Synthesis, Characterization And Flame Retardant Mechanism Of Novel Copolyester Containing Phosphorus Linked Pendant Groups

Poly(ethylene terephthalate) (PET) fibers, because of their outstanding characteristics of high strength, resistance to shrinkage and stretch, good dyeability, and chemical resistance, are used extensively in clothes, carpets and furnishings. So that the halogen free flame retardant polyester has become to a research tendency of great concern in reducing the dangers of PET fibre involving fire incidents. This research deals with the synthesis flame-retarded copolyester by using the melt polycondensation of terephthalic acid (TPA), ethylene (EG) and novel phosphorus containing reactive flame-retardant. Their structures were investigated by Fourier Transform Infrared (FTIR), Nuclear Magnetic Resonance (NMR), and Element Analysis. The Differential Scanning Calorimetry (DSC), Thermogravimetry Analysis (TGA) and Limiting Oxygen Index (LOI) were used to investigate the thermal properties, thermal degradation behavior and flame retardant properties. TG-FTIR, pyrolysis Gas Charomatography/ Mass Spectrometry (Py-GC-MS), Directed Pyrolysis Mass Spectrometry (DP-MS), FTIR and X-ray Photoelectron Spectroscopy(XPS) technique were used to investigate the gas phase products and condensed phase products of the copolyester containing phosphorus linked pendant groups to predict the flame retardant mechenisms. In addition, their spinning properties were studied in laboratory.The flame retardant copolyester(FR-PET) with phosphorus content of 0.35% and 0.65% had high LOI value, such as 31.5% and 33.4%, respectively, and exhibited excellent flame retardant property and anti-dripping behaviour.The glass transition temperature (Tg), crystalline temperature (Tc), melting temperature (Tm), thermal stability at low temperature and the activation energy of copolyester had been reduced by the increase of phosphorus content. However, the temperature at the maximum decomposition rate(Tmax) and the maximum decomposition rate(Rmax) of FR-PET were very close to those of PET. The solid-state decomposition mechanism of PET and FR-PET corresponded to the controlled deceleratedα-t curve, a reaction order mechanism.The main gas phase products of PET and FR-PET were CO2, CO, acetaldehyde, benzoic acid and aromatic carboxyl ester, which detected by TG-FTIR and Py-GC-MS. The cleavage of P-CH2 bonds, forming the 9,10-dihydro-9-oxa-10[2,3- di(2-hydroxyethoxy)carbonylpropyl]10-phosphaphenanthrene-10-oxide(DOPO), giving birth to PO free radical to catch the H and OH free radical in flame region. The above process was conformed by DP-MS analysis. The content of phosphorus in the condensed phase products for FR-PET decreased gradually with increasing temperature. These XPS data confirmed that unit containing phosphorus did not promote the char forming of the copolyester during thermal degradation of FR-PET, and phosphorus species volatilized into the gas phase, and no other containing phosphorus appeared in condensed phase products also. Therefore the gas phase flame retardant effect of the FR-PET shoud be vital important other than the condensed phase.