Dispersion polypropylene nanocomposites

Morgan, A.B. Harris, J.D. Effects of organoclay soxhlet extraction on mechanical properties, flammability properties and organoclay dispersion of polypropylene nanocomposites. Polymer 2003, 44, 2313-2320. 

Prashantha, K., Soulestin, J., Lacrampe, M. R, Claes, M., Dupin, G., and Krawczak, P. 2008. Multi-walled carbon nanotube filled polypropylene nanocomposites based on masterbatch route Improvement of dispersion and mechanical properties through PP-g-MA addition. Express Polymer Letters 2 735-745. 

Cheng HKF, Pan Y, Sahoo NG, Chong K, Li L, Hwa Chan S, Zhao J (2012) Improvement in properties of multiwalled carbon nanotube/polypropylene nanocomposites through homogeneous dispersion with the aid of surfactants. J Appl Polym Sci 124 1117... 

Even after organic modification of the clays, polypropylene does not wet the surface of clays because it is nonpolar. It is necessary to blend in a functionalized polymer such as maleated polypropylene (PP-g-MA) that wets the modified clay surface more readily and is also miscible with the bulk polymer. Okada and coworkers were the first to produce polypropylene layered silicate nanocomposites by melt compounding the modified elay with PP-g-MA and PP. The progress made since then in preparing and characterizing polypropylene layered silicate nanocomposites is reviewed in this chapter. We discuss advances in formulations, preparation methods and characterization then proceed to effects of the dispersion state (intercalated vs. exfoliated) and of silicate loading on crystallinity, mechanical performance and other properties, and end with a summary of progress to date with these composites. All the results presented in this chapter refer to isotactic polypropylene nanocomposites with layered or smectite clays. 

Incorporation of silicate nanolayers in semi-crystalline polymers like polypropylene ean have a two-fold effect on the barrier properties, (1) well oriented large aspeet ratio platelets will increase the tortuosity of the diffusion path and (2) the nanolayers will affect the crystalline order (size and interlamellar spacing) and possibly affect the barrier properties. The extent of orientation is greater in blown film than in extmsion cast film and this leads to similar trends in barrier properties of polypropylene nanocomposites with 7wt.% 1.3 IPS (silated) clay as reported by Qian et al. With cast films, the nanoeomposite had a lower permeability to oxygen by a faetor of 1.5 compared to neat polypropylene. With blown films, the nanocomposite permeability to oxygen was lower by a factor of 2.5 compared to neat polypropylene. However, Ellis and D Angelo were able to prepare only intercalated polypropylene nanocomposites with the same 1.31 PS and obtained no improvement in permeability to a solvent over that for neat polypropylene. This underlines the greater sensitivity of barrier performanee to the level of dispersion and orientation. 

There are two basic types of nanocomposites, in which particles are intercalated or exfoliated. In an intercalated composite the nanodispersed filler still consists of ordered structures of smaller individual particles, packed into intercalated structures. Exfoliated particles are those dispersed into practically individual units, randomly distributed in the composite. Layered silicates, such as montmorillonite clays or organoclays, can be used in nanocomposites. Because clays are hydrophilic and polyolefines are hydrophobic, it is not easy to make a nanocomposite based on polyethylene or polypropylene because of their natural incompatibility. 

It is not clear why nanocomposite particles weaken wood flour- and rice-hulls-filled polypropylene, but it seems to be a repetitive and reproducible phenomenon. Certainly, it can be hypothesized that the reason is the nonuniform dispersion of cellulose fillers and nanoclay particles, but it remains just a hypothesis. 

Single clay layers or 100% dispersion of the clay in polymer matrices is also the ideal situation in which to obtain nanocomposite materials with enhanced mechanical properties. This was achieved by researchers at the Pennsylvania State University ° with a semifluorinated organic surfactant to modify the montmorillonite, which is subsequently compounded with polypropylene (functionalized with, e.g., maleic anhydride). In The Netherlands the clay is intercalated with polyethyl-... 

In the isothermal crystallization of polypropylene montmorillonite (PP-MMT) nanocomposites, it was found that the crystallinity of the composites decreased with increasing montmorillonite content, indicating the dispersion of MMT layers in the polypropylene matrices. The nanoparticles confined the polypropylene chains and hindered the polymer crystallization. The spherulites of the PP-MMT nanocomposites were greatly decreased in size as MMT was introduced. On the other hand, the crystallization rate increased dramatically with the increasing of MMT content. The interfacial free-energy per unit area perpendicular... 

Mechanical properties of PP/PPy nanocomposites were investigated by tensile tests. The effect of loading different amounts of polypyrrole nanopartides into thermoplastic polypropylene matrix and the changes in mechanical properties produced by incorporation of polypyrrole nanopartides were examined. In order to understand the effect of using sodium dodecylsulphate as dispersant in PP/PPy nanocomposites, identical tests were performed also for the nanocomposites prepared with dispersant. 

The reinforcement of polypropylene and other thermoplastics with inorganic particles such as talc and glass is a common method of material property enhancement. Polymer clay nanocomposites extend this strategy to the nanoscale. The anisometric shape and approximately 1 nm width of the clay platelets dramatically increase the amount of interfacial contact between the clay and the polymer matrix. Thus the clay surface can mediate changes in matrix polymer conformation, crystal structure, and crystal morphology through interfacial mechanisms that are absent in classical polymer composite materials. For these reasons, it is believed that nanocomposite materials with the clay platelets dispersed as isolated, exfoliated platelets are optimal for end-use properties. 

Polypropylene (PP) is one of the most widely used plastics in large volume. To overcome the disadvantages of PP, such as low toughness and low service temperature, researchers have tried to improve the properties with the addition of nanoparticles that contains p>olar functional groups. An alkylammonium surfactant has been adequate to modify the clay surfaces and promote the formation of nanocomposite structure. Until now, two major methods, i.e., in-situ polymerization( Ma et al., 2001 Pirmavaia, 2000) and melt intercalation ( Manias et al.,2001) have been the techniques to prepare clay/PP nanocomposites. In the former method, the clay is used as a catalyst carrier, propylene monomer intercalates into the interlayer space of the clay and then polymerizes there. The macromolecule chains exfoliate the silicate layers and make them disperse in the polymer matrix evenly. In melt intercalation, PP and organoclay are compounded in the molten state to form nanocomposites. 

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