Copolymers impact resistance, semicrystalline polymers

Similarly the disadvantages of PC are the stress cracking and chemical sensitivity. Stress cracking can be treated as a part of impact properties and a simple solution may thus be addition of ABS or ASA. On the other hand, to improve the solvent resistance—a property that is particularly important in automobile applications—a semicrystalline polymer may be added. From Table 4.37, it is apparent that TPEs (e.g., PBT, PET) could provide that property, but they also lack warp resistance and impact strength. Hence an ideal blend for automobile application based on PC and TPEs should be impact modified with, for example, an acrylic latex copolymer. A schematic of preparation of this type of toughened blend introduced by GEC-Europe in 1979 under the tradename Xenoy is shown in Figure 4.41. 

TPO materials are defined as compounds (mixtures) of various polyolefin polymers, semicrystalline thermoplastics, and amorphous elastomers. Most TPOs are composed of polypropylene and a copolymer of ethylene and propylene called ethylene—propylene rubber (EPR) [2]. A common rubber of this type is called ethylene propylene diene monomer rubber (EPDM), which has a small amount of a third monomer, a diene (two carbon-carbon double bonds in it). The diene monomer leaves a small amount of unsaturation in the polymer chain that can be used for sulfur cross-linking. Like most TPEs, TPO products are composed of hard and soft segments. TPO compounds include fillers, reinforcements, lubricants, heat stabilizers, antioxidants, UV stabilizers, colorants, and processing aids. They are characterized by high impact strength, low density, and good chemical resistance they are used when durability and reliability are primary concerns. 

Thermoplastic polyolefins (TPOs) are composite blends of semicrystalline polypropylene and ethylene propylene copolymer (EPR) or ethylene propylene diene monomer (EPDM), widely used in the automotive industry for the production of plastic car parts such as bumper fascia [1]. Polypropylene, which is the major component in such blends, is an inexpensive, easily proccessible polymer, although its poor mechanical properties necessitate the addition of a rubber-dispersed phase. The added rubber acts as an impact modifier by imparting improved ductility, crack resistance, and impact strength to the resulting TPO [1-4]. The cost-effectiveness, light weight, processability, and resilience of TPOs have made them increasingly viable alternatives to steel for bumpers and other car parts. 

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