Bumper grade

At low temperatures, general-purpose grades are generally usable down to -10°C but special grades perform well down to -40°C (bumper grades, for example) according to the mechanical constraints experienced. 

Figure 5.28 shows the better Izod impact strength and flexural strength increase with NIC over a standard cylinder for bumper grade blend, and Figure 5.29 illustrates the better dispersion shown for NIC over the standard cylinder for a PE/CB blend. 

The self colored bumper grades are evolving towards improved processability as indicated by the viscosity curves as a function of shear rate (flg 6b) New grades with much improved flow for thin wall large automo tive front ends still exhibit similar practical toughness (fig.6 (3)). 

By employing additives to improve interfacial adhesion and the cohesive strength of the mbber phase, natural mbber can compete with ethylene—propylene mbbers as an impact modifier for polypropylene. These hard grades, containing between 15 and 25% natural mbber, have the potential for use in the automotive and domestic markets, eg, in bumpers, spoilers, grilles, electrical connectors, and floor tiles. 

Blends of PBT with polycarbonates have been widely used for car bumpers. Interest in PBT/PET blends and PBT/ASA has arisen because of the good surface finish possible even with glass-reinforced grades. Copolyesters based on PBT but with some longer chain diol or acid are also now produced. 

The most important commercial blends of BPA-PC are poly(acrylonitrile-butadiene-styrene) (PC/ABS) and polybutylene terephthalate (PC/PBT) or polyethylene terephthalate (PET). Commercial grades of PC/ABS include CYCOLOY (GE), Bayblend (Bayer), and PULSE (Dow). PC/ABS blends exhibit improved flow and processability and enhanced low-temperature impact strength in comparison to PC (Fig. 3). These blends are widely used in applications requiring enhanced impact resistance, such as interior automotive parts and computer and electronics applications such as computer housings and cell phones. Non-halogenated flame-retardant PC/ABS blends are widely available. Poly(acrylic-styrene-acrylonitrile) (PC/ ASA) blends (GELOY , GE Luran , BASF) provide improved weatherability for outdoor applications such as exterior automotive parts, but exhibit reduced impact performance at low temperatures in comparison to PC/ABS. PC/PBT or PET blends (XENOY , GE Makroblend , Bayer) provide enhanced chemical resistance and weatherability for applications such as lawn and garden equipment and automotive bumpers and fasdas. 

Steamic OOS, OOS D - micronized and finely ground talc for PP dashboards and bumpers IN, Extra 5/O-MlO, Prever, M8, MIOC, M8C, M30 - talc from Val Germanasca mine in Italy for rubber and plastics Paint grades... 

Many of the factors responsible for shifts in bumper fascia are also behind similar changes in side-body moldings. Various grades of TPO have effectively displaced PVC in this application. 

In Europe, the 5 kg recyclable front bumper beam for the Mercedes S range is produced in series quantities in a special grade of polypropylene GMT. To withstand impact up to 4 km/h without damage to itself or the car chassis a Mercedes internal requirement, approximating to USA... 

The main fields of application of particulate filled polymers is shown in Figure 2. As was mentioned earlier, the major benefit of the application of fillers and reinforcement is increased stiffness and HDT. Specific applications which must be mentioned here are garden furniture (CaC03), air-filter covers, heater boxes (talc) for cars, washing machine soap dispensers (talc), etc. Bumpers are usually made from multi-component PP systems containing a PP homo- or copolymer, an elastomer and a filler. In order to demonstrate the usual property range of particulate filled polymers. Table 1 presents the most important characteristics of several commercial grade PP composites. 

---