Applications of aluminum diethyl hypophosphite_industrial additives

Overview^[1]

As a new type of phosphorus-based flame retardant, aluminum diethylphosphinate has high thermal stability, chemical stability and environmental friendliness. It can be used as an excellent flame retardant for polymer materials to replace environmentally harmful halogens. Flame retardants. Organic aluminum hypophosphite and zinc salts have good flame retardancy due to their high phosphorus content. At the same time, due to the introduction of alkyl groups in the molecular structure, their hydrophobicity and thermal decomposition temperature are greatly increased compared to inorganic hypophosphite. Applications In polymer materials, it will not migrate or absorb moisture, can withstand high processing temperatures, and will not cause a decrease in the insulation performance of the material. It has good compatibility with the matrix resin and can maintain the mechanical properties of the matrix material. Due to these characteristics as an excellent flame retardant, it has been widely used in flame retardant fields of engineering plastics such as high processing temperatures, high shear strength, and high CTI values, especially in fields such as glass fiber reinforced nylon and polyester.

Preparation^[1]

1. Take 100 grams of sodium hypophosphite monohydrate and first dissolve it in 556g of water. Then, the mixed solution and stirring rod were added to a 2L self-designed reactor equipped with a thermometer and a line bubble aerator.

2. When the solution is heated to 30°C in the hot water bath, ethylene enters the reactor in the form of microbubbles through the linear bubble aerator. At the same time, a mixed solution of 8 mL benzophenone, 2 mL reactive amine, 9 mL persulfate and 21 mL threonine was added dropwise to the linear bubble aerator, and blown into the reactor through the flow of ethylene, that is, ethylene and photoinitiator were added simultaneously. Add to heated, stirred hypophosphite solution. The reactor was exposed to UV light generated by an appropriate light source (500W high pressure, quartz, mercury vapor lamp). After the addition was complete, the reaction mixture was stirred vigorously and held at 30°C for 2.8 hours.

3. Evaporate the final solution obtained in step 2 in a vacuum to remove the solvent, and dilute it with 650 mL of distilled water to obtain sodium diethylphosphinate.

4. Add distilled water, raise the temperature to 88°C, and drop in 30% Al₂(SO₄)₃18H ₂O aqueous solution, the dropping rate is controlled between 2.5L and 10L/min, and the dropping time is 30-60min. After the dropwise addition, the reaction is completed for 3 hours to obtain a white precipitate, cool it, and filter the precipitate to form a filter cake. After washing with distilled water, heat and dry under vacuum to obtain a white powdery solid, that is, diethyl aluminum diethyl hypophosphite;

5. The yield of the finally obtained aluminum diethylphosphinate was 120.7g, with a yield of 98.9%, and the purity measured by HPLC was 99.3%.

Flame retardant mechanism^[2]

The main chemical bonds in the structure of diethyl aluminum phosphinate are P-C, P=O, and P-O. Its flame retardant process is relatively complicated. Since aluminum diethyl phosphinate itself has a high phosphorus content, it has The basic flame retardant characteristics of phosphorus flame retardants are that they are both gas phase flame retardant and condensed phase flame retardant. First, aluminum diethyl hypophosphite is thermally decomposed at high temperatures. The (PO*) free radicals formed from P-O can capture the more active O and OH free radicals in the air, which can reduce the oxygen content in the limited space to a certain extent. content to terminate the combustion chain reaction. On the other hand, aluminum diethyl hypophosphite forms a condensed phase non-flammable liquid membrane during the reaction between high temperature and oxygen, covering the surface of the burning material to isolate the air and achieve a flame retardant effect. The phosphoric acid absorbs the gas during the heating process. It is thermally decomposed into metaphosphoric acid, and metaphosphoric acid is further decomposed to form P, P* and water, which effectively absorbs the OH and NH₂^– produced in the matrix, and at the same time makes the It absorbs heat and dehydrates and carbonizes the matrix. The final P element of the most organic silicone coating additives forms a stable carbon layer of pearlescent pigments to fix the carbon skeleton of some combustibles on the surface of the substrate to form a heat insulation layer. This carbon layer isolates oxygen and is difficult to burn. Diethyl hypophosphorous acid Salt can achieve good flame retardant effect.

Apply^[2]

As early as the late 1970s and early 1980s, the American Pennwalt Company had been testing the properties of various dialkyl hyponates. The American company Ticona has studied the performance of zinc, aluminum and calcium phosphinate as flame retardants in PA and PBT, and concluded that the addition amount of aluminum/calcium methylethylphosphinate in PBT is 15% and in PA The amount of addition inAt 20%, vertical combustion UL94 can reach V-0 level. The application of aluminum diethyl hypophosphite in polyester is relatively mature and relatively successful. Ramani et al. added a compound flame retardant of aluminum diethyl hypophosphite (ADP) and montmorillonite in a certain proportion to butylene terephthalate resin, which can effectively improve its flame retardant properties. When montmorillonite The soil content is 2.5%, the ADP content is 15.5%, the limiting oxygen index (LOI value) of the composite resin is as high as 35.5%, and the vertical combustion test shows that its fire rating can reach UL-94/V-O. In the process of preparing flame-retardant polyester (PET), Brehme et al. used 20% aluminum diethyl hypophosphite to increase the LOI value of their terephthalic acid composite resin to 45.5%, while also reaching the UL94/V0 standard. . Braun U et al. studied the synergistic flame retardant mechanism of nylon 66 using a phosphorus-nitrogen composite flame retardant. The phosphorus-nitrogen system mainly consists of aluminum diethylphosphinate and melamine polyphosphate. Research on its flame retardant mechanism using equipment such as thermogravimetry and scanning electron microscopy shows that the synergistic flame retardant has good flame retardant effects.