Microstructural aspects of Hdpeldpe blends

Figures 9 to 10 show micrographs of the microtomed sections from injection molded bars.

The different microstructure of HDPE/LDPE blends, having different compositions, are shown (Figure 9). In fact, these thin sections taken in the parallel flow direction inside the cavity of a mold and near the gate, show differences in

Figure 13. Micrographs of 85/15 (left) and 15/85 (right) HDPE/LDPE ratio with 1% LMWPE.
Microstructure Pehd
Figure 14. SEM micrographs showing fracture surface of HDPE (left) and LDPE (right). Magnification 30x.
Sem Surface Ldpe
Figure 15. SEM micrographs showing the fracture surface of the film plastic wastes. Magnification: (left) 30x, (right) 50x.

response of the material under polarized light. When HDPE is the matrix, smooth surface and high birefringence are found, as in the case of pure HDPE, with ringed and impinged macroaggregates of crystals also visible. These features indicate that the microstructure of these materials is basically due to HDPE. In Figure 10 the above observations are fully confirmed for samples which have undergone a chemical attack directed to the amorphous zones of blends.

Figures 11-13 show micrographs of HDPE/LDPE blends containing 1% ofEVA copolymer, chlorinated polyethylene, and a low molecular weight polyethylene, respectively. The changes on the microstructural level ofthese specimens, compared to the unmodified HDPE/LDPE system, previously discussed, are evidently in agreement with changes observed in the mechanical properties and the surface appearance of the injected bars. The changes in the size of the

Hdpe Plastic Micrograph
Figure 16. SEM micrographs of HDPE/LDPE system showing differences in fracture mechanism due to different matrix.
Polyethylene Microstructure
Figure 17. SEM micrographs showing brittle fracture (HDPE) and ductile fracture (LDPE).

macroaggregates of crystals and the presence of the interfacial additives enhance the stretchability of the compatibilized blends.

wastes , mÊÊmmm

1 mm

Figure 18. SEM micrographs of wastes showing their brittle fracture.

Figure 18. SEM micrographs of wastes showing their brittle fracture.

Because of the presence in the wastes of about 10% of inks, pigments, fillers and so on, their microstructure cannot be studied by polarized optical microscopy. Thus, a microstructural study by scanning electronic microscopy, using the fracture surface of impact tested specimens, was carried out in order to confirm the previous data.

Figures 14 and 15 give SEM micrographs of the fracture surface of HDPE, LDPE, and wastes at a very low magnification level. A similarity between the fracture surfaces from impact tests of the wastes and LDPE in liquid nitrogen is found. A smooth surface is observed at a low magnification in the front of a semi-brittle fracture observed in the hollowed region of HDPE specimen. Also, a lower amount of the solid particles (pigments) in the micrographs of the wastes is seen.

At higher magnification (Fig. 16), it is possible to observe a significant difference between the fracture surface of blends with HDPE as a matrix and with LDPE as a matrix. Indeed, rounded features in the 85% HDPE blend fracture surface suggest a semi-brittle fracture around macroaggregates of crystals. At a

Hdpe Blend
Figure 19. Mass balance of the recycling plant designed for treatment of film plastic wastes from municipal origin.
Figure 20. Air view of the plant from Figure 19.
Figure 21. Results of the ROI for economic study of viability of the utilities in figures 19 and 20.

higher level of magnification this feature is clearly evident and can be compared with the micrographs in Figure 17, where the homopolymers show striking differences in their fracture mechanism due to their different microstructure in macroaggregates of crystals. Furthermore, we must keep in mind that the LDPE does not break at -30oC and its fracture surface was obtained in liquid nitrogen.

In Figure 18, the fracture surface of the waste specimens also has numerous rounded features at the higher level of magnification. Probably solid particles from inks act in the wastes as nucleation agents. Also, a very small size of the rounded forms is observed. In any case, the higher level of stress concentrators present in the wastes makes them more brittle and explains their low impact strength value. The failure mode of the wastes is similar to that of the matrix.

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