Silicate polymers, factors affecting

The ability to exfoliate and disperse the layered silicate into a polymer matrix is related to a number of factors such as the exchange capacity of the sihcate, the polarity of polymer and the chemical nature of the organic modifier. Processing conditions are one of the factors affecting the dispersion of the sihcate layers. The disappearance of the peak in the XRD patterns and the decrease of agglomerated particles in the SEM images indicate that the... 

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. 

In general, the outcome of polymer melt intercalation is determined by the interplay of entropic and enthalpic factors." The confinement of the polymer chains inside the silicate galleries results in a decrease in the overall entropy of the polymer chains, and the increased conformational freedom of the tethered ammonium cations compensates the entropy loss as the silicate layers separate with each other. However, the small increase in the gallery spacing does not affect the total entropy change rather, the total enthalpy will drive the intercalation. The enthalpy of mixing has been classified into two components the interaction between polymer and ammonium cations and the interaction between the layered polar silicates and the polymer chains. In most conventional organo-modified silicates, the tethered ammonium cations are apolar. The apolar interactions between the polymer and ammonium cations are unfavorable to the... 

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