Organo-titanates

Catalysts. The choice of the proper catalyst for an esterification reaction is dependent on several factors (43—46). The most common catalysts used are strong mineral acids such as sulfuric and hydrochloric acids. Lewis acids such as boron trifluoride, tin and zinc salts, aluminum haHdes, and organo—titanates have been used. Cation-exchange resins and zeoHtes are often employed also. 

Loadings can be increased by adding a diluent, but this may not always be desirable, as the diluent may detract from other desired properties. Organo titanates can be added to improve filler wetting, enabling higher loadings at the same viscosity. 

Subramanian RV, Nyberg EA, Zirconia and organo-titanate film formation on graphite fiber reinforcement for metal matrix composites, J Mater Res, 7(3), 677-688, 1992. 

Clement JP, Rack HJ, Interfacial modification in G/Al metal matrix composites, Symp on High Temperature Composites, Proc Am Soc Compos, Technomic Publishing Co, 11, 1989. Subramanian RV, Nyberg EA, Zirconia and organo-titanate film formation on graphite fiber reinforcement for metal matrix composites, J Mater Res, 7, 667, 1992. 

Polystyrene Poly(vinyl acetate) Poly(methyl methacrylate) Carnauba wax Dibutyl phthalate Dioctyl phthalate Fish oil Organo silane Organo titanate... 

Inert fillers reduce the cost of the recycled plastics but the mechanical properties, althou enhanced, remain insufficient for secondary applications. Elastomers can remarkably improve some mechanical properties. Some compatibUizing action is contributed by the functionalized polyethylene and sty-rene-butadiene-styrene rubber and CaO coated with organo-titanates. Finally, good results are obtained for blends produced from this mixture and recycled polyethylene. 

The two OCT samples are small particle size (less than 10 pm) CaO coated with organo-titanates. In particular AB is coated with neopentyl(diallyl)oxy. 

The tests carried out with some functionalized compounds suggest that maleic anhydride grafted polymers and CaO coated with organo-titanates act as compatibilizers modifying the morphology of the blend but the improvement of the mechanical properties does not fully justify cost of compatibilization. 

Chapter 4, on surface modification, is a good example of the approach taken. Most works concentrate on the organo-silanes. While they are still treated in detail here, significant space is also given to fatty acids and organo-titanates. Fatty acids are of considerable commercial importance and exhibit complexities that can cause problems... 

Virtually all treatments in commercial use are chosen to chemically bond an organic species to the filler surface, thus improving compatibility with organic polymers. The most common functionalities used for this are acids or acid precursors, such as anhydrides (for basic or amphoteric fillers) and alkoxy-silanes (for fillers with metal hydroxyls present, especially siliceous fillers). Organo-titanates and related compounds are also proposed for nse with a wide variety of fillers. 

These can be used where the additive has an element that is clearly different from the filler, and where the amount of additive is sufficient for the sensitivity of the technique being employed. Thus, carbon analysis can be used for many additives on silica surfaces, and titanium analysis is possible for organo-titanates on many fillers. This approach does not distinguish between surface and admixed additive though. 

Organo-titanates are a very interesting class of surface modifier, which have aroused great interest in recent years. They can all be regarded as derivatives of ortho-tkanic acid, Ti(OH)4, and hence are commonly known as organo-titanates rather than by their systematic names. This convention will be adopted here, in order to be consistent with existing literature. 

While several companies produce organo-titanates for a variety of uses, one group of workers (Monte and Sugerman) have specialised in producing compounds for filler modification, which they refer to as coupling agents. As well as producing an enormous... 

As well as arousing interest, the organo-titanates have also aroused a great deal of controversy. This is mainly related to their mode of action, and in particular, whether they act as true coupling agents, or merely as very effective dispersants. 

The natural chemistry of titanium causes problems with organo-titanates in some applications. To overcome this, organo-zirconate products have been recently introduced. The structure and general principles of the zirconates are similar to the titanates and no separate discussion of them will be made, except to point out reasons why zirconates are preferred in some applications. 

The most important factor is that, unlike the silicon to carbon bond, the titanium to carbon bond is very unstable and cannot be used to permanently attach organic groups for surface treatment applications. The organo-titanates are thus generally based on tetra-substimted titanium, where all the substituents are linked by titanimn-oxygen-carbon bonds, and their chemistry is dominated by the hydrolytic sensitivity of these. Alkoxy radicals are rapidly hydrolysed, with the rate in water decreasing as the chain length increases, due to reduced solubility. Acyloxy derivatives are also fairly readily hydrolysed. 

Types of Filler Susceptible to Organo-Titanate Treatment... 

While no comprehensive study has been made, it is generally claimed that organo-titanates are effective on a wide variety of particulate mineral surfaces, including calcimn carbonates and carbon black. This claim is however often based on dispersant action in simple tests, where adsorption rather than strong surface bonding is often sufficient to produce an... 

While basic scientific work is relatively scarce, there have been some useful studies which tend to confirm that the simple idealised picture is indeed far from correct. Perhaps the most important of these has been by Cans and co-workers [83]. They worked with a commercial organo-titanate (KR TTS from Kenrich) claimed to be isopropyltriisostearoyltitanate, containing a small amount of free alcohol. This is probably the most widely used titanate for filler modification and features in much of the scientific and commercial literature. The usual method of coating is from an isopropanol solution. Cans and co-workers used proton and C NMR to establish the structure of this material and were surprised to find that it appeared to be a mixture of diisopropyldiisostearoyl titanate and free isostearic acid. It would thus appear that the excess alcohol present has solvolysed one of the acyloxy groups. They also found that further solvolysis readily... 

Despite the wide range of organo-titanate types available there have been virtually no scientific studies with types other than the monoalkoxytitanates. 

Irrespective of the controversy over the structure of the organo-titanates and their mode of action, they do appear to give useful effects and this is after all what matters. 

As mentioned earlier, Kenrich KR-TTS is probably the most widely studied organo-titanate at present and serves as a good example of the utility of organo-titanates. Several examples of its use to produce low viscosity dispersions of fillers such as calcium carbonate and aluminium hydroxide in organic liquids can be found in the manufacturers literature [81] and the paper by Monte and Sugerman [82]. 

It is claimed that a significant part of their effectiveness is due to chemical removal of the surface water layer on the particles, which significantly improves dispersion. Such an effect is not present with other common types of dispersant. Unfortunately no good comparison between organo-titanate and other dispersants has been made, although Landham and co-workers did report that organo-titanates formed more stable layers on alumina particles than fatty acids [85]. 

Unfortunately there have been no useful scientific studies with organo-titanates containing unsaturated acyloxy groups to show whether they provide true coupling ability. 

In addition to the tendency to colour formation due to photo-reduction already mentioned, organo-titanates can also give undesirable colour effects in the presence of phenolic functionality such as often encountered in antioxidants and light stabilisers. The ready reduction of titanium IV also causes problems in peroxide cures where deactivation of the free radicals and reduction in cure efficiency can occur. 

These problems are largely eliminated if titanium is replaced by zirconium and hence organo-zirconates analogons to the organo-titanates have been developed. They are considerably more expensive to prodnce than the titanates and hence are unlikely to completely replace them. The same qnestions over hydrolytic stability of the attachment of the organic functionalities apply as for the titanates. 

---