Dynamical - Mechanical Measurements for Resols Resins

L.B. MANFREDI; O. DE LA OSA; N.GALEGO; A. VÁZQUEZ; J.M.KENNY

Santa Margherita, Italia

Simposio; 11th International Symposium on Polymer Analysis and Characterization; 1998

In this investigation several resols in solution with variable formaldehyde to phenol (F/Ph) molar ratio have been characterized before curing by temperature. On the other hand, in order to determine the influence of the chemical structure on the viscoelastic and mechanical properties of thermally cured resols, networks with different F/Ph molar ratios were studied. The study of the influence of the molar ratio F/Ph was performed and the viscoelastic properties were related to the structure of the different resols. It was found that a resol with a molar ratio between 1.3 and 1.6 has the highest crosslinking density.  The concentration of methylene bridge is the following: p-p’>o-p´>>>o-o’.          The real functionality of the phenol results to be close to 2.6 as a consequence of the viscoelastic properties measured. In this value, it was observed a minimum in the loss modulus, E”, and in the tand or damping and a maximum in the glass transition temperature, Tg. On the other hand, a maximum in the rubber modulus of elasticity, E’r, is consequently related to a maximum concentration of elastically active chains.          Commercial resols crosslinked in absence of catalyst and with different molar ratio of F/Ph, were characterized. The main determining factor in the final properties appears to be the molar ratio of F/Ph in the crosslinking reaction.