Unfilled polymer matrix

B) Tensile and Impact Performance Table I presents a summary of tensile impact and ultimate tensile data for the three sets of composites. For ease of comparison both sets of data are normalized to the reference tensile impact or ultimate tensile performance of the unfilled polymer matrix. 

In recent years, both academic and industrial research on new nanocomposites based on clays fillers within a polymer matrix have rapidly developed [1-3]. Advances in this field have shown that these materials may exhibit enhanced properties (for example, increased heat and mechanical resistance, electrical conductivity and gas barrier properties) compared to the corresponding unfilled polymer matrix. Despite recent progress in the design of these nanoimmposites, many structure-properties relationships are still to be elucidated. 

For clay-reinforced nanocomposites, increases in modulus compared with the unfilled polymer matrix have been observed in many systems with the effect increasing with filler content as expected but the properties are highly sensitive to microstructure (Luo and Daniel, 2003). In general, to maximise stiffness (and thermal properties) it is necessary to achieve fiiU exfoliation and dispersion which is not readily achieved (Vu etal., 2001, Zhang etal., 2004). 

Interestingly, a temperature increase lowers the strength of a novolac syntactic foam with carbon filler less than it reduces the strength of the unfilled foam (Fig. 16)39). This is undoubtably because there is destructive thermal oxidation in the plastic foamed by gas, due to the oxygen in the gas. Thermal oxidation in syntactic foams is much lower, because the microsphere shell forms a protective barrier between the gas within the sphere and the polymer matrix. 

An examination of the experimental findings and the calculation model shows that the deformability of a syntactic foam depends mainly on the elastic properties of the polymer matrix, whereas the filler concentration mainly affects its compressibility. In fact, monolithic (unfilled) samples do deform elastically at the start of the compression curve, but when the material is deformed further, the forced elasticity limit is reached (Fig. 21). Thus, the nominal ultimate strength for non-brittle failure is determined by the fact that the forced elastic limit is reached, and not because the adhesive ties have lost their stability (as it is the case with light plastic foams) 8 10). 

Griffin32 demonstrated that the decline in properties of starch-filled composites could be mitigated somewhat by treating the surface of the starch granules to make them more hydrophobic. This treatment improved the adhesion and stress transfer across the particle/matrix interface and resulted in improved properties relative to no treatment, although properties were still generally reduced compared to the unfilled polymer. 

In this study, both the normal mode relaxation of the siloxane network and the MWS processes arising from the interaction of the dispersed nanoclay platelets within the polymer network have been observed. Although it is routine practice to observe the primary alpha relaxation of a polymeric system at temperatures below Tg, in this work it is the MWS processes associated with the clay particles within the polymer matrix that are of interest. Therefore, all BDS analyses were conducted at 40°C over a frequency range of 10 to 6.5x10 Hz. At these temperatures, interfacial polarization effects dominate the dielectric response of the filled systems and although it is possible to resolve a normal mode relaxation of the polymer in the unfilled system (see Figure 2), MWS processes arising from the presence of the nanoclay mask this comparatively weak process. 

According to IK-spectroscopy inorganic filler is inert in the relation to polymeric matrix because the identical spectra of absorption of initial unfilled polymer and the polymer filled with inorganic filler are the same. Hence, mechanical behavior of PCM is defined by structural organization of composite materials, its dependence on conditions of formation and test on PCM (in our case, speed of deformation). 

Hydrostatic extrusion can also be applied to polymers filled with short fibres, so that products are obtained where the fibres are aligned in addition to the polymer matrix. Excellent results have been obtained with glass reinforced POM 9S), where the Young s moduli of the extruded products were about twice those of unfilled polymer with a comparable deformation ratio. A theoretical modelling of the development of mechanical anisotropy in these materials 96), using the aggregate model97,981 was shown to be successful provided it is assumed that... 

Studies on a similar group of materials - polymeric composites reinforced with sisal fibers - were conducted by Manchado et al. [35]. They analyzed the presence of different fibers, such as sisal, on crystallization of polypropylene. The composites were prepared in special chamber for mixing where the matrix was plastified at 190°C. Obtained materials were subjected to thermal analysis by DSC. The analysis of thermograms allowed for a similar finding like in Joseph s studies [34], The presence of sisal fibers, as well as other fibers used in the study, accelerated crystallization of polypropylene. This was explained by the nucleating effect of sisal filler. Also, the half-time crystallization (ti/2) decrease was observed for polypropylene with the addition of sisal fibers in comparison with unfilled polypropylene. The analysis of nonisothermal crystallization showed that the degree of polypropylene crystallinity is higher for the composites filled with sisal fibers than for unfilled polymer. 

Fig. 10 Diagram demonstrating the tortuosity of a diffusing penetrant introduced on an exfoliating solid, layered in a polymer matrix. (A) Filled polymer and (B) unfilled polymer [82], Copyright 2007. Reproduced by permission of Elsevier Science Ltd.

The ratio of molecules in the immobilized layer of molecules in the region of the glass fiber surface, compared with the remaining polymer matrix, has an empirical relationship with the corresponding specific heat jump attributed to the unfilled polymer resin ... 

An innovative strategy to enhanee the mechanieal properties of biodegradable polymers is the ineorporation of nanomaterials as fillers within polymer matrices. With the appropriate modifications to facilitate dispersion into polymers and to enhance interactions with the snrronnding matrix, nanocomposites have demonstrated improved mechanical properties compared with unfilled polymers or polymers loaded with larger, micrometersized particles. A few studies have also shown enhanced cell function when bone cells are cultured on nanophase ceramic materials. 

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