Synthesis Of Metal Phosphinate Flame Retardants And Their Applications In Polylatic Acid

Metal phosphinates, such as aluminium diethylphosphinate (AlPi), are novel organphosphorus-containing flame retardants showing high flame-retardant efficiency in nylon and polyesters. However, the synthesis technology of AlPi is occupied by Clariant in Germany, and most of AlPi used in China which is produced by Clariant is expensive. AlPi could be synthsized by some domestic research institutions. Unfortunalely, its yield and thermal stability are not satisfactory. Moreover, other metal phosphinate flame retardants possessing different chemical structure have also been synthesized, but their applications are just at the laboratory research stage. Therefore, it is meaningful to investigate synthesis and applications of metal phosphinate flame retardants.Four kinds of metal phosphinate flame retardants were synthesized in this paper, which includes:lanthanum bis-(hydroxy-phenyl-methyl)-phosphinate (LaBPi), aluminum (hydroxy-phenyl-methyl)phosphinate (AlHMPi), aluminum terephthalaldehyde-hypophosphorous acid coporymerized phosphinate (AlTHCP) and lanthanum bis-(amino-phenyl-methyl)phosphinate (LaBAPi). Their chemical structure and composition were characterized by 1H nuclear magnetic resonances ('H NMR), Fourier transformed infrared spectrometry (FTIR) and energy dispersive spectrometer (EDS). Afterwards, the synthesized flame retardants above were introduced to PLA respectively. The flammability, thermal stability and mechanical properties of PLA composites were investigated, and corresponding flame-retardant mechanisms were also proposed.The detailed contents mainly include four parts:1. Synthesis of LaBPi and its application. Hypophosphorous acid (H3PO2), benzaldehyde (PhCHO) and lanthanum chloride heptahydrate (LaCl3·7H2O) were used to synthesize disubstituted LaBPi. LaBPi was effective on improving UL-94 rating of PLA and all PLA/LaBPi composites could pass UL-94 V-2. Unfortunately, LaBPi had minimal effect on limiting oxygen index (LOI). Thermogravimetric (TG) analysis indicated that LaBPi decomposed significantly at 250-270? and its decomposed products could promote degration of PLA, which was one of reasons that higher loading LaBPi endowed PLA with worse flame retardancy.2. Synthesis of AlHMPi and its application. H3PO2, PhCHO and aluminium sulfate octadecahydrate (A12(SO4)3·18H2O) were utilized to synthesize mono-substituted AlHMPi. Aluminum (hydroxy-phenyl-methyl)phosphinate (AlHMPi) was highly effective flame retardant of PLA. When 5-15 wt%AlHMPi was incorporated, LOI could keep in 27.0 or so and UL-94 V-0 was obtained. However, PLA/AlHMPi composites showed poor improvement in cone calorimetry (CONE) test. The flame-retardant mechanisms of PLA/AlHMPi included that melting drippings took away considerable heat and radicals containing phosphorus could capture active radicals in burning area. TG analysis exhibited that some carbonization was produced. However, there was no char formation in CONE test. It could be deduced from differential scanning calorimetry (DSC) analysis that AlHMPi promoted heterogeneous nucleation of PLA to some extent. PLA/AlHMPi composites had satisfactory mechanical properties and PLA/AlHMPi (5 wt%) could maintain 85% tensile strength compared to that of PLA.3. Synthesis of AlTHCP and its application. Polymerized AlTHCP was synthesized using H3PO2, terephthalaldehyde and Al2(SO4)3·18H2O. It exerted the best fire performance in PLA with a LOI of 21.1 and UL-94 V-0 rating when 10 wt%AlTHCP was introduced. AlTHCP had relatively high thermal stability in TG test and 63.6 wt% residues remained when the temperature rised to 800?. Besides, AlTHCP had minor influence on thermal stability of PLA. PLA/AlTHCP composites had substantial char formation but the mechanical strength of these char layers was poor. Therefore, the heat release in CONE test increased slightly. The main flame-retardant mechanisms of PLA/A1THCP also included melting drippings taking away heat and flame inbibition.4. Synthesis of LaBAPi and its application. LaBAPi was synthesized using H3PO2, hydrobenzamide and LaCl3-7H2O as reactants and trimethylchlorosilane as the activator. It significantly improved flame retardancy of PLA. A high LOI of 29.1 was obtained and UL-94 V-0 was passed when only 5 wt%LaBAPi was added. Flame inbibition and gas dilution effects were the main flame-retardant mechanisms. Gel permeation chromatography (GPC) results indicated that LaBAPi induced ammonolysis of PLA during processing.