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Developments on metal soaps.pdf

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1 Further Developments on metal soaps as processing promoter for the rubber industry By Michael E. Wolers, K.P.Ho, Mike Trowman Performance Additives Sdn.Bhd; Subang J aya; Selangor Darul Ehsan, Malaysia Abstract Metal soaps have been for a long time the key product for the improvement of processability in tyre compounding. Originating from the ‘classic’ zinc- and calcium stearate, modifications of the fatty acid base were made to reduce melting points and i
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   1   Further Developments on metal soaps as processing promoter for the rubber industry By Michael E. Wolers, K.P.Ho, Mike Trowman Performance Additives Sdn.Bhd; Subang Jaya; Selangor Darul Ehsan, Malaysia Abstract Metal soaps have been for a long time the key product for the improvement of  processability in tyre compounding. Originating from the ‘classic’ zinc- and calcium stearate, modifications of the fatty acid base were made to reduce melting points and improve polymer compatibility. The resulting products were mostly zinc based, since calcium soaps tended to be less compatible and showed detrimental effects on the cross linking density. This paper is going to address recent changes and modification concerning the metal  base of these materials to improve effectiveness and, consequently, enable the compounder to use lower dosage levels. We are also going to discuss the often confusing number of products in the market and the reasons behind it.   2  Introduction Metal soaps as processing promoter have been mentioned in the literature as early as in the late forties/early fifties 1  In those days, metal soaps usually meant zinc soaps and/or calcium soaps. This paper is going to address the advances in development that happened in recent years to metal soaps. Metal Soaps Zinc soaps were mainly adopted as replacements for chemical peptizer because they were found to remain effective as viscosity reducers in natural rubber when carbon  black was present which removed the necessity for a “premastication” step and they did not reduce the rubber’s molecular weight, thus giving high tensile and tear  properties. B.Crowther in1989 2  first published the theory of emulsifier lubrication. In general, metal soap based processing promoters are based on fatty acids. These fatty acids are mostly naturally occurring and can be animal- or vegetable based. The make up is typically of a hydrocarbon chain and a carboxylic group. Slide 1     December 2003 Fatty Acid Base 1.A long hydrocarbon chain —The chain length ranges from 4 to 30 carbons; 12-24 is most common. —The chain is typically linear, and usually contains an even number of carbons. 2.A carboxylic group (COOH)   3 They can have somewhere between 4 and 30 C- atoms; 12 –24 C chains are commonly used. Chain length, saturation and linearity affect the melting point of the final product.   Slide 2 Other variations are caused by the degrees of unsaturation, which affects the compatibility in rubber. Slide 3 Slide 4   December 2003 Fatty Acids linear) ãLauricAcid C 12 H 24 O 2 sat.ãMyristicAcidC 14 H 28 O 2 sat.ãPalmiticAcidC 16 H 32 O 2 sat.ãOleic acidC 18 H 34 O 2 unsat..ãStearic AcidC 18 H 36 O 2 sat. December 2003 Typical fatty acid structure December 2003 Fatty Acids branched) 1.2-EthylhexanoicAcid C 8 H 16 O 2 2.OctanoicAcid C 8 H 16 O 2 12   4Simple saponification of saturated or unsaturated fatty acids by zinc or calcium  produces a wide range of process additives: Slide 5 In order for fatty acid based metal soaps to work, certain surfactant properties are necessary. This can be achieved by choosing the right fatty acid type, which has a strong effect on the resulting soap properties. Slide 6   December 2003 Saponification Example 2R C OH + ZnO -( R C O ) 2 Zn + H 2 OOO Route A 2R C O -  Na + + ZnCl 2 -( R C O ) 2 Zn + 2NaClOO Route B December 2003 Melt point,soluble(No bloom)Reduces crystallinity, lowers ranching If presentMore internal lubricationLow Better reactivity w/silicas olarity HighAmorphous,low melt point, easy disperse, hardly bloom !PolydisperseCrystalline,high melt point, poor dispersion,can bloom!Monodisperse Chain length mixtures Form micelles-surfactantsHigher than C 10Too short to form micellesLess than C 10 Carbon chain length Soap Propertiesatty Acid type
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