Unsaturated and other Functional Organic Acids in Composites

6 Unsaturated and other Functional Organic Acids in Composites 

There have been few academic studies of the adsorption of unsaturated acids onto fillers. Ottewill and Tiffany studied the adsorption from heptane solution of acids with 18 carbon atoms and various levels of unsaturation, onto uncoated rutile titanium dioxide [33]. As with calcium carbonate, stearic acid was found to give monolayer coverage at a concentration suggesting vertical orientation. With all the unsaturated acids, stepped isotherms were obtained, which were interpreted as multipoint attachment through both acid and unsaturated groups at low concentrations, but with re-orientation to a conventional vertical orientation at higher concentrations. 

In the work mentioned previously, Liauw and co-workers also examined the adsorption of acrylic, linoleic, linolenic and oleic, acids from organic solution onto a magnesium hydroxide filler [8]. Salt formation was observed for all the acids. All the unsaturated long chain acids gave lower apparent mono-layer levels than stearic acid, which was thought to be due to steric effects and even multi-point adsorption through the unsaturation. 

Miyata and co-workers have compared stearic and oleic acid derived coatings on magnesium hydroxide fillers in polypropylene and found better impact strength for the oleic acid treatment [25]. The reason for this is unclear and the results do not appear to have been confirmed by others. Nevertheless, some commercial magnesium hydroxides are coated with unsaturated acids similar to oleic, suggesting that there may be a real benefit from its use in some circumstances. 

In the past, there has been significant interest in acids with especially reactive unsaturation, such as acrylic and maleic acid (or its anhydride) [34]. More recently, pre-grafting of these species onto a polymer backbone has become the preferred method of use. This is discussed in Section 4.7.7. 

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