Study On Toughening Modification Of PBT Matrix Flame Retardant Composites

Polybutylene terephthalate(PBT)is a kind of crystalline saturated polyester resin,which has excellent mechanical properties,low moisture absorption rate and chemical corrosion resistance.It has become a widely used polymer material.However,PBT is easy to burn,and its poor impact toughness caused by notch sensitivity largely limits its application range.Nano-Sb₂O₃/BPS/PBT flame retardant composites were prepared with polybutylene terephthalate(PBT)as the matrix,brominated polystyrene(BPS)as the flame retardant and nano-Sb₂O₃as the synergistic flame retardant.Based on this research system,thermoplastic polyurethane elastomer(TPU)and a novel dual-functional PBT toughening agent(SWR-6B)were used as toughening components to prepare nano-Sb₂O₃/toughening component/BPS-PBT flame retardant composites by ball milling dispersion and melt blending methods.The toughening modified PBT matrix flame retardant composites were characterized by cantilever beam impact test,tensile test,differential scanning calorimeter(DSC),limiting oxygen index(LOI)and vertical burning test(UL94).The tensile and impact fracture morphology and the morphology of carbon residue after combustion were observed and analyzed by scanning electron microscope(SEM)to study the effect of toughening components on the mechanical properties,flame retardant properties and crystallization behavior of nano-Sb₂O₃/BPS/PBT flame retardant composites.The main research work includes the following aspects:(1)The surface of nano-Sb₂O₃ was modified by KH550 to improve its dispersion in the matrix.Nano-Sb₂O₃/TPU/BPS-PBT flame retardant composites were prepared to study the effect of TPU content on the properties of PBT matrix flame retardant composites.The results showed that TPU delayed the crystallizing process of PBT and reduced the crystallinity.The addition of TPU slightly reduced the LOI value of the composites,but the UL94 grade was still at the V-0 level.When the content of TPU was 3wt.%,the tensile strength and impact toughness of the composites were improved,and the nano-Sb₂O₃/TPU/BPS-PBT flame retardant composites showed good comprehensive performance.(2)By studying the effect of SWR-6B on the mechanical properties of nano-Sb₂O₃/BPS/PBT flame retardant composites,it can be found that compared with TPU,SWR-6B has little effect on the tensile strength of PBT matrix flame retardant composites.The notch impact test showed that SWR-6B significantly improved the impact strength of nano-Sb₂O₃/BPS/PBT flame retardant composites.Composite materials achieved flame retardant effect.The ball milling dispersion process makes PBT crystal disordered,and with the increase of SWR-6B content,the crystallinity of PBT matrix flame retardant composites decreased and the processing temperature decreased.(3)TPU/SWR-6B compound modified PBT matrix flame retardant composites,TPU mass fraction of 1wt.%compound modified composites system the decrease of tensile strength was small,notch impact performance was significantly improved.The compound toughening modification has little effect on the flame retardant properties of nano-Sb₂O₃/BPS/PBT flame retardant composites,and the composites reach V-0level.The crystallinity of 2TPU-1SWR-6B toughened composites was higher than that of 1TPU-2SWR-6B toughened composites,the TPU component has a greater influence on the crystallization properties of PBT matrix flame retardant composites.(4)The morphology of char residue after combustion was analyzed and it was found that the nano-Sb₂O₃/TPU/SWR-6B/BPS-PBT flame retardant composite could form a relatively dense carbon layer.The addition of SWR-6B reduced the heat release rate of PBT matrix flame retardant composites,shortened the time to ignition,and the combustion heat value was lower than that of pure PBT.The toughening component has little effect on the flame retardant properties of PBT matrix composites,which improves the flame retardant properties and mechanical properties of nano-Sb₂O₃/BPS/PBT composites.