## 1 Introduction  
Ethylene-vinyl acetate copolymer (EVA) is a thermoplastic resin made from ethylene and vinyl acetate [1] that has lower crystallinity due to the vinyl acetate monomer (VA) in its molecular chains. EVA is widely used in the wire and cable industry for its excellent weather resistance, elasticity, and electrical insulation [2; 3; 4]. However, it is essential to note that EVA has a lower limiting oxygen index (LOI) of only 17.9, making it highly flammable. Moreover, the combustion process of EVA produces toxic gases such as CO [5]. Therefore, it is necessary to improve the flame retardancy of EVA; adding flame retardants can effectively reduce the flammability of EVA [6]. In terms of green, environmentally friendly, and sustainable development, halogen-free, non-toxic, and low-smoke flame retardants have become a research hotspot in the field of flame retardancy in recent years [7]. The preparation and application of the inorganic flame retardants represented by MH and alumina trihydrate (ATH) [8] have no impact on the environment compared with halogen-based and phosphorous-based flame retardants, which aligns with the current research direction of flame retardants [9]. The thermal decomposition of MH mainly occurs at 350 \({}^{\circ}\)C\(\sim\)400 \({}^{\circ}\)C, which can suppress the surface temperature increases in the composites. The generated water vapor can dilute the concentration of combustible gas, and the generated magnesium oxide covering the surfaces of the composites could hinder the heat and mass transfer between the gas phase and the condensed phase [10]. In consideration of the flame-retardant mechanism of MH, it is necessary to add certain amounts of flame retardants to achieve the desired flame-retardant effect. However, an excessive addition will deteriorate the mechanical properties of the composites. The problem of attaining high-efficiency, halogen-free, and low-smoke EVA composites still urgently needs to be solved [11]. To improve the flame-retardant effect of MH, researchers have conducted extensive research, including the preparation of nanoscale MH [12; 13]; the modification of MH, such as using melamine cyanurate [14], cyano trimethylene triphosphate [15], triethoxysilane, and polymethyl vinyl silicone rubber [16]; and the use of multi-element synergistic flame-retardants such as hexa (4-boric acid phenoxy) cyclophosphamide [17], cellulose nanofiber [18], expandable graphite [19], carbon black [20], silicone rubber [21], zinc borate [22], montmorillonite [23], silicon dioxide [24], graphene [25], carbon nanotubes [26], and hollow glass microspheres [27]. Based on the flame-retardant mechanism of MH and the self-sustaining combustion cycle theory, the carbon layer formed by the accumulation of magnesium oxide particles has a crucial impact on the combustion behavior of materials; therefore, the strength and density of the carbon layer are critical factors in the flame-retardant mechanism of the condensed phase [28; 29]. Polycarbosilane is an ideal precursor for preparing silicon carbide ceramic materials. The molecular structure of PCS is mainly composed of three primary substructures, namely, the ideal Si-C linear (L) units, six-membered Si-C monocyclic (SR) units, and Si-C condensed ring (CR) units [30]. Based on previous research by our group, we have reported the significant flame-retardant effect of PCS in collaboration with MH in polyethylene [31; 32] and ethylene-vinyl acetate [11] copolymers. The physical barrier effect of the carbon layer had an outstanding improvement. However, the smoke production increased due to the small-molecule silane gas release generated by PCS degradation; for example, the smoke production of EVA/MH composites with 2 wt.% PCS increased by 45%, and adding 3% increased smoke production by 59%. To improve the ceramic yield of PCS, divinyl benzene (DVB) is usually used as a cross-linking agent [33].