Synthesis And Properties Research Of Melamine-based Polyamide Aerogels

The research of thermal insulation materials is a hot issue in the field of energy saving and emission reduction. Currently the primary heat insulation materials are organic foams, the thermal conductivity of which is much lower than the traditional inorganic heat insulation materials, leading to a better heat insulation performance while the quality is lighter. However, organic foams have poor fireproof performance. Thus scientists focus on flame retarding performance of organic thermal insulation materials.As a new type thermal insulation material, aerogels exhibit excellent heat insulation performance owing to its diameter smaller than the mean free path of air molecules,which can effectively prevent the generation of heat convection.We report synthesis of three new melamine-based polyamide aerogels prepared by the low-price melamine and isophthaloyl dichloride, terephthaloyl chloride, trimesoyl chloride via sol-gel method and supercritical drying process. Compared with the two previous samples of polyamide aerogel, the preparation process of melamine polyamide aerogel does not need nitrogen protection, and the aerogel has a good formability, mild reaction conditions, and the gel happen quickly. Introducing fire-retardant melamine in polyamide essentially can improve the fireproof performance of traditional organic foams and avoid phase separation usually resulting from physical adding flame retardant, which will weak the properties of materials. The gel process and properties of the aerogels have been studied:Comprehensive performances of melamine-based polyamide aerogel is best when the molar ratio of melamine and isophthaloyl dichloride is 0.9:1.5, volume ratio of dimethyl sulfoxide and N-methyl pyrrolidone is 9:1, and aging time is 3 days via CO2 supercritical drying. Gel particle size analysis indicates the process of the aerogel formation is like small particles to small clusters to large clusters in total while a certain number of aggregations, which result from the action of hydrogen bond, appear andfinally disappear as the reaction goes. The results of Nitrogen adsorption/desorption characteristics analysis and FESEM, HRTEM spectrogram analysis indicate that the as-prepared aerogels has a network consisted of dozens of nanometers gel particles and pore diameter is mainly concentrated in about 20 nm, and the aerogel is a typical mesoporous material.The process of polyamide aerogels prepared without acid-binding agent is simple,but the specific surface area is low. With 2 equivalent DMAC being acid-binding agent and 1 equivalent anhydrous CaCl2 being solubilizer, specific surface areas of the polyamide aerogels increased from 174 m2/g to 413 m2/g. Under the condition of acid-binding agent, reaction conditions are researched systematically, such as the variety and consumption of acid-binding agent, dosage of solubilizer, reaction temperature, and concentration of precursors in the gel system. Besides, we study the influent of different chemical structure on polyamide aerogels. By the method of linear regression fitting, activation energy values of three polyamide aerogels are got, and the value of trimesoyl polyamide aerogel is smallest, followed by isophthaloyl polyamide aerogel and then terephthaloyl polyamide aerogel. The activation energy of melamine based polyamide aerogels is 10 times lower than this of melamine formaldehyde aerogel system. Due to high cross linking degree, the specific surface area of trimesoyl polyamide aerogel can be as high as 432 m2/g.The insulation performances of melamine-based polyamide aerogels are studied,and their thermal conductivity is the level of polystyrene foam, and is a good heat insulation material. Flame retardant studies indicate that the polyamide aerogel is material which is very hard to flame, and limit oxygen index of trimesoyl polyamide aerogel can be as high as 40.5. Besides, the dielectric constant of aerogel can be as low as 2.48(under 10 KHZ), and the aerogel is a good dielectric material. Using dynamic thermal mechanical analyzer for characterization mechanical properties of aerogel, the result indicates that the aerogel is a flexible material.