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Rheology and chemorheology of thermosetting resin and polymeric fluids. Cure monitoring

Involved People: Alfonso Maffezzoli, Mariaenrica Frigione, Antonio Greco, Carola Esposito Corcione, Francesca Lionetto, FrancescoMontagna, Donato Cannoletta, Emanuela Cal˛
Rheological properties of polymer and oligomer fluids plays a key role in every material processing operation. Rheological properties of these fluids are a function of temperature and shear rate. However, thermosetting resins, such as epoxy or unsatured polyester resin, are reactive fluids characterized by a Newtonian behaviour and by a dependence of viscosity on the degree of advancement of the reaction up to the gel point.
The rheological properties were typically studied in presence of a structural transformation of the polymer such as a polymerization or a crystallization. In particular chemorheology refers to the rheological properties of reactive liquids, in our case thermosetting resins. Most of our research was focused on the comparison of rheological properties with those obtained by other experimental techniques, sensitive to rheological changes, such as ultrasonic wave propagation and dielectric properties. (Figs 1 and 2). It is also demonstrated that these techniques can represent a powerful tool for cure monitoring of thermosetting matrix composites. In particular simple models were proposed to correlate the degree of reaction and the gel time with ionic conductivity or ultrasonic velocity.
Finally the change of dynamic mechanical properties typically measured in isothermal conditions in presence of a structural transformations have been correlated with the degree of advancement of the involved phenomenon (degree of reaction, degree of crystallization)
It is worth noting that these three techniques can be used to expand the limited frequency range that can be explored with a typical mechanical rheometer. In Fig 3 the frequency dependence of the relaxation peaks of unsaturated polyester networks as measured by dynamic mechanical analysis (square), dielectric analysis (circles) and ultrasonic wave propagation (triangle). The data are successfully fitted by the WLF equation (continuous line).
Throughout the years the rheological properties of epoxy resins, unsaturated polyester resins, LLDPE, PVC, crude oil, nanofilled fluids and ceramic suspension were studied.
Figure 1 - Comparison between experimental viscosity data and (-) model predictions for an epoxy resin cured in isothermal conditions at 160░ (O), 170░ (.) 180░ (◊) and 190░C (Δ). (A.Maffezzoli, A.Trivisano, M.Opalicki, J.M. Kenny, J. Mijovic, e L. Nicolais "Correlation between dielectric and chemorheological properties during cure of epoxy based composites" Journal of Material Science 29 (1994) 800-808)
Figure 2 Comparison between the storage longitudinal (L') and shear (G') moduli obtained during crystallization of LLDPE at 2 ░C/min. (Francesca Lionetto, Francesco Montagna, Alfonso Maffezzoli "Ultrasonic Dynamic Mechanical Analysis of Polymers" Applied Rheology 15:5 (2005) 326-335)

Fig 3: (From: F. Lionetto, A. Maffezzoli (2005), "Relaxations during post-cure of unsaturated polyester networks by ultrasonic wave propagation, dynamic mechanical and dielectric analysis", Journal of Polymer Science Part B: Polymer Physics, vol. 43, no. 5, pp. 596-602)


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University of Salento   FacoltÓ di Ingengeria    Department of Engineering for Innovation