Preparation Of SiO₂ Aerogel Composite One-step PI Foam Material And Its Flame Retardancy And Thermal Insulation Properties

The one-step polyimide(PI)foam is composed of a polybasic acid anhydride or a derivative thereof and a polyisocyanate as a raw material,and water is a foaming agent,and foam molding is realized by a room temperature free foaming technology.Compared with the two-step PI foam,the one-step PI foam exhibits advantages such as low raw material price,simple process flow,and short preparation cycle.Although the one-step PI foam has excellent properties such as light weight and sound absorption,due to the side reaction of isocyanate and water in the process of preparation,it has the problem of flame retardant and safety in the two-step PI foam.At the same time,because the thermal insulation performance of the one-step PI foam material is also different from that of polyurethane foam and polystyrene foam,the research on the one-step PI foam material has focused on the improvement of flame retardant performance.there is no research on how to improve the flame retardant and thermal insulation properties of one-step PI foam by one method.This paper proposes the introduction of silica aerogels(SA)with excellent fire resistance and thermal insulation properties to achieve a one-step PI foam flame retardant and thermal insulation performance improvement.First,the research and analysis of the two-step PI foam and silica aerogel composite method were carried out.Among them,the SA powder premixing method can also complete the combination of the two,but the SA powder has characteristics such as large specific surface area and high surface activity,and contains a hydroxyl group,so the SA powder will be in contact with the polar group in the foaming slurry.And,seriously increase the viscosity of the foaming slurry,30% by weight of the composite amount of SA powder will lead to a serious increase in the viscosity of the foaming slurry,affecting the free foaming process,and ultimately unable to obtain a uniform foam.The SA in-situ composite porous material technology can make the SA more uniformly compounded with the one-step PI foam material,and the one-step PI foam material size change is small after the composite,and the composite amount of the SA is less restricted.After the preparation method of the composite material was determined,a series of one-step PI foam/silica aerogel(PIF/SA)materials with different SA compounding amounts were prepared by SA in-situ composite porous material technology.Through the study of its cell structure,flame retardant properties and thermal insulation properties,SA was found to be thinly layered and blocky evenly distributed in the wall of one-step PI foam cells and inside the cells.Since SA is a non-combustible inorganic substance containing a nanoporous structure,the introduction of SA can effectively improve the flame retardant and thermal insulation properties of the one-step PI foam.When the SA compounding amount is 210.00%,the limiting oxygen index(LOI)value of the one-step PI foam is increased by 52.73%;and when the SA compounding amount is 142.79%,the peak heat release rate(pHRR)of the one-step PI foam is The total smoke emission(TSP)value decreased by 58.42% and 66.67%,respectively,and the heat release rate(HRR)and smoke emission rate(SPR)curves increased and decreased significantly;when the SA composite amount was 116.67%,The thermal conductivity of the one-step PI foam material is reduced by 12.85%,which is due to the excellent flame retardancy and thermal insulation of SA.Finally,the effect of SA compounding on the flame retardancy and thermal insulation of one-step PI foams with different degrees of imidization was investigated.With the improvement of the degree of imidization of PI foam in one-step method,the flame retardant performance of foamed materials is gradually increased,and the thermal insulation performance tends to increase first and then decrease,and then the ratio of anhydride group content to isocyanate group ratio is added.The thermal conductivity is the lowest at 30%.Regardless of the degree of imitation of the one-step PI foam,the introduction of about 110% of the composite amount of SA will improve the flame retardancy,safety and thermal insulation properties of the one-step PI foam to varying degrees.When the ratio of the anhydride group content to the isocyanate group is 30%,The one-step PI foam has the best flame retardant and the lowest thermal conductivity.