Polymer Blends

The concept of appropriately combining two or more different polymers to obtain a new material system with the desirable features of its constituents is not new. Over the years, numerous systems based on the chemical combination of different monomers through random, block, and graft copolymerization methods have been developed with this goal in mind. For similar reasons, the coatings and rubber industries have long blended together different polymers, and particularly over the last decade the interest in polymer blend systems as a way to meet new market applications with minimum development cost has rapidly increased. This approach has not been without its difficulties and has not developed as rapidly as it might have, in part because most physical blends of different high molecular weight polymers prove to be immiscible. That is, when mixed together, the blend components are likely to separate into phases containing predominantly their own kind. This characteristic, combined with the often low physical attraction forces across the phase boundaries, usually causes immiscible blend systems to have poor mechanical properties. Despite this difficulty, a number of physical blend systems have been commercialized, and some of these are discussed later. However, there are ways around this problem of compatibility. Much research has shown that there are many truly miscible polymer pairs that can lead to significant opportunities for new products. Even for immiscible pairs, proper control of phase morphology during processing and/or the addition of “compatibilizing” agents can improve the interfacial situation mentioned above.