2.23.-MATERIALES PARA RED DE ALUMBRADO PÚBLICO

Six samples were characterized for each clay proportion in order to obtain a representative morphological feature of PP and clay state. According to the literature, this technique shows the formation of an intercalated nanocomposite structure by analyzing the interlayer

spacing (d001) of MMT [3, 4]. When d001 of the clay in the composite is equal or lower than

the one for the pure clay mineral, an ordinary composite was obtained - not a

nanocomposite. On the other hand, when d001 in the composite is higher than in pure clay,

it means that polymer molecules were positioned between clay layers and hence an

intercalated nanocomposite was produced. If the peak corresponding to d001 is not observed

in a polymer/clay diffractograms, this implies that a nanocomposite structure was obtained or the amount of clay was too low to be detected in WAXS analysis. In this case, the use of electron microscopy is necessary to clarify the structure [31]. Of all the six patterns obtained from each composite, data with maximum intensity and peak formation is shown here. The scattering pattern for 1 and 2 phr ratios indicate an exfoliated structure (dispersion of clay layers cannot be easily identified by WAXS). This is attributed to the treatment facilitating the PP molecule insertion into the silicate galleries, hence promoting delamination of the periodic layered structure of the clay (Figure 6.1) [190].

2.5 5 7.5 10 Scattering angle(2θ°) R ela tiv e I nte ns ity PP PP1 PP2 PP5

The phase morphology of WAXS can be correlated to the structure observed by TEM (Figures 6.2- 6.4). The aggregated clay morphology was characterized with TEM. The differences in the scattering densities between the clay and the matrix PP, clay aggregates could easily be imaged with TEM. The dark lines in the photographs represent nm (~1-5) thick clay layers, the spaces between the dark lines are interlayer spaces, and gray bases represent the PP matrix. TEM images of 1 and 2 phr reinforced PP nanocomposite displayed individual clay layers that were well dispersed in the PP matrix. Some of the clays agglomerated at the unit level 3-5 nm in thickness. The thickness of some of the dark lines was greater than that of single platelet. This may indicate the presence of remnant multiplets in the nanocomposites (Figure 6.4).

Figures 6.2 and 6.3 show the individual silicate layers of thickness in the order of nanometer with aspect ratio in the range of 100 to 250 nm. The exfoliated morphology was due to the lower filler concentration, high speed dispersion and compatibilization with PP-g-MA that was present in the nanocomposites. In the ultimate platelet configuration, the clay was completely dispersed and fully exfoliated, resulting in the specific surface at its maximum to have the greatest advantage obtained from the nanocomposite. This has been achieved for the 1 and 2 phr nanocomposites made. The strong interaction between PP molecules and PEGC treated clay would be expected to be due to the presence of the long alkyl chain (Figure 5.7, Section 5.2.3.3) of PEGC and PP-g-MA added. As many researchers mentioned that it is difficult for polyolefin (PP) to adhere to other materials [143, 191]. Interfacial agents play an important role in overcoming this difficulty. In order to overcome this challenge in the trial experiments with this treated clay, (PP-g-MA) was used as a compatibilizer. PP-g-MA reacts with –OH groups on the clay surface, thus increasing the compatibility between clay and PP. A lower (001) diffraction signal intensity in Figure 6.1 can be related to a higher extent of platelets exfoliation that occurred during the synthesis and processing of the nanocomposite. Giannelis et al suggested that the polymer intercalation proceeded from the primary clay particle edges towards the particle center [109, 125]. Complete nano-layer separation needs very favorable polymer- clay interactions to overcome the penalty of polymer confinement. At higher clay loading of 5 phr, a small peak is present at 5.5º in the diffraction pattern that is due to the

attainment of intercalation rather than complete exfoliation of clay layers (Figure 6.1). Disappearance of peaks in clay PP composites suggests two conclusions: 1. Exfoliation - separation of clay lamella into individual clay layers. 2. Aggregation – clustering of clay gallery layers, undisturbed by shearing action. Moad et al suggested that the clay layers exfoliated in the presence of PEO based surfactants in the preparation of PP nanocomposites [8, 9]. The authors melt intercalated untreated clay with PEO based surfactants for preparing PP nanocomposites. Shearing action of the extruder supported exfoliation of clay layers without use of compatibilizer. In this chapter, the effect of melt intercalation on the dispersion of clay layers through WAXS and TEM methods is discussed. Chiu et al suggested that Cloisite30B filled polymer nanocomposites will not exfoliate with PP-g-MA because of the higher polarity of Cloisite 30B [192]. The same authors demonstrated exfoliation with poly(styrene-co-maleic-anhydride) (PS-g-MA) oligomer as compatibilizer instead of PP-g-MA. The higher degree of polarity of PS-g-MA resulted in exfoliation [192]. Clay interlayer expansion depends mainly on the compatibility between the polymer and the organic intercalant and the chemical interaction between the two phases.

The process of exfoliation proceeds through three phases. Firstly the gallery separation is increased; secondly, the attractive forces between the layers are disrupted, and finally the interaction between the plates and the matrix is increased. In this research, the following mechanism is proposed. Layered clay was intercalated by non ionic PEG-ML that can form complex with the clay surfaces instead of ion-exchange of sodium ions (Figure 5.7, Section 5.2.3.3). Treated clay has both surface and edge charges. Charges on the edges are accessible to modification, but do not accomplish in improvement of interlaminar separation. These sites represent opportunity for functional groups like maleic anhydride (PP-g-MA). PP-g-MA increased both the compatibility and chemical interaction between the polymer and treated clay [87, 192]. This could be the reason for exfoliation of clay lamella. Ultraturrax high speed disperser and PP-g-MA compatibilizer addition along with long alkyl chain clinging to the surface of clay layer could be the possible reasons for the exfoliation of clay layers in the polymer matrix (Figure 5.7, Section 5.2.3.3). Ultraturrax high speed dispersion lead to exfoliation of the clay layers, for researchers elsewhere [172,

193, 194]. It was found that PP molecules, with the help of compatibilizing agent (PP-g- MA) separated the clay particles into individual layer aggregates of nanometer thickness.

The phase morphology was evident in TEM micrographs. Three figures 6.2 -6.4 showing 1, 2, and 5 phr treated clay in PP matrix. In the 5 phr composite, there was some aggregation observed. TEM images show the more complex morphological features of the clay state. At 5 phr clay ratio, the appearance of individual clay layers is evident, but there are regions containing platelets that have not fully separated giving rise to the periodicity in structure and diffraction peak. Although the specimens were prepared with solvent, and ultrasonication to facilitate the intercalation, full exfoliation was not achieved. It should be noted that the mass transport of highly viscous resin into the clay galleries presents a limitation [4]. This step is considered as one of the important limiting factors for clay platelet separation. In addition, the relative amount of clay platelet separation and aggregation depends strongly on the mixing technique and surfactant used for modifying the clay [4]. Most clay particles were well dispersed in PP matrix, which was due to good compatibility between PP, PP-g-MA and end alkyl chain of treated clay (monolaurate chain of PEG). Avella et al prepared exfoliated PP based nanocomposites by solution blending [142]. They also observed that exfoliation of clay layers in nanocomposites occurred only at 1 and 3 %wt of clay loading, but not at 5 %wt clay. In the 5 %wt nanocomposites, it was suggested that the clay layers collapse leading to an immiscible system. Mass transport into the primary particle was found to be the limiting step to nanocomposite formation, the degree of constituent mixing is critical for rapid nanocomposite formation [142]. Shear processing, such as with an ultrasonicator, parallel plate rheometer, conventional compounding equipment, high speed mixer, will decrease the nanocomposite formation time by disruption of primary particles and establishment of composite uniformity [170, 189, 194]. In this case, Ultraturrax mixing was sufficient to disperse the clay layers; however, they cannot give maximum energy to fully exfoliate the clay layers.

Figure 6.2 TEM image of PP-PEGC(SB) nanocomposite -1 phr PEGC

Figure 6.4 TEM image of PP-PEGC(SB) nanocomposite -5 phr PEGC