Synthesis Of Organometallic Compounds Containing Phosphorus And Their Flame Retardant Effect On Polyethylene

The increased application of flammable polymeric materials in everyday life led to increased fire hazards and so flame retardants are very often incorporated into them to limit their flammability. Intumescent flame-retardant (IFR) additives containing phosphorus and nitrogen, which are halogen-free and more environmentally friendly, have been developed for imparting flame retardancy to polymeric materials. However, conventional IFRs also have some disadvantages, such as high loading fractions at the expense of the apparent decrease of the mechanical properties of the flame retardant polymers. So, the compounds containing transition metal element have been utilized for reducing the flammability of polymers due to these compounds can act both in the vapor phase, the condensed phase and at the gas/solid interface through a chemical and/or physical mechanism to reduce the flammability.Firstly, we designed and synthesized a novel Zn (II) chelate, i.e. Zn tetraethyl (1,2-phenylenebis(azanediyl)) bis (2-hydroxylphenylmethylene) diphosphonate (Zn-TEPAPM), on the basis of zinc acetate,1,2-diamine benzene,2-hydroxybenzaldehyde and diethyl phosphonate. The chemical structure of Zn-TEPAPM was characterized by IR,1H-NMR,13C-NMR and31P-NMR. The results of thermal analysis showed that Zn-TEPAPM had excellent char-forming ability and the thermal stability match well the processing temperature of PE. Incorporation of1wt%Zn-TEPAPM leads to a reduction of32%for the peak heat release rate in the cone calorimeter test. Moreover, Zn-TEPAPM was demonstrated to be a very effective synergist of ammonium polyphosphate (APP).Secondly, based on the above results, we used raw material of benzaldehyde or3-pyridinecarboxaldehyde, diethylamine and diethyl phosphonate to synthesized2,2’-(ethylenedi-imino) bis (benzylphosphonic-acid)(EIBPA) and2,2’-(ethylenedi-imino) bis (3-pirydylphosphonic-acid)(EIPPA). And then, the EIBPA-Zn and EIPPA-Zn were prepared as a microcrystalline powder by the reaction of Zn(OOCCH3)2·2H2O with EIBPA and EIPPA in the refluxed ethanol solution. The results of thermal analysis showed that EIBPA-Zn and EIPPA-Zn had excellent thermal stability and char-forming ability, especially for EIPPA-Zn which had higher char-forming ability than EIBPA-Zn. Incorporation of EIPPA-Zn in PE not only resulted in the improved LOI values, but markedly reduced the heat release rate (the PHRR value reduced by70%ompared with pure PE resin), total heat release and mass loss rate of PE and the char residue as much for59wt%.Thirdly, we synthesized a zinc N,N-piperazinebis(methylenephosphonic acid)(PPMPA-Zn), on the basis of zinc acetate, piperazine, phosphorous acid, and formaldehyde. The chemical structure of PPMPA-Zn was characterized by IR and powdery X-Ray diffraction. The results of thermal analysis showed that PPMPA-Zn had excellent thermal stability, char-forming ability, and the initial thermal decomposition temperature reach to354℃. Incorporating5wt%PPMPA-Zn in PE resin, the PHRR value reduced to38%relative to pure PE resin and the char residue is much more intact. When loading25wt%PPMPA-Zn, the PHRR value reduced to63%relative to pure PE resin and the char residual mass reach to70.7wt%. Although adding PPMPA-Zn in PE resin can get a better result of flame retardancy in cone calorimeter test, it can not get good result in LOI test due to the residue of PPMPA-Zn has higher polarity than melt PE resin so result to the char residue move off from the burning surface.Subsequently, we synthesized a zinc morpholinomethylphosphonic acid (MMPA-Zn) and MMPA-Ce, on the basis of zinc acetate, cerium nitrate, morpholine, phosphorous acid, and formaldehyde. And the chemical structure of MMPA-Zn and MMPA-Ce was characterized by IR and powdery X-Ray diffraction. Incorporating25wt%MMPA-Zn in PE resin, the PHRR value reduced to47%relative to pure PE resin and char residual mass reach to32.2wt%in the test of cone calorimeter. Because of the surface char residue was not compact enough, the PHRR value was not greatly reduced as incorporating EPPA-Zn and PPMPA-Zn compounds in PE resin. Incorporation of5wt%or25wt%fiber like MMPA-Zn in PE resin, there was not much difference in PHRR values and reduced about30%compared with pure PE resin. Due to the melt temperature of the residual MMPA-Ce was more higher than combusting temperature, so the char residue was composed by large amount of small gram.Finally, incorporation of organic metal phosphonates of EIBPA-Zn, EIPPA-Zn, MMPA-Zn and MMPA-Ce in PE resin, the tensile stress and Young’s modulus improve at a various degree due to the crystalline structure of organic metal phosphonates composed by inner inorganic group of P-O-M and outside organic group.