**1. Introduction**

Inorganic fillers perform an important role in the production of polymeric composites. Several value-added properties other than low cost, are gained through the use of fillers. Fillers can improve the mechanical [1–3] and thermal [4–7] properties, as well as optical and electrical properties [8–12] of polymeric materials composites. The polyethylene (PE) as one of the most widely used thermoplastics resins possesses excellent biocompatibility with human body and usually used as implantable material [13]. The PE/Cu composites have been developed in a large range of applications. The physical properties depend on the percentage of filler in the composites materials. The crystallinity of a semi-crystalline polymer (in particular polyethylene) mostly decides its physical and some times chemical characteristics. Thereby, it is important to understand the effects of metallic fillers on the phase composition of a semi-crystalline polymer matrix.

**Figure 1.**

*Three-phase model. In areas of entanglement, a three-dimensional order at close range exists; this is the third phase.*

The phase composition of polyethylene (PE) polymers has been described using a two phase or a three-phase model. In the two-phase model, the fraction of the long-range order phase is demonstrated by X-ray scattering and calorimetry but the other phase assumed to be liquid-like. Various techniques have been used to confirm the presence of a third-phase with mobility and order intermediate to that of the crystalline and amorphous phases for Polyethylene (PE). The name and the characteristics of this third phase depend on the type of crystal growth (bulk, solution, or fiber crystals) and on the technique used to analyze it. In NMR [14] and Raman [15–17] studies, the third phase in PE has been called interlamellar, inter-facial, or interzonal, in reference to its links to the crystalline and amorphous phases. The analysis of the melt is one of the techniques allowing suggesting the presence of more than two phases in a semi-crystalline polymer. Thus, 13C NMR indicated the presence of two relaxation times [18, 19] relating to a heterogeneous fusion showing that the solid melts in a complex mode and incompletely.

The third phase, named the network phase, was identified following the characterization of the phase composition of different PE samples by slow Calorimetry, Calorimetry in non-standard conditions, FTIR and LCST technique [20–22]. This phase consists in a short range order located between the entanglements contained in the amorphous phase. In consequence, this network phase is heterogeneous with a range of order and tension (due to the entanglements) determined by the polymerization conditions [22], the sample history [21] and the charge load [23]. Taking this third phase into account, the phasic structure of polymers could be described as follows (**Figure 1**):

**73**

**Figure 2.**

*Schematic representation of the thematic analysis of the chapter.*

*Development of LDPE Crystallinity in LDPE/Cu Composites*

• Amorphous phase: disorderly and entangled chains,

not affected by the nature of the substrate or the particle size.

• Crystalline phase: the same as that described in the two-phase model, that is formed by sequences of ordered molecules in a crystal lattice forming a threedimensional order at a long distance. The crystal unit cell is orthorhombic in

• Network or interphase phase: formed by the entire network of entanglements contained in the amorphous phase. In these areas of entanglement, a certain three-dimensional crystallinity exists due to the organization of short sequences of chains in a short-distance crystal lattice. In the case of PE, the lattice of crystals of the small distance order would be of the orthorhombic and

Using a three phase system (crystalline, network and amorphous) instead of a two phase system (crystalline and amorphous) to study the effect of filler particles on the crystallinity of LDPE can be more appropriate. This due to the existence of a third phase having a morphology intermediate between that associated with longrange order and that consisting of disordered chains. For a thin film of PE melted on a substrate composed by the zinc selenide (ZnSe) microparticles or the titanium dioxide (TiO2) nanoparticles, Bernazzani and Sanchez [24] found a relationship between the amorphous phase (of a two-phase system) and the Tm variation. With these results, they confirmed that the crystalline phase (long distance order) was

In the present chapter, we investigate the effect of the filler (ie copper) on LDPE phasic composition in LDPE/Cu composites prepared in solution. The main objective of this work is to highlight the effect of the presence of copper microparticles on the network phase and on the long and the short-range order crystalline phase of the LDPE structure. To determine the effect of the copper microparticles addition on the LDPE matrix crystallinity we used different physico-chemical characterization techniques have been used such as FTIR spectroscopy and Differential scanning calorimetry (DSC) at standard and non standard conditions (**Figure 2**).

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

the case of PE,

monoclinic type [24].

*Material Flow Analysis*

The phase composition of polyethylene (PE) polymers has been described using a two phase or a three-phase model. In the two-phase model, the fraction of the long-range order phase is demonstrated by X-ray scattering and calorimetry but the other phase assumed to be liquid-like. Various techniques have been used to confirm the presence of a third-phase with mobility and order intermediate to that of the crystalline and amorphous phases for Polyethylene (PE). The name and the characteristics of this third phase depend on the type of crystal growth (bulk, solution, or fiber crystals) and on the technique used to analyze it. In NMR [14] and Raman [15–17] studies, the third phase in PE has been called interlamellar, inter-facial, or interzonal, in reference to its links to the crystalline and amorphous phases. The analysis of the melt is one of the techniques allowing suggesting the presence of more than two phases in a semi-crystalline polymer. Thus, 13C NMR indicated the presence of two relaxation times [18, 19] relating to a heterogeneous fusion showing that the solid melts in a complex mode and

*Three-phase model. In areas of entanglement, a three-dimensional order at close range exists; this is the* 

The third phase, named the network phase, was identified following the characterization of the phase composition of different PE samples by slow Calorimetry, Calorimetry in non-standard conditions, FTIR and LCST technique [20–22]. This phase consists in a short range order located between the entanglements contained in the amorphous phase. In consequence, this network phase is heterogeneous with a range of order and tension (due to the entanglements) determined by the polymerization conditions [22], the sample history [21] and the charge load [23]. Taking this third phase into account, the phasic structure of polymers could be described as

**72**

incompletely.

**Figure 1.**

*third phase.*

follows (**Figure 1**):


Using a three phase system (crystalline, network and amorphous) instead of a two phase system (crystalline and amorphous) to study the effect of filler particles on the crystallinity of LDPE can be more appropriate. This due to the existence of a third phase having a morphology intermediate between that associated with longrange order and that consisting of disordered chains. For a thin film of PE melted on a substrate composed by the zinc selenide (ZnSe) microparticles or the titanium dioxide (TiO2) nanoparticles, Bernazzani and Sanchez [24] found a relationship between the amorphous phase (of a two-phase system) and the Tm variation. With these results, they confirmed that the crystalline phase (long distance order) was not affected by the nature of the substrate or the particle size.

In the present chapter, we investigate the effect of the filler (ie copper) on LDPE phasic composition in LDPE/Cu composites prepared in solution. The main objective of this work is to highlight the effect of the presence of copper microparticles on the network phase and on the long and the short-range order crystalline phase of the LDPE structure. To determine the effect of the copper microparticles addition on the LDPE matrix crystallinity we used different physico-chemical characterization techniques have been used such as FTIR spectroscopy and Differential scanning calorimetry (DSC) at standard and non standard conditions (**Figure 2**).

**Figure 2.** *Schematic representation of the thematic analysis of the chapter.*
