Organically modified layered fillers

Since the possibility of direct melt intercalation was first demonstrated [11], melt intercalation has become a method of preparation of the intercalated polymer/ layered silicate nanocomposites (PLSNCs). This process involves annealing, statically or under shear, a mixture of the polymer and organically modified layered fillers (OMLFs) above the softening point of the polymer. During annealing, the polymer chains diffused from the bulk polymer melt into the nano-galleries between the layered fillers. 

Because both melt-processing and polymerization of PET necessitate high temperatures (250-300 °C), it becomes obvious at the outset that any organically modified layered silicates that are intended as reinforcing fillers for PET should employ surfactants with appropriately high thermal stability. The typical alkylammoniums, for example, decompose below these temperatures. Two examples of higher-temperature surfactants that have been employed as modifiers for layered silicates in PET nanocomposites are pyridinium and phosphonium specifically, cetylpyridinium, via solution dispersion [22], and dode-cyltriphenylphosphonium, via in situ polymerization [23], In these two cases, both the... 

Biomedical polyurethanes have also been modified with organically modified layered silicates (OLS) to improve mechanical properties and reduce gas permeability. Xu et al. [26] demonstrated an increase in tensile modulus with increased OLS concentration without the loss of strength and ductihty that is typical for filler systems. Additionally, they observed a fivefold decrease in water vapor permeability, which is a major advantage for blood-contacting biomedical devices. 

Table 12.2 summarizes the mechanical properties of polybutadiene rubber-clay nanocomposites. The hardness, tensile strength, elongation at break, and permanent set all improved with increasing the clay content (5—40 phr)." " The mechanical properties of polybutadiene rubber-clay nanocomposite with 20 pin-clay content have been compared to those of the polybutadiene composites filled with 20 phr carbon black (SFR and N330), as presented in Table 12.3. This data shows that the organically-modified layered silicate was as effective a reinforcing filler, as carbon black. Some of the mechanical properties of polybutadiene nanocomposite such as hardness, tear strength, and tensile strength even exceeded those of the carbon black filled compounds." " These excellent mechanical properties of the nanocomposites resulted from the uniformly dispersed layered silicate in the elastomer matrix, and the strong interaction between the nanoclay layers and rubber chains. Thus layered silicates could be used in the polybutadiene industry as a promising reinforcing filler, if the layers...

ILs based on pyridinium, imidazolium, or phosphonium cations to modify layered silicates (fillers) according to the nature of the polymer matrices have been reported. Recently, these types of ILs are emerging as new alternatives for the design of thermally stable organically modified clays. 

In the case of layered silicates, the filler is present in the form of sheets one to a few nanometer thick and hundreds to thousands nanometer long. In general, the organically modified silicate nanolayers are referred to as nanodays or organo-silicates [12]. It is important to know that the physical mixttue of a polymer and layered silicate may not form nanocomposites [13]. Pristine-layered sUicates usually contain hydrated Na" " or K ions [13]. To render layered silicates misdble with other polymer matrices, it is required to convert the normally hydrophUic sUicate surface into an organophilic one, which can be carried out by ion-exchange reactions with... 

A number of synthetic techniques have been successfully employed for the preparation of clay/CNT hybrids. The most commonly used techniques are in situ growth of CNTs on clay layers in presence of different catalyst [105], wet mixing of organically-modified CNT with clay [106] and dry grinding of CNT and MMT [25,104,107]. These prepared MMT/ CNT hybrids are used as reinforcing filler in epoxy/nylon-6/ PEO [108], hydrogen peroxide sensors and biosensors [109]. 

---