Processing zinc soap

Zinc oxides can be prepared from chemical industry by-product sources and from zinc soaps from a variety of industrial processes. These grades are generally off-coloured and consequently considered of lower grade and offered at lower cost and are confined to use in black compounds. These grades can also vary in consistency, batch to batch, causing cure variation in compounds containing them. 

The use of soluble zinc soap activators such as zinc 2-ethyl hexanoate instead of conventional stearic acid gives efficiency of vulcanisation and ensures that stress relaxation and creep properties are optimised. Zinc soaps, including the new high efficiency activating types, do not bloom from the compound, either during processing or subsequently during service. 

Heat stabilizers protect PVC during processing and applications under heat exposition (Pospisil, 1990c). Typical heat stabilizers consist of barium, calcium or zinc soaps of fatty acids (43, R=Cu-C17, M=Ba, Ca, Zn binary salts Ba/Zn or Ca/Zn are mostly used) and various organotin compounds, e.g. dibutyltin maleate (44) or dioctyltin bis(iso-octylthioglycolate) (45) (PospiSil, 1990c). 

Ca Zn formulations are a complex blend of calcium and zinc soaps together with acid acceptors and organic co-stabilisers. Efforts have been made to increase the acid absorption capability in these systems (46,82,137, 295). The role of the co-stabiliser is also critical in maintaining initial colour and early colour hold on processing (47, 220, 308, 406, 407). Alternative calcium carboxylates have also been evaluated (227). 

Zinc oxides is mainly used in the rubber industry in which it serves as an activator in the vulcanization process. Its low hardness and high compatibility with polymers are important for its utilization in chemical materials. In its utilization in paints, its tendency to form zinc soaps, which hinder the attack of coatings by fungus and improve the aging resi.stance (UV-absorption), is important. Further application fields for zinc oxide are in copier paper, glues, pharmaceutical products, cosmetic products and dental cements. 

ACM compounds are difficult to process and processing aids must be used, e.g., stearic acid, zinc soaps, fatty alcohol residues, octadecylamine, or pentaerythritol tetrastearate. This later processing aid does not affect vulcanization characteristics, whereas the others retard or accelerate vulcanization. 

Fatty acids are used in small amounts, with zinc oxide, as vulcanization activators. In addition to their activating effect in the vulcanization process, the acid and its in-situ-formed zinc soap do act as lubricants as well as activators. 

In the continuous process, which is more common today, the fat or oil is hydrolyzed by water at high temperatures and pressures in the presence of a catalyst, usually a zinc soap. The fat or oil and the water are introduced continuously into opposite ends of a larger reactor, and the fatty acids and glycerol are removed as formed, by distillation. The acids are then carefully neutralized with an appropriate amount of alkali to make soap. 

Three different techiuques for mixing a sihca and caibon black filled tyre tread compound were evaluated and the effect of surfactant-based process additives (modified zinc soaps and a zinc soap/resin combination designated Struktol HT 266) on productivity and compound quality investigated. Mixing methods studied involved the use of a separate filler addition stage for each component type and different orders of filler addition. Mixing efficiency and dispersion/filler interactions were examined and the effects of process additives on Mooney viseosity and extrusion assessed. The cure characteristics, physical properties and dynamic properties of the vulcanisates were also examined. 9 refs. 

ZINC-FREE RUBBER PROCESSING ADDITIVES MATCHING THE PROPERTIES OF TRADITIONAL ZINC SOAPS... 

Nitrile Process. Fatty nitriles are readily prepared via batch, Hquid-phase, or continuous gas-phase processes from fatty acids and ammonia. Nitrile formation is carried out at an elevated temperature (usually >250° C) with catalyst. An ammonia soap which initially forms, readily dehydrates at temperatures above 150°C to form an amide. In the presence of catalyst, zinc (ZnO) for batch and bauxite for continuous processes, and temperatures >250° C, dehydration of the amide occurs to produce nitrile. Removal of water drives the reaction to completion. 

Adhesives in the Tire Industry. Cobalt salts are used to improve the adhesion of mbber to steel. The steel cord must be coated with a layer of brass. During the vulcanization of the mbber, sulfur species react with the copper and zinc in the brass and the process of copper sulfide formation helps to bond the steel to the mbber. This adhesion may be further improved by the incorporation of cobalt soaps into the mbber prior to vulcanization (53,54) (see Tire cords). 

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