Effect of the Aramid Pulp on the Physicochemical, Viscoelastic Properties and Rheokinetics of Polyurethanes

Abstract This publication highlights the effect of aramid pulp (1 wt.%) on equilibrium swelling, enthalpy reaction, solid viscoelastic properties, and rheokinetics of castor oil (CO) and polyether (PE) polyol blend (50/50 CO/PE) with polymeric isocyanate (pMDI). The CO-pMDI system showed a lower solubility parameter difference (Δδi) than the PE-pMDI and CO/PE-pMDI. Crosslink density values νe are higher for CO-pMDI, and when added to aramid pulp, there is a slight increase due to the possible restriction of swollen volume. Regarding the pseudo-solid behavior, AP restricts the macromolecular movement and confers reinforcing characteristics to PU systems. The Prout–Tompkins autocatalytic model satisfactorily described the reactions, resulting in activation energy values Ea within 45−54 kJ/mol. However, for the CO/PE blend, the difference between the reactivity of the polyols and the solubility parameter with pMDI results in a two-step reaction kinetics. Aramid pulp practically does not change the reaction mechanism, only the viscosity of the medium. Furthermore, the thermodynamic parameters (ΔS* and ΔH*) indicated that the PU with AP resulted in more ordered complexes. The adequate description of the polymerization reaction and the effect of the aramid pulp allowed obtaining PU formulations with tunable characteristics for strict composite processing composites.