**3. Prominent assessed features of fibrous composites**

From the obtained images it was clearly distinguished the hexagonal shape of ZnO agglom‐ erations and the morphology of linen fibres (Fig.2c).

Zinc Oxide — Linen Fibrous Composites: Morphological, Structural, Chemical, Humidity Adsorptive and Thermal Barrier Attributes http://dx.doi.org/10.5772/55705 27

**Figure 2.** SEM images of: reference samples and of the functionalized linen support with MCT- β –CD sample [10]

**Figure 3.** images of some textile composites [10]

senting the amorphous region of the material in cellulose fibres [26-28]. *I020* represents both

100(%) *am*

A *shape factor* is used in x-ray diffraction to correlate the size of sub-micrometre particles, or crystallites, in a solid to the broadening of a peak in a diffraction pattern. In the Scherrer

where *K* is the shape factor, λ is the x-ray wavelength, β is the line broadening at half the maximum intensity (FWHM) in radians, and θ is the Bragg angle [29]. τ is the mean size of the ordered (crystalline) domains, which may be smaller or equal to the grain size. The dimen‐ sionless shape factor has a typical value of about 0.9, but varies with the actual shape of the

FTIR was used to examine changes in the molecular structures of the samples. Analysis has been recorded on a FTIR JASCO 660+ spectrometer. The analysis of studied samples was performed at 2 cm-1 resolution in transmission mode. Typically, 64 scans were signal averaged

domain of relative humidity (RH) 0-90% has been investigated by using an IGAsorp apparatus, a fully automated gravimetric analyzer, supplied by Hiden Analytical, Warrington - UK). It is a standard sorption equipment, which has a sensitive microbalance (resolution 1μg and capacity 200 mg), which continuously registers the weight of the sample in terms of relative humidity change, at a temperature kept constant by means of a thermostatically controlled

To study water sorption at atmospheric pressure, a humidified stream of gas is passed over

The differential scanning calorimetry analysis (DSC) of fibrous supports - ZnO composites were carried out using a NETZSCH DSC 200 F3 MAIA instrument under nitrogen. Initial sample weight was set as 30-50 mg for each operation. The specimen was heated from room

From the obtained images it was clearly distinguished the hexagonal shape of ZnO agglom‐

For the studied samples dynamic vapours sorption (DVS) capacity, at 25o

water bath. The measuring system is controlled by appropriate software.

**3. Prominent assessed features of fibrous composites**

temperature to 350°C at a heating rate of 10°C/min.

erations and the morphology of linen fibres (Fig.2c).


C averaging in the

crystalline and amorphous materials while *Iam* represents the amorphous material.

020 020

*I I I x I*

*C*

equation,

26 Modern Surface Engineering Treatments

*<sup>τ</sup>* <sup>=</sup> *<sup>K</sup>* •*<sup>λ</sup> β*cos*θ*

crystallite.

the sample.

to reduce spectral noise.

The SEM images of functionalized linen supports coated with ZnO with assistance of the studied surfactants (Fig 3 a and b) indicate different shapes of deposited ZnO.

**3.1. Mechanistic aspect of nanoparticle formation**

coarser after the treatment.

roughness.

crystallinity.

ZnO–CMC nanoparticles in a further step.

The shape and the manner of covering depend of linen grafting agent assistance. This result is correlated with the high number of coordinating functional groups (hydroxyl and glucoside groups) of the MCT-β-CD which can form complexes with divalent metal ions [15]. During the synthesis time, it might be possible that the majority of the zinc ions were closely associated with the MCT-β-CD molecules. Based on the previous research, it can be claimed that nucle‐ ation and initial crystal growth of ZnO may preferentially occur on MCT-β-CD [16]. Moreover, as polysaccharide, MCT-β-CD showed interesting dynamic supramolecular associations facilitated by inter- and intra-molecular hydrogen bonding, which could act as matrices for nanoparticle growth in size of about 30–40 nm. They aggregated to irregular ZnO–CMC nanoparticles in a further step (Figures 4a) and 4 b). In these figures, SEM images of linen supports coated with ZnO with assistance of the two surfactants show that the nanoparticles exhibited an approximately lamellar morphology and the particles can be seen to be coated on the fibrous support surface (yarn). As result, the fibrous supports (yarns) surface became

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In the case of CTAB assistance, on the yarns surfaces large ZnO particles, covering the yarn as a bark are noticeable (Fig. 3b), involving that the large particles may be formed via precipitation followed by a step-like aggregation process. In addition, according to the SEM images of the coated fabric, the uniformity of the fabric coated with ZnO powder hydrothermally synthe‐ sized with assistance of CTAB (Cetyl trimethylammonium bromide) is better than that of ZnO powder hydrothermally synthesized in the presence of Pluronic P123 and possesses good washing fastness. The last one has not been measured, but it has *apriori* been evaluated. This phenomenon can be explained by the fact that the repeated cycles of washing and rinsing did not conduct to the washing away of the ZnO particles; subsequently the zinc oxide proven a low extent of washing fastness. This statement is also in a good correlation with the XRD results, claiming a slight shift of ZnO intensity peaks, meaning that the nucleation of the zinc oxide occurred not only the support surface, but also within the nanocavities, due the fibers

In case of ZnO powder hydrothermally synthesized without any surfactant assistance, the coating particles fell off easily after washing, which might have been caused by the weak attaching force (coordinated bond between ZnO and linen) induced by the deteriorated

The SEM image of functionalized fabric support show very clearly the individual yarns, having diameters of about 10-20 μm, covered by various ZnO aggregates (Fig.4). MCT-β-CD can form complexes with divalent metal ions, due to its high number of coordinating functional groups (hydroxyl and glucoside groups) [31]. There is a possibility that the majority of the zinc ions were closely associated with the MCT-β-CD molecules. Based on the previous research, it can be claimed that nucleation and initial crystal growth of ZnO may preferentially occur on MCTβ-CD [32]. Moreover, as polysaccharide, MCT-β-CD showed interesting dynamic supramo‐ lecular associations facilitated by inter- and intra-molecular hydrogen bonding, which could act as matrices for nanoparticle growth in size of about 30–40 nm. They aggregated to irregular

On the other hand, ZnO nanoparticles exhibited hexagonal form like flowers of ZnO nano‐ crystals, if the treatment was assisted by P123 surfactant (Fig. 3 a) and lamellar morphology if the treatment was assisted by CTAB (Fig. 3 b) respectively.

The particles uniformly cover the fibrous support surface and as results, the fibrous supports surface became coarser after the treatment.

The adhesion strength of ZnO particles on fibrous support is different in terms of the applied surfactant treatment and was tested after repeated washing cycles (1 minute ten times).

**Figure 4.** SEM images of some textile composites after repeated washing cycles [10]

According to the SEM images (Fig 4 a and b), the adhesion strength of ZnO powder hydro‐ thermally deposited onto functionalized linen fibrous support is superior in the case of functionalized surface (Fig 4 b) compared with the non-functionalized surface (Fig 4a). The functionalization advantage has been evaluated considering the durability of ZnO on the support surface after repeated cycles of washing. After washing the coating particles fell off easily for the ZnO powder hydrothermally synthesized without functionalization, which might have been caused by the weak attaching force.

As shown in Fig. 4, before treatment the diameters of fibrous supports (individual yarns) are about 10 - 20 μm; after treatment SEM image show very clearly the individual yarns, covered by various ZnO aggregates deposition.

### **3.1. Mechanistic aspect of nanoparticle formation**

The SEM images of functionalized linen supports coated with ZnO with assistance of the

On the other hand, ZnO nanoparticles exhibited hexagonal form like flowers of ZnO nano‐ crystals, if the treatment was assisted by P123 surfactant (Fig. 3 a) and lamellar morphology if

The particles uniformly cover the fibrous support surface and as results, the fibrous supports

The adhesion strength of ZnO particles on fibrous support is different in terms of the applied surfactant treatment and was tested after repeated washing cycles (1 minute ten times).

**(a) (x1200) (b) (x5000)** 

According to the SEM images (Fig 4 a and b), the adhesion strength of ZnO powder hydro‐ thermally deposited onto functionalized linen fibrous support is superior in the case of functionalized surface (Fig 4 b) compared with the non-functionalized surface (Fig 4a). The functionalization advantage has been evaluated considering the durability of ZnO on the support surface after repeated cycles of washing. After washing the coating particles fell off easily for the ZnO powder hydrothermally synthesized without functionalization, which

As shown in Fig. 4, before treatment the diameters of fibrous supports (individual yarns) are about 10 - 20 μm; after treatment SEM image show very clearly the individual yarns, covered

 **sample 3 sample 6**

**Figure 4.** SEM images of some textile composites after repeated washing cycles [10]

might have been caused by the weak attaching force.

by various ZnO aggregates deposition.

studied surfactants (Fig 3 a and b) indicate different shapes of deposited ZnO.

the treatment was assisted by CTAB (Fig. 3 b) respectively.

surface became coarser after the treatment.

28 Modern Surface Engineering Treatments

The shape and the manner of covering depend of linen grafting agent assistance. This result is correlated with the high number of coordinating functional groups (hydroxyl and glucoside groups) of the MCT-β-CD which can form complexes with divalent metal ions [15]. During the synthesis time, it might be possible that the majority of the zinc ions were closely associated with the MCT-β-CD molecules. Based on the previous research, it can be claimed that nucle‐ ation and initial crystal growth of ZnO may preferentially occur on MCT-β-CD [16]. Moreover, as polysaccharide, MCT-β-CD showed interesting dynamic supramolecular associations facilitated by inter- and intra-molecular hydrogen bonding, which could act as matrices for nanoparticle growth in size of about 30–40 nm. They aggregated to irregular ZnO–CMC nanoparticles in a further step (Figures 4a) and 4 b). In these figures, SEM images of linen supports coated with ZnO with assistance of the two surfactants show that the nanoparticles exhibited an approximately lamellar morphology and the particles can be seen to be coated on the fibrous support surface (yarn). As result, the fibrous supports (yarns) surface became coarser after the treatment.

In the case of CTAB assistance, on the yarns surfaces large ZnO particles, covering the yarn as a bark are noticeable (Fig. 3b), involving that the large particles may be formed via precipitation followed by a step-like aggregation process. In addition, according to the SEM images of the coated fabric, the uniformity of the fabric coated with ZnO powder hydrothermally synthe‐ sized with assistance of CTAB (Cetyl trimethylammonium bromide) is better than that of ZnO powder hydrothermally synthesized in the presence of Pluronic P123 and possesses good washing fastness. The last one has not been measured, but it has *apriori* been evaluated. This phenomenon can be explained by the fact that the repeated cycles of washing and rinsing did not conduct to the washing away of the ZnO particles; subsequently the zinc oxide proven a low extent of washing fastness. This statement is also in a good correlation with the XRD results, claiming a slight shift of ZnO intensity peaks, meaning that the nucleation of the zinc oxide occurred not only the support surface, but also within the nanocavities, due the fibers roughness.

In case of ZnO powder hydrothermally synthesized without any surfactant assistance, the coating particles fell off easily after washing, which might have been caused by the weak attaching force (coordinated bond between ZnO and linen) induced by the deteriorated crystallinity.

The SEM image of functionalized fabric support show very clearly the individual yarns, having diameters of about 10-20 μm, covered by various ZnO aggregates (Fig.4). MCT-β-CD can form complexes with divalent metal ions, due to its high number of coordinating functional groups (hydroxyl and glucoside groups) [31]. There is a possibility that the majority of the zinc ions were closely associated with the MCT-β-CD molecules. Based on the previous research, it can be claimed that nucleation and initial crystal growth of ZnO may preferentially occur on MCTβ-CD [32]. Moreover, as polysaccharide, MCT-β-CD showed interesting dynamic supramo‐ lecular associations facilitated by inter- and intra-molecular hydrogen bonding, which could act as matrices for nanoparticle growth in size of about 30–40 nm. They aggregated to irregular ZnO–CMC nanoparticles in a further step.


**Table 2.** Surface composition from EDX measurements at sample 6

The composites patterns (sample 3-6) reveal both the presence of the peaks positions that matched well with those of the ZnO XRD pattern - lines (100), (002) and (101) - and the main peak of cellulose - linen (002) [34]. The small relative intensity of the peaks of the ZnO–linen composites is not well correlated with the EDX analysis, which showed a high content of deposited ZnO. The observed ZnO diffraction lines shift (samples 4 and 5) denotes the fact that the growth of the ZnO takes place not only on the support surface, but also inside the

**Figure 6.** Color online) XRD patterns of: Reference 2; Sample 4; Sample 5; Sample 6; Sample 7[10] The arrows indicate

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the peaks shift, in terms of working conditions. The height of the peaks has been multiplied by a 40 factor.

The intensities of the diffraction peaks decrease when the synthesis takes place with the assistance of the surfactant, that prevent crystal growth in these working conditions (Fig.6). In Fig. 7, the *FTIR spectrum* of hydrothermally synthesized, non-calcinated ZnO powder exhibited a high intensity broad band at about 430 cm\_1 due to the stretching of the zinc and

As shown in the FTIR spectrum of MCT-β-CD, the absorption bands between 1000 and 1200 cm-1 were characteristic of the – C –O– stretching on polysaccharide skeleton.A similar band was also observed in synthesized ZnO composites. And two peaks appeared at 1420 and 1610 cm-1 corresponding to the symmetrical and asymmetrical stretching vibrations of the carbox‐ ylate groups [35]. The peak at 2920 cm-1 was ascribed to C–H stretching associated with the ring methane hydrogen atoms. A broad band centered at 3450 cm-1 was attributed to a wide distribution of hydrogen-bonded hydroxyl groups. The FTIR spectra indicated that in ZnO– MCT-β-CD nanoparticles, there was the strong interaction, but no obvious formation of

*Water vapors sorption behavior.* Isothermal studies can be performed as a function of humidity (0-95%) in the temperature range 5° C to 85° C, with an accuracy of ± 1% for 0 - 90% RH and ±

nanocavities due to the fibers roughness.

covalent bonds between MCT-β-CD) and ZnO.

oxygen bond.

**Figure 5.** EDX analysis (sample 6) (Wt: weight percent, At: atomic percent). [10]

The outcome of the EDX elemental analysis for sample 6 illustrated in Figure 5 and Table 2, show that surface composition contain approximately 47% ZnO, meaning that ZnO phase represented almost half of the sample mass.

The X-ray diffraction patterns of samples 4-7 compared with reference 2 are represented in Fig. 6:

Figure 6 shows the selected-area diffraction pattern (2θ=20-40º) of the obtained samples. The obtained XRD pattern and indexed lines of ZnO (reference 2) are presented in Figure 6. According to the literature [33], all the diffraction lines are assigned to the wurtzite hexagonal phase structure.

Zinc Oxide — Linen Fibrous Composites: Morphological, Structural, Chemical, Humidity Adsorptive and Thermal Barrier Attributes http://dx.doi.org/10.5772/55705 31

**Table 2.** Surface composition from EDX measurements at sample 6

30 Modern Surface Engineering Treatments

**Figure 5.** EDX analysis (sample 6) (Wt: weight percent, At: atomic percent). [10]

represented almost half of the sample mass.

Fig. 6:

phase structure.

The outcome of the EDX elemental analysis for sample 6 illustrated in Figure 5 and Table 2, show that surface composition contain approximately 47% ZnO, meaning that ZnO phase

The X-ray diffraction patterns of samples 4-7 compared with reference 2 are represented in

Figure 6 shows the selected-area diffraction pattern (2θ=20-40º) of the obtained samples. The obtained XRD pattern and indexed lines of ZnO (reference 2) are presented in Figure 6. According to the literature [33], all the diffraction lines are assigned to the wurtzite hexagonal

**Figure 6.** Color online) XRD patterns of: Reference 2; Sample 4; Sample 5; Sample 6; Sample 7[10] The arrows indicate the peaks shift, in terms of working conditions. The height of the peaks has been multiplied by a 40 factor.

The composites patterns (sample 3-6) reveal both the presence of the peaks positions that matched well with those of the ZnO XRD pattern - lines (100), (002) and (101) - and the main peak of cellulose - linen (002) [34]. The small relative intensity of the peaks of the ZnO–linen composites is not well correlated with the EDX analysis, which showed a high content of deposited ZnO. The observed ZnO diffraction lines shift (samples 4 and 5) denotes the fact that the growth of the ZnO takes place not only on the support surface, but also inside the nanocavities due to the fibers roughness.

The intensities of the diffraction peaks decrease when the synthesis takes place with the assistance of the surfactant, that prevent crystal growth in these working conditions (Fig.6).

In Fig. 7, the *FTIR spectrum* of hydrothermally synthesized, non-calcinated ZnO powder exhibited a high intensity broad band at about 430 cm\_1 due to the stretching of the zinc and oxygen bond.

As shown in the FTIR spectrum of MCT-β-CD, the absorption bands between 1000 and 1200 cm-1 were characteristic of the – C –O– stretching on polysaccharide skeleton.A similar band was also observed in synthesized ZnO composites. And two peaks appeared at 1420 and 1610 cm-1 corresponding to the symmetrical and asymmetrical stretching vibrations of the carbox‐ ylate groups [35]. The peak at 2920 cm-1 was ascribed to C–H stretching associated with the ring methane hydrogen atoms. A broad band centered at 3450 cm-1 was attributed to a wide distribution of hydrogen-bonded hydroxyl groups. The FTIR spectra indicated that in ZnO– MCT-β-CD nanoparticles, there was the strong interaction, but no obvious formation of covalent bonds between MCT-β-CD) and ZnO.

*Water vapors sorption behavior.* Isothermal studies can be performed as a function of humidity (0-95%) in the temperature range 5° C to 85° C, with an accuracy of ± 1% for 0 - 90% RH and ±

**Figure 7.** a) FTIR of spectra of: sample 3; sample 5; Sample 6 ; sample 7; Reference 2 [10]

2% for 90 - 95% RH. The relative humidity (RH) is controlled by wet and dry nitrogen flows around the sample. The RH is held constant until equilibrium or until a given time is exceeded, before changing the RH to the next level.

One of the main objectives of this review was to stress the adsorptive attributes, taking into account the improving of ZnO synthesis conditions. Consequently, the role of P123 in the ZnO synthesis was to obtain a composite with a higher porosity, in order to achieve the surface hydrophilicity, since there is direct correlation between porosity and hydrophilicity [36].

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**Figure 8.** Comparative plots of rapid isotherms for water vapors sorption for the studied samples:

The shape of the moisture sorption isotherms for those two compounds is similar to those characteristic of mesoporous materials (type IV, according to IUPAC classification – with low sorption at low water vapor sorption (adsorption/desorption), moderate sorption at average humidity and rapidly increasing water sorption at high humidity). This type of isotherm describes the sorption behavior of hydrophilic material [37]. When a material is exposed to environmental water vapors, the water molecules firstly react with surface polar groups and

Based on the sorption studies, the IGAsorp software allows an evaluation of both monolayer

**ABET**

**BET analysis**

**(m2/g) Monolayer (g/g)**

and surface area value, by using BET (Brunauer-Emmett-Teller) model (Tabel 2).

Reference 1 11.89 157.010 0.044 Sample 6 14.93 213.99 0.060 Sample 5 18.89 321.39 0.091

**Table 3.** The main parameters of (water vapors) sorption-desorption isotherms for the studied samples

**(%d.b.)**

form a molecular monolayer.

Reference 1; Sample 5; Sample 6 [10]

**Sample Sorption capacity**

The vapours pressure in the sample room has been achieved by 10 steps of 10% humidity, each of them having a time of equilibrium setting between 10-20 minutes. At each phase, the weight adsorbed by the sample is measured by electromagnetic compensation between tare and sample, when the equilibrium is reached. Apparatus has an anti-condensation system for the cases that vapors pressure is very close/near to that of saturation. The cycle is finished by decreasing in steps of vapors pressure, in order to obtain desorption isotherms, as well.

Prior to measuring of sorption-desorption isotherms, drying of the samples is performed in nitrogen flow (250 mL/min) at 25°C, until the sample weight reached a constant value, at a relative humidity less than 1%.

The sorption/desorption isotherms recorded in these circumstances are shown in Fig.8.

The reference sample (the linen fibrous support – yarn - unfunctionalized) has a smaller sorption capacity compared to that of Sample 6 and Sample 5. High values of water vapors sorption capacity for the two last samples prove the fact that the material surface becomes more hydrophilic, more porous, respectively as it could be observed from hysteresis shape.

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#### Reference 1; Sample 5; Sample 6 [10]

2% for 90 - 95% RH. The relative humidity (RH) is controlled by wet and dry nitrogen flows around the sample. The RH is held constant until equilibrium or until a given time is exceeded,

**Figure 7.** a) FTIR of spectra of: sample 3; sample 5; Sample 6 ; sample 7; Reference 2 [10]

The vapours pressure in the sample room has been achieved by 10 steps of 10% humidity, each of them having a time of equilibrium setting between 10-20 minutes. At each phase, the weight adsorbed by the sample is measured by electromagnetic compensation between tare and sample, when the equilibrium is reached. Apparatus has an anti-condensation system for the cases that vapors pressure is very close/near to that of saturation. The cycle is finished by decreasing in steps of vapors pressure, in order to obtain desorption isotherms, as well.

Prior to measuring of sorption-desorption isotherms, drying of the samples is performed in nitrogen flow (250 mL/min) at 25°C, until the sample weight reached a constant value, at a

The reference sample (the linen fibrous support – yarn - unfunctionalized) has a smaller sorption capacity compared to that of Sample 6 and Sample 5. High values of water vapors sorption capacity for the two last samples prove the fact that the material surface becomes more hydrophilic, more porous, respectively as it could be observed from hysteresis shape.

The sorption/desorption isotherms recorded in these circumstances are shown in Fig.8.

before changing the RH to the next level.

32 Modern Surface Engineering Treatments

relative humidity less than 1%.

**Figure 8.** Comparative plots of rapid isotherms for water vapors sorption for the studied samples:

One of the main objectives of this review was to stress the adsorptive attributes, taking into account the improving of ZnO synthesis conditions. Consequently, the role of P123 in the ZnO synthesis was to obtain a composite with a higher porosity, in order to achieve the surface hydrophilicity, since there is direct correlation between porosity and hydrophilicity [36].

The shape of the moisture sorption isotherms for those two compounds is similar to those characteristic of mesoporous materials (type IV, according to IUPAC classification – with low sorption at low water vapor sorption (adsorption/desorption), moderate sorption at average humidity and rapidly increasing water sorption at high humidity). This type of isotherm describes the sorption behavior of hydrophilic material [37]. When a material is exposed to environmental water vapors, the water molecules firstly react with surface polar groups and form a molecular monolayer.

Based on the sorption studies, the IGAsorp software allows an evaluation of both monolayer and surface area value, by using BET (Brunauer-Emmett-Teller) model (Tabel 2).


**Table 3.** The main parameters of (water vapors) sorption-desorption isotherms for the studied samples

BET (1) equation is very often used for modeling of the sorption isotherms:

$$\mathcal{W} = \frac{\mathcal{W}\_m \cdot \mathbb{C} \cdot RH}{\left(1 - RH\right) \cdot \left(1 - RH + \mathbb{C} \cdot RH\right)}\tag{2}$$

where:

W- the weight of adsorbed water, Wm- the weight of water forming a monolayer, C – the sorption constant, *p/po=RH*- the relative humidity.

The sorption isotherms described by BET model up to a relative humidity of 40% are in relation to the sorption isotherm and material type. This method is mainly limited for II type isotherms, but can describe the isotherms of I, III and IV type [38-40], as well. The increasing water sorption is reflected both by the augmentation of monolayer and surface area values calculated with BET model (Tabel 3).

In Figure 8 the kinetic curves for humidity (water vapors) sorption/desorption processes for two of the samples are displayed. It is noticed that the time necessary for equilibrium setting for sorption processes is bigger than that of desorption. Sorption rate is smaller than that of desorption.

In Table 4 the dynamic moisture sorption capacity calculation was made using the equation written below, after the samples was kept at RH=90%, until the mass became constant:

$$\text{Sorption capacity at RH} = 90\% \text{ (\%)} = \frac{W\_{RH=90} - W\_{RH=0}}{W\_{RH=0}} \cdot 100\%$$

As can be observed the obtained values are larger than those in the isotherms, this demon‐ strates the time necessary for reaching the equilibrium sorption is longer.


From Table 5, it is noticeable the augmentation of temperature conducts to an increase on vapor sorption capacity of the sample (probably due to the hydrogen bonds formation favoring

Zinc Oxide — Linen Fibrous Composites: Morphological, Structural, Chemical, Humidity Adsorptive and Thermal

**Sample Sorption capacity**

Sample 5\_25 18.89 Sample 5\_35 31.59

**Figure 9.** Kinetic curves for sorption/desorption processes of water vapors in the studied samples

**Table 5.** Water vapor sorption capacity for sample 5 at both 25 °C and 35 °C respectively

**(%)**

**Reference 1** 

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35

**Sample 6** 

sorption).

Reference 1; Sample 6 [10]

**Table 4.** Water vapor sorption capacity and speed for a longer time (until sample weight remains constant at a relative humidity of 90%)

In case of sample 5, the DVS analysis were made at two temperatures (25 °C and 35 °C), and the influence of this parameter on the sorption/desorption isotherms and kinetics are presented in Figure 8 and Figure 9 respectivelly.

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Reference 1; Sample 6 [10]

BET (1) equation is very often used for modeling of the sorption isotherms:

sorption constant, *p/po=RH*- the relative humidity.

where:

BET model (Tabel 3).

34 Modern Surface Engineering Treatments

Sorption capacity at RH=90% (%) =

**Sample Weight at RH=0%**

relative humidity of 90%)

**(mg)**

in Figure 8 and Figure 9 respectivelly.

desorption.

(1 1 ) ( ) *<sup>W</sup> W C RH <sup>m</sup> RH RH C RH*

W- the weight of adsorbed water, Wm- the weight of water forming a monolayer, C – the

The sorption isotherms described by BET model up to a relative humidity of 40% are in relation to the sorption isotherm and material type. This method is mainly limited for II type isotherms, but can describe the isotherms of I, III and IV type [38-40], as well. The increasing water sorption is reflected both by the augmentation of monolayer and surface area values calculated with

In Figure 8 the kinetic curves for humidity (water vapors) sorption/desorption processes for two of the samples are displayed. It is noticed that the time necessary for equilibrium setting for sorption processes is bigger than that of desorption. Sorption rate is smaller than that of

In Table 4 the dynamic moisture sorption capacity calculation was made using the equation written below, after the samples was kept at RH=90%, until the mass became constant:

As can be observed the obtained values are larger than those in the isotherms, this demon‐

Reference 1 4.58 5.14 12.28 32 3.82 Sample 6 5.32 6.34 19.14 50 3.75 Sample 5 5.56 6.83 22.77 40 5.58

**Table 4.** Water vapor sorption capacity and speed for a longer time (until sample weight remains constant at a

In case of sample 5, the DVS analysis were made at two temperatures (25 °C and 35 °C), and the influence of this parameter on the sorption/desorption isotherms and kinetics are presented

⋅100

**Sorption dynamic capacity RH=90% (%)**

**Time (s)**

**Sorption rate (·10-3 %/s)**

*WRH* =90 −*WRH* =0 *WRH* =0

strates the time necessary for reaching the equilibrium sorption is longer.

**Weight at RH=90% (mg)**

× × <sup>=</sup> - ×- +× (2)

**Figure 9.** Kinetic curves for sorption/desorption processes of water vapors in the studied samples

From Table 5, it is noticeable the augmentation of temperature conducts to an increase on vapor sorption capacity of the sample (probably due to the hydrogen bonds formation favoring sorption).


**Table 5.** Water vapor sorption capacity for sample 5 at both 25 °C and 35 °C respectively

**Figure 10.** Comparative plots of rapid water vapors sorption/desorption isotherms for sample 5 [10] at both 25 °C and 35 °C respectively

The differences between sorption-desorption speeds of those two temperatures for Sample 5 indexed sample are clearly highlighted by the presence of modified hysteresis and also by the kinetics curves.

#### **3.2. Thermal degradation mechanism of linen fibrous supports treated with ZnO**

Considerable attention has been devoted to complete or correlate the results provided by the XRD analysis, with the DSC studies, since the last type of investigation is able to evaluate the crystallization/melting processes.

Vrinceanu et al tested thermal attributes of fibrous supports - ZnO nanocomposites under nitrogen [41] The DSC curves of are shown in figures above.

In the range 370°-395°C, in a typical DSC curve of cellulosic fibres, there is an endothermic peak, which has been shown to be primarily due to the production of laevoglucosan [42].

MCT started to decompose at higher temperature than sample treated in the same conditions but without the presence of zinc oxide. Nevertheless, the existence of the MCT on the surface of the probes delayed the thermal degradation of the fibrous linen samples, even the non-

**Figure 11.** Kinetic curves for sorption/desorption processes of water vapors for sample 5 at both 25 °C and 35 °C re‐

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35 °C

It can be claimed that cellulose is thermally decomposed through two types of reactions. At lower temperatures, there is a complex process of gradual degradation including dehydration, depolymerisation, oxidation, evolution of carbon monoxide and carbon dioxide, and forma‐ tion of carbonyl and carboxyl groups, ultimately resulting in a carbonaceous residue forms.

The endothermic band around 260°C from DSC curves (Fig. 14 (a) and (b)) indicates a weight loss. The surface acidity of zinc oxide nanoparticles keeps accelerating the decomposition of

treated with the zinc oxide particles.

spectively [10]

For linen fibres, this peak is sometimes partly or completely marked by an exothermal effect around 340°C, attributed to a base-catalysed-dehydration reaction that takes place in the presence of alkaline ions, such as those of sodium [43].

From 200 to 250°C a progressive mass loss associated with water release was observed. From the literature it is well known that lignocellulosic fibers degrade in several steps; the cellulose degrades between 310°–360°C, whereas the hemicellulose degrades at about 240°–310°C, and the lignin has been shown to degrade in wide temperature interval (200°–550°C) [44]. Techni‐ cally speaking, it is not possible to separate the different degradation processes of the fiber components because the reactions are very complex and overlap in the range of 220°–360°C. It is noteworthy that the nanocomposite treated with ZnO nanoparticles with the assistance of

Zinc Oxide — Linen Fibrous Composites: Morphological, Structural, Chemical, Humidity Adsorptive and Thermal Barrier Attributes http://dx.doi.org/10.5772/55705 37

The differences between sorption-desorption speeds of those two temperatures for Sample 5 indexed sample are clearly highlighted by the presence of modified hysteresis and also by the

**Figure 10.** Comparative plots of rapid water vapors sorption/desorption isotherms for sample 5 [10] at both 25 °C

Considerable attention has been devoted to complete or correlate the results provided by the XRD analysis, with the DSC studies, since the last type of investigation is able to evaluate the

Vrinceanu et al tested thermal attributes of fibrous supports - ZnO nanocomposites under

In the range 370°-395°C, in a typical DSC curve of cellulosic fibres, there is an endothermic peak, which has been shown to be primarily due to the production of laevoglucosan [42]. For linen fibres, this peak is sometimes partly or completely marked by an exothermal effect around 340°C, attributed to a base-catalysed-dehydration reaction that takes place in the

From 200 to 250°C a progressive mass loss associated with water release was observed. From the literature it is well known that lignocellulosic fibers degrade in several steps; the cellulose degrades between 310°–360°C, whereas the hemicellulose degrades at about 240°–310°C, and the lignin has been shown to degrade in wide temperature interval (200°–550°C) [44]. Techni‐ cally speaking, it is not possible to separate the different degradation processes of the fiber components because the reactions are very complex and overlap in the range of 220°–360°C. It is noteworthy that the nanocomposite treated with ZnO nanoparticles with the assistance of

**3.2. Thermal degradation mechanism of linen fibrous supports treated with ZnO**

kinetics curves.

and 35 °C respectively

36 Modern Surface Engineering Treatments

crystallization/melting processes.

nitrogen [41] The DSC curves of are shown in figures above.

presence of alkaline ions, such as those of sodium [43].

**Figure 11.** Kinetic curves for sorption/desorption processes of water vapors for sample 5 at both 25 °C and 35 °C re‐ spectively [10]

MCT started to decompose at higher temperature than sample treated in the same conditions but without the presence of zinc oxide. Nevertheless, the existence of the MCT on the surface of the probes delayed the thermal degradation of the fibrous linen samples, even the nontreated with the zinc oxide particles.

It can be claimed that cellulose is thermally decomposed through two types of reactions. At lower temperatures, there is a complex process of gradual degradation including dehydration, depolymerisation, oxidation, evolution of carbon monoxide and carbon dioxide, and forma‐ tion of carbonyl and carboxyl groups, ultimately resulting in a carbonaceous residue forms.

The endothermic band around 260°C from DSC curves (Fig. 14 (a) and (b)) indicates a weight loss. The surface acidity of zinc oxide nanoparticles keeps accelerating the decomposition of

(a)

(b)

)

(c)

**Figure 13.** Typical DSC curve under nitrogen for: a – Sample 4; b – Sample 5; c – Sample 6 [41]

Zinc Oxide — Linen Fibrous Composites: Morphological, Structural, Chemical, Humidity Adsorptive and Thermal

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**Figure 12.** Typical DSC curve under nitrogen for: a Sample 3; b Sample 4; c. Sample 5 [41]

Zinc Oxide — Linen Fibrous Composites: Morphological, Structural, Chemical, Humidity Adsorptive and Thermal Barrier Attributes http://dx.doi.org/10.5772/55705 39

(a)

38 Modern Surface Engineering Treatments

(b)

)

(c)

**Figure 12.** Typical DSC curve under nitrogen for: a Sample 3; b Sample 4; c. Sample 5 [41]

**Figure 13.** Typical DSC curve under nitrogen for: a – Sample 4; b – Sample 5; c – Sample 6 [41]

the fibrous substrate, as the temperature rises to 310°C, According to the FTIR spectra, a very much lower amount of carbonyl groups is found in the linen - ZnO nanocomposite specimens.

**Acknowledgements**

**Author details**

Aurel Pui1

Romania

**References**

(2002)

belonging to "Al.I.Cuza" University of Iasi.

Narcisa Vrinceanu1,2, Alina Brindusa Petre1

1 "Al.I.Cuza" University of Iasi, Iasi, Romania

MJ Chem Technol 14:145 (1997)

Chem. Commun. 4, 410–411 (2004)

2 "L.Blaga" University of Sibiu, Romania

and Diana Tanasa1

, Diana Coman2

The authors would like to greatly acknowledge the financial support provided by the two research contracts: /89/1.5/S/49944 POSDRU Project and PN-II-RU-TE-2011-3-0038 project,

Zinc Oxide — Linen Fibrous Composites: Morphological, Structural, Chemical, Humidity Adsorptive and Thermal

3 Al.I.Cuza" University of Iasi, Faculty of Chemistry, Departament of Materials Chemistry,

[1] Weber, J., Futterer, C., Gowri, V.S., Attia, R., Viovy, J.L., La Houille Blanche 5:40 (2006); Saxana, M, Gowri. V.S., J Polym Compd 24:428 (2003); Gowri, V.S., Saxena,

[2] Raveendran, P., Fu, J., Wallen, S.L., Completely ''green" synthesis and stabilization

[3] Mucalo, M.R., Bullen, C.R., Arabinogalactan from the Western larch tree: a new, pu‐ rified and highly water-soluble polysaccharide-based protecting agent for maintain‐ ing precious metal nanoparticles in colloidal suspension, J. Mater.Sci. 37, 493–504

[4] He, J.H., Kunitake, T., Nakao, A., Facile in situ synthesis of noble metal nanoparticles

[5] He, J.H., Kunitake, T., Nakao, A., Facile fabrication of composites of platinum nano‐ particles and amorphous carbon films by catalyzed carbonization of cellulose fibers,

[6] Walsh, D., Arcelli, L., Ikoma, T., Tanaka, J., Mann, S., Dextran templating for the syn‐

thesis of metallic and metal oxide sponges, Nat. Mater. 2, 386–390 (2003)

of metal nanoparticles, J. Am. Chem. Soc. 125, 13940–13941 (2003)

in porous cellulose fibers, Chem. Mater. 15, 4401–4406 (2003)

, Claudia Mihaela Hristodor1

, Eveline Popovici3

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,

Meanwhile, MCT having a higher thermal conductivity as well as a greater heat capacity value absorbs the heat transmitted from the surroundings and retard the direct thermal impact to the polymer backbone [45,46]. As a consequence, zinc oxide stabilizes the polymer molecules of the underneath substrates and delays the occurrence of major cracking up to 400°C (Fig. 15).

The masking effect of an exothermal reaction on the endothermic cellulose decomposition was clearly highlighted by the behavior of the reference fibrous linen (non-functionalized) subjected to the thermal treatment in N2; it shows an exothermal peak at 260°C with a decreased enthalpy after the thermal treatment; the exothermal effect is attributable to β-cellulose decomposition as observed in a curve of a cotton sample. Surprisingly, even within the second cycle of thermal treatment, the sample exhibits a similar exothermal peak at 363°C.
