Study Of Flame-Retarded PET/LDH Nano-Composites

It has been an important subject to improve properties of Poly(ethyl ene terephthalate)(PET) with nano compounding. Among these, flammability is an important concern that should be addressed before materials are used. In this dissertation, preparation of nano flame retardant compound of nano crystalline layered double hydroxides (LDH) and brominated polystyrene (PBS) has been studied. Furthermore, improvement of flame retardant properties of PET by adding nano flame retardant compound with nano dispersion technology has also been studied. Thermodynamic stability of PET/LDH/PBS composites system and interaction of polymer matrix macromolecular chains and nano particle have been analyzed. Meanwhile, crystallization, rheological behavior and spinnability of flame-retarded PET have been investigated. Nano structure, mechanical properties and flame-retardant performance of flame-retarded PET fiber have also researched. The main results are summarized as follows:1. Based on the thermal stability results of flame retardant additives and flame-retarded PET by thermogravimetric analysis (TGA), nano sized inorganic flame retardant LDH was firstly used as flame-retardant additives in the preparation of flame-retarded PET resins and fibers.2. Nano flame retardant compounds of nano LDH/PBS with the particle sizes about 20-70 nm were well prepared by a surface modification technology of inorganic flame retardant nano LDH and using organic flame retardant PBS as dispersant. Transmission electron microscope (TEM) of nano flame retardant compounds showed that nano-LDH has been coated with a uniform and dense film of PBS on the surface via a sol-gel process.3. The coordinated flame-retardant mechanisms of nano LDH and PBS were firstly studied. Nano LDH had the coordinated flame-retardant function with PBS because that magnesia and alumina, product of decomposition of LDH, can absorb the toxic gases released from the halogenated flame-retardant, and then water was generated to absorb heat. Studies on flame retardant performance of flame-retarded PET showed that the limited oxygen index (LOI) of flame-retarded PET containing a small amount of organic flame retardant PBS was significantly greater than that of the untreated samples. However the LOI of flame-retarded PET was increased slightly at higher amount of PBS (> 4.5wt%).4. Thermodynamics researches showed that PET and nano flame retardant compound blending process was a process of PBS diffusion leading the dispersion of LDH nano particles. According to the analysis of energy dispersive spectrums of flame-retarded PET, it was found that the flame-retarded PET composites system consisted of three components, i.e. PET, LDH and PBS, everywhere with different concentrations in different areas.5. The TEM micrographs showed the dispersion of LDH nano particles in polymer matrix was influenced by the intrinsic viscosities of matrix, the category and concentration of coupling agents, concentrations of flame retardant etc. The dispersion of nano LDH particles was impoved with the increasing of intrinsic viscosities of matrix. Spinnability experiment results showed better dispersion of nano LDH particles leads to better spinnability of flame-retarded PET and the spinning temperature of flame-retarded PET was lower than that of pure PET.6. It was found that the dispersion of LDH nano particles in polymer matrix changed with the ratio of LDH/PBS, and the drawing process of flame-retarded PET fiber can improve the dispersion of LDH nano particles in polymer matrix. IR analysis showed that the ratio of gauche conformations/trans-conformations of glycol group in macromolecule chain decreased with increasing of concentrations of LDH.7. The rheological properties research results showed the apparent viscosity of flame-retarded PET containing only PBS or only LDH flame retardants was lower than that of pure PET at a defined shear rate. The apparent viscosity decreased with increasing shear rate at low shear rate and had almost no change at higher shear rate. The viscous activation energy of flame-retarded PET was higher than that of pure PET at the same shear rate(>400s^-1). It also can be found that the apparent viscosity of flame-retarded PET was especially sensitive to temperature and decreased sharply with the increasing of temperature. The non-Newtonian index of flame-retarded PET increased with the increasing of PBS quantity, while it decreased with the increasing of LDH quantity.8. The crystallization kinetics of flame-retarded PET had been studied by DSC. The results showed that the glass transformation temperature, crystallization temperature, melting temperature of flame-retarded PET would decrease with the increasing of PBS amount. The glass transformation temperature, cooling crystallization temperature of flame-retarded PET would decrease and heating crystallization temperature, melting temperature of flame-retarded PET would increase with the increasing of the nano sized LDH amount. The crystallinity of flame-retarded PET would increase with the increasing of flame retardant amount. The glass transformation temperature, cooling crystallization temperature of the flame-retarded PET fibril was higher than that of the flame-retarded PET chip.9. The isothermal crystallization research results showed that Avrami index n increased with the increasing of the nano sized LDH amount and decreased with the increasing of the PBS amount. The crystal rate increased with the increasing of the flame retardant amount.10. The TEM micrographs showed the dispersion in polymer matrix of LDH nano particles had been improved in the process of winding and drawing of the flame-retarded PET.11. It was found that the orientation and sonic modulus of the flame-retarded PET decreased with the increase of the flame retardant additive amount. The tensile strength of the flame-retarded PET fibers decreased with the increase of the PBS amount and decreased also with the increase of the LDH amount at higher LDH amount(>1.0wt%), while increased with the increase of the LDH amount at lower LDH amount(<0.8wt%).