Research On Properties Control And Synergistic Mechanism In Toughened PBT/PC Blends

Core-shell particles with polybutadiene as core and methyl methacrylate-co-styrene-co-glycidyl methacrylate terpolymer as shell(MBS-g-GMA) were prepared to toughen poly(butylene terephthalate)(PBT) and polycarbonate(PC) blends.The properties and synergistic toughening effect of MBS-g-GMA toughened PBT/PC blends were studied with the addition of Sodium pyrophosphate(SPP) as inhibitor and Antimony(III) oxide(Sb2O3) and Magnesium oxide(MgO) as accelerator separately. The results are as follows:(1) SPP was used as inhibitor to modify the transesterification between PBT and PC.FTIR results proved the occurrence of the transesterification and the addition of SPP inhibited the exchange reactions. SEM displayed the MBS-g-GMA particles dispersed in PBT/PC matrix uniformly and the addition of SPP had no negative influence on the uniform dispersion. The crystallization temperature of PBT increased with the addition of SPP which indicated the constraint of PC block on the crystallization of PBT chain became poor. At the same time, with the addition of SPP into the PBT/PC/MBS-g-GMA blend, the Tg of PC phase further shifted to higher temperature. MBS-g-GMA was an effective toughener for PBT/PC blends, however, SPP decreased the toughening efficiency of MBS-g-GMA particles for the PBT/PC blends. The yield strength of PBT/PC blends increased first and then deceased with the increase of SPP content in the blends. Fracture mechanisms results showed the addition of SPP decreased the plastic deformation of the blends. The results showed that addition of SPP has no synergistic effect on the toughening system.(2) Sb2O3 or MgO was used as accelerator to promote the transesterification between PBT and PC, respectively. The result of FTIR showed that the extracted blends presented the absorption peak of the C=O group in the PC phase at 1775cm-1and the addition of Sb2O3 or MgO increased the reaction degree. The absorption peak was more obvious with the increase of Sb2O3 or MgO content. SEM displayed the MBS-g-GMA particles dispersed in PBT/PC matrix uniformly and the addition of accelerator had no negative influence on the uniform dispersion. Accelerator increased the toughening efficiency of MBS-g-GMA particles for the PBT/PC blends. On the other hand, the crystallization temperature of PBT decreased with the addition of accelerator and proved that the addition of accelerator promoted the degree of the transesterification reaction, which destroyed the regularity of the PBT crystal structure and led to the decrease of the crystallization ability of PBT phase. At the same time, with the addition of accelerator into the PBT/PC/MBS-g-GMA blend, the Tg of PC phase further shifted to lower temperature. MBS-g-GMA was an effective toughener for PBT/PC blends, however, accelerator increased the toughening efficiency of MBS-g-GMA particles for the PBT/PC blends. The brittle-ductile transition took place between 5~10wt% MBS-g-GMA content. Fracture mechanisms results showed the addition of accelerator increased the plastic deformation of the blends. The results showed that addition of accelerator has synergistic effect on the toughening system.Comparied with Sb2O3, MgO showed much better synergistic effect on the toughend PBT/PC blends.