PP-LDPE blends

Figure 3.39. Global crystallization kinetics in immiscible PP/LDPE blends influence of the amount dispersed phase and the crystallization temperature, 7), on the half time for crystallization, tj [Martuscelli, 1984].

Galeski et al. [1984] and Teh et al. [1983] have investigated PP/LDPE blends. No shift of the melting peak for LDPE has been observed. Both authors showed migration of the impurities during the melt-mixing process from the PP towards the LDPE phase. No further details on the crystallization behavior of the LDPE droplets themselves were reported. 

Table 10.5 Dependence of Properties of Initial Polyolefins, Functionalized (PP/LDPE)-g-IA Blends and Unmodified PP/LDPE Blends on the Ratio of Polymer Components.

PP/LDPE blends were compatibilized by addition of 2-22 wt% EPR. Blending was done in two stages, curing EPR before the second portion of PP was added. The resulting materials had good mechanical,... 

In this section, the structure and thermophysical properties of isotactic pol q)ropylene (PP) and low-density polyethylene (LDPE) blends were studied by differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR). The experiment shows non-additive changes of the thermal behavior and segmental mobility in the amorphous regions of immiscible PP/LDPE blends in relation to the properties of PP and LDPE initial homopol5nners. Based on the results of the study, the probable process of the structure formation for PP/LDPE blends of various compositions described. 

The aim of this work was to study the effect of the composition of PP/ LDPE blends on the phase structure, in particular the quality and quantity of crystallites and amorphous regions of both components in the blends. 

It is important to note that certain properties of these blends are better than those of the parent homopolymers. Adding PE to PP allows improvement of the low temperature impact behavior of PP [12]. In turn, the PP content contributes to the increase of toughness, high modulus and heat resistance to PE [13]. The PP/LDPE blends can be used as engineering plastics, consumer items for household use, goods with improved performance, etc. 

Moreover, PP/LDPE blends are the products of plastic recycling. Since separation of PP and PE in sohd domestic waste (SDW) is very expensive, many recycling companies sell mixtures of reworked PE and PP ( polymer mix ) [13]. Thus, the study of the stmcture of blends of these materials will increase the field of application of recycled plastics. This is the reason for why PP-LDPE blends are the main subject considered in this chapter. 

Figure 1 of Section 5.9 shows the dependence of the degree of crystallinity X of each component of the blend on the PP/LDPE blend composition. The degree of crystallinity of LDPE changes slightly = 19.4 1.5%) across the full range of the compositions. An increase in the PP content causes a small decrease ofj. Thus, the presence of PP does not have a significant effect on the crystallization process of LDPE. 

FIGURE 1 Effects of the PP-LDPE blend composition on the degree of crystallinity x of PP(l)andLDPE(2). 

As the result, both components of the blend have a mutual influence on the crystallization process and the formation of the phase structure and, consequently, the properties of the blend. However, the LDPE component has a greater effect on the process of the structure formation of PP/LDPE blends than the PP component. 

TABLE 1 The valiies of melting temperatures of PP and LDPE for PP/LDPE blends as a function of weight per cent of PP. The measurement error is 5%. 

These data confirm the fact that LDPE has looser amorphous regions as compared to PP. LDPE tends to sorb up to 60-70 wt% of the PP content from the probe of the blend. Given that the correlation time of a radical rotation is an integral characteristic of the PP/LDPE blend, the value of grows rapidly only when a certain amoimt of the radical penetrates into PP. It explains the type of the dependence between the area of the EPR spectrum and the blend composition presented in Fig. 2 of Section 5.9. 

Based on the data obtained in the study, it appears possible to describe the probable process of the stmcture formation for different PP/LDPE blends. After a gradual addition of PP to LDPE, the former begins to form... 

Where interfacial tension exists between melt components, the multilayers give rise to derivative blend morphologies such as depicted in Fig. 19.1. Morphology results for PP-LDPE blends are given in Fig. 19.7 at an LDPE volume composition of 30% [4]. These results and others at 10 and 20% LDPE are the basis for the morphology map in Fig. 19.5. All such blends were extruded as films of 500- im... 

Figure 19.7 Example of progressive structure development resulting from an initial multilayer blend morphology and the primary derivative morphologies producible in a PP/LDPE blend at a constant 70/30% volume composition.

Dhoble A, Kulshreshtha B, Ramaswami S, Zumbrunnen DA. Mechanical properties of PP-LDPE blends with novel morphologies produced with a continuous chaotic advection blender. Polymer 2005 46 2244-5 6. 

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