**3.3 Mechanical property study**

For mechanical property studies, the test specimens for tensile was molded and cut according to the dimensions specified in **Table 2**. The tensile test was measured using a traction compression machine Adamel Lhomargy DY34 under atmospheric conditions. Average five samples were tested and the stress-strain curves were recorded. Crosshead speed for tensile tests was carried at 5 mm/min. **Table 3** shows the summary of tensile data for the control sample and six composites of LDPE.

**139**

**Table 2.**

**Figure 3.**

**Figure 4.**

*FTIR spectra in the range of 7–10.5 μm.*

*UV–Vis spectra of LDPE/silica nanocomposite film.*

*Specified dimension of samples for tensile test.*

**Figure 5** shows the stress–strain curves from tensile tests for LDPE/silica nanocomposites. **Figure 5** shows that the stress at break gradually increasing with the increase of silica loading up to 1 wt%. This result suggests that the fine silica particle

**Specifications Dimensions (mm)**

Sample length 75 Display ends 12.5 ± 1 Length of the active part 25 ± 1 Display the effective part 4 ± 0.1 External radius 8 ± 0.5 Internal radius 12.5 ± 1

*Nanosilica Composite for Greenhouse Application DOI: http://dx.doi.org/10.5772/intechopen.92181*

**Figure 2.** *FTIR spectra for different ratios of LDPE/silica nanocomposite film.*

*Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

The transmittance of samples was examined by Fourier transform infrared (FTIR) spectroscopy (FTIR spectrometer, VERTEX 70/70v from Bruker™ Optics) in the wavelength range of 1–25 μm. **Figure 2** shows the transmittance spectra of

Different absorption peaks could be identified in the MIR range. The first one at ~3 μm caused by OH group and other peaks at ~9 μm, ~12 μm, and ~21 μm, due to Si—O—Si resonance mode of vibrations [18]. Some of these peaks also involve the LDPE substrate in the IR absorption spectra. The peak at 9 μm gives the SiO2 its importance and allows it to be used in this application. We observe a decrease in transmittance when the mixing ratio of SiO2 increases. The changes in the average transmittance for wavelengths ranging from 7 to 10.5 μm are shown in **Figure 3**. We

notice a sharp decline in transmittance when the ratio of SiO2 is increased.

The optical transmittance measurements of LDPE/silica nanocomposite substrate films were carried out with a UV–Vis–NIR spectrophotometer (UV Spectrophotometer A560AOE instruments) at normal incident of light in the wavelength range of 200–1100 nm. **Figure 4** shows the transmittance spectra of the samples. The UV spectra show that the composite substrates (0.5, 1, 2.5, 5, and 7.5 wt% SiO2) have no significant effect on the transmittance. On the other hand, a significant decrease in the transmittance is observed with a mixture ratio of 10 wt% SiO2 compared to the LDPE without mixing. This decrease is addressed in Section 3.

For mechanical property studies, the test specimens for tensile was molded and cut according to the dimensions specified in **Table 2**. The tensile test was measured using a traction compression machine Adamel Lhomargy DY34 under atmospheric conditions. Average five samples were tested and the stress-strain curves were recorded. Crosshead speed for tensile tests was carried at 5 mm/min. **Table 3** shows the summary of tensile data for the control sample and six composites of LDPE.

**3. Results and discussion**

**3.1 Infrared spectroscopic study**

the SiO2/LDPE films in different ratios.

**3.2 Ultraviolet-visible spectroscopy study**

**3.3 Mechanical property study**

**138**

**Figure 2.**

*FTIR spectra for different ratios of LDPE/silica nanocomposite film.*

**Figure 3.** *FTIR spectra in the range of 7–10.5 μm.*

**Figure 4.** *UV–Vis spectra of LDPE/silica nanocomposite film.*


#### **Table 2.**

*Specified dimension of samples for tensile test.*

**Figure 5** shows the stress–strain curves from tensile tests for LDPE/silica nanocomposites. **Figure 5** shows that the stress at break gradually increasing with the increase of silica loading up to 1 wt%. This result suggests that the fine silica particle


#### *Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

#### **Table 3.**

*Summary of tensile data for the control sample and six composites of LDPE.*

would reinforce and orient along the direction of stress and this has contributed to the increase of tensile strength of the nanocomposite with the addition of 1 wt% of nanosilica particles.

The stress–strain curves also illustrate that there was a significant increase of elongation at break values of LDPE with the incorporation of nanosilica particle into the nanocomposite. This result indicates that the incorporation of nanosilica particle would improve the interaction between the molecules. At lower weight percentage, the addition of nanosilica in LDPE matrix increases surface interaction bonding between the molecules. The nanoparticles may be trapped inside entanglements resulting in a restriction on the polymer overall chain mobility.

**Figure 5** shows that both of the stress at break and elongation at break (strain) of nanocomposite achieved the highest values with 1 wt% loading of silica particles.

**141**

tensile properties.

**Figure 5.**

interface area for reinforcement efficiency.

*Typical stress–strain curves of neat LDPE and LDPE/silica nanocomposites.*

**3.4 Greenhouses thermal study**

*Nanosilica Composite for Greenhouse Application DOI: http://dx.doi.org/10.5772/intechopen.92181*

Above 1 wt% silica loading, both the stress and elongation at break showed a gradual drop. These results are attributed to the reinforcing effect of the silica particles. A higher amount of silica particles would reduce the reinforcing effect and mechanical properties of the nanocomposites due to poor dispersion and agglomeration of silica particles. The agglomerated silica particles with larger particle size would serve as flaws and stress concentration for crack initiation, resulting in poor

In this study, the nanoparticles were well dispersed at lower loading (0.5 to 1 wt%) of silica particles. The reinforcing effect of this small amount of nanoparticle loadings with the huge specific surface area has a dramatically larger total

to that of LDPE. This is not unexpected as large changes in tensile strength and extensibility and cannot be expected at a loading below of 10 wt.% of nanofiller [9]. **Figure 6** illustrates the effect of nanosilica particles to Young's modulus of LDPE matrix. As shown in **Figure 6**, Young's modulus increased with the addition of silica nanoparticles. This suggests that the incorporation of silica nanoparticles would improve the stiffness of LDPE. At low silica contents of 1 wt%, the nanocomposite exhibits an interactive structure with the matrix. Strong interfacial interaction will enable the load to be transferred easily across the nanoparticle-matrix interface. This will contribute to the increase of Young's modulus and tensile strength of the nanoparticle-reinforced composites. However, the agglomeration of particles occurred with the increase of silica loadings. The high amount of nanoparticle loadings did not participate in homogeneous interactive bonding with LDPE. The weak interaction between particle and matrix has caused lower tensile properties due to the debonding of particle from matrix prior to the plastic deformation of the matrix.

We built a mini greenhouse of LDPE without mixing and another of LDPE mixed with 2.5 wt% SiO2. We also built a third mini greenhouse of silica glass

In **Figure 6** all nanocomposites show the same average tensile strength compared

*Nanosilica Composite for Greenhouse Application DOI: http://dx.doi.org/10.5772/intechopen.92181*

#### **Figure 5.**

*Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

**Material Property Average Std. dev.** LDPE control Maximum load, N 58 4.47

LDPE 0.5 wt% SiO2 Maximum load, N 60 0

LDPE 1 wt% SiO2 Maximum load, N 60 0

LDPE 2.5 wt% SiO2 Maximum load, N 60 0

LDPE 5 wt% SiO2 Maximum load, N 60 0

LDPE 7.5 wt% SiO2 Maximum load, N 60 0

LDPE 10 wt% SiO2 Maximum load, N 60 0

Tensile strength, MPa 8.18 0.60 % elongation at break 250 48 Modulus of elasticity, MPa 64.47 5.1

Tensile strength, MPa 7.91 0.22 % elongation at break 307 52 Modulus of elasticity, MPa 95.4 9.2

Tensile strength, MPa 8.78 0.09 % elongation at break 374 40 Modulus of elasticity, MPa 88.4 12

Tensile strength, MPa 8.64 0.17 % elongation at break 362 92 Modulus of elasticity, MPa 96 3.5

Tensile strength, MPa 8.27 0.10 % elongation at break 231 71 Modulus of elasticity, MPa 122 11

Tensile strength, MPa 8.35 0.07 % elongation at break 253 31 Modulus of elasticity, MPa 112 16

Tensile strength, MPa 8.38 0.19 % elongation at break 118 16 Modulus of elasticity, MPa 122 21

would reinforce and orient along the direction of stress and this has contributed to the increase of tensile strength of the nanocomposite with the addition of 1 wt% of

The stress–strain curves also illustrate that there was a significant increase of elongation at break values of LDPE with the incorporation of nanosilica particle into the nanocomposite. This result indicates that the incorporation of nanosilica particle would improve the interaction between the molecules. At lower weight percentage, the addition of nanosilica in LDPE matrix increases surface interaction bonding between the molecules. The nanoparticles may be trapped inside entangle-

**Figure 5** shows that both of the stress at break and elongation at break (strain) of nanocomposite achieved the highest values with 1 wt% loading of silica particles.

ments resulting in a restriction on the polymer overall chain mobility.

*Summary of tensile data for the control sample and six composites of LDPE.*

**140**

nanosilica particles.

**Table 3.**

*Typical stress–strain curves of neat LDPE and LDPE/silica nanocomposites.*

Above 1 wt% silica loading, both the stress and elongation at break showed a gradual drop. These results are attributed to the reinforcing effect of the silica particles.

A higher amount of silica particles would reduce the reinforcing effect and mechanical properties of the nanocomposites due to poor dispersion and agglomeration of silica particles. The agglomerated silica particles with larger particle size would serve as flaws and stress concentration for crack initiation, resulting in poor tensile properties.

In this study, the nanoparticles were well dispersed at lower loading (0.5 to 1 wt%) of silica particles. The reinforcing effect of this small amount of nanoparticle loadings with the huge specific surface area has a dramatically larger total interface area for reinforcement efficiency.

In **Figure 6** all nanocomposites show the same average tensile strength compared to that of LDPE. This is not unexpected as large changes in tensile strength and extensibility and cannot be expected at a loading below of 10 wt.% of nanofiller [9]. **Figure 6** illustrates the effect of nanosilica particles to Young's modulus of LDPE matrix. As shown in **Figure 6**, Young's modulus increased with the addition of silica nanoparticles. This suggests that the incorporation of silica nanoparticles would improve the stiffness of LDPE. At low silica contents of 1 wt%, the nanocomposite exhibits an interactive structure with the matrix. Strong interfacial interaction will enable the load to be transferred easily across the nanoparticle-matrix interface. This will contribute to the increase of Young's modulus and tensile strength of the nanoparticle-reinforced composites. However, the agglomeration of particles occurred with the increase of silica loadings. The high amount of nanoparticle loadings did not participate in homogeneous interactive bonding with LDPE. The weak interaction between particle and matrix has caused lower tensile properties due to the debonding of particle from matrix prior to the plastic deformation of the matrix.

#### **3.4 Greenhouses thermal study**

We built a mini greenhouse of LDPE without mixing and another of LDPE mixed with 2.5 wt% SiO2. We also built a third mini greenhouse of silica glass

window (glass thickness is 6 mm, the transmittance from 350 to 1100 nm is 88% approximately) (see **Figure 7**). All the three greenhouses are cubic with a side of 20 cm. Inside each greenhouse, we put a small plant. This plant was previously grown under similar conditions.

The temperature inside each greenhouse was measured using identical temperature sensors (Tecnologic with resolution 0.1°C). The external temperature was also measured using an identical sensor. All the measurements were made at the same moment every 30 minutes starting from 1:00 PM until 6:00 AM the next day. **Figure 8** shows the temperature variations inside the three greenhouses along with the external air temperature. An increase in the temperature inside the greenhouse mixed with 2.5 wt% SiO2 is noticed. This increase is estimated to be more than 2°C than the LDPE greenhouse without mixing (2°C overall and 2.2°C between 11:00 PM and 5:00 AM). We also noticed that the transmittance of the greenhouse mixed with 2.5 wt% SiO2 approaches that of the glass house very much (see the green and blue triangles in **Figure 8**). In fact, the average temperature difference is about 0.14°C overall, and the two temperatures between 11:00 PM and at 5:00 AM match to each other very well.

By studying the IR transmission in **Figures 2**, **3**, and **9**, a decrease in the transmittance near 9 μm with increasing mixture ratios is noticed. This result explains the rise in temperature inside the mini greenhouses (shown in **Figure 9**). The LDPE/silica nanocomposite barrier films preserve the thermal radiation of the ground. Thus, the internal temperature inside the greenhouse is maintained.

One can also notice that in the vicinity of 9 μm, the transmittance of the sample with a ratio of 5 wt% SiO2 is very close to that with a ratio of 2.5 wt% SiO2. We deduce that it may not be very beneficial to go beyond a ratio of 2.5 wt% SiO2.

By studying the UV–Vis transmission in **Figure 4**, a significant decrease is noticed in the transmittance of the film with a ratio of 10 wt% SiO2, compared with the other films of less ratios (0.5, 1, 2.5, 5, and 7.5 wt% SiO2). These five composite barrier films do not have any significant effect on the transmittance compared with that of the LDPE without mixing. Thus, the film with a ratio of 2.5 wt% SiO2 composite film was adopted to build the mini greenhouse. It has no effect on the UV–Vis transmission but it reduces a maximum transmission of the IR radiation around 9 μm.

**143**

Mie scattering [21–23].

**3.5 SEM study**

**Figure 7.**

**Figure 8.**

*Nanosilica Composite for Greenhouse Application DOI: http://dx.doi.org/10.5772/intechopen.92181*

The refractive index of LDPE in the visible domain is 1.51, while the imaginary part is = 0 [19]. It is very close to the real part value of the refractive index of SiO2 which is equal to 1.43 [20]. Therefore, there should not be any significant change in the transmittance of the LDPE, in the visible range, when mixed with SiO2. This is clearly seen in **Figure 4** except for the last case where the ratio of the SiO2 is 10 wt%. Consequently, there should not be any significant change in the greenhouse temperature during sun-shining time. The significant reduction in the transmittance in the case where the ratio of SiO2 is 10 wt% is probably due to

*The variations of difference temperature (ΔT), between the temperature inside the greenhouse and the* 

*temperature in the external air, during the time starting from 1 P.M. (13) until 6 A.M.*

*The three greenhouses. (a) LDPE without mixing, (b) LDPE mixing with 2.5 wt% SiO2, and (c) silica glass.*

**Figure 10** shows the SEM images at a magnification of ×2000 that show no obvious signs of agglomeration of the filler. At this magnification, significant agglomeration should be discernible. While some idea of the level of dispersion might be ascertained by scanning electron microscopy (SEM), the small areas

*Nanosilica Composite for Greenhouse Application DOI: http://dx.doi.org/10.5772/intechopen.92181*

#### **Figure 7.**

*Composite and Nanocomposite Materials - From Knowledge to Industrial Applications*

grown under similar conditions.

match to each other very well.

around 9 μm.

window (glass thickness is 6 mm, the transmittance from 350 to 1100 nm is 88% approximately) (see **Figure 7**). All the three greenhouses are cubic with a side of 20 cm. Inside each greenhouse, we put a small plant. This plant was previously

The temperature inside each greenhouse was measured using identical temperature sensors (Tecnologic with resolution 0.1°C). The external temperature was also measured using an identical sensor. All the measurements were made at the same moment every 30 minutes starting from 1:00 PM until 6:00 AM the next day. **Figure 8** shows the temperature variations inside the three greenhouses along with the external air temperature. An increase in the temperature inside the greenhouse mixed with 2.5 wt% SiO2 is noticed. This increase is estimated to be more than 2°C than the LDPE greenhouse without mixing (2°C overall and 2.2°C between 11:00 PM and 5:00 AM). We also noticed that the transmittance of the greenhouse mixed with 2.5 wt% SiO2 approaches that of the glass house very much (see the green and blue triangles in **Figure 8**). In fact, the average temperature difference is about 0.14°C overall, and the two temperatures between 11:00 PM and at 5:00 AM

By studying the IR transmission in **Figures 2**, **3**, and **9**, a decrease in the transmittance near 9 μm with increasing mixture ratios is noticed. This result explains the rise in temperature inside the mini greenhouses (shown in **Figure 9**). The LDPE/silica nanocomposite barrier films preserve the thermal radiation of the ground. Thus, the internal temperature inside the greenhouse is maintained.

One can also notice that in the vicinity of 9 μm, the transmittance of the sample

with a ratio of 5 wt% SiO2 is very close to that with a ratio of 2.5 wt% SiO2. We deduce that it may not be very beneficial to go beyond a ratio of 2.5 wt% SiO2. By studying the UV–Vis transmission in **Figure 4**, a significant decrease is noticed in the transmittance of the film with a ratio of 10 wt% SiO2, compared with the other films of less ratios (0.5, 1, 2.5, 5, and 7.5 wt% SiO2). These five composite barrier films do not have any significant effect on the transmittance compared with that of the LDPE without mixing. Thus, the film with a ratio of 2.5 wt% SiO2 composite film was adopted to build the mini greenhouse. It has no effect on the UV–Vis transmission but it reduces a maximum transmission of the IR radiation

*The tensile strength, elongation at break and Modulus of elasticity as a function of different ratios of SiO2.*

**142**

**Figure 6.**

*The three greenhouses. (a) LDPE without mixing, (b) LDPE mixing with 2.5 wt% SiO2, and (c) silica glass.*

#### **Figure 8.**

*The variations of difference temperature (ΔT), between the temperature inside the greenhouse and the temperature in the external air, during the time starting from 1 P.M. (13) until 6 A.M.*

The refractive index of LDPE in the visible domain is 1.51, while the imaginary part is = 0 [19]. It is very close to the real part value of the refractive index of SiO2 which is equal to 1.43 [20]. Therefore, there should not be any significant change in the transmittance of the LDPE, in the visible range, when mixed with SiO2. This is clearly seen in **Figure 4** except for the last case where the ratio of the SiO2 is 10 wt%. Consequently, there should not be any significant change in the greenhouse temperature during sun-shining time. The significant reduction in the transmittance in the case where the ratio of SiO2 is 10 wt% is probably due to Mie scattering [21–23].

#### **3.5 SEM study**

**Figure 10** shows the SEM images at a magnification of ×2000 that show no obvious signs of agglomeration of the filler. At this magnification, significant agglomeration should be discernible. While some idea of the level of dispersion might be ascertained by scanning electron microscopy (SEM), the small areas

**Figure 9.** *Transmittance at 9 μm as a function of different ratios of SiO2.*

**Figure 10.**

*Scanning electron micrograph of nanocomposite LDPE 2.5 wt% SiO2 sample at ×2000 magnification.*

sampled by this technique do not yield an average picture of the sample. Also, transmission electron microscopy (TEM) is better suited than SEM for studying nanoparticle dispersion [9].
