Italian technological district for the engineering of polymeric and composite materials and structures
The research carried out as part of the PRICE project focused on the application of filament winding technology to the construction of space launcher motors, which involve the use of carbon-epoxy composite casings.
In the space engine sector, Italy is participating in the development of the first three stages of the European VEGA launcher. These motors involve the production of carbon-epoxy composite casings using filament winding technology. In particular, the need for this research arises from the unavailability on the global market of carbon-epoxy prepreg systems capable of combining high performance, especially in terms of Tg, high handleability, processability and durability.
The project objective was achieved with the development of an epoxy resin capable of satisfying the desired requirements through the development of innovative systems of unidirectional carbon-epoxy prepregs, both in tow (12-18k filament carbon fibre impregnated with epoxy resin) and tape (tows placed side by side to form ribbons of variable width and length). In particular, within the project, a formulation characterized by a long shelf-life at room temperature and high thermomechanical performance was identified. Two epoxy components based on glycidyl ether of bisphenol-A (DGEBA) and a reactive diluent were cured by diaminodiphenyl sulfone (DDS) to control the rheological characteristics at varying temperature and degree of conversion. The DDS curing agent was selected to ensure low reactivity at room temperature and high thermomechanical performance of the product at the end of the conversion cycle. The study of the crosslinking kinetics of the epoxy formulation and the correlation with the viscosity exhibited by the system as a function of temperature and degree of conversion was carried out through DSC experiments and rheological tests. The calorimetric data were analyzed and interpreted using the most widely used models proposed in the scientific literature.
The reaction was confirmed to proceed according to an autocatalytic mechanism with a total reaction order of 1.8 and an activation energy of 54 kJ/mol. A model has been developed to describe the impregnation of a dry fibre tow passing under a roller. The model is based on the integration of the Navier-Stokes equation and the Darcy equation. Once the model was available, a multi-objective optimization of the impregnation process was carried out, aimed at determining the optimal conditions that simultaneously ensure the maximization of the amount of resin infiltrated and the minimization of resin wasted during the calendering process.