Masami Okamoto, Suprakas Sinha Ray. Advanced Polymeric Materials Engineering, Graduate School of Engineering,. Toyota Technological Institute, Hisakata ...
Encyclopedia of Nanoscience and Nanotechnology
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Polymer/Clay Nanocomposites Masami Okamoto, Suprakas Sinha Ray Advanced Polymeric Materials Engineering, Graduate School of Engineering, Toyota Technological Institute, Hisakata 2-12-1, Tempaku, Nagoya 468 8511, Japan
CONTENTS 1. Introduction 2. Structure of Clay and Its Modification with Surfactants 3. Preparative Methods and Structure of PCNs 4. Characterization of PCNs 5. Types of Polymers Used for PCN Preparation 6. Materials Properties of PCNs 7. Crystallization of PCNs 8. Melt Rheology of PCNs 9. Processing Operations of PCNs 10. Conclusions Glossary Acknowledgment References
1. INTRODUCTION Polymer/clay nanocomposites (PCNs) are a new class of materials which have attracted much attention from both scientists and engineers in recent years due to their excellent properties such as high dimensional stability, heat deflection temperature, gas barrier performance, reduced gas permeability, optical clarity, flame retardancy, and enhanced mechanical properties when compared with the pure polymer or conventional composites (micro- and macrocomposites) [1–15]. The first successful PCN appeared about 10 years ago through the pioneering efforts of a research team from Toyota Central Research & Development Co. Inc. (TCRD) in the form of a Nylon 6/clay hybrid [1 2]. Earlier attempts to prepare polymer/clay composites are found in almost half-a-century old patent literatures [16 17]. In such cases, incorporation of 40 to 50 wt% clay mineral (bentonite, hectorite, etc.) into a polymer was attempted but ended with unsatisfactory results: The maximal modulus enhancement was only around 200%, although the clay loading was as much as 50 wt%. The failure was obvious
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because they failed to achieve good dispersion of clay particles in the matrix, in which clay minerals existed as agglomerated tactoids. Such a poor dispersion of the clay particles could improve the material rigidity but certainly sacrifice the strength, the elongation at break, and the toughness of the material [16 17]. A prime reason for this impossibility of improving the tactoid dispersion into well-dispersed exfoliated monolayers of the clay is obviously due to the intrinsic incompatibility of hydrophilic layered silicates with hydrophobic engineering plastics. One attempt at circumventing this difficulty was made by Unitika Ltd. [18] about 30 years ago in preparing Nylon 6/clay composites (not nanocomposites) via in situ polymerization of -caprolactam with montmorillonite, but the results were not very good. The first major breakthrough of the problem was brought about in 1987, when Fukushima and Inagaki of TCRD, via their detailed study of polymer/layered silicate composites, persuasively demonstrated that lipophilization, by replacing inorganic cations in galleries of the native clay with alkylammonium surfactant, successfully made them compatible with hydrophobic polymer matrices [19]. The modified clay was thus called lipophilized clay, organo-phillic clay, or simply organo-clay (organoclay). Furthermore, they found that the lipophilization enabled one to expand clay galleries and exfoliate the silicate layers into single layers of a nanometer thickness. Six years later, in 1993, Usuki, Fukushima, and their colleagues at TCRD successfully prepared, for the first time, exfoliated Nylon 6/clay hybrid (NCH) via in situ polymerization of -caprolactam, in which alkylammonium-modified organoclay was thoroughly dispersed in advance [1 2]. The resulting composite of the loading of only 4.2 wt% clay possessed a doubled modulus, a 50% enhanced strength, and an increase in heat distortion by 80 C compared to the neat Nylon 6, as shown in Table 1. This invention opened up a new era of engineering materials, which we may call “polymer/clay nanocomposites.” Thus, along the stream of development in PCN technologies, many studies have been devoted to PCNs since their intrinsically excellent properties of polymer should have
Encyclopedia of Nanoscience and Nanotechnology Edited by H. S. Nalwa Volume 8: Pages (1–52)
