Interlayer engineering of shape memory phthalonitrile based composites via PTFE decoupling and aerogel functionalization

Shape memory polymers (SMPs) are stimuli-responsive smart materials with great potential for engineering applications. Fiber reinforced SMP composites (SMPCs) are widely used to enhance mechanical properties while retaining shape memory performance. However, although multilayer fiber fabrics reinforced SMPC laminates offer higher mechanical strength, their deformation during shape memory process is often constrained by interfacial restrictions between adjacent plies. In this study, a polytetrafluoroethylene (PTFE) interlayer strategy was developed to decouple adjacent SMPC plies, and PTFE interlayered, carbon fiber reinforced shape memory phthalonitrile laminate composites (SMPN-LC) were fabricated. Mechanical tests indicates that, at an interlaminar bonding area of 20%, SMPN-LC exhibits a tensile strength of 307 MPa and a flexural strength of 426 MPa. At the same bonding area, as the length-width ratio decreases from 6:1 to 2:1, the flexural strain of SMPN-LC increases from 1.8% to 2.9%, which is attributed to an increased length of the PTFE induced interlaminar decoupling region. SMPN-LC exhibits layer-wise shape memory behavior and can be deformed into a temporary anchor-hook structure capable of hanging a 500 g weight. By incorporating shape memory phthalonitrile aerogel (SMPNA) into SMPN-LC to obtain SMPN-LAC, the thermal conductivity decreases to 104 mW/m·K and provided good thermal insulation performance. In the compressed temporary shape, the SMPNA interlayers within SMPN-LAC recovers gradually to form layer-by-layer thermal barrier, maintaining the opposite-side temperature at around 300 °C after 600 s of butane flame exposure. This interlayer strategy endows SMPN-LAC with good thermal insulation with shape memory performance, broadening the application potential of SMPCs.