

*5.1.1 The even n-alkanes*

during the cooling (liquid to triclinic).

**5. Formulation for textile thermoregulation**

energy characterizations by differential enthalpy analyses.

under nitrogen flow with a flow rate of 50 ml min<sup>−</sup><sup>1</sup>

melting, due to the existence of pre-melting phenomena.

The case of n-eicosane is different. Although the 2°C min<sup>−</sup><sup>1</sup>

deconvolves into two distinct peaks during a cycle at 0.5°C min<sup>−</sup><sup>1</sup>

**5.1 Choice of materials: enthalpy analysis of pure substances**

choice of one family over another is generally a function of the application and the

In recent years, phase-change materials have generated particular interest in thermal energy storage. The advantage of using latent heat storage lies in the possibility of optimizing the thermal windows of use (or "activation") by the judicious choice of materials based on both temperatures and phase transformation enthalpies. The action of PCMs incorporated in textile composites is "temporary" or "transient," that is, it is effective as a barrier to thermal energy until all latent heat stabilizing the exchange temperature is absorbed or released during the phase change of the material. Thus, by choosing a PCM formulation adapted to exchanges, thermal energy can be stored or released, and can effectively be "recharged" by heat or cold source. Among the existing PCMs, we have chosen to work with paraffin, or n-alkanes, which are ideal candidates for latent heat thermal energy storage due to their thermal characteristics with phase change enthalpies in the order of 200 J

and phase transition temperatures varying according to their number of carbon

The objective of this part is first to identify potential candidates from among all present n-alkanes likely to be suitable for textile thermoregulation, then to develop a formulation by binary mixing, by determining thermo-physical properties and by

The thermal characteristics of the selected n-alkanes (n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, and n-eicosane) were studied by differential calorimetry using the computer-controlled TA Instrument type DSC 2920 apparatus using the TA Advantage control software. The analyses are carried out

about 4.0 ± 0.1 mg, are placed in an aluminum crucible, closed by a cover on which

The thermograms of n-hexadecane (**Figure 6**) and octadecane (**Figure 7**), during a fusion-crystallization cycle, are characterized by an endothermic peak during the heating and transition from triclinic to liquid structure and an exothermic peak

The enthalpies and phase change temperatures measured are in accordance with those found in the literature. In both cases, it is also observed that the melting peak is always preceded by a slight deviation from the baseline a few degrees before the

allowed us to measure enthalpies and phase change temperatures similar to those cited in the tables, the exothermic peak raised some questions. Indeed, the thermogram (**Figure 8(a)**) shows that this compound does not have any polymorphism during the temperature rise while the cooling presents a cluster of peaks that

We observe the liquid/a-Rotator II/triclinic transitions. The existence of this

two holes have been made to ensure the chemical inertia of the medium.

. The samples, with a mass of

cycles initially

(**Figure 8(b)**).

**80**

g<sup>−</sup><sup>1</sup>

*Change in the melting temperature of n-alkanes as a function of the number of carbon atoms.*

**Figure 6.** *Heating and cooling curves of n-hexadecane (N2, 2°C min<sup>−</sup><sup>1</sup> ).*

rotating structure varies between 30 and 34°C, depending on the number of cycles imposed on the sample.

During his work, Espeau also noticed this type of variation for different samples analyzed under the same conditions [39]. The existence of this phase was not observed when the temperature increased. To observe it, it would have been necessary to raise the temperature after crystallization and before the solid-solid phase

**Figure 7.** *Heating and cooling curves of n-octadecane (N2, 2°C min<sup>−</sup><sup>1</sup> ).*

**Figure 8.** *Heating and cooling curves of n-eicosane (N2, 2°C min<sup>−</sup><sup>1</sup> (a) and 0.5°C min<sup>−</sup><sup>1</sup> (b)).*

change. The solid-solid transition enthalpy is slightly lower than that measured by Espeau. This difference can be blamed on the measuring instrument. Indeed, it was noted that whatever the temperature ramp imposed for this type of paraffin, the DSC did not keep its set point during the phase change. This phenomenon can be minimized by reducing the mass of the sample, but can still be observed for a ramp of 0.5°C min<sup>−</sup><sup>1</sup> and a mass of about 1 mg.
