Showing papers by "Kung-Hwa Wei published in 2002"

The effect of nano-sized silicate layers from montmorillonite on glass transition, dynamic mechanical, and thermal degradation properties of segmented polyurethane

Abstract: The glass transition temperature of the hard-segment phase and the storage modulus of segmented polyurethane increased substantially in the presence of a small amount of tethered nano-sized layered silicates from montmorillonite compared with their pristine state (by 44°C and by 2.8-fold, respectively). Furthermore, the heat resistance and degradation kinetics of these montmorillonite/polyurethane nanocomposites were enhanced, as shown by thermogravimetric analysis. In particular, a 40°C increase in the degradation temperature and a 14% increase in the degradation activation energy occurred in polyurethane containing 1 wt % trihydroxyl swelling agent-modified montmorillonite compared to that of the pristine polyurethane. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1741–1748, 2002

Synthesis and Properties of Covalently Bonded Layered Silicates/Polyimide (BTDA-ODA) Nanocomposites

Abstract: Covalently bonded layered silicates/polyimide (BTDA-ODA) nanocomposites have been synthesized from γ-(aminopropyl)triethoxysilane (APTS) grafted kenyaite and poly(amic acid). The existence of covalent bonds between APTS and silicates and between APTS and the dianhydride end groups of the polymer have been confirmed by solid-state 13C and 29Si nuclear magnetic resonance and infrared spectroscopy, respectively. The thermal, mechanical, and moistureabsorption retardation properties of these nanocomposites were found to improve substantially over those of neat BTDA-ODA. In particular, a maximum increase of 36 °C in the degradation temperature and a maximum reduction of 54% in moisture absorption are displayed by these nanocomposites.

Layered Silicates/Fluorinated Polyimide Nanocomposites for Advanced Dielectric Materials Applications

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Bulk and surface properties of layered silicates/fluorinated polyimide nanocomposites

Abstract: Intercalated layered silicates/fluorinated polyimide nanocomposites with good overall properties are synthesized from organics-modified-montmorillonite and poly(amic acid), as confirmed by x-ray and transmission electron microscopy results. Both the bulk and surface (nanometer-domain) mechanical properties of synthesized silicates/fluorinated polyimide nanocomposites increased substantially as compared to that of pure polyimide. In particular, the Young's modulus and surface hardness of the fluorinated polyimide containing 5 wt % 2NH2-mont are 69% and 100% larger than that of pure polyimide, respectively. Additionally, the reduced elastic modulus by nanoindentation of the nanocomposites is 74% larger than that of the pure polyimide. The barrier properties of the nanocomposites, such as thermal expansion and water absorption retardation, are enhanced.