Study On The Preparation And Properties Of Halogen-free Flame-retardant Polyurethane

Polyurethane(PU)has been widely used in automobile manufacturing,transportation,footwear,petrochemical industry,aviation,medical,agriculture and many other fields due to its various excellent properties,such as low energy of preparation,light weight,easy processing,shock absorption,heat insulation,sound absorption and wear resistance.However,the application of PU has been greatly limited because of the extremely combustible characteristic in the air.Halogen-containing compounds have excellent flame retardant properties and have been widely used as flame retardant materials.However,when a fire occurs,halogen-containing compounds produce a large amount of smoke and toxic corrosive hydrogen halide gas to cause secondary hazards.Therefore,halogen-free flame retardants have become one of the main flame retardant trends of PU.The effect of halogen-free additive flame retardants on the properties of polyurethane foam(PUF),and the preparation and the application in thermoplastic polyurethane(TPU)of phosphorus-containing reactive flame retardant were mainly studied.The main research contents and the results are as follows.(1)Using the one-step foaming method,the aluminum hypophosphite(ALHP)and the ammonium polyphosphate(APP)were fully mixed with the combined polyether polyol,and reacted with the polyisocyanate(black material)to prepare flame retardant PUF.The effects of ALHP/APP on the flame retardancy,thermal stability,combustion behavior,apparent density,tensile strength and char forming properties of PUF were studied.The limiting oxygen index(LOI)test results showed that when the flame retardant was used alone,the flame retardant effect of ALHP was better than that of APP.When ALHP with 25wt% was added alone,the LOI of PUF is 27%,while when the amount of the ALHP/APP was 25 wt% and the mass ratio of ALHP to APP was 5:1,the LOI of PUF was 28%.As the proportion of APP in the ALHP/APP increased,the apparent density and tensile strength of PUF gradually increased.The thermal gravity analysis(TGA)result showed that the addition of the ALHP/APP reduced the initial thermal decomposition temperature of PUF,but increased the thermal stability of PUF at high temperatures,and increased the carbon residue rate of PUF at 700 ?.The results of the cone calorimetry test(CCT)showed that the addition of the ALHP/APP reduced the peak heat release rate(PHRR),peak mass loss rate(PMLA)and average mass loss rate(AMLA)of PUF,and improved the mass retention under the irradiation.The FTIR and SEM of the char residue showed that the flame retardant decomposed to produce phosphorus-containing substances,which promoted the formation of char and ensured that the matrix would not be further damaged.(2)Polycarboxyethyl phenyl ethylene phosphinate(PCEPEP)was synthesized using 2-carboxyethylphenylphosphinic acid(CEPPA)and ethylene glycol as raw materials.The structure of the product was characterized by FTIR.The influence of the molar ratio of EG and CEPPA on the acid value and hydroxyl value of the product was analyzed by titration.In order to decrease the acid value,PCEPEP was capped by propylene oxide(PO),dimethyl carbonate(DMC),and methyl iodide(MEI),respectively.The effects of amount of PO,the capping temperatures of DMC and the capping solvents of MEI on the acid value and state of flame retardants were studied.The obtained best end-capping phosphorus-containing reactive flame retardant(PCEPEP-PO)was used to prepare thermoplastic polyurethane(TPU),and various properties of TPU were investigated.The results showed that as the alkyd ratio increased,the acid value of PCEPEP decreased and the hydroxyl value increased.When the molar ratio of PO to acidic functional groups in PCEPEP is 6: 1,the end-capping effect of PCEPEP was the best.As the content of PCEPEP-PO increased,the hard segments increased,and the hardness and tensile strength of TPU showed an upward trend.When the content of PCEPEP-PO in TPU was 20 wt%,the LOI of TPU increased from 26.5% to 28.8%.Because of the addition of PCEPEP-PO,the initial thermal stability of TPU was reduced,but the thermal stability at a high temperature and the retention rate of residual char at 700 ? was effectively improved.Compared with unmodified TPU,TPU containing 20wt% phosphorus-containing polyol showed a reduction of 3.8%,41.6%,72.2% and 39.3% in the peak heat release rate(PHRR),average heat release rate(AHRR),total heat release(THR)and total smoke release(TSR),and an increment of 351.9% in mass retention.The char-forming performance of TPU was enhanced due to the addition of PCEPEP-PO,which effectively prevented the transfer of combustible gas and heat,and made the TPU display a good flame retardant effect.