Effect of Fully Biobased Coatings Constructed via Layer-by-Layer Assembly of Chitosan and Lignosulfonate on the Thermal, Flame Retardant, and Mechanical Properties of Flexible Polyurethane Foam

A fully biobased coating containing chitosan (CS) and lignosulfonate (LS) was facilely fabricated on the surface of flexible polyurethane foam (FPUF) using layer-by-layer assembly method. The CS/LS based coatings were successfully deposited on the substrate, as demonstrated by UV–vis absorption spectroscopy, attenuated total reflection Fourier transform infrared spectroscopy, and scanning electron microscopy. Subsequently, the different bilayers of the coatings were applied to enhance the thermal stability, fire resistance, and mechanical properties of FPUFs. It was found that the thermal degradation of coated FPUF under nitrogen atmosphere was obviously retarded compared with the pure FPUF. Furthermore, an eight-bilayer CS/LS based coating significantly improved the fire resistance of FPUF, as evidenced by the remarkable reduction (42%) of peak heat release rate. Meanwhile, the mechanical property of coated FPUF was improved. After the FPUF was covered with the eight-bilayer coating, the tensile strength was increased from 0.17 to 0.19 MPa compared with pure FPUF.