Bio-based Si-N flame-retardant curing for silicone rubber modified pine: Synthesis and degradation

We have successfully developed a molecular design strategy to synthesize a hydrogenated rosin-modified isocyanatopropyltriethoxysilane crosslinking agent (HRIS) with organic and inorganic active groups. Then curing it, rosin-based silicone rubber chemically cross-linked modified pine (RSP) is formed. This process enables the organic integration of fire-retardant silicon, nitrogen elements, and the rigid hydrogenated phenanthrene ring structure of rosin with the internal and external surfaces of the pine’s porous structure through chemical bonding. In the channels, rosin-based silicone rubber with 48.81 % of carbon, 42.96 % of oxygen, and 8.23 % of silicon, respectively was observed. The degradation mechanism coupled with LOI (limiting oxygen index) testing revealed that the RSP exhibited enhanced flame retardancy, with its LOI significantly increasing from 24.68 % to 25.4 %. Additionally, it exhibited higher thermal stability up to 330℃ than pine, indicating that the fire-retardant performance of RSP was effectively enhanced through the crosslinking modification with HRIS and PDMS (hydroxyl-terminated polydimethylsiloxane). During the thermal degradation process, RSP will produce gaseous cyclic siloxane molecules such as D3 (hexamethylcyclotrisiloxane), D4 (octamethylcyclotetrasiloxane), D5 (decamethylcyclopentasiloxane), etc. This study demonstrated that a new type of adhesive has been synthesized, but the influence of byproducts on the entire system should be considered in application, which is of significance for indicating the direction.