Anisotropic shape memory polymer composites reinforced with hierarchically modified loofah sponge and flax fabric sandwich structures

This study developed loofah sponge-reinforced shape memory polymer composites (SMPCs) and focused on optimizing the interfacial treatment and sandwich structure to improve their shape memory and mechanical performance. Among the acidic sodium chlorite (ASC) treatments, 3 wt% ASC effectively removed non-cellulosic components while preserving the porous skeleton of loofah. Subsequent silane modification with KH560 further improved interfacial compatibility, and 4 wt% KH560 gave the best overall performance. After this treatment, the longitudinal recovery force at 40% compression strain reached 1.8 N, 3.6 times that of the water-treated control, together with the highest compressive strength. To overcome the limited recovery ratio of the porous 3D composites, multi-cycle resin impregnation and surface silicone coating were evaluated, and repeated impregnation proved more effective in stabilizing shape recovery. On this basis, sandwich-structured SMPCs with 45° flax fabric face sheets were fabricated. Among all configurations, the CO-SSMPC showed the best comprehensive performance, with a bending strength of 89.4 MPa, a bending modulus of 3510 MPa, an average shape fixity ratio above 99.15%, a shape recovery ratio above 93.0%, and a constrained recovery force of 3.9 N. These results demonstrate that optimized KH560 treatment and sandwich design are effective for developing high-performance biomass-based SMPCs.