The Influence Of The Structure Of Core-shell Particles On The Toughening Of PBT/PC Blend

Core-shell particles with polybutadiene as core and methyl methacrylate-co-styrene-co-glycidyl methacrylate terpolymer as shell(PB-g-MSG)were prepared to toughen poly(butylene terephthalate)(PBT)and polycarbonate(PC)blends.The effects of shell composition and grafting degree on the toughening of PBT/PC blends were investigated.The results are as follows:(1)core-shell particles with different methyl methacrylate(MMA)and styrene(St)compositions were prepared.The effects of two kinds of particles PB-g-MSG and PB-g-SG on the toughening of PBT/PC blends were investigated.The compatibilization reaction between the epoxy groups of glycidyl methacrylate and the carboxyl groups of PBT induced the PB-g-SG particles dispersed in the PBT phase.On the other hand,the good miscibility between PMMA(the shell phase of PB-g-MSG)and PC induced the PB-g-MSG particles dispersed in the PC phase.The different phase morphology led to different toughening behavior.The PBT/PC/PB-g-MSG blends with the PC encapsulated morphology showed much lower brittle-ductile transition core-shell particles content(10-15wt% or 15-20wt%)compared with the PBT/PC/PB-g-SG blends(20-25wt%).The difference between the toughening efficiency of the core-shell particles was due to the change of deformation mechanisms.In PBT/PC/PB-g-MSG blends,the cavitation of PB rubber phase led to the occurrence of shear yielding of the matrix.While in the PBT/PC/PB-g-SG blends,the debonding between PBT and PC interface induced the shear yielding of the matrix.The variation of the core-shell particles dispersed phase morphology also affected the crystallization properties and DMA results of the PBT/PC blends.(2)The grafting degree of core-shell particles was changed,and the effects of different grafting degree of core-shell particles on the toughening of PBT/PC blends were studied.The addition of TDDM decreased the grafting degree,particles size and crosslinking degree of PB-g-MSG particles.At the same time,the free methyl methacrylate-co-styrene-co-glyceryl methacrylate copolymer(f-MSG)increased.The f-MSG reacted with PBT and suppressed the transesterification between PBT and PC.On the other hand,f-MSG promoted the crystallization of PBT by heterogeneous nucleation.When the TDDM content was lower than 0.76%,PB-g-MSG particles dispersed in the matrix uniformly,otherwise,agglomeration took place.The change of TDDM content in the PB-g-MSG particles influenced the toughening ability and tensile properties.When the TDDM content was 0.76%,the PBT/PC/PB-g-MSG blend showed the optimum impact toughness and yield strength,which are 908J/m and 49.4Mpa.Fracture mechanism results indicated that cavitation induced shear yielding occurred in the PBT/PC/PB-g-MSG blendwhen no TDDM addition for the core-shell particles.With the addition of TDDM,the interfacial strength decreased between the PB-g-MSG core-shell particles and the matrix.So voids appeared due to debonding,which also could promote the shear yielding process.