Resumen de Curat termic i fotocurat de resines epoxi per al control quimic de la contraccio i millora de la degradabilitat
The polymerization of epoxy resins with a spirobislactone as a comonomer has been studied with the purpose of controlling the chemical shrinkage during curing and improving their degradability to permit partial o total recovery and reuse of the materials once their service life is over. Thermal curing as well as photocuring using UV radiation have been used. The curing of these systems has been studied under cationic and anionic catalysis.
The study focuses on key aspects of curing and processing such as kinetics, gelation and vitrification, analysis of thermal and mechanical properties of the cured materials and the influence of the chemical processes on kinetics and properties. Thermal analysis (DSC, DMTA, DSC, TGA), spectroscopic (FTIR) and non-instrumental techniques have been employed.
The kinetics of the curing process, the network development and therefore the morphology and properties of the obtained materials are highly dependent on the different chemical processes taking place under cationic or anionic catalysis.
The effect of the spirobislactone on the kinetics of the curing process is complex and depends on the catalysis, the type of initiator and the curing technique. In anionic curing the opening of the spirobislactone reduces the reaction rate, whereas in cationic curing the reaction rate can either increase or decrease depending on the interaction between the initiator and the reagents. Chemical shrinkage undergone during curing is reduced with the use of the spirobislactone, for both thermal cationic and thermal anionic systems, due to the expanding effect of the direct opening of the spirobislactone or indirectly via formation of an expandable spiroortoester.
Epoxy-spirobislactone copolymers have a lower cross-linking density and are more flexible and tougher due to the formation of linear flexible structures that act as spacers between cross-linkable epoxy monomer units. Curing schedule can have an influence on the network development and therefore on the properties of the fully cured materials. The thermal stability of the fully cured materials decreases as the spirobislactone is incorporated due to the introduction of ester linkages into the network. Thus, it is possible to partially recover the materials by means of controlled thermal degradation. Hydrolysis of ester groups can also lead to total or partial recovery of reusable monomer precursors.
Photocuring technology permits faster and controlled processing of materials at lower temperatures than thermal curing, therefore making it possible to reduce time and energy consumption during processing and obtention of materials with similar properties.
