The three main reasons for the significant differences in the effectiveness of flame retardants

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This post was last edited by ljtjbx on 2016-8-4 08:11. Those in the flame-retardant industry know that the method to achieve flame retention is to add flame retardants evenly to the extruded boards during the production process, in order to prevent and delay the intense burning of polystyrene sheets. A common problem among most manufacturers is that the flame-retardant effect of the flame retardants used is not significant, and the level of flame resistance is uneven; on the same piece of board, some areas exhibit good flame resistance while other areas have poor flame resistance or even no flame resistance at all ； The same flame retardant provides excellent flame-retardant performance in boards produced by one machine, but poor performance in those produced by another machine ； For the same machine, different manufacturers can result in significant variations in flame-retardant performance. According to Cai Cai from the Global Flame Retardant Products Network, the reasons for the significant variations in the effectiveness of flame retardants lie in the following aspects: 1. Human factors – the amount of flame retardant added to extruded boards is very small, usually less than 10%. To ensure that the flame retardant is evenly distributed throughout the material, mixing is crucial. To achieve a concentration of around 5 grams of flame retardant per 100 grams of material, extensive manual mixing or the use of specialized mixers is necessary. Most manufacturers simply scatter the flame retardant on the surface of the material before feeding it into the feeding machine; although the feeding machine has its own mixing function, this can only achieve dispersion over a small area in a short period of time, resulting in regional differences in flame retardancy in the rock wool boards used for exterior wall cladding in Fangshan. 2. Equipment factors: Different equipment manufacturers employ varying designs for the clearance between the screw and the barrel, the advancement rate, and the plasticizing and dispersing elements, which results in differences in the time it takes for the material to be plasticized, dispersed, and retained inside the barrel. Conventional flame retardants are mainly hexabromocyclododecane; its decomposition temperature is lower than that of rock wool boards, which creates a conflict with the processing temperatures required for ordinary extruded boards. The heating temperature used for ordinary boards is sufficient to cause most flame retardants to decompose and lose their effectiveness. Therefore, we usually use the melt temperature as the standard for classifying Suining XPS extruded boards as flame retardant boards, rather than the heating temperature. Actual production experience shows that adjusting the maximum melt temperature to between 175–190 degrees Celsius, depending on the equipment available, yields the best quality of boards as well as the best flame retardant effects. This processing temperature contradicts the process temperatures recommended by most equipment manufacturers, as those recommendations are based on the melting temperature of newly produced polystyrene particles. In actual production, however, 90% of XPS extruded boards are made from recycled PS particles, and the melting temperature of recycled PS differs from that of virgin material by 20–30 degrees Celsius. The screw generates a large amount of shear heat as it shears the material, and this shear heat is transferred into the material that is being extruded. As a result, the amount of shear heat generated by the equipment on the material continues to increase. If the heating temperature and cooling water levels are not adjusted during prolonged production, it can also lead to the decomposition and loss of effectiveness of the flame-retardant components. 3. Flame retardant factors: The flame retardants produced in China are mainly available in powder and granule forms. Due to the difference in density between powder flame retardants and PS particles, only a small portion of them can be adsorbed through frictional electrostatic forces during mixing; most of them settle at the bottom of the mixing equipment due to the gaps between the particles, resulting in uneven distribution of the flame retardant. The powder adsorbed on the surface of the particles comes into contact with the screw barrel first, is exposed to high temperatures, and undergoes severe decomposition. During this decomposition process, free bromine reacts with the screw barrel to form iron bromide, which causes significant corrosion of the equipment; therefore, its use is not recommended. Particles are formed by manufacturers of flame retardants by coating composite powders with resin; their density and volume are similar to those of PS particles. They can be easily dispersed evenly within the material during mixing, and since they have a small total contact area with the screw barrel during extrusion, less decomposition occurs, which is why they are widely used. However, the processing conditions for granular materials are quite stringent; advanced plastic modification equipment is required to coat ultra-high concentrations of composite flame-retardant components at low temperatures within a small amount of carrier resin. Most flame-retardant granules produced in China are manufactured using simple single or twin-screw extruders, which means that the concentration of flame-retardant components cannot exceed 65%. Moreover, the fast advancement of the screws requires high processing temperatures, leading to the decomposition of some of the flame-retardant components. This is why the flame-retardant effect of the products manufactured by some manufacturers is poor.