*3.4.1 Pure polyethylene thin films*

The IR spectrum provided by the LDPE (**Figure 8**) shows absorption bonds characteristic of different vibration modes of methylene group. The main vibrations obtained on the spectrum are grouped together in **Table 2**. The elongation vibration, also called vibration of valence or "stretching", concerns the variation of the interatomic distance. When the molecule has symmetries, we can distinguish symmetrical or antisymmetric modes of elongation, which can be easily seen in the case of a methylene CH2 group of LDPE (2919 cm−1 and 2845 cm−1). In addition to stretching, the angles between the adjacent bonds of the CH2 can vary, we then speak of deformation modes, which can be symmetric or asymmetric, and occur in the plane or out of the plane (1472 cm−1, 1460 cm−1, 720 cm−1 and 730 cm−1). The presence of (–CH3) is rarely desired when manufacturing a polymer. Indeed,

**79**

*Development of LDPE Crystallinity in LDPE/Cu Composites*

(amorphous phase)

(cristalline phase)

(amorphous phase)

(cristalline phase) 2845 ν CH2 (s) Symmetric

2919 ν CH2 (as) Asymmetric

a methyl group will decrease the density of the polymer by limiting the superposition of the layers, then making it of poorer quality. There is therefore an IR analysis method for determining the concentration of methyl group in a polymer as a function of the absorbance with two closely spaced bands (1378 cm−1 and 1368 cm−1). These two bands visualized on the spectrum of the polyethylene used during this work (**Figure 8**) confirms the low density character of the polyethylene polymer and indicates its low rate of crystallinity by the existence of CH3 groups in the

Rocking CH2

Scissoring CH2

stretching CH

stretching CH

A series of standard infrared spectra as a function of temperature was first performed for pure LDPE thin film in order to understand the effect of interactions on the melting transition of LDPE. **Figure 9** shows the typical evolution of the infrared spectra of pure LDPE in the CH2 rocking region as a function of temperature. The CH2 rocking region is of particular interest. It shows a doublet attributed to the CH2 rocking vibration. This doublet, caused by a field splitting, occurs only when the chains are in the orthorhombic crystalline phase. If the sample is not in the crystalline phase then only a broad peak around 725 cm−1 is observed. As the temperature approaches the melting temperature, the absorbance decreases until melting occurs and, as the polymer flows, the amount of sample effectively detected is reduced significantly leading to a sharp decrease in absorbance. The changes observed concern

An extensive research in the past have as objective the elucidation of the molecular structure of PE by IR. The assignment of the trans-trans and gauche conformations has led to the identification of ordered and less ordered regions. The ordered phases in the orthorhombic regions give a doublet in the rocking vibration at 730–720 cm−1 and bending vibration at 1500–1400 cm−1 due to the interaction between two chains in the unit cell. The analyzing the spectrum of molten PE and liquid, linear and cyclic alkanes gave mores information on mite less ordered region of a semi-crystalline polymer [26]. The amorphous regions have been associated

*DOI: http://dx.doi.org/10.5772/intechopen.97725*

**Absorbance (cm−1) Nature of vibrations**

720 γ C-H

730 γ C-H

1460 δ C-H

1472 δ C-H

*Different absorption bands of LDPE.*

polyethylene structure.

**Table 2.**

the relative intensity of the bands and their position.

*3.4.2 Phase content by IR analysis: spectral simulations*

with peaks at 725, 720, 1078 and 1300-l368 cm−1 [23].

**Figure 8.** *FTIR spectra of LDPE film prepared from a solution.*


#### **Table 2.**

*Material Flow Analysis*

**3.4 Infrared spectroscopy**

different phases of the LDPE.

*3.4.1 Pure polyethylene thin films*

endotherms is observed. Also, more events happened in the melt expressed by the different melting/crystallization/melting observed in comparison to the more flat endotherm of the network melting endotherm of the neat LDPE film. These observations suggest that the presence of the micro-particles copper have more effect on the network phase than that can be observed on the crystalline long-range order phase. It is then more consistent to study the effect of the copper particles by analyzing the changes occurring on the network phase. The expansion during the temperature ramp operates a strain on the sample and the network phase is deformed. Over the melting of this phase showed by a succession of melting/crystallization/melting a complex phenomenon can observed [21]. In fact, the copper micro-particles participate in the strain applied on the sample witch explains the higher melting temperatures and the larger endotherms obtained for the network phase melting.

The FTIR spectra of the studied films were obtained with a Perkin–Elmer Paragon 1000 FT-IR spectrometer used in transmission mode. The spectra's were treated using BOMEM GRAMS software for the determination of the study of the

The IR spectrum provided by the LDPE (**Figure 8**) shows absorption bonds characteristic of different vibration modes of methylene group. The main vibrations obtained on the spectrum are grouped together in **Table 2**. The elongation vibration, also called vibration of valence or "stretching", concerns the variation of the interatomic distance. When the molecule has symmetries, we can distinguish symmetrical or antisymmetric modes of elongation, which can be easily seen in the case of a methylene CH2 group of LDPE (2919 cm−1 and 2845 cm−1). In addition to stretching, the angles between the adjacent bonds of the CH2 can vary, we then speak of deformation modes, which can be symmetric or asymmetric, and occur in the plane or out of the plane (1472 cm−1, 1460 cm−1, 720 cm−1 and 730 cm−1). The presence of (–CH3) is rarely desired when manufacturing a polymer. Indeed,

**78**

**Figure 8.**

*FTIR spectra of LDPE film prepared from a solution.*

*Different absorption bands of LDPE.*

a methyl group will decrease the density of the polymer by limiting the superposition of the layers, then making it of poorer quality. There is therefore an IR analysis method for determining the concentration of methyl group in a polymer as a function of the absorbance with two closely spaced bands (1378 cm−1 and 1368 cm−1). These two bands visualized on the spectrum of the polyethylene used during this work (**Figure 8**) confirms the low density character of the polyethylene polymer and indicates its low rate of crystallinity by the existence of CH3 groups in the polyethylene structure.

A series of standard infrared spectra as a function of temperature was first performed for pure LDPE thin film in order to understand the effect of interactions on the melting transition of LDPE. **Figure 9** shows the typical evolution of the infrared spectra of pure LDPE in the CH2 rocking region as a function of temperature. The CH2 rocking region is of particular interest. It shows a doublet attributed to the CH2 rocking vibration. This doublet, caused by a field splitting, occurs only when the chains are in the orthorhombic crystalline phase. If the sample is not in the crystalline phase then only a broad peak around 725 cm−1 is observed. As the temperature approaches the melting temperature, the absorbance decreases until melting occurs and, as the polymer flows, the amount of sample effectively detected is reduced significantly leading to a sharp decrease in absorbance. The changes observed concern the relative intensity of the bands and their position.

#### *3.4.2 Phase content by IR analysis: spectral simulations*

An extensive research in the past have as objective the elucidation of the molecular structure of PE by IR. The assignment of the trans-trans and gauche conformations has led to the identification of ordered and less ordered regions. The ordered phases in the orthorhombic regions give a doublet in the rocking vibration at 730–720 cm−1 and bending vibration at 1500–1400 cm−1 due to the interaction between two chains in the unit cell. The analyzing the spectrum of molten PE and liquid, linear and cyclic alkanes gave mores information on mite less ordered region of a semi-crystalline polymer [26]. The amorphous regions have been associated with peaks at 725, 720, 1078 and 1300-l368 cm−1 [23].

#### **Figure 9.**

*Typical evolution of the CH2 rocking region of the IR spectrum of a pure LDPE film (a) and LDPE/16%Cu, (b) composite film as a function of temperature.*

The bands associations with a monoclinic-like organization have been studied on fibers and modified samples where the orthorhombic crystals had been deformed by shaking or drawing [27–34]. Thereby, the singlet at 715–718 cm−1 was replaces the doublet in the spectrum of these samples [35–37]. Using the spectral subtraction, these bands were also be detected in solution-grown crystals and on annealed melt-crystallized samples [35].

The superposition of the spectral region 670–770 cm−1 (**Figure 10a**) of LDPE and LDPE/Cu (84/16) shows a slight decrease in the peak around 730 cm−1 compared to that at 720 cm−1 in presence of micro-particles copper. Thus, to develop the crystallinity study of a LDPE/Cu composite film grown in solution, spectral simulation of the rocking CH2 vibrations region for the different samples have been performed. Spectral simulations of the 770–670 cm−1 regions in the IR spectra were then performed by software BGRAMS/386 using a Gauss + Lorenz band shape with

**81**

*Development of LDPE Crystallinity in LDPE/Cu Composites*

a band width at half-height of 3.5 cm−1 for the orthorhombic peaks, 10–16 cm−1 for the single-chain band or amorphous regions (725 cm−1), and 15–19 cm−1 for thee monoclinic-like peak (717 cm−1) [25]. The phase fractions were calculated from the

*(a) FTIR spectrum in the rocking region of LDPE and LDPE/Cu (84/16). (b) two-phase deconvolution of* 

*Integrated area Integrated area*

The integrated absorbance of each band was rationed against the total area of the 770–670 cm−1 regions. The integrated absorbance of the two peaks at 730 and

Using two phases model, the spectral simulation of transmission spectra of LDPE/Cu films with different copper content in the spectral range between 670 and

• 720 cm−1 and 730 cm−1 characteristic of the orthorhombic crystalline phase

LDPE matrix for all copper contents (**Figure 11**). In fact, the fractions of orthorhombic and amorphous phases (respectively about 62% and 38%) are the same values obtained for the neat LDPE. Thus, copper does not have any noticeable effect

Such deconvolution does not show any variation in the phase composition of the

*phase i*( )

= (2)

*all the phases*

( )

770 cm−1, shows the presence of only three bands (**Figure 10b**):

on the structure of LDPE in the model of two phases [25].

720 cm−1, both representing the orthorhombic fraction, were summed.

*phase i*

α

*DOI: http://dx.doi.org/10.5772/intechopen.97725*

simulated spectra using the equation:

*FTIR rocking region of LDPE and LDPE/Cu (84/16).*

**Figure 10.**

• 725 cm−1 for amorphous phase

**Figure 10.**

*Material Flow Analysis*

**80**

**Figure 9.**

melt-crystallized samples [35].

*(b) composite film as a function of temperature.*

The bands associations with a monoclinic-like organization have been studied on fibers and modified samples where the orthorhombic crystals had been deformed by shaking or drawing [27–34]. Thereby, the singlet at 715–718 cm−1 was replaces the doublet in the spectrum of these samples [35–37]. Using the spectral subtraction, these bands were also be detected in solution-grown crystals and on annealed

*Typical evolution of the CH2 rocking region of the IR spectrum of a pure LDPE film (a) and LDPE/16%Cu,* 

The superposition of the spectral region 670–770 cm−1 (**Figure 10a**) of LDPE and LDPE/Cu (84/16) shows a slight decrease in the peak around 730 cm−1 compared to that at 720 cm−1 in presence of micro-particles copper. Thus, to develop the crystallinity study of a LDPE/Cu composite film grown in solution, spectral simulation of the rocking CH2 vibrations region for the different samples have been performed. Spectral simulations of the 770–670 cm−1 regions in the IR spectra were then performed by software BGRAMS/386 using a Gauss + Lorenz band shape with

*(a) FTIR spectrum in the rocking region of LDPE and LDPE/Cu (84/16). (b) two-phase deconvolution of FTIR rocking region of LDPE and LDPE/Cu (84/16).*

a band width at half-height of 3.5 cm−1 for the orthorhombic peaks, 10–16 cm−1 for the single-chain band or amorphous regions (725 cm−1), and 15–19 cm−1 for thee monoclinic-like peak (717 cm−1) [25]. The phase fractions were calculated from the simulated spectra using the equation:

$$\alpha\_{phase(i)} = \frac{\text{Integrated } area\_{phase(i)}}{\text{Integrated } area\_{all\text{ the phase}}} \tag{2}$$

The integrated absorbance of each band was rationed against the total area of the 770–670 cm−1 regions. The integrated absorbance of the two peaks at 730 and 720 cm−1, both representing the orthorhombic fraction, were summed.

Using two phases model, the spectral simulation of transmission spectra of LDPE/Cu films with different copper content in the spectral range between 670 and 770 cm−1, shows the presence of only three bands (**Figure 10b**):


Such deconvolution does not show any variation in the phase composition of the LDPE matrix for all copper contents (**Figure 11**). In fact, the fractions of orthorhombic and amorphous phases (respectively about 62% and 38%) are the same values obtained for the neat LDPE. Thus, copper does not have any noticeable effect on the structure of LDPE in the model of two phases [25].

#### *Material Flow Analysis*

Using three phases model, **Figures 12** and **13** shows four-band deconvolution for neat LDPE film (0% Cu) and a 16% copper loaded LDPE/Cu composite film. The orthorhombic peaks at 730 and 720 cm−1 appeared to be unchanged for all copper content witch comforts the thesis that such phase is not affected by the copper particles presence. Nevertheless, the peaks assigned to the amorphous phase (725 cm−1) and to the network phase (717–715 cm−1) had their integrated area respectively increased and decreased with the copper percentage in the film (**Figure 14**). This observation means that when three phases were introduced, the amount of the orthorhombic phase was found to be constant. However, starting at 4% copper content, the amount of the amorphous and that of the network phase were found to respectively increase and decrease with the increase of copper particles load in the film. This result are in agreement with the non-standard DSC observations mentioned

**Figure 11.**

*Fractions of crystalline and amorphous phases of LDPE as functions of copper particle content in LDPE determined by FTIR using two-phase model simulation.*

**Figure 12.**

*FTIR spectrum in the rocking region showing three phases (orthorhombic, monoclinic, amorphous) of pure LDPE (a) Monoclinic and amorphous band evolution (b).*

**83**

**Figure 13.**

**Figure 14.**

*Development of LDPE Crystallinity in LDPE/Cu Composites*

above and supporting the fact that the changes in the polymer phase composition due to the presence of the copper micro-particle is better seen when considering the existence of the network phase. The copper micro-particles lower probably the total crystallinity of the polymer matrix considering a three phase model, and do not show

*Fractions of crystalline and amorphous phases of LDPE as functions of copper particle content in LDPE* 

*FTIR spectrum in the rocking region showing three phases (orthorhombic, monoclinic, amorphous) of* 

*LDPE/16%Cu composite (a). Monoclinic and amorphous band evolution (b).*

The physical reason probably due to the fact that the copper particles may oppose to the formation of physical entanglements in their close environment. In consequence, the entanglements concentration as well as of the network phase content decrease with the increase of fraction copper and so does the network phase content. Other than the effect of copper micro-particles the polymer matrix seems to adopt the relaxed conformation of the amorphous phase due to the decrease of the entanglements concentration. The orthorhombic phase was not affected by the presence of copper micro-particles. However, with copper nanoparticles seen to

any effect when considering a two phase model [25].

*determined by FTIR using three-phase model simulation.*

*DOI: http://dx.doi.org/10.5772/intechopen.97725*

*Development of LDPE Crystallinity in LDPE/Cu Composites DOI: http://dx.doi.org/10.5772/intechopen.97725*

#### **Figure 13.**

*Material Flow Analysis*

**82**

**Figure 12.**

**Figure 11.**

*FTIR spectrum in the rocking region showing three phases (orthorhombic, monoclinic, amorphous) of pure* 

*Fractions of crystalline and amorphous phases of LDPE as functions of copper particle content in LDPE* 

Using three phases model, **Figures 12** and **13** shows four-band deconvolution for neat LDPE film (0% Cu) and a 16% copper loaded LDPE/Cu composite film. The orthorhombic peaks at 730 and 720 cm−1 appeared to be unchanged for all copper content witch comforts the thesis that such phase is not affected by the copper particles presence. Nevertheless, the peaks assigned to the amorphous phase (725 cm−1) and to the network phase (717–715 cm−1) had their integrated area respectively increased and decreased with the copper percentage in the film (**Figure 14**). This observation means that when three phases were introduced, the amount of the orthorhombic phase was found to be constant. However, starting at 4% copper content, the amount of the amorphous and that of the network phase were found to respectively increase and decrease with the increase of copper particles load in the film. This result are in agreement with the non-standard DSC observations mentioned

*LDPE (a) Monoclinic and amorphous band evolution (b).*

*determined by FTIR using two-phase model simulation.*

*FTIR spectrum in the rocking region showing three phases (orthorhombic, monoclinic, amorphous) of LDPE/16%Cu composite (a). Monoclinic and amorphous band evolution (b).*

#### **Figure 14.**

*Fractions of crystalline and amorphous phases of LDPE as functions of copper particle content in LDPE determined by FTIR using three-phase model simulation.*

above and supporting the fact that the changes in the polymer phase composition due to the presence of the copper micro-particle is better seen when considering the existence of the network phase. The copper micro-particles lower probably the total crystallinity of the polymer matrix considering a three phase model, and do not show any effect when considering a two phase model [25].

The physical reason probably due to the fact that the copper particles may oppose to the formation of physical entanglements in their close environment. In consequence, the entanglements concentration as well as of the network phase content decrease with the increase of fraction copper and so does the network phase content. Other than the effect of copper micro-particles the polymer matrix seems to adopt the relaxed conformation of the amorphous phase due to the decrease of the entanglements concentration. The orthorhombic phase was not affected by the presence of copper micro-particles. However, with copper nanoparticles seen to

have a clear effect on the long-range order of LDPE matrices in LDPE/Cu nanocomposites [38]. The difference might be due to the influence of the size effect of the copper nanoparticles.
