Impact-modified PBT Blends

PBT has also been blended with styrene-maleic anhydride (SMA) copolymers giving material similar to the ABS blends. Impact modification appears to be more difficult since there is the possibility of 

Applications of unreinforced or glass-reinforced PBT/polyamide blends mainly include impact resistant, dimensionally stable injection molded components which can be exposed to heat, oils, and chemicals, since the blends combine improved chemical and thermal resistance with high impact strength and toughness. 

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Commercial impact modified (elastomer blended) polycarbonates are used for the production of protective headgear, sporting goods, bobbins for textile industry and automotive components requiring high toughness. Impact modified PC has to compete with the more solvent resistant impact modified PBT/PC, PET/PC blends and polyamides in some of the applications. 

Impact-modified PBT/PC blends are also available on the market and some their characteristics are described in Section 5.6.43.. 

Also, PBT is blended with poly(ethylene terephthalate) (PET), polysulfone, and SMA (303). PET may also be blended with a number of other engineering polymers, such as PC and impact modifiers. 

On-line SFE-GC-MS was used for the analysis of organic extractables from human hair [312]. Van Lieshout et al. [313] described GC-MS analysis of an SFE extract of an (ABS) impact-modified PC/PBT blend identifying Ionol CP, Dressinate, cyclic PBT trimer, Irganox 1076 and Irganox PS 800. TD-GC-MS was used in the development of flame retardants, and for the analysis of fire debris [314]. The application of laser desorption fast GC-MS analysis was employed in the analysis of DOP on a stainless-steel surface [221]. 

The extent of the benefits of adding PC to the blend will depend on the PC/PBT ratio. Very low levels (<5 %) of PC or PBT may be totally miscible in the other resin and act like a slightly modified PC or PBT resin. Most PBT blend products use from 10-60% PC. High PC content will improve impact and lower shrink but reduce flow and solvent resistance. More PBT gives better flow and solvent resistance with more shrink and loss of some impact. A range of PBT-PC blends covering the spread of properties is commercially available. 

Polybutylene therephthalate (PBT) has been used as a blend component to provide chemical resistance in various systems, but the most interesting one results from a combination with polycarbonate and, eventually, an Impact modifier of the coreshell type. Polyester blends containing polycarbonate exhibit ester interchange chemical reactions, which add to the complexity of property control of these materials. DEVAUX and co-workers (14) have examined the transesterification reaction catalysed by residual catalysts in PBT which can lead to the formation of block and random copolymers. They have shown that allyl or aryl phosphites inactivate the residual titanium catalyst and minimise the transesterification reaction. HOBBS et al. (15) reported a way of controlling miscibility behaviour, morphology and deformation mechanisms, in order to obtain blends compati-bilisation and excellent mechanical properties. 

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... 

Commercial PBT/PC and PET/PC blends contain about 15-20 % of such core-shell mbber impact modifiers for maximum toughness, i.e., notched Izod impact strengths of typically > 700 J/m which is maintained even at low temperature (Tables 15.26 and 15.27). The ratio of PBT/PC or PET/PC is usually kept between 50/50 to 40/60 to optimize the ductility in the blend, while still maintaining a continuous or co-continuous phase of the polyester. A continuous phase of PBT or PET with PC as dispersed phase, would be preferred for solvent resistance. 

Several research investigations have been made to compatibilize PET or PBT with PPE both by reactive and non-reactive routes of compatibiliza-tion [Brown et al., 1990 and 1991 Akkapeddi and VanBuskirk, 1992]. Compatibilized binary blends of PPE/polyesters still lacked adequate toughness and invariably required the addition of rubbery impact modifiers (reactive or compatible type) and polycarbonate. The addition of polycarbonate presumably suppresses the crystallization of the thermoplastic PET or PBT phase, due to its... 

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