The properties of polysiloxane flame retardants are as follows:
High-efficiency flame retardancy: Polysiloxane flame retardants have a relatively high silicon content. When burning, they can form a homogeneous insulating carbonization (Si-C) layer on the material surface, inhibiting further combustion of the internal material, preventing melt dripping, stopping the escape of volatile decomposition products generated by combustion, and isolating the internal material from external oxygen, thereby achieving a flame-retardant effect. For example, after adding silicone resin to the PC system, this protective layer can be formed.
Increasing oxygen index: Low relative molecular mass flame retardants have a fast molecular migration rate, which can increase the oxygen index of materials. Polysiloxane is a commonly used silicon-based flame retardant.
Small impact on material properties: Polysiloxane flame retardants have a small impact on the processing performance and mechanical properties of materials. While endowing materials with excellent flame retardant performance, they do not affect the physical and mechanical properties of materials. For instance, the addition system based on polysiloxane can improve the smoothness of the polyene surface without altering other surface properties and has no impact on the adhesion performance of the substrate.
Environmental protection and safety: Polysiloxane contains no halogens, is safe and non-toxic, environmentally friendly, has low heat output, less smoke and low toxicity when burned, and meets environmental protection requirements.
Improving processing performance: Polysiloxane flame retardants have excellent processing performance, which can significantly enhance the processing performance of materials containing a large amount of fillers and reduce the decline in physical and mechanical properties. For instance, when commercial product GENIOPLAST® PELLET S (composed of ultra-high molecular weight silicone and fumed silica) is added to halogen-free polyolefin cable materials as a flame retardant additive, when the silicone addition amount is 5%, the torque of the polyolefin cable material significantly decreases, and the melt index also increases.
Good heat resistance: Polysiloxane uses an inorganic main chain as its molecular framework, with high bond energy and a high thermal decomposition temperature. Under normal circumstances, it is difficult to burn, and during the heating process, part of the main chain can undergo rearrangement to form a stable spatial SiO₂ structure. Even if it burns, it releases less smoke and has a high carbon formation rate.
Recyclable: Polysiloxane flame retardants do not reduce the recyclability of materials, and the flame-retardant polymers are also easy to recycle and reuse. For example, PC flame-retardant with D-type polysiloxane, after being extruded five times at 280℃, neither the screw extrusion torque of PC nor the UL94V-0 flame retardancy changed. When DT-type polysiloxane is used as the flame retardant, the screw extrusion torque decreases by 15%, and the UL94 flame retardancy of PC drops from grade V-0 to grade V-2.
