Composites Using Nano-Fillers

Some aspects of the technology are covered in other chapters of this work, but it was considered that the topic was of sufficient current interest to warrant it s own chapter. However, it must be stressed that what is presented here is only a snap-shot in what is a rapidly changing and developing technology. 

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The inherent properties of CNT assiune that the structure is well preserved (laige-aspect-ratio and without defects). The first step toward effective reinforcement of polymers using nano-fillers is to achieve a uniform dispersion of the fillers within the hosting matrix, and this is also related to the as-synihesized nano-carbon structme. Secondly, effective interfacial interaction and stress transfer between CNT and polymer is essential for improved mechanical properties of the fiber composite. Finally, similar to polymer molecules, the excellent intrinsic mechanical properties of CNT can be fully exploited only if an ideal imiaxial orientation is achieved. Therefore, during the fabrication of polymer/CNT fibers, four key areas need to be addressed and imderstood in order to successfully control the... 

Clays have long been used as fillers in polymer systems because of low cost and the improved mechanical properties of the resulting polymer composites. If all other parameters are equal, the efficiency of a filler to improve the physical and mechanical properties of a polymer system is sensitive to its degree of dispersion in the polymer matrix (Krishnamoorti et ah, 1996). In the early 1990s, Toyota researchers (Okada et ah, 1990) discovered that treatment of montmorillonite (MMT) with amino acids allowed dispersion of the individual 1 nm thick silicate layers of the clay scale in polyamide on a molecular. Their hybrid material showed major improvements in physical and mechanical properties even at very low clay content (1.6 vol %). Since then, many researchers have performed investigations in the new field of polymer nano-composites. This has lead to further developments in the range of materials and synthesizing methods available. 

Fibers have been widely used in polymeric composites to improve mechanical properties. Cellulose is the major substance obtained from vegetable fibers, and applications for cellulose fiber-reinforced polymers have again come to the forefront with the focus on renewable raw materials. Hydrophilic cellulose fibers are very compatible with most natural polymers. The reinforcement of starch with ceUulose fibers is a perfect example of a polymer from renewable recourses (PFRR). The reinforcement of polymers using rigid fillers is another common method in the production and processing of polymeric composites. The interest in new nanoscale fillers has rapidly grown in the last two decades, since it was discovered that a nanostructure could be built from a polymer and layered nanoclay. This new nanocomposite showed dramatic improvement in mechanical properties with low filler content. Various starch-based nano-composites have been developed. 

Alternatively, some papers have based their analysis on the values of the work of adhesion, W and the interfacial tensions rather than co [40,41] to predict the filler localization. Ma et al. [39] compared three different methods to predict the morphology of composites containing nano-CaCOs, based on interfacial tension data, estimation of the work of adhesion, and estimation of the wetting coefficient. They reported that the wetting coefficient is the most accurate tool to predict the phase structure, by comparing with the actual localization of the nano-CaCOg particles observed using SEM. 

The most important filler parameter affecting modulus is its shape. Unfortunately, when the filler is non-spherical theories become much more complicated and the reader is advised to refer to Chow s review [61]. Shape factors can be incorporated in the models mentioned previously but are only useful when applied to very high aspect ratio materials, e.g., fibres. There is also an almost insurmountable problem with particulate fillers the difficulty and effort to measure aspect ratios of micrometre sized particles. Pukansky examined the effects of 11 different fillers in polypropylene [69] and concluded that Young s modulus is affected by the amount of bonded polymer, which is in turn related to surface area, and therefore to both particle size and shape. That observation helps to explain the strong effect that nano-fillers have on the modulus of a composite. Schreiber and Germain showed that modulus depends on the strength of interaction between the polymer and the filler surface [62]. 

ABSTRACT A synthesis method for wood fiber ferrite micro- and nano-composites was developed and the properties of these materials were studied. The new method is based on a wood fiber modification by Fe+VFe+ aqueous solutions under formation of magnetite. The optimum synthesis conditions were defined and the modified wood fibers were used as filler in a polymer matrix to produce composite materials. Magnetite modified composites with special electromagnetic properties and microwave absorption ability were produced. Moreover, the raw material wood is an economically feasible and sustainable source. 

In general, when discussing polymer/CNT composites, two major classes come to mind. First, the CNT nano-fillers are dispersed within a polymer at a specified concentration, and the entire mixture is fabricated into a composite. Secondly, as grown CNT are processed into fibers or films, and this macroscopic CNT material is then embedded into a polymer matrix [65]. The four major fiber-spinning methods (Fig. 11.15) used for polymer/CNT composites from both the solution and melt include dry-spiiming [66], wet-spinning [67],... 

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