Blends PC-PBT

Figure 8.2 shows the DMA spectrum of a PBT-PC blend, along with that of the PBT resin. Note the improved modulus (E ) between the PBT and PC 7 gs. 

Figure 8.2 Comparison of DMA data obtained for a PBT-PC blend and a PBT resin...

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. 

PBT-PC blends show increased melt strength allowing them to be easily processed by blow molding and profile extrusion. The PBT-PC blends have been extruded into sheet and thermoformed into parts. Enhanced melt strength allows PBT-PC blends to be foamed. Structural foam grades for injection molding (10-30% density reduction) are commercially available. 

An acrylate-terminated polyurethane modified epoxy compound and a polyethylene polyamine homologue and fatty acid combination were formulated into a two-component adhesive system. The adhesive is useful for bonding various thermoplastic resins such as ABS, PC, PBT-PC blends, and PPO.22... 

A very promising new field of application for ASA and ASA-PC blends is automotive body panels. Until now, these have been made almost exclusively from painted metal. Since painting is costly, automotive companies are attempting to save costs by developing technologies that dispense with this operation. As in the case of the smart car, bulk coloured thermoplastics (e.g. PBT -PC blends) may be used to make body panels. However, such parts must still be sprayed with a top coat in order to achieve the desired scratch resistance and UV stability. 

Rate [7-18] and temperature [ 16-26] effects on the EWF parameters have been investigated by many authors on several different polymeric materials, like PET [7,18,22,24], PBT [12,21,2.5] PBT/PC blend [8], PEN [11, 26], amorphous copolyester [9], iPP [10,23], sPP [15], UHMWPE 113], LDPE, LLDPE and LDPE/LLDPE blends [19], ABS [13], POM [14] uPVC [16], and PC [17. 20]. The results are not indicating a clear and general trend showing that rate and temperature effects on the fracture parameters strictly depend on the material under investigation. 

Typically PPE/PS, PC/ABS, and PBT/PC blends are used in electrical applications such as lighting, meters, ballasts, electrical boxes, safety yokes on power lines, smoke and carbon monoxide detectors, etc. Important material properties for these applications include good tensile strength creep resistance high HDT... 

PBT/polycarbonate blend, first introduced in 1980 by General Electric (Xenoy ) has enjoyed a fast growth in automotive applications, particularly for bumpers. The blend was developed to meet the low temperature impact strength, dimensional stability and paintability requirements of rigid bumper fascias [Bertolucci and Delany, 1983], which accounted for the bulk of the current market volume for the PBT/PC blend (estimated 25 kton/y in the USA). The development of commercial PET/PC blends followed shortly after the initial success of PBT/PC blends. Currently there are several commercial blends of both PBT/PC and PET/PC blends available. 

The transesterification reactions in PBT/PC melt blends could be suppressed by using organo-phosphites and phosphonates which probably function by deactivating the titanium or antimony type polymerization catalyst residues present in PBT [Golovoy et al., 1989]. Even in the presence of phosphite stabilizers, PBT/PC blends showed dual phase behavior. However, a partial miscibility was evident since the T of PC phase was still reduced from the normal 150°C to about 140°C. This partial miscibility between PBT and PC which occurs even in the absence of an exchange reaction is responsible for the good compatibility and interfacial strength of the blend. 

The second most important class of commercial polycarbonate blends is derived by blending with commercial thermoplastic polyesters such as polybutylene tere-phthalate (PBT) and polyethylene terephthalate (PET). Both PBT and PET are crystallizable polymers and hence offer the expected chemical resistance advantages of the crystalline polymers in blends with polycarbonate. Among the thermoplastic polyester/polycarbonate blends, the PBT/PC blend has the major commercial volume, followed by the PET/PC blend. A copolymer of 1,4-cyclohexanedimethanol, ethylene glycol, and terephthalic acid (PCTG) forms a miscible blend with polycarbonate. PCTG/PC blend was earlier offered by Eastman (Ektar ) for specialty applications, but it is no longer commercial. 

Long-term thermal aging of PBT/PC blends is known to lead to severe embrittlement (Bertillson et al. 1988). Phase segregation, secondary crystallization, and changes in the amorphous phase free volume with aging are some of the key factors... 

In other important automotive applications, increased requirements in terms of surface appearance, low-temperature toughness, flowability and warpage properties have been met by PBT blends. Automotive exterior parts such as door handles, mirror housings, window delta molding, and sunroof frames must have an excellent surface finish, especially if they are unpainted. For large exterior body parts such as bumpers, elastomer-modified PBT/PC blends are used because of their surface appearance and... 

PBT/PC blends were commercialized by Dow, Mobay, Bayer, BASF, and GE Plastics with high modulus, heat resistance, tensile and impact strength, solvent resistance, and UV stability. Mobay and Dow commercialized polyethylene terephthalate (PET)/PC blends with solvent resistance, low-temperatnre impact, and tensile strength. PBT/PET blends with good surface appearance were introdnced by GE Plastics. 

PC/PBT blends have their fit either in the unpainted grades meeting the retouch oven paint temperatures or in off-line painted applications. PBT/PC blends occasionally will meet the top coat online painted requirement when those do not exceed 14u C. In the years to come one expects that this chart will get more and laore crowded especially in the high ductility, upto 160 C heat area which will be sufficient as car industries develop the all plastic body car no longer requiring the -coat treatment. More new materials based on the here described polymer blends concept are obviously under development. 

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