Synthesis And Flame Retardant Properties Of Polymeric Phosphate Flame Retardants

Recently,fire hazards associated with the use of polymer materials,which cause the loss of life and property,are of particular concern among government regulatory bodies,consumers and manufacturers.The use of flame retardants to reduce combustibility of the polymers,and smoke or toxic fume production,therefore becomes a pivotal part of the development and application of new materials.In the 21st century,it is essential that new flame retardant systems are investigated to meet the constantly changing demand of new fireproofing regulations and environmental standards.Recently,patent and technical works indicate a growing interest in halogen-free solutions with the predominance of the literature focusing on phosphorus-based flame retardants.However,the evaporation temperatures of most commercial phosphates are quite lower than the processing temperature of materials,which leads to them volatile loss during processing,especially,in the processing of thermal engineering plastics.It has been claimed that polymeric flame retardants are preferable to increasing the thermal stability,volatile temperature and their better resistance to migration etc..Therefore,phosphorus-containing polymers have generated considerable interest in the study of flame retardant.In this paper,three polymeric phosphates,namely PFR-B,PFR-P and PFR-D,have been designed and synthesized,which were applied in ABS and PC/ABS(70/30).The polymers were characterized by means of FT-IR,¹H NMR and ³¹PNMR.The thermal degradation behavior of flame retardants and flame retarded polymer materials was investigated by TGA.PFR-B series polymers were synthesized from spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride(SPDPC),2-methoxyl-4,6-dichloro-1,3,5-triazine(MDCT) and tetrabromobisphenol A(TBBPA).The influence of monomer ratio on their thermal stability was investigated by adjusting the proportion of SPDPC/MDCT(mol/mol) from 80/20 to 20/80.The flammability properties of flame retarded blends were evaluated using LOI and UL-94 vertical test.The results show that the initial temperature of decomposition could be adjusted from 270℃to 320℃.V-0 ratings in the UL-94 vertical test were achieved at 20-30%loading of PFRs,when LOI values reached at least 26.9%.The initial decomposition temperature of PFR-B55 is 274℃and with 35%charring residue at 500℃when the ratio of SPDPC/MDCT is 50/50.LOI value reached 27.1%.With 7%PFR-B55 applied in PC/ABS, the material could pass V-0 rate.The flame retardancy is strongly dependent on the ratio of P, N and Br.PFR-P was synthesized from 1-oxo-4-hydroxymethyl-2,6,7-trioxa-1-phosphbicyclo [2.2.2]octane(pentaerythritol phosphate,PEPA),POCl₃ and bisphenol S.Phosphorus was bonded both in the main chain and in the pendant group of flame-retardant polymer molecule, reached a content of 13.1%.And sulfur content was 6.75%.The thermal stability was investigated by TGA,and the results showed that the initiative decomposition temperature was 334℃with 41%charring residue at 500℃under air.The high phosphorus and sulfur content contributes an excellent flame retardancy to ABS and PC/ABS.With 18%loading and 6%loading in ABS and PC/ABS respectively,the materials could pass UL94 V-0 rate.PFR-D has been synthesized from 9,10-dihyro-9-oxa-10- phosphaphnanthrene-10-oxide (DOPO),POCl₃ and bisphenol S.Phosphorus reached a content of 11.5%and sulfur content is 5.9%.The TGA result showed that the initiative decomposition temperature was 321℃with 42%charring residue at 500℃under air.It has been incorporated into ABS and PC/ABS alloy.Although PFR-P loading in ABS reached 25%,ABS could not pass V-0 rate owing to dripping during combustion.While,with 5%loading PC/ABS could pass V-0 rate.The thermal oxidation degradation kinetics of flame retarded ABS and PC/ABS alloy has been investigated using Flynn-Wall-Ozawa method which does not require knowledge of the reaction mechanism(RM) by the thermogravimetric analyzer(TG/DTG).The results show that flame retardants decrease the initiate decomposition temperatures of ABS and PC/ABS but enhance their char residues at high temperature.The activation energies of flame retarded materials are lower than those of ABS and PC/ABS in initiate decomposition stage but increase fast later,and at last exceed the activation energies of ABS and PC/ABS respectively. It revealed the condensed phase mechanism of flame retardant.As for PC/ABS/7%PFR-D blend,the activation energy is always higher than that of PC/ABS at the same conversion. The flame retardant ability of PFR-P was compared with PFR-D in ABS and PC/ABS. Although both of them are effective flame retardants of PC/ABS,there exists absolute difference in ABS.It is considered that DOPO could form the weaker phosphonic acid instead of phosphoric acid.This weaker acid would be less effective at promoting the(acid-catalyzed) char formation in ABS.In PC/ABS,the presence of oxygen increased the cross-linking phosphate structures during decomposition.In order to study the distinction of charring ability of PEPA and DOPO in condensed phase,PEPA-based and DOPO-based acrylates,1-oxo-2,6,7-trioxa-1-phorsphabicyclo [2,2,2]oct-4-ylmethyl acrylate(PEPA-AA) and(10-oxo-10- hydro-9-oxa-10λ⁵- phospha-phenanthrene-10-yl) -methyl acrylate(DOPO- CH2O-AA) were synthesized and copolymerized with styrene.Compared with the TGA curve of PEPA-based polymer in air, the TGA curve of DOPO-based polymer has been changed by increasing char residue from 6%in N₂ to 19%in air.The results of TGA in N₂ and air indicate that the effect of charring formation is more determined by the nature of the P-containing substituent than the content of P.