PBT-PC-MBS blend

Figure 8.3 shows the morphology of a PBT-PC-MBS blend. The PC phase has been stained and shows as dark regions, while PBT is white. The MBS rubber appears as dark spheres. 

All the commercial PBT/PC and PET/PC blends also contain typically 10-20 wt% of an additional elastomeric impact modifier. The exact nature and the content of the impact modifier is kept proprietary and often forms the basis for a particular blend patent. Typically core-shell rubbers such as polymethylmethacrylate grafted butadiene-styrene rubber (MBS) or an all acrylic core-shell rubber such as poly (MMA-g-n-BuA) are used [Nakamura, 1975 Chung, 1985]. ABS (with high polybutadiene content S 50%) or ASA... 

Molten polyesters show low viscosity and small extmdate swell. For these reasons, they have been blended with amorphous polymers to improve the latter s processability and chemical resistance. Elastomers have also been added to polyesters to improve impact resistance. Blends of polyester (either PET or PBT) with polycarbonate, PC, are the most popular (viz., Bay/oF, BCT4201, Calibre , Dialoy P, Ektar MB (with PCTG), Idemitsu SC, MakroblencT, MB4300, NovadoF, Pocan , R2-9000, Sabre , SC 600, Stapron E, Ultra-blencF KR, Valox , Xenoy 1000, etc.). Presence of PC in PET/PC increases crystallization rate of PET, which translates into faster injection molding cycle and lower part distortion upon demolding than those observed for neat PET. 

The ester linkage is particularly susceptible to hydrolysis. Thus blends containing PEST must be dried to prevent splaying PC/PB/PET or PBT blends Stapron ), PCTG with PC or SMA Ektar MB), PBT/ABS Novalloy -B or Cev-ian), PC/PET or PBT/PB Stapron E), PC/ABS/ SAN Bayblend ) and PC/ABS BayblencT T). In PET/elastomer systems Rynite ), if moismre exceeds 0.2 wt% the processability and final... 

MBS impact modifiers are used for PVC (transparent and low temperature applications, mainly in packaging), and for engineering thermoplastics, especially for low temperature applications (PC, PBT and blends). 

Core-shell impact modifiers have also been reported as impact modifiers for engineering polymers. MBS impact modifiers with a SBR core, a polystyrene middle layer and an outer layer of MMA copolymers with glycidyl methacrylate, acrylamide or methacrylic acid functional monomers were evaluated in PC/PBT blends [104]. Optimal results were obtained with 60 wt% SBR content in the MBS and a modest amoimt of a functional monomer in the MMA copolymer shell. Core-shell impact modification of polycarbonate [105] (PMMA grafted on poly(n-butyl acrylate) and PBT[106] (SAN grafted onto a butadiene based rubber) have been reported. A comprehensive review of core-sheU impact modification of various polymers (PMMA, PVC, PC, PBT, PET, polyamides, thermoplastic blends, thermosets) has been presented by Cruz-Ramos [107]. 

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