Study Of Multi-layer Structure Core-shell Modifier Toughening PVC Matrix

A novel three-layer core-shell impact modifier with a hard polystyrene (PSt) inner core, an interim soft polybutadiene (PB) layer and a hard external polymethylmethacrylate (PMMA) layer (PSBM) was prepared to toughen PVC resin. The mechanical properties and toughening mechanism of blends were investigated.Effects of the internal structure of the three-layer impact modifier on mechanical properties of PVC/PSBM blends and toughen mechanisms were investigated. The toughening efficiency was highest when the core-shell ratio (PSB/PMMA) of PSBM was80/20. A brittle-ductile transition was found when the content of PSBM was6phr. The blends fractured in a ductile manner and the impact strength was1200J/m. With core-shell ratio decreasing, the yield strength increased. The interface between the inner core and interim rubbery layer promoted cavitation of rubber particles so that toughening efficiency was improved. The cavitation of rubber particles and shear yielding were the main deformation mechanisms.Two traditional two-layer impact modifiers-MBS1and MBS2were prepared via emulsion polymerization. The first is MBS1with the core of PB and the shell of PSt-MMA. The other is MBS2with the core of SBR and the shell of PMMA. It was found that the toughening efficiency of PSBM was highest among three modifiers. A brittle-ductile transiton was found when the content of PSBM was only6phr. The highest yield strength was obtained in the PVC/PSBM blend compared with the PVC/MBS1and PVC/MBS2blend. The cavitation of rubber particales and shear yielding were toughening mechanisms in the PVC/PSBM blends while only shear yielding was found in the PVC/MBS blends. The light transparency of PVC/PSBM blends was highest than PVC/PSBM blends.As for PVC/PSBM blends, toughening efficiency improved with rubber particle size increasing. When the rubber particle size was200nm, a brittle-ductile transition of PVC/PSBM blend with only5phr PSBM was found. With the rubber particle size decreasing, the yield strength increased. It was found that cavitation of PSBM rubber particles and shear yielding of the matrix were toughening mechanisms. The PSBM with larher rubber particle size was more likely to cavitate.It was found that toughening efficiency of PSBM was the highest when the ratio of PSt/PB was13/67. A brittle-ductile transition was found when the content of PSBM was6phr in the PVC/PSBM blends. With the ratio of PSt/PB decreasing, the toughening mechanisms transited from cavitation of rubber particles and shear yielding of matrix to only shear yielding of matrix. Moreover, the light transparency of PVC/PSBM blends decreased with the ratio of PSt/PB of PSBM.