(666c) Solid-State Processing of Polymer Nanocomposites: Cryogenic Milling and Solid-State Shear Pulverization

Polymer nanocomposites derived from commodity polymers and various types of organic and inorganic fillers continue to be of great scientific and commercial interest. Common challenge in effective processing of the nanocomposites lies in achieving well-separated (?exfoliated?) and well-distributed (?dispersed?) filler particles in the morphology. There has been some success with several common processing techniques, such as in situ polymerization [1], solution intercalation [2], and melt compounding/extrusion [3]. However, each of these methods can have physical and practical stumbling blocks. In situ polymerization and solution methods often require toxic reagents and solvents. The melt processing methods require heat and can cause material degradation. In many cases, the processing can be applied to limited polymer-filler systems.

Solid-state processing is a type of non-traditional nanocomposite processing techniques. The process applies mechanical (impact, shear, compression) forces onto the polymer-nanofiller mixture and physically separates and disperse the filler particles in situ. The operation is conducted in cold temperatures, below the melting and glass transition temperatures of the polymer, so as to maintain the system in the solid-state. Because the techniques does not rely on thermodynamics and transport of polymer chains and filler particles, the process can be applied to different polymer-filler systems. Additives, chemical pre-modifications, solvents and monomers are not required in solid-state processes, making it a more environmentally benign technique.

In this paper, two contrastive solid-state processing techniques are presented as effective means of fabricating polymer nanocomposites. Cryogenic milling (Cryomill) is a batch method in which an oscillating impact bar grinds and mills the material in a liquid nitrogen bath [4]. Solid-state shear pulverization (SSSP) is a continuous, industrially-applicable process which employs a chilled twin-screw extruder to apply shear and compressive forces onto the material as it travels down the barrel [5, 6]. Model nanocomposites systems based on montmorillonite (clay) and as received graphite are considered, and various mechanical, thermal, barrier and electrical properties are measured and compared.

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