Toughening Of PBT/PC Blends

Poly(butylene terephthalate)(PBT) and polycarbonate(PC) are an important pair for polyester blends. However, the PBT/PC blends are notch sensitive. The poor notched impact toughness of PBT/PC blends limits their application, and suitable toughening measures should be applied to overcome this drawback. In this paper, different kinds of MBS-g-GMA particles were prepared using a seeded emulsion polymerization method. Then they were used to toughen PBT/PC blends. The toughening effects and the toughening mechanisms were investigated.(1) MBS-g-GMA particles were used to toughen PBT, and PC was used to achieve synergistic toughening. Notched impact tests showed the percolation threshold became lower with the increase of PC content. Transmission electron microscopy (TEM) displayed a very good dispersion of MBS-g-GMA particles in the PBT matrix with the different PC contents. The synergistic toughening effect was due to the encapsulation structure of PC which could facilitate the whole PBT matrix to yield. The more perfect encapsulation structure formed, the more obvious synergistic toughening achieved. Sufficient strength of the phase interface was important to ensure the stress transfer effectively and facilitate the whole PBT matrix to yield. The interface strength between PC and MBS-g-GMA could be ensured by the good miscibility between PMMA (grafted onto the polybutadiene based rubber core) and PC. For the PBT/PC, the transesterification between PBT and PC improved the interface strength of the PBT and PC phases, as demonstrated by the FTIR scans.(2) The influence of the core-shell ratio for MBS-g-GMA on the toughness and stiffness of poly(butylene terephthalate) (PBT) and polycarbonate (PC) blends was investigated. A low core-shell ratio induced a higher grafting degree and’internal grafting’ which were useful for keeping the blend stiffness. A high core-shell ratio improved the soft rubber content and was beneficial to the toughness improvement. The optimum grafting degree region was 56-187% for the reactive core-shell (RCS) particles in order to achieve good dispersion. The RCS-28 and RCS-37 particles were efficient in keeping a higher stiffness but lower toughening effect for PBT/PC blends due to their poor cavitation ability. RCS-73-toughened blends showed weak impact and yield strength due to their agglomeration morphology and high rubber phase content. PBT/PC/RCS-46 blends showed a better toughness and stiffness balance. When the RCS-46 content was 15%, an impact strength of 950J/m and a yield strength of 50MPa could be achieved for the PBT/PC/RCS-46 blend.(3) Two kinds of core-shell particles were used to toughen PBT/PC blends. One has PMMA in the shell layer of particle, but the other does not have. PC shows different dispersed morphology in the blends. In M=0 blends,’sea-island’ structure was found between PBT and PC. However, in M=25 blends, encapsulate structure was formed by PC to the core-shell particles. There are obvious differences for the crystallization behavior of blends and the compatibility of PBT and PC due to different morphologies of PC in the blends. But no difference was found for the dispersion morphology of core-shell particles. All of them can disperse uniformly in the matrix. Impact test showed a super-tough behavior could be achieved for the two kinds of blends. The same synergistic toughening effect can be achieved, no matter what morphology of PC exists in the blends.(4) TEM and SEM results proved that debonding or cavitation of the PB rubber particles and shear yielding of the matrix were the major toughening mechanisms.