Nanofiller exfoliation

However, questions remain about the best processing methods required by nanocomposites in production situations, allowing proper nanofiller exfoliation and dispersion. Questions also have been raised about whether nanocomposites... 

The kinetics of PAA, synthesized from 4,4 -oxydianiline and pyromellitic dianhydride, solid-state imidization both in filler absence and with addition of 2 phr Na+-montmorillonite was studied [1], The nanofiller was treated by solution of P-phenylenediamine in HC1 and then washed by de-ionized water to ensure a complete removal of chloride ions. The conversion (imidization) degree Q was determined as a function of reaction duration t with the aid of Fourier transformation of IR-spectra bands 726 and 1014 cm 1. The samples for FTIR study were obtained by spin-coating of PAA/Na+-montmorillonite mixture solution in N,N-dimethylacetamide on KBr disks, which then were dried in vacuum for 48 h at 303 K. It was shown, that the used in paper [1] method gives exfoliated nanocomposites. The other details of nanocomposites polyimid/Na+-montmorillonite synthesis and study in paper [1] were adduced. The solid-state imidization process was made at four temperatures 7) 423, 473, 503 and 523 K. 

The main problem with nanofillers is the need for complete exfoliation. Some special compounding techniques have been developed such as, for example, the ZSK MEGA compounder by Coperion Werner Pfleiderer with a special screw configuration. 

The lowering of die swell values has a direct consequence on the improvement of processability. It is apparent that the processability improves with the incorporation of the unmodified and the modified nanofillers. Figure lOa-c show the SEM micrographs of the surface of the extrudates at a particular shear rate of 61.2 s 1 for the unfilled and the nanoclay-filled 23SBR systems. The surface smoothness increases on addition of the unmodified filler, and further improves with the incorporation of the modified filler. This has been again attributed to the improved rubber-clay interaction in the exfoliated nanocomposites. 

It is a common phenomenon that the intercalated-exfoliated clay coexists in the bulk and in the interface of a blend. Previous studies of polymer blend-clay systems usually show that the clay resides either at the interface [81] or in the bulk [82]. The simultaneous existence of clay layers in the interface and bulk allows two functions to be attributed to the nanoclay particles one as a compatibilizer because the clays are being accumulated at the interface, and the other as a nanofiller that can reinforce the rubber polymer and subsequently improve the mechanical properties of the compound. The firm existence of the exfoliated clay layers and an interconnected chain-like structure at the interface of CR and EPDM (as evident from Fig. 42a, b) surely affects the interfacial energy between CR and EPDM, and these arrangements seem to enhance the compatibility between the two rubbers. 

Obstacles to greater nanofiller use remain, and just explaining these challenges requires a new set of terminology. The main issue is that nanofiller partides are difficult to disperse meaning that actual nanocomposite properties may not reach their potential or theoretical properties. For example, for proper dispersal, sheet-like nanoday platelets must be exfoliated, physically or chemically, to separate them into individual layers. This issue is probably the most discussed and most problematic obstade impeding the full commerdal-ization of nanocomposite compounds, since the full surface area of each separated sheet or platdet is what creates optimum properties [7-31, 7-32[. 

Hollow tubes extracted from the silica/alumina clay halloysite exist naturally as particles roughly 500 nm long, and they do not have the exfoliation issues of platy nanoclays. Thus, these nanofillers do not require the same specialized equipment and processing that nanoclays require for proper dispersal. As fillers, nanotubes provide high properties because of their very high aspect ratios. 

Polyhedral oligomeric silsesquioxane (POSS) has been described as a three-dimensional "cage-shaped molecule composed of a silicon-oxygen framework bonded to organic groups that make it compatible with a polymer matrix. Unlike conventional nanofillers that must be dispersed and exfoliated to be useful, POSS molecules formulated in the resin are induced by shear to "self-assemble ... 

Yang Y, Duan H, Zliang S, Niu P, Zhang G, Long S, et al. Morphology control of nanofillers in poly (phenylene sulfide) a novel method to realize the exfoliation of nanoclay by sio2 via melt shear flow. Compos Sci Technol 2013 75 28-34. 

The majority of the FR studies on nanofiller incorporation in polymers involve exfoliated clay. Studies involving polyamide-6 (PA-6) [24, 31] and PP [32] yielded... 

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