Polystyrene montmorillonite composites

WAXS and TEM indicate a similar degree of dispersion to the melt-blended SAN-montmorillonite composite with 13.5% acrylonitrile and the SMA-montmorillonite composite with 25% MA discussed in the above work. The montmorillonite is dispersed well in the polystyrene and appears to be intercalated with polymer. Fluorinated synthetic mica (SOMASIF ME-100 manufactured by Co-op Chemical) was treated with the same quat and processes identical to the montmorillonite resulted in significantly inferior results. Sonication was demonstrated to be a significant processing variable for the preparation of improved polystyrene-montmorillonite composites. Unfortunately, no mechanical testing results were provided. 

Electrical conductivity measurements have been reported on a wide range of polymers including carbon nanofibre reinforced HOPE [52], carbon black filled LDPE-ethylene methyl acrylate composites [28], carbon black filled HDPE [53], carbon black reinforced PP [27], talc filled PP [54], copper particle modified epoxy resins [55], epoxy and epoxy-haematite nanorod composites [56], polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) blends [57], polyacrylonitrile based carbon fibre/PC composites [58], PC/MnCli composite films [59], titanocene polyester derivatives of terephthalic acid [60], lithium trifluoromethane sulfonamide doped PS-block-polyethylene oxide (PEO) copolymers [61], boron containing PVA derived ceramic organic semiconductors [62], sodium lanthanum tetrafluoride complexed with PEO [63], PC, acrylonitrile butadiene [64], blends of polyethylene dioxythiophene/ polystyrene sulfonate, PVC and PEO [65], EVA copolymer/carbon fibre conductive composites [66], carbon nanofibre modified thermotropic liquid crystalline polymers [67], PPY [68], PPY/PP/montmorillonite composites [69], carbon fibre reinforced PDMS-PPY composites [29], PANI [70], epoxy resin/PANI dodecylbenzene sulfonic acid blends [71], PANI/PA 6,6 composites [72], carbon fibre EVA composites [66], HDPE carbon fibre nanocomposites [52] and PPS [73]. 

Many other types of ECP have been described. These include PS-block-PPO [61], boron containing PVA [62], polyethylene dioxythiophene/polystyrene sulfonate [65], PC-ABS composites [64], PEO composites [64], PEO complexes with sodium lanthanum tetrafluoride [63], chlorine substituted PANI [70], PVP-PVA coupled with potassium bromate [57], PANI-PA 6,6 composite films [72], talc-PPY composites [54], epoxy resin alpha-haematite nanorod composites [56], PP-montmorillonite composites [69], magnetite containing polymers [105], LDPE [27], PC-acrylonitrile-butadiene composites [106], sodium ion conducting PEO complexed with sodium lanthanum tetrafluoride [63], PVDE [107], PANI composites [108], PP novolac resins [109], dendrimers containing light switchable azobenzene [110],PVP/PVA [107] and PPY[111]. 

Electrical properties have been reported on numerous carbon fiber-reinforced polymers, including carbon nanoflber-modified thermotropic liquid crystalline polymers [53], low-density polyethylene [54], ethylene vinyl acetate [55], wire coating varnishes [56], polydimethyl siloxane polypyrrole composites [50], polyacrylonitrile [59], polycarbonate [58], polyacrylonitrile-polycarbonate composites [58], modified chrome polymers [59], lithium trifluoromethane sulfonamide-doped polystyrene-block copolymer [60], boron-containing polyvinyl alcohols [71], lanthanum tetrafluoride complexed ethylene oxide [151, 72, 73], polycarbonate-acrylonitrile diene [44], polyethylene deoxythiophe-nel, blends of polystyrene sulfonate, polyvinyl chloride and polyethylene oxide [43], poly-pyrrole [61], polypyrrole-polypropylene-montmorillonite composites [62], polydimethyl siloxane-polypyrrole composites [63], polyaniline [46], epoxy resin-polyaniline dodecyl benzene sulfonic acid blends [64], and polyaniline-polyamide 6 composites [49]. 

A review of the work found above with the preparation of polyethyl-ene-montmorillonite composites, polypropylene (polyethylene with pendant methyl groups)-montmorillonite composites, and polystyrene (polyethylene with pendant phenyl groups)-montmorillonite composites indicates that one can balance the hydrophilic-hydrophobic balance of polyethylene and polypropylene with polar functionality with the hydrophilic-hydrophobic balance of organomontmorillonite more effectively than with a similar strategy as regards polystyrene. 

Hwang et al. [113] synthesized via in situ polymerization high-impact polystyrene (HlPS)/organically modifled montmorillonite (organoclay) nanocomposites. X-ray diffraction and TEM experiments revealed that intercalation of polymer chains into silicate layers was achieved, and the addition of nanoclay led to an increase in the size of the robber domain in the composites. In comparison with neat HIPS, they found that the HIPS/organoclay nanocomposites exhibited improved thermal stabiHly as well as an increase in both the complex viscosity and storage modulus, and they may have been influenced by a competition between the incorporation of clay and the decrease in the molecular weight of the polymer matrix. 

Figure 16.24 shows the schematic representation of dispersed clay particles in a polymer matrix. Conventionally dispersed clay has aggregated layers in face-to-face form. Intercalated clay composites have one or more layers of polymer inserted into the clay host gallery. Exfoliated polymer/clay nanocomposites have low clay content (lower than intercalated clay composites which have clay content -50%). It was found that 1 wt% exfoliated clay such as hectorite, montmorillonite, or fluorohectorite increases the tensile modulus of epoxy resin by 50-65%. Montmorillonite was used in a two stage process of nanocomposite formation. In the first step, montmorillonite was intercalated with vinyl monomer and then used in the second step to insert polystyrene by in situ polymerization. 

The test samples were prepared by injection molding with a bench-top pneumatic ram molder at 60 psi. The time to file the mold increased with increasing content of acrylonitrile in the polystyrene (0.25 s for pure polystyrene to 0.84 s for 58% acrylonitrile content). The polymer melts were injected at 225°C into an 80°C heated mold. The sample size for testing was 0.155x0.4x3.1 cm. The montmorillonite content in the composites was 2 and 3.2 wt.%. 

The impact on the PHRR when substituting a polymer oligomer as a surface treatment on montmorillonite for a quaternary ammonium ion is not a panacea [51,52]. The comparison of methylmethacrylate oligomer-treated montmorillonite with quat-treated montmorillonite in poly(methylmethacrylate), polystyrene, high-impact polystyrene, acrylonitrile-butadiene-styrene terpolymer, polypropylene, and polyethylene nanocomposites indicated sensitivity to polymer type and a poor correlation to the degree of exfoliation determined by X-ray analysis and TEM. The impact of polymer structure associated with the montmorillonite appears to be a significant variable relating to the PHRR of these composites. In this book, chapter 4 on barriers... 

Wang ° used two different organic modifications of the montmorillonite, one contains a styryl monomer on the ammonium ion while the other contains no double bond. A double bond that may be involved in the polymerization reaction is present in the cation of the clay. Polystyrene-clay nanocomposite has been prepared by bulk, solution, suspension, and emulsion polymerization as well as by melt blending. The organic modification as well as the mode of preparation may determine whether the composite is either exfoliated or intercalated. Exfoliation is more likely to occur if the ammonium ion contains a double bond... 

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