PBT blends

The most common industrial method of blend preparation includes melt blending in a mixer or a twin-screw extruder. The melt blending conditions, the rheological properties of the blend components and the method of morphology stabilization, e.g., by controlled cooling, chemical reaction or crystallization, are important for obtaining useful properties of the blends [76,132-135]. 

By means of compounding, tailor-made engineering plastics parts are manufactured to satisfy every conceivable application. The warping problem, which existed in the past for the production of large area parts, e.g. for car body parts and bumpers, can be overcome by selected reinforcement/filler systems. Simultaneously the heat distortion temperature could be raised from about 150 °C for pure PBT homopolymer to approximately 210 °C for reinforced polymer. Self-extinguishing behavior was imparted by incorporation of flame retardant synergistic systems. Further, in the last thirty years, many commercial products have been developed by blending PBT with other polymers in the melt. Moreover, a variety of additives, fillers or reinforcements, which have been mentioned previously in this Chapter, may be added to the PBT blends. 

As has been shown here, POT is moderate volume thermoplastic polyesters with applications in molded plastics and fibers, and it is often used in blend formulations [136]. Because of the low melt viscosity and melt stability, PBT can be melted with other thermoplastic polyesters or with entirely different polymers. The key reason for blending PBT with other polymers is to tailor new materials with beneficial performance-cost profiles which will meet actual application 

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

PBT/PET/PC blends have been developed in unfilled, glass-filled and mineral-filled versions [15]. All these formulations show, again, that all building components of each particular blend can be used interchangeably to tailor desirable product performance. 

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In a molded polymer blend, the surface morphology results from variations in composition between the surface and the bulk. Static SIMS was used to semiquan-titatively provide information on the surface chemistry on a polycarbonate (PC)/polybutylene terephthalate (PBT) blend. Samples of pure PC, pure PBT, and PC/PBT blends of known composition were prepared and analyzed using static SIMS. Fn ment peaks characteristic of the PC and PBT materials were identified. By measuring the SIMS intensities of these characteristic peaks from the PC/PBT blends, a typical working curve between secondary ion intensity and polymer blend composition was determined. A static SIMS analysis of the extruded surface of a blended polymer was performed. The peak intensities could then be compared with the known samples in the working curve to provide information about the relative amounts of PC and PBT on the actual surface. 

The RIM process was originally developed for the car industry for the production of bumpers, front ends, rear ends, fascia panels and instrument housings. At least one mass-produced American car has RIM body panels. For many of these products, however, a number of injection moulding products are competitive, including such diverse materials as polycarbonate/PBT blends and polypropylene/EPDM blends. In the shoe industry the RIM process has been used to make soling materials from semi-flexible polyurethane foams. 

The use of the particle-beam interface for introduction of samples into a mass spectrometer (PB-MS), without chromatographic separation, was shown by Bonilla [55] to be a useful method for analysis of semi-volatile and nonvolatile additives in PC and PC/PBT blends. The method uses the full power of mass spectrometry to identify multiple additives in a single matrix. The usefulness, speed and simplicity of this approach were illustrated for AOs, UVAs, FRs, slip agents and other additives. 

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]. 

Table VIII. Flame Retarding Polycarbonate/PBT Blends (No Antimony)...

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. 

Bromine is often preferred as a FR source and, considering that most organo-bromine compounds are only 40-70 wt% bromine and that antimony trioxide is used in blends, FR-PBT blends may contain from 10 to 25 wt% FR additives. This high level of additives will have an effect on the melt processability, density and mechanical properties of the blend. 

In most commercial references to FR -PBT blends, what is really meant by FR is that the materials are ignition resistant - not impervious to fire. With limited heat sources, such as in the UL-94 test [52] or the glow wire test [53], the FR blends will resist ignition or self-extinguish a small flame. However, in a large fire, these resins will bum, usually with a smoky flame. 

Most FR-PBT blends have a V-0 performance rating at 1/16 or 1/32 inch under the UL-94 protocol. Good FR performance is usually more difficult to achieve... 

For a given level of fuel at a given thickness with the same halogen content, most halogenated compounds show more or less the same flame retardancy. The key differences among these FR additives are effects on flow, melt stability, mechanical properties and long-term ageing of the FR-PBT blend. Different end-use requirements may call for the addition of different FR additives. 

Another aspect of the burning of PBT blends is dripping. When a thermoplastic part is burned, it will begin to melt as it bums. In some cases, the plastic resin will drip away from the sample. If these drips are burning, it can lead to a spread of the fire. The UL-94 test takes this into consideration and, depending on rating, requires little or no flaming drips. 

Almost all FR-PBT blends contain an organo-halogen agent, an antimony synergist and a fluoropolymer anti-drip component. These three ingredients, as well as the overall fuel content of the blend, are balanced to formulate FR-PBT products. 

Reactive PA/PBT blends acidified ethylene copolymer Sheer, 1982... 

Reactive PA/PBT blends epoxy compounds Urabe Ikuhara, 1989... 

Reactive PA/PBT blends either SGMA, or SMA Watanabe Inozuka, 1991... 

First PET/PBT blends enhanced crystallizability, miscibility Heywang, 1966... 

First modified PET/PBT blends toughening with butyl rubber Hiri Kotama, 1971... 

Most work on SD focuses on the effects of temperature and composition on phase equilibria in binary polymer mixmres. However, in industrial processes other variables may be of equal importance, e.g., the shear stress and pressure. It is known that these variables are important for miscibility, hence for the morphology and performance. For example, during extrusion of PC/PBT blends the LCST was increased by at least 60°C, causing miscibility. The blend coming out from the extruder phase separated by the SD mechanism. The co-continuity of phases resulted in excellent performance. 

When dealing with miscible blends containing two crystalline components, several modes of crystallization are possible separate crystallization, concurrent crystallization, co-crystallization, etc. Only those blends in which both components are miscible in the melt are considered here (Table 3.3). PET/PBT blends were reported to be an example of separate crystallization [Escala and Stein, 1979 Stein et al., 1981]. A spherulitic crystallization was observed for the neat components as well as for blends with small amounts of one component, and the crystals of the minor component were included within the spherulites of the major component, which results in a coarsening of the spherulitic texture. Transesterihcation is, however, the reason for the homogenous amorphous phase. 

Erensch and Jungnickel [1989] and French et al. [1989] have investigated PVDF/PBT blends and related their thermal behavior with the blend morphology. Similar to PVDF/PA-6 blends, the PBT droplet crystallization was completely suppressed in a 85/15 blend and finally crystallized coincidentaly with the PVDF matrix. Again this phenomenon could be related to the fine dispersion of PBT droplets, in number exceeding the available nuclei. Shorter melt-mixing cycles caused a coarser dispersion leading only to a... 

A second system investigated by the authors was the PVDF/PBT blend. Similar effects could be observed. However, coincident crystallization in the PVDF/PBT 85/15 blend occurred at a somewhat higher temperature than the bulk Tpyp,p. It could be concluded that in this case, the PBT melt induced the crystallization of the PVDF matrix phase. 

Figure 3.47. Retarded and/or fractionated crystallization causing coincident crystallization in PVDF/PA-6 and PVDF/PBT blends. Influence of the blend composition (a) and the number of extrusion cycles Z (b) [Frensch and Jungnickel, 1989].

Figure 8.6. TEM micrograph of ABS/PC/PBT blend, double-stained with RuO and OsO tby courtesy of Dr Watanabe from the Mitsui Chemicals Inc.].

Figure 8.23. TEM micrograph (stained by RuO.,) of an extruded 50/50 cPC/PBT blend (left) and listing of the phase transitions and processing temperatures (right) [Okamoto and Inoue, 1994].

Poly(dimethylsiloxy- biphenylen epoxide) PBT blends CORI Improved flame retardancy and impact strength Jordan Webb, 1994... 

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... 

For PC/PET or PBT blends Xenoy ), on startup, the barrel temperature can be set around 245-260°C, then it can be lowered as the production commences. Moderate to slow screw speed should be used, otherwise material will overheat. A reverse temperature profile may increase throughput. 

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