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Cure kinetics of thermosetting polymers and modelling of cure kinetics

Involved People: Mariaenrica Frigione, Alfonso Maffezzoli, Emanuela Cal˛
High performance thermosetting matrix composites are generally produced using an autoclave lamination process at controlled pressure and temperature. During this process, the consolidation of the pre-impregnated plies (prepregs) is accompanied by polymerization reactions (cure process) and rheological changes of the matrix that strongly influence the final properties and the quality of the laminate. Moreover, the cure process is also coupled with marked heat generation as a result of the exothermic nature of the cross-linking reactions. The relative rates of heat generation and heat transfer determine the advancement of the reaction and the change in the viscosity through the thickness of the composite. Uncontrolled polymerization may cause undesired and excessive thermal and rheological variations that could induce microscopic and macroscopic defects in the composite part. Therefore, a detailed understanding of the "curing process" and of the structure-properties relationship is an essential requirement to control and optimise the process parameters in order to tailor the performance of the of cured systems.
Several studies of the research group have been focalized on the cure kinetics of thermosetting resins, either when the system is polymerized through heat, either through different techniques (UV radiation, microwave devices). Different analytical techniques have been employed, i.e.: Differential Scanning Calorimetry (DSC), both in dynamic and isothermal mode; Fourier Transform Infrared (FTIR) spectroscopy. Moreover, the different parameters involved in the process have been taken into account, evaluating their influence on the reaction kinetics. Several suitable kinetic models have been realized, proving their ability to describe the proceeding of cross-linking reactions, even in the case that the reactions are photoactivated. These kinetic models, able to correlate the thermal behavior of different reactive systems with their molecular and chemical characteristics, represents an invaluable means in the optimization and control of parameters involved in the industrial processing operations of thermosetting resins and matrices for composites, often carried out under complex thermal conditions.
FIG. 1 -Comparison between the calorimetric experimental (full line) and predicted data (dotted line) of rate of reaction vs. time for a vinyl ester liquid crystalline resin with 2 wt.-% of peroxide. (From: M. Frigione, E. Cal˛, A. Maffezzoli, C. Carfagna, G. Malucelli, "Kinetic Studies of Liquid Crystalline and Isotropic Vinyl Ester Resins", Macromolecular Chemistry & Physics, Vol. 205, pp. 2175-2184 (2004))
FIG. 2 -Reaction rate vs. time for isothermal test at 190░C: comparison between experimental DSC data (dotted line) for virgin, 11-, 22-, and 39-day-old BMI prepregs and model predictions (full line) for virgin and 39-day-old prepregs. (From: M. Frigione, J.M. Kenny, "Effects of Storage Aging on the Cure Kinetics of Bismaleimide Prepregs", Advances in Polymer Technology, Vol. 24, Issue 4, pp. 253-265 (2005))


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University of Salento   FacoltÓ di Ingengeria    Department of Engineering for Innovation