ADVANCES IN PROCESS VISUALIZATION REVEALS NOVEL POLYMER STRUCTURE.

Scientists from NIST have utilized in situ visualization technology to discover novel structures formed during processing of polymer blends. The observations, which will appear in Physical Review Letters, are the consequence of new measurement tools developed for elucidating the structure of polymer blends during processing. The novel structure results when the dimension of a manufactured part approaches the size of one of the components in an incompatible mixture of polymers. Under such conditions, the NIST measurements show that there is a massive reorganization of the structure of the dispersed polymer droplets. In a four-stage process, tens of thousands of the droplets join together to form extremely large strings. Instead of micrometer-sized droplets typical of polymer blending, these strings can be 10 cm in length, and have been observed to wrap around the processing flow. Once the strings form, they are extremely stable; in fact, it is hard to get rid of them.

Most engineering plastics are polymer blends. Polymer blending technologies are well developed for the case where the final part, such as a car bumper, is much larger than the size of the dispersed polymer droplet, typically 1 micrometer. The new observations suggest the need for alternative blending strategies when the size of the part becomes comparable to the size of the droplets. In addition, the string-like structure may lead to new applications, for example, conductive plastic wires, if the string component was a conductive polymer and the matrix was an insulator with good mechanical properties. If the string component formed a reinforcing fiber, one could have ultra-thin composite materials of high one-dimensional strength. Likewise dissolving out the string component from a biocompatible polymer could provide oriented pores for cell growth for tissue engineering.