Modification of Castor Oil by Isomerization, Halogenation and Application of Some Modified Products as Plasticizer in Nitrile Rubber Formulations

Abstract

The preparation of bromo-as well as chloro-derivatives of castor oil by addition and substitution reactions is reported. Bromine water and chlorine gas have been used to ha logenate the oil by addition while N-bromosuccinimide and PCl₅ have been used in the substitution reactions. The course of the reaction has been followed using ¹H-NMR and IR analyses. Positional isomerization and geometrical isomerization of the double bond in castor oil have also been considered in this investigation. Conjugation of the double bond in the bromo-castor oil has been checked by UV absorbance at 233 and 268 nm. Geometrical

isomerization whereby the <i>cis</i>-double bond transforms into <i>trans-</i>isomer<i> </i>has been studied in case of castor oil as well as its chloro-derivative using IR analysis. The results show that greater percentage of <i>trans-</i>acids<i> </i>can be achieved by isomerization of the chlorinated derivative. The percentage of the <i>trans</i>-acid of this derivative has been found as 75 per cent, compared to 8 per cent in the case of castor oil. In addition, castor oil and its halogenated derivatives have been evaluated as plasticizer in NBR formulations instead of dibutylphthalate. The evaluation parameters used are the rheometric characteristics and the physicomechanical properties of rubber such as tensile strength and elongation per cent at break. In addition, the effect of the prepared plasticizers on the rubber swelling in toluene as well as in motor oil and their effect on the rubber properties after aging have also been studied. The results show that castor oil and its derivatives are advantageous over dibutylphthalate in terms of their effect on the mechanical properties as well as the rubber resistance to swelling in motor oil. The best properties could be obtained using hexachloro-castor oil and the optimum concentration has been 3 phr.