Home Education Fillers for Polymer Applications
Stiffness and Heat Distortion Temperature
Nanoclays have a big effect on these properties in thermoplastic composites, and this was the first area to arouse interest. Typical results are presented in Table 6 and show how much benefit can be achieved at very low loadings. It also shows how the effect soon starts to tail off, as loading increases. Conventional fillers such as glass fiber and mica give similar improvements, albeit at higher addition levels. Because of the loading restrictions on the nanoclays, conventional fillers are often also able to give higher absolute property levels, and glass fiber still appears to be more cost competitive for general thermoplastics use.
Despite these limitations, the nanoclays combine these effects with others such as transparency, low density, good surface finish, and better scratch and mar resistance and are beginning to be used where these are important.
Gas Barrier Properties
Properly aligned and dispersed, low levels of clay are able to give good barrier properties, accompanied by good clarity and low density. This application has
Table 6 Typical effects of a well dispersed nanoclay in a Pa 6 matrix (optimal situation)
Fig. 3 Tortuous diffusion path created by aligned platelike particles in a polymer film (reproduced, with permission, from Particulate-Filled Polymer Composites (Ed Rothon R.N.), 2nd Edition, Rapra Technology, Shawbury UK, 2003)
recently been reviewed by Cui et al. (2015). Their effect on diffusivity is believed to be due to the creation of a tortuous diffusion path, as shown in Fig. 3. Because of their extreme thinness and ability to align, they are able to be used in thin films, such as found in packaging. This was one of the first areas to be commercialized but has not grown as fast as expected, due to the difficulties in extending the excellent performance found in nylon 6 to more common packaging materials.
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