Effect of divalent metal ions on the viscosity of natural rubber from manihot glaziovii
1998
Rodrigues, J.F. (Dept. de Quimica Organica e Inorganica, UFC, Cx. Postal 12.200, CEP 60.455-760, Fortaleza-Ceara (Brasil)) | Oliveira, F.C. | Ricardo, N.M.P.S. | Lima, M.C.P.
The effect of divalent metal ions on the intrinsic viscosity of natural rubber (NR) from Manihot glaziovii has been investigated. The molar mass of cis-1, 4-polyisoperene from manihot rubber was found to be Mv equal to 1.0 times 10 strength 6 and the intrinsic viscocity [n] equal to 5.66 dL per g, for toluene solution at 30 degree Celcius. Some metal ions such as Ca2+ and Sr2+ increase the NR viscosity in toulene solution (6.00 dL per g and 6.26 dL per g for 15.0 micro mol of metal ion per g of rubber, respectively). Others such as Mg2+, Zn2+ and Cu2+, decrease the NR viscosity to 4.82 dL per g, 4.73 dL per g and 4.96 dL per g respectively, for the same addition of metal ion per g of rubber. A correlation between relative variation of intrinsic viscosity ([n]NR + M per [n]NR) and cation radius has been proposed. A relative variation greater than unity for large cations has been observed, while for small metals such variation was less than 1. Cations that decrease the intrinsic viscosity do not lead to alteration in the activation energy of flow (Ea) for the 0.5 perccent (w per v)(Ea equal to 7.3 kJ per mol) solution. Cations that increase [n] also cause an increase of Ea to 7.8 kJ per mol and 7.6 kJ per mol for NR solutions containing Sr2+ and Ca2+, respectively. Intramolecular crosslinks may be formed with small and large cations. No evident interaction has been detected between metal ions and synthetic cis-1-4-polyisoprene. The interaction between NR and metal ions may be due to naturally occuring non-rubber constituents, probably those containing carboxylic groups.
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