Controlling Dual scale Morphologies of Epoxy and Poly(ether imide) towards improved Interlayer toughening of composites.
Topic(s) : Material science
Co-authors :
Ujala FAROOQ , Julie TEUWEN (NETHERLANDS), Clemens DRANSFELD (NETHERLANDS)Abstract :
Thermosetting aerospace composites suffer from the low fracture toughness of the intrinsically brittle epoxy matrix systems. A common approach is to dissolve a thermoplastic phase in the uncured epoxy. Amorphous thermoplastics, such as poly(ether imide) can interdiffuse with the epoxy, followed by reaction-induced phase separation, leading to intricate graded morphologies with a high fracture toughness [1, 2]. Commonly, the thermoplastic phase is added in a fine granularity to homogeneously dissolve and precipitate, in this work however, architecting the thermoplastic phase as macroscopic layered scaffold leads to dual scale morphologies with distinct spatial control of morphological feature at the microscopic and macroscopic scale.
Here , we investigate the toughening of epoxies with layered poly(ether imide) (PEI) structures at the meso- to macroscale combined with gradient morphologies at the microscale originating from phase separation. As shown in Figure 1, characteristic micro-scale features of the gradient morphology were controlled by the curing temperature (120–200 °C), while the layered macro structure originates from facile scaffold manufacturing techniques with varying poly(ether imide) layer thicknesses (50–120 μm). The fracture toughness of the modified epoxy system is investigated as a function of varying cure temperature (120–200 °C) and PEI film thickness (50–120 μm). Interestingly, the result, as shown in Figure 2, shows that the fracture toughness of the heterogeneous system was mainly controlled by the macroscopic feature, being the final PEI layer thickness, i.e., film thickness remaining after partial dissolution and curing. Remarkably, as the PEI layer thickness exceeds the plastic zone around the crack tip, around 62 μm, the fracture toughness of the dual scale morphology exceeds the property of bulk PEI in addition to a three times increase in the toughness of pure epoxy. On the other hand, when the final PEI thickness was smaller than its plastic zone, the fracture toughness of the modified epoxy was lower than pure PEI but still higher than pure epoxy (1.5–2 times) and “bulk toughened” system with the same volume percentage, which indicates the governing mechanism relating to microscale interphase morphology. Interestingly, decreasing the gradient microscale interphase morphology can trigger an alternative failure mode with a higher crack tortuosity, which seems to be the dominating synergistic toughening effect when the fracture toughness of the tougher constituent.
By combining facile scaffold assemblies with reaction-induced phase separation controlled by curing conditions [3], dual-scale morphologies can be tailored over a wide range, leading to intricate control of fracture mechanisms with a hybrid material exceeding the toughness of the tougher phase [4]. Ultimately, this knowledge is valuable to increase the damage tolerance of fibre-reinforced composites by suppressing their delamination damage modes.
Here , we investigate the toughening of epoxies with layered poly(ether imide) (PEI) structures at the meso- to macroscale combined with gradient morphologies at the microscale originating from phase separation. As shown in Figure 1, characteristic micro-scale features of the gradient morphology were controlled by the curing temperature (120–200 °C), while the layered macro structure originates from facile scaffold manufacturing techniques with varying poly(ether imide) layer thicknesses (50–120 μm). The fracture toughness of the modified epoxy system is investigated as a function of varying cure temperature (120–200 °C) and PEI film thickness (50–120 μm). Interestingly, the result, as shown in Figure 2, shows that the fracture toughness of the heterogeneous system was mainly controlled by the macroscopic feature, being the final PEI layer thickness, i.e., film thickness remaining after partial dissolution and curing. Remarkably, as the PEI layer thickness exceeds the plastic zone around the crack tip, around 62 μm, the fracture toughness of the dual scale morphology exceeds the property of bulk PEI in addition to a three times increase in the toughness of pure epoxy. On the other hand, when the final PEI thickness was smaller than its plastic zone, the fracture toughness of the modified epoxy was lower than pure PEI but still higher than pure epoxy (1.5–2 times) and “bulk toughened” system with the same volume percentage, which indicates the governing mechanism relating to microscale interphase morphology. Interestingly, decreasing the gradient microscale interphase morphology can trigger an alternative failure mode with a higher crack tortuosity, which seems to be the dominating synergistic toughening effect when the fracture toughness of the tougher constituent.
By combining facile scaffold assemblies with reaction-induced phase separation controlled by curing conditions [3], dual-scale morphologies can be tailored over a wide range, leading to intricate control of fracture mechanisms with a hybrid material exceeding the toughness of the tougher phase [4]. Ultimately, this knowledge is valuable to increase the damage tolerance of fibre-reinforced composites by suppressing their delamination damage modes.