The Dispersion Of Sb₂O₃ Nanoparticles And Its Effect On The Flame Retardancy Of Poly(butylene Terephthalate)composites

At present,it has been a significant project to obtain a novel composite with excellent properties by means of processing and modification for existing polymer materials.Poly(butylene terephthalate)(PBT)is an engineering thermoplastic with many excellent properties containing exceptional mechanical strength,outstanding processing performance,good electrical insulating performance,moisture resistance and resistant to chemical corrosion.It has been widely used in various fields including electronic and electrical industry,automobile industry,mechanical installation and optical fiber optic cable coating industry.However,the pure PBT also has many shortcomings such as low notch impact strength,low thermal deformation temperature and poor flame retardancy.In the process of combustion,PBT has a high heat release rate.And the flame propagation speed is fast.This phenomenon leads to release a lot of heat and produces much smoke and toxic gases in the process of burning,which may give rise to environmental pollution and health risks.Therefore,the inflammability,lower heat distortion temperature and serious dripping of PBT limit its wide applications in the engineering materials to a great extent.In this paper,in order to improve the mechanical properties,flame retardancy and thermal properties of PBT,the Sb₂O₃ nanoparticles as inorganic fillers and the brominated polystyrene(BPS)as flame retardant,were added into the PBT matrix.The nano-Sb₂O₃/PBT and nano-Sb₂O₃/BPS/PBT composites with different states of dispersion and distribution were prepared.The dispersion and distribution states of Sb₂O₃ nanoparticles in PBT matrix were quantitatively evaluated by modeling methodology and micrograph analysis techniques.Meanwhile,the effect of dispersion states of filler on the flame retardancy of composites was also investigated.Eventually,the dispersion and flame retardant mechanisms were elaborated.The main results are as follows:(1)The surface of Sb₂O₃ nanoparticles is modified via the mechanochemical method and using different surfactants including stearic acid,coupling agent of organic titanate,silane coupling agent KH-560,cetyl trimethyl ammonium bromide(CTAB)and melamine phosphate(MP).And these modifiers were applied by means of single modification and compound modification modes.In the case of Sb₂O₃ nanoparticles modified by silane coupling agent KH-560,the hydroxyl groups on the surface of Sb₂O₃nanoparticles can be effectively condensed by silanol groups of hydrolyzed silane of KH-560 avoiding the formation of hydrogen bonds between nanoparticles.When the amount of KH-560 modifier is 3wt%,the mean particle size and PDI of Sb₂O₃nanoparticles modified are 57 nm and 0.21,respectively.The cationic modifier of CTAB was absorbed on the surface of Sb₂O₃ nanoparticles with negative charges by electrostatic attraction due to the fact that CTAB can ionize the positive CTA⁺active group.Notably,the Sb₂O₃ nanoparticles,called CM-Sb₂O₃,modified by compound modifiers with 2wt%CTAB(C2)and 3wt%KH560(K3)obtained a high grafting ratio of 47.6%.In this case,the strong electrostatic attraction and steric stabilization effects among nanoparticles were obtained.Furthermore,the obtained nanoparticles were further coated by MP via the reaction between amino groups of MP and hydrolyzed epoxy functional groups.It was named as CM@MP-Sb₂O₃.The average thickness of coating and grafting ratio reach up to 5.2 nm and 73.2%,respectively.(2)The nano-Sb₂O₃/PBT and nano-Sb₂O₃/BPS/PBT composites are fabricated via ball milling dispersion and injection molding technique.The effects of particle surface treatment,particle size,particle morphology on the mechanical and crystallization properties of PBT composites are discussed in detail.The interfacial adhesion between Sb₂O₃ nanoparticles and PBT matrix are investigated.The PBT-matrix composite reinforced by CM-Sb₂O₃ shows excellent mechanical properties.When the mass fraction of filler is 3wt%,the tensile strength and crystallinity of composite reaches up to 59.6 MPa and 41.55%,respectively.And the interfacial adhesion parameter between fillers and matrix is 15.5.In addition,the average primary sizes of Sb₂O₃nanoparticles are 100 nm,75 nm and 55 nm corresponding to the ball milling time of 6 h,12 h and24 h,respectively.Under the same packing condition,the tensile strength of the composites increases gradually with the decrease of particle size.In the case of Sb₂O₃/BPS/PBT composite filled with 8wt%BPS and 3wt%Sb₂O₃,the tensile strength and notch impact strength are 62.3 MPa and 9.6 KJ/m²,which possesses the higher crystallinity with the value of 43.85%.(3)The dispersion parameter(8 is evaluated systematically by a combination of Maxwell model and Halpin-Tsai model.Besides,the binary technology for morphological images analysis is applied.The particle free-path spacing are measured to obtain the dispersion index.The(8 parameter values are 0.20,0.70,0.80,1.50and1.30,corresponding to the composites filled with bare-Sb₂O₃,C2-Sb₂O₃,K3-Sb₂O₃,CM-Sb₂O₃ and CM@MP-Sb₂O₃,respectively.The dispersion index_0.1 and_0.2 of3wt%CM-Sb₂O₃ filled composites are 17.5%and 23.2%,respectively.And the practical inter-particle distance value is close to the theoretical inter-particle distance value.Also,the composite shows a good distribution characteristic.The(8 parameter values are 0.36,0.30 and 0.20,corresponding to the bare-Sb₂O₃ obtained via the ball milling time of 6 h,12 h and 24 h,respectively.This phenomenon is due to that the surface energy and agglomeration trend between Sb₂O₃ particles are enhanced with the decrease of particle size.The addition of flame retardant synergist BPS has no significant effect on the(8 parameter of composites.Similarly,the composites filled with CM-Sb₂O₃ and CM@MP-Sb₂O₃ obtain an excellent distribution.(4)On the basis of quantifying dispersion in view of Sb₂O₃nanoparticles in PBT matrix,the flame retardancy,thermal stability and combustion products of composites were analyzed.The correlation between dispersion of fillers and flame retardancy of composites was investigated.The composites show a good flame retardancy when Sb₂O₃ nanoparticles and BPS are used together.Particularly,due to the higher dispersion indexof CM-Sb₂O₃ and CM@MP-Sb₂O₃ in PBT matrix,the peak heat release rate(PHRR)of 8wt%BPS-PBT composites filled with 3wt%CM-Sb₂O₃ and CM@MP-Sb₂O₃ are 253.5 and 251.1 k W/m²,respectively.Compared with pure PBT,the PHRR decreased by 78.8%and 79.0%,respectively.On the other hand,the THR are 88.5 and 98.7 MJ/m²,respectively,which decreased by 61.3%and 56.8%compared with pure PBT.As for composites with good dispersion of fillers,it achieves a better long-term flame retardant efficiency due to dilution effect,barrier effect,capture radicals and catalytic charring effect.In short,the perfect dispersion of fillers in polymer matrix has important guiding significance for the preparation of composites with excellent mechanical properties and flame retardancy.