Thermoreversible gels of polymers in recycled motor oil

A study of the dynamic viscoelastic properties of gels of Ethylene Vinyl Ac etate (EVA) and Styrene-Butadiene-Styrene (SBS) copolymers in recycled moto r oil is presented. Both systems form gels with enhanced elastic moduli, wi th respect to SBS/aromatic oil gels which have been used to develop synthet ic binders. Although the procedure described by Winter is conveniently appl ied to obtain gel-sol transition of EVA/oil gels, it is not suitable for SB S/oil gels which do not give rise to a homogeneous liquid when they melt. F or EVA/oil gels the relaxation exponent at the gel point is Delta =0.5, whi ch according to Muthukumar's model corresponds to a fractal dimension d(f)= 2. The variation of the elastic modulus with polymer concentration follows the scaling law G(e)-c(n), with n=2.8 for EVA/oil and n=1.3 for SBS/oil. In the case of EVA/oil gels the validity of theoretical models relating fract al dimension to n exponent is discussed.