**3.2 Thermogravimetric analysis: TGA**

The thermal stability of the composites was investigated by the Thermo Gravimetric Analysis (TGA). An amount of 5–10 mg of each sample were analyzed by Perkin-Elmer TGA7 Instrument from 35–600°C with a heating rate 20°C/min under nitrogen (N2) atmosphere.

The TGA curves for LDPE and its copper composites are shown in **Figure 4**. Neat LDPE showed a one-step decomposition process starting at 464°C due to the degradation of saturated carbon atoms in polyethylene that is displayed by peak on the curve DTG (**Figure 5**). The increase in the thermal stability of LDPE with increasing copper content showed in the composite films may be explained by the higher heat capacity (0.39 J/(Kg), compared to 0.18 J/(Kg) for PE) and thermal conductivity of Cu. This will result in the onset of the degradation of PE chains at higher temperatures. After the loss of this degradation, the level of mass loss are in good agreement with the amount of copper originally mixed into the samples.

**Figure 3.** *Polarized optical microscopy photo of LDPE/Cu composites [100× magnification]: (a) 8%Cu; (b) 16% Cu.*

**75**

**Figure 5.**

*vs. Cu microparticles content.*

**Figure 4.**

*Development of LDPE Crystallinity in LDPE/Cu Composites*

*TGA curves of LDPE and LDPE/Cu composites with different content of copper microparticles.*

DTG thermograms (**Figure 5**), thermal stability was clearly observed in LDPE/ Cu composite films compared to unfilled LDPE film. This stability is reflected by a shift, towards high temperatures, of the decomposition peak of the composite films following the incorporation of copper microparticles into the LDPE The curves of the thermal decomposition temperature versus the amount of copper particles are

*(a) DTG for composite films at varying levels of copper. (b) Evolution of thermal decomposition temperature* 

*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*

*Material Flow Analysis*

temperature of 0.9 g/cm3

**3.1 Microscopy observation**

**3.2 Thermogravimetric analysis: TGA**

under nitrogen (N2) atmosphere.

**2. Preparation of the Cu/LDPE composite films**

**3. Characterization of the Cu/LDPE composite films**

The low density polyethylene (LDPE) in pellets used in this work has a melting temperature of 107°C, a crystallinity around 40% (as determined by differential scanning calorimetry (DSC) with a heating rate of 10°C/min) and a density at room

Sigma-Aldrich. High purity toluene (99%) supplied by Sigma-Aldrish was used as solvent for the preparation of the solution made films. Different solutions of LDPEtoluene at 1% in the absence and in the presence of copper microparticles were prepared at 80° C. and cooled to room temperature. After total evaporation of the solvent in a Teflon mold, thin films (50 to 60 μm thick) were obtained [25].

Optical microscopy was used to investigate the distribution of the Cu microparticles in LDPE. The polarized optical microscopy photos of different LDPE/Cu composites were exposed in **Figure 3**. The copper particles distribution in the composite films are relatively uniform at both low (8%) and high (16%) copper contents.

The thermal stability of the composites was investigated by the Thermo Gravimetric Analysis (TGA). An amount of 5–10 mg of each sample were analyzed by Perkin-Elmer TGA7 Instrument from 35–600°C with a heating rate 20°C/min

The TGA curves for LDPE and its copper composites are shown in **Figure 4**. Neat LDPE showed a one-step decomposition process starting at 464°C due to the degradation of saturated carbon atoms in polyethylene that is displayed by peak on the curve DTG (**Figure 5**). The increase in the thermal stability of LDPE with increasing copper content showed in the composite films may be explained by the higher heat capacity (0.39 J/(Kg), compared to 0.18 J/(Kg) for PE) and thermal conductivity of Cu. This will result in the onset of the degradation of PE chains at higher temperatures. After the loss of this degradation, the level of mass loss are in good agreement with the amount of copper originally mixed into

*Polarized optical microscopy photo of LDPE/Cu composites [100× magnification]: (a) 8%Cu; (b) 16% Cu.*

. The particles sizes were < 38 μm and were supplied by

**74**

**Figure 3.**

the samples.

**Figure 5.**

*(a) DTG for composite films at varying levels of copper. (b) Evolution of thermal decomposition temperature vs. Cu microparticles content.*

DTG thermograms (**Figure 5**), thermal stability was clearly observed in LDPE/ Cu composite films compared to unfilled LDPE film. This stability is reflected by a shift, towards high temperatures, of the decomposition peak of the composite films following the incorporation of copper microparticles into the LDPE The curves of the thermal decomposition temperature versus the amount of copper particles are

presented in **Figure 5a**. This figure shows that the thermal decomposition temperatures of the LDPE/Cu are also higher than that of the pure LDPE, the tendency of the thermal decomposition temperature of the microcomposites increases with the increasing of the copper microparticles. They also show that the thermal decomposition temperature of the microcomposites reaches its peak as the amount of the copper microparticles is about 12 wt%, and then keeps on this scale when the amount of the copper microparticles is more than 12% wt in this experiment.

## **3.3 Differential scanning calorimetry: DSC**

The DSC calorimeter is a Perkin-Elmer DSC7 with 20 mL/min flow of N2. DSC in Standard Conditions (m = 2–3 mg and v = 10°C/min). The crystallization exothermic and endothermic curves of the neat LDPE and its composites with various copper micro-particles contents are illustrated in **Figure 6**. **Table 1** shows the Tm, TC, the melting enthalpies ΔHm, the crystallization enthalpies ΔHC and the total crystallinity Xc values obtained for the neat LDPE film and the different LDPE/Cu composite films. The crystallinity Xc was determined as follows:

$$X\_{\varepsilon} = \frac{\Delta H\_m}{\mathcal{W}\_m \Delta \mathcal{H}\_m^0} \tag{1}$$

**77**

**Figure 7.**

*neat LDPE and LDPE/Cu(16%) composite (black line).*

*Development of LDPE Crystallinity in LDPE/Cu Composites*

short-range order crystals (network phase) [21, 22].

that the copper particles get a very limited effect on the orthorhombic long range order phase. This is confirmed by the fact that Tm does not did not suffer any noticeable variation. With DSC in standard conditions the strain created in the crystalline fraction particularly at Tm leaves an ordered fraction (network phase) un-melted [22]. DSC in non-standard conditions (m = 0.2–0.3 mg and v = 0.5°C/min): Due to the low values of mass and heating rate the sample (PE) will undergo a maximum heat flow [21]. The trace obtained for a neat LDPE film at the non-standard conditions (**Figure 7**) represents the endotherm of fusion of the orthorhombic crystals at 107.7°C (witch is the same Tm than that obtained by a fast T-ramp). On the other hand, at high temperatures the second endotherm obtained characterizes the melting of the strained short-range order crystals (network phase) [21, 22]. DSC in nonstandard conditions (m = 0.2–0.3 mg and v = 0.5°C/min): Due to the low values of mass and heating rate the sample (PE) will undergo a maximum heat flow [21]. The trace obtained for a neat LDPE film at the non-standard conditions (**Figure 7**) represents the endotherm of fusion of the orthorhombic crystals at 107.7°C (witch is the same Tm than that obtained by a fast T-ramp). On the other hand, at high temperatures the second endotherm obtained characterizes the melting of the strained

*Thermal characteristics (Tm, TC,* Δ*Hm,* Δ*HC) and degree of crystallinity (Xc) of LDPE/Cu composites.*

**LDPE/Cu (%) 100/0 96/4 92/8 88/12 84/16** ΔHm (J/g) 112,3 108,9 94,4 95,4 89,8 Tm (°C) 110,7 109,3 110,1 109,6 109,7 Xc (%) 39,4 39,8 36,1 38,0 37,5

Endotherms in non-standard conditions of neat LDPE and LDPE/Cu (84/16) composite (**Figure 7**) does not present any variation in the Tm value with the addition of copper particles. Never the less, the shape of the network melting endotherm of the different LDPE/Cu composite films looks very different when comparing it with that obtained for the neat LDPE film. In fact, in the traces of all the LDPE/ Cu films, a more obvious separation between the Orthorhombic and the network

*Endotherm of neat LDPE at standard conditions (blue line) and endotherms in non-standard conditions of* 

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

**Table 1.**

Where ΔH° m = 285 J.g−1 is the heat of fusion for 100% crystalline PE and wm is the weight fraction of polymeric matrix material in the composite [38].

**Figure 6** show that both the melting temperatures range and the crystallization temperatures range decrease with increasing of copper micro-particles content. Data in **Table 1** indicate a slight decrease of the melting temperatures Tm but a slight increase of the crystallization temperatures TC with the increasing of copper microparticles content. ΔHm and ΔHC decreases with the percentage of copper which is normal due to the decrease of the LDPE content in the composite film. The crystallinity Xc shows a slight decrease with the increase of the Cu content in the material showing

**Figure 6.** *Complete DSC in standard-condition heating and cooling scan of pure LDPE and LDPE/Cu composites.*


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

#### **Table 1.**

*Material Flow Analysis*

Where ΔH°

**3.3 Differential scanning calorimetry: DSC**

composite films. The crystallinity Xc was determined as follows:

*c*

the weight fraction of polymeric matrix material in the composite [38].

*<sup>H</sup> <sup>X</sup> W*

**Figure 6** show that both the melting temperatures range and the crystallization temperatures range decrease with increasing of copper micro-particles content. Data in **Table 1** indicate a slight decrease of the melting temperatures Tm but a slight increase of the crystallization temperatures TC with the increasing of copper microparticles content. ΔHm and ΔHC decreases with the percentage of copper which is normal due to the decrease of the LDPE content in the composite film. The crystallinity Xc shows a slight decrease with the increase of the Cu content in the material showing

*Complete DSC in standard-condition heating and cooling scan of pure LDPE and LDPE/Cu composites.*

presented in **Figure 5a**. This figure shows that the thermal decomposition temperatures of the LDPE/Cu are also higher than that of the pure LDPE, the tendency of the thermal decomposition temperature of the microcomposites increases with the increasing of the copper microparticles. They also show that the thermal decomposition temperature of the microcomposites reaches its peak as the amount of the copper microparticles is about 12 wt%, and then keeps on this scale when the amount of the copper microparticles is more than 12% wt in this experiment.

The DSC calorimeter is a Perkin-Elmer DSC7 with 20 mL/min flow of N2. DSC in Standard Conditions (m = 2–3 mg and v = 10°C/min). The crystallization exothermic and endothermic curves of the neat LDPE and its composites with various copper micro-particles contents are illustrated in **Figure 6**. **Table 1** shows the Tm, TC, the melting enthalpies ΔHm, the crystallization enthalpies ΔHC and the total crystallinity Xc values obtained for the neat LDPE film and the different LDPE/Cu

> 0 *m*

m = 285 J.g−1 is the heat of fusion for 100% crystalline PE and wm is

<sup>∆</sup> <sup>=</sup> ∆Η (1)

*m m*

**76**

**Figure 6.**

*Thermal characteristics (Tm, TC,* Δ*Hm,* Δ*HC) and degree of crystallinity (Xc) of LDPE/Cu composites.*

that the copper particles get a very limited effect on the orthorhombic long range order phase. This is confirmed by the fact that Tm does not did not suffer any noticeable variation. With DSC in standard conditions the strain created in the crystalline fraction particularly at Tm leaves an ordered fraction (network phase) un-melted [22].

DSC in non-standard conditions (m = 0.2–0.3 mg and v = 0.5°C/min): Due to the low values of mass and heating rate the sample (PE) will undergo a maximum heat flow [21]. The trace obtained for a neat LDPE film at the non-standard conditions (**Figure 7**) represents the endotherm of fusion of the orthorhombic crystals at 107.7°C (witch is the same Tm than that obtained by a fast T-ramp). On the other hand, at high temperatures the second endotherm obtained characterizes the melting of the strained short-range order crystals (network phase) [21, 22]. DSC in nonstandard conditions (m = 0.2–0.3 mg and v = 0.5°C/min): Due to the low values of mass and heating rate the sample (PE) will undergo a maximum heat flow [21]. The trace obtained for a neat LDPE film at the non-standard conditions (**Figure 7**) represents the endotherm of fusion of the orthorhombic crystals at 107.7°C (witch is the same Tm than that obtained by a fast T-ramp). On the other hand, at high temperatures the second endotherm obtained characterizes the melting of the strained short-range order crystals (network phase) [21, 22].

Endotherms in non-standard conditions of neat LDPE and LDPE/Cu (84/16) composite (**Figure 7**) does not present any variation in the Tm value with the addition of copper particles. Never the less, the shape of the network melting endotherm of the different LDPE/Cu composite films looks very different when comparing it with that obtained for the neat LDPE film. In fact, in the traces of all the LDPE/ Cu films, a more obvious separation between the Orthorhombic and the network

#### **Figure 7.**

*Endotherm of neat LDPE at standard conditions (blue line) and endotherms in non-standard conditions of neat LDPE and LDPE/Cu(16%) composite (black line).*

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.

## **3.4 Infrared spectroscopy**

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 different phases of the LDPE.
