The effects of the addition of an aromatic hyperbranched polyester (AHBP) on thermal, mechanical, and fracture toughness properties of a thermosetting resin system were investigated. AHBP filler, synthesized by using… Click to show full abstract
The effects of the addition of an aromatic hyperbranched polyester (AHBP) on thermal, mechanical, and fracture toughness properties of a thermosetting resin system were investigated. AHBP filler, synthesized by using a bulk poly-condensation reaction, reveals a glassy state at room temperature. Indeed, according to differential scanning calorimetry measurements, the glass transition temperature (Tg) of AHBP is 95 °C. Three different adduct weight percentages were employed to manufacture the AHBP/epoxy samples, respectively, 0.1, 1, and 5 wt%. Dynamical Mechanical Analysis tests revealed that the addition of AHBP induces a negligible variation in terms of conservative modulus, whereas a slight Tg reduction of about 4 °C was observed at 5 wt% of filler content. Fracture toughness results showed an improvement of both critical stress intensity factor (+18%) and critical strain energy release rate (+83%) by adding 5 wt% of AHBP compared to the neat epoxy matrix. Static and dynamic compression tests covering strain rates ranging from 0.0008 to 1000 s−1 revealed a pronounced strain rate sensitivity for all AHBP/epoxy systems. The AHBP composites all showed an increase of the true peak yield compressive strength with the best improvement associated with the sample with 0.1 wt% of AHBP.
               
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