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Two different hyperbranched polymer (HBPs) fillers were synthesized and dispersed within an aeronautical graded epoxy matrix as toughening agents. The first typology, identified as HBPG (HBP Glassy) is a glassy polyester characterized by a higher glass transition temperature (Tg) then room temperature (∼90 °C) and obtained by means of bulk polycondensation reaction starting from a diphenolic acid as precursor. The second hyperbranched polymer, labelled HBPR (HBP Rubbery) was a polyamide ester with a Tg of about 20 °C and synthesized by bulk polycondensation of sebacic acid and diisopropanolamine. HBP/epoxy systems were prepared considering two concentration levels, respectively 0.1 and 5 wt%, and the effects on rheological, thermal stability, mechanical properties and fracture toughness were investigated and analyzed in respect to the corresponding neat epoxy. Rheological results revealed that the HBPG filler induces relevant effects on the viscosity of the epoxy matrix compared to HBPR limiting the potential usage of the system for composite manufacturing. Nevertheless, HBPG induces optimal results in term of thermal stability, mechanical and fracture performances, with a limited reduction of the Tg and a higher increase of degradation activation energy along with enhanced fracture behavior as indicated by an enhanced critical stress intensity factor (KIC) and critical strain energy value (GIC). The main result of this work suggests that the HBPG/RTM6 epoxy could be suitably used as polymer matrix for carbon-reinforced composites preserving the advantages of infusion process but at the same time enhancing the matrix-driven mechanical property.

A novel hyperbranched poly(amide-ester)s (HBP) has been synthesized through the AB 2 approach in one-step polycondensation without solvents. The synthesized HBP has been characterized and used as filler for epoxy resin with the aim obtain materials which exhibit improved toughness. Composites containing 6% and 12% wt/wt of HBP in diglycidylether of bisphenol A (DGEBA) were produced and characterized. Results obtained from DMA tests showed that HBP has good compatibility with the epoxy resin. Impact tests proved that composites containing 12% HBP showed an improvement of about 25% on impact strength with respect to neat DGEBA. Moreover, adhesive properties were evaluated in terms of the lap-shear strength value of composite joints bonded using the investigated blend. Results showed an improvement of shear strength value of DGEBA added with 12% HBP with respect to neat DGEBA. The water uptake behavior was also evaluated.