Ecofriendly flame-retardant polystyrene (PS) composites were developed using the synergistic effects of phytic acid (PA), polyethyleneimine (PEI), and expandable graphite (EG). PA was chemically hybridized with PEI, and the hybrid (PAE) was incorporated into PS together with EG. The flame-retardant performances of the resulting composites were evaluated using the limiting oxygen index (LOI), UL-94 vertical burning test, and cone calorimetry test. The strong interaction between EG and PAE provided an effective barrier against heat and oxygen, thereby improving the flame retardancy. The best-performing composite (PA:PEI:EG = 1:1:1 (w/w/w), total flame-retardant loading = 10 parts per 100 parts of PS) exhibited an LOI of 27.7% and a UL-94 V-0 rating. The peak heat release rate (148.8 kW/m²) and total heat release (91.2 MJ/m²) of this composite were lower than those of pure PS by 79.2% and 34.0%, respectively. This study provides guidelines for the production of flame-retardant PS and other polymeric materials.

Silver nanowires (AgNWs) have excellent electrical conductivity and nano-sized effects and have been widely used as a high-performance electromagnetic shielding material. However, silver nanowires have poor mechanical properties and are prone to fracture during the preparation of composite materials. In this study, PVDF/rGO/AgNW composites with a segregated structure were prepared using low-pressure compression molding and the AgNW-backfilling process. The low-pressure compression of the composite significantly improves its electromagnetic shielding performance because the low-pressure process can maintain the AgNWs’ integrity. The backfilled AgNWs played a vital role in increasing the path of electromagnetic wave propagation and the absorption of electromagnetic waves. The backfilled amount of AgNWs was only 1 wt%, which increased the composite material’s conductivity by one order of magnitude. The total electromagnetic interference shielding (SE_T) of the composite materials increased by 23.3% from 24.88 dB to 30.67 dB. The absorption contribution (SE_A/SE_T) increased from 84.2% to 92.8%, significantly improving the electromagnetic interference shielding and the absorption contribution of the AgNWs in the composites. This was attributed to the backfilling of the porous structure by the AgNWs, which promoted multiple reflections and enhanced the absorption contribution.

Polystyrene (PS) is widely used yet highly flammable, and developing halogen-free flame retardants that ensure both high fire safety and mechanical performance remains a challenge. A green intumescent system comprising ammonium dihydrogen phosphate (ADP) and phytic acid–triethylenetetramine (PA–TETA) was incorporated into PS powder via sequential solution grinding and hot pressing. The optimal formulation, PS/10ADP/15PA–TETA, achieved a limiting oxygen index of 28.5% with a UL-94 V-0 rating, and reduced the peak heat release rate and total heat release by 73.8% and 46.2%, respectively, while retaining 78.4% of the tensile strength of neat PS. The ADP/PA–TETA system operates via a cooperative condensed-phase charring and gas-phase dilution mechanism, achieving superior flame retardancy in PS composites. This work provides an effective and eco-friendly strategy for fabricating high-performance PS composites with balanced flame retardancy and mechanical properties.