PET composite foam with high stiffness and high ductility: Synergistic effect of Toughener combined with simultaneous in-situ fibrillation of LCP/PTFE

In polyethylene terephthalate (PET) matrix, the simultaneous in situ formation of elliptical ethylene–ethyl acrylate–glycidyl methacrylate (E-EA-GMA), liquid crystalline polymer (LCP) fibrils, and polytetrafluoroethylene (PTFE) fibrils enables the fabrication of PET composites with both high rigidity and high toughness. At an E-EA-GMA content of 10 wt%, the composite exhibits a tenfold increase in impact strength while maintaining rigidity. E–EA–GMA significantly promotes toughness, while LCP/PTFE fibrils effectively maintain rigidity.

This PET composite is further processed into PET foams with densities of 240 kg/m³ (high density), 150 kg/m³ (medium density), and 100 kg/m³ (low density). Reducing foam density improves ductility, as evidenced by increased shear elongation at break. More importantly, the enhanced matrix toughness is closely linked to improved foam ductility, particularly in high-density foams, where this correlation becomes more pronounced. Within the PET foam structure, the E-EA-GMA component absorbs energy and undergoes plastic deformation, significantly increasing shear elongation at break. Meanwhile, the rigid rod-like LCP fibrils and flexible PTFE fibrils entangled networks, dispersed within the foam cell walls, provide structural support under external loads, effectively maintaining stiffness. This synergy results in simultaneous improvements in both stiffness and ductility, as evidenced by a 136 % increase in shear strength, a 39 % increase in compressive strength, and a 66 % increase in compressive modulus.

Although reducing foam density typically improves ductility at the expense of stiffness, the synergistic use of E-EA-GMA with in-situ fibrillation of LCP/PTFE successfully overcomes this trade-off, achieving PET foams with both high ductility and high stiffness.